<PAGE>   1
EXHIBIT 4.6


                      ------------------------------------


                                CIENA CORPORATION

                                     ISSUER

                                       TO

                            FIRST UNION NATIONAL BANK

                                     TRUSTEE

                               ------------------

                                    INDENTURE

                          Dated as of February 9, 2001

                               -------------------

                  3.75% CONVERTIBLE NOTES DUE FEBRUARY 1, 2008


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                                TABLE OF CONTENTS

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ARTICLE I DEFINITIONS AND OTHER PROVISIONS OF GENERAL APPLICATION................................1

        SECTION 1.1 Definitions..................................................................1
        SECTION 1.2 Compliance Certificates and Opinions.........................................8
        SECTION 1.3 Form of Documents Delivered to the Trustee...................................8
        SECTION 1.4 Acts of Holders of Securities................................................9
        SECTION 1.5 Notices, Etc to the Trustee and Company.....................................11
        SECTION 1.6 Notice to Holders of Securities; Waiver.....................................11
        SECTION 1.7 Effect of Headings and Table of Contents....................................12
        SECTION 1.8 Successors and Assigns......................................................12
        SECTION 1.9 Separability Clause.........................................................12
        SECTION 1.10 Benefits of Indenture......................................................12
        SECTION 1.11 Governing Law..............................................................12
        SECTION 1.12 Legal Holidays.............................................................12
        SECTION 1.13 Conflict With Trust Indenture Act..........................................13

ARTICLE II SECURITY FORMS.......................................................................13

        SECTION 2.1 Form Generally..............................................................13
        SECTION 2.2 Form of Security............................................................14
        SECTION 2.3 Form of Certificate of Authentication.......................................24
        SECTION 2.4 Form of Conversion Notice...................................................24
        SECTION 2.5 Form of Assignment..........................................................26

ARTICLE III THE SECURITIES......................................................................26

        SECTION 3.1 Title and Terms.............................................................26
        SECTION 3.2 Denominations...............................................................27
        SECTION 3.3 Execution, Authentication, Delivery and Dating..............................27
        SECTION 3.4 Global Securities; Non-global Securities; Book-entry Provisions.............27
        SECTION 3.5 Registration; Registration of Transfer and Exchange; Restrictions on
                             Transfer...........................................................29
        SECTION 3.6 Mutilated, Destroyed, Lost or Stolen Securities.............................30
        SECTION 3.7 Payment of Interest; Interest Rights Preserved..............................31
        SECTION 3.8 Persons Deemed Owners.......................................................32
        SECTION 3.9 Cancellation................................................................32
        SECTION 3.10 Computation of Interest....................................................32
        SECTION 3.11 CUSIP Numbers..............................................................32

ARTICLE IV SATISFACTION AND DISCHARGE...........................................................33

        SECTION 4.1 Satisfaction And Discharge of Indenture.....................................33
        SECTION 4.2 Application of Trust Money..................................................34
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                                TABLE OF CONTENTS
                                   (CONTINUED)

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ARTICLE V REMEDIES..............................................................................34

        SECTION 5.1 Events of Default...........................................................34
        SECTION 5.2 Acceleration of Maturity; Rescission and Annulment..........................36
        SECTION 5.3 Collection of Indebtedness and Suits for Enforcement by Trustee.............36
        SECTION 5.4 Trustee May File Proofs of Claim............................................37
        SECTION 5.5 Trustee May Enforce Claims Without Possession of Securities.................38
        SECTION 5.6 Application of Money Collected..............................................38
        SECTION 5.7 Limitation on Suits.........................................................39
        SECTION 5.8 Unconditional Right of Holders to Receive Principal, Premium and
                             Interest and to Convert............................................39
        SECTION 5.9 Restoration of Rights and Remedies..........................................39
        SECTION 5.10 Rights and Remedies Cumulative.............................................40
        SECTION 5.11 Delay or Omission Not Waiver...............................................40
        SECTION 5.12 Control by Holders of Securities...........................................40
        SECTION 5.13 Waiver of Past Defaults....................................................40
        SECTION 5.14 Undertaking for Costs......................................................41
        SECTION 5.15 Waiver of Stay, Usury or Extension Laws....................................41

ARTICLE VI THE TRUSTEE..........................................................................41

        SECTION 6.1 Certain Duties and Responsibilities.........................................41
        SECTION 6.2 Notice of Defaults..........................................................42
        SECTION 6.3 Certain Rights of Trustee...................................................43
        SECTION 6.4 Not Responsible for Recitals or Issuance of Securities......................44
        SECTION 6.5 May Hold Securities, Act as Trustee under Other Indentures..................44
        SECTION 6.6 Money Held in Trust.........................................................44
        SECTION 6.7 Compensation and Reimbursement..............................................44
        SECTION 6.8 Corporate Trustee Required; Eligibility.....................................45
        SECTION 6.9 Resignation and Removal; Appointment of Successor...........................45
        SECTION 6.10 Acceptance of Appointment by Successor.....................................46
        SECTION 6.11 Merger, Conversion, Consolidation or Succession to Business................47
        SECTION 6.12 Authenticating Agents......................................................47
        SECTION 6.13 Disqualification; Conflicting Interests....................................48
        SECTION 6.14 Preferential Collection of Claims Against Company..........................49

ARTICLE VII CONSOLIDATION, MERGER, CONVEYANCE, TRANSFER OR LEASE................................49

        SECTION 7.1 Company May Consolidate, Etc. Only on Certain Terms.........................49
        SECTION 7.2 Successor Substituted.......................................................49
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                                TABLE OF CONTENTS
                                   (CONTINUED)

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ARTICLE VIII SUPPLEMENTAL INDENTURES............................................................50

        SECTION 8.1 Supplemental Indentures Without Consent of Holders of Securities............50
        SECTION 8.2 Supplemental Indentures with Consent of Holders of Securities...............50
        SECTION 8.3 Execution of Supplemental Indentures........................................51
        SECTION 8.4 Effect of Supplemental Indentures...........................................52
        SECTION 8.5 Reference in Securities to Supplemental Indentures..........................52
        SECTION 8.6 Notice of Supplemental Indentures...........................................52
        SECTION 8.7 Conformity with Trust Indenture Act.........................................52

ARTICLE IX MEETINGS OF HOLDERS OF SECURITIES....................................................52

        SECTION 9.1 Purposes for Which Meetings May Be Called...................................52
        SECTION 9.2 Call, Notice and Place of Meetings..........................................53
        SECTION 9.3 Persons Entitled to Vote at Meetings........................................53
        SECTION 9.4 Quorum; Action..............................................................53
        SECTION 9.5 Determination of Voting Rights; Conduct and Adjournment of Meetings.........54
        SECTION 9.6 Counting Votes and Recording Action of Meetings.............................55

ARTICLE X COVENANTS.............................................................................55

        SECTION 10.1 Payment of Principal, Premium and Interest.................................55
        SECTION 10.2 Maintenance of Offices or Agencies.........................................55
        SECTION 10.3 Money for Security Payments to Be Held in Trust............................56
        SECTION 10.4 Existence..................................................................57
        SECTION 10.5 Maintenance of Properties..................................................57
        SECTION 10.6 Payment of Taxes and Other Claims..........................................58
        SECTION 10.7 Reserved...................................................................58
        SECTION 10.8 Statement by Officers as to Default........................................58
        SECTION 10.9 Reserved...................................................................58
        SECTION 10.10 Reserved..................................................................58
        SECTION 10.11 Reserved..................................................................58
        SECTION 10.12 Waiver of Certain Covenants...............................................58

ARTICLE XI REDEMPTION OF SECURITIES.............................................................59

        SECTION 11.1 Right of Redemption........................................................59
        SECTION 11.2 Applicability of Article...................................................59
        SECTION 11.3 Election to Redeem; Notice to Trustee......................................59
        SECTION 11.4 Selection by Trustee of Securities to Be Redeemed..........................59
        SECTION 11.5 Notice of Redemption.......................................................60
        SECTION 11.6 Deposit of Redemption Price................................................61
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        SECTION 11.7 Securities Payable on Redemption Date......................................61
        SECTION 11.8 Conversion Arrangement on Call for Redemption..............................62

ARTICLE XII CONVERSION OF SECURITIES............................................................62

        SECTION 12.1 Conversion Privilege and Conversion Rate...................................62
        SECTION 12.2 Exercise of Conversion Privilege...........................................63
        SECTION 12.3 Fractions of Shares........................................................64
        SECTION 12.4 Adjustment of Conversion Rate..............................................64
        SECTION 12.5 Notice of Adjustments of Conversion Rate...................................68
        SECTION 12.6 Notice of Certain Corporate Action.........................................69
        SECTION 12.7 Company to Reserve Common Stock............................................70
        SECTION 12.8 Taxes on Conversions.......................................................70
        SECTION 12.9 Covenant as to Common Stock................................................70
        SECTION 12.10 Cancellation of Converted Securities......................................70
        SECTION 12.11 Provision in Case of Consolidation, Merger or Sale of Assets..............70
        SECTION 12.12 Rights Issued in Respect of Common Stock..................................71
        SECTION 12.13 Responsibility of Trustee for Conversion Provisions.......................72

ARTICLE XIII [RESERVED].........................................................................72

ARTICLE XIV REPURCHASE OF SECURITIES AT THE OPTION OF THE HOLDER UPON A CHANGE IN CONTROL.......73

        SECTION 14.1 Right to Require Repurchase................................................73
        SECTION 14.2 Conditions to the Company's Election to Pay the Repurchase Price in
                             Common Stock.......................................................73
        SECTION 14.3 Notices; Method of Exercising Repurchase Right, Etc........................74
        SECTION 14.4 Certain Definitions........................................................77
        SECTION 14.5 Consolidation, Merger, etc.................................................78

ARTICLE XV HOLDERS LISTS AND REPORTS BY TRUSTEE AND COMPANY; NON-RECOURSE.......................78

        SECTION 15.1 Company to Furnish Trustee Names and Addresses of Holders..................78
        SECTION 15.2 Preservation of Information................................................79
        SECTION 15.3 Reserved...................................................................79
        SECTION 15.4 Reports by Trustee.........................................................79
        SECTION 15.5 Reports by Company.........................................................79

ARTICLE XVI IMMUNITY OF INCORPORATORS, STOCKHOLDERS, OFFICERS AND DIRECTORS.....................80

        SECTION 16.1 Indenture and Securities Solely Corporate Obligations......................80
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        INDENTURE, dated as of February 9, 2001, between CIENA CORPORATION, a
corporation duly organized and existing under the laws of the State of Delaware,
having its principal office at 1201 Winterson Road, Linthicum, Maryland 21090
(herein called the "Company"), and FIRST UNION NATIONAL BANK, a national banking
association, as Trustee hereunder (herein called the "Trustee").

                             RECITALS OF THE COMPANY

        The Company has duly authorized the creation of an issue of its 3.75%
Convertible Notes due February 1, 2008 (herein called the "Securities") of
substantially the tenor and amount hereinafter set forth, and to provide
therefor the Company has duly authorized the execution and delivery of this
Indenture.

        All things necessary to make the Securities, when the Securities are
executed by the Company and authenticated and delivered hereunder, the valid
obligations of the Company, and to make this Indenture a valid agreement of the
Company, in accordance with their and its terms, have been done. Further, all
things necessary to duly authorize the issuance of the Common Stock of the
Company issuable upon the conversion of the Securities, and to duly reserve for
issuance the number of shares of Common Stock issuable upon such conversion,
have been done.

                   NOW, THEREFORE, THIS INDENTURE WITNESSETH:

        For and in consideration of the premises and the purchase of the
Securities by the Holders thereof, it is mutually covenanted and agreed, for the
equal and proportionate benefit of all Holders of the Securities, as follows:

                                   ARTICLE I
            DEFINITIONS AND OTHER PROVISIONS OF GENERAL APPLICATION

SECTION 1.1     Definitions.

        For all purposes of this Indenture, except as otherwise expressly
provided or unless the context otherwise requires:

        (1)     the terms defined in this Article have the meanings assigned to
them in this Article and include the plural as well as the singular;

        (2)     all accounting terms not otherwise defined herein have the
meanings assigned to them in accordance with generally accepted accounting
principles in the United States, and, except as otherwise herein expressly
provided, the term "generally accepted accounting principles" with respect to
any computation required or permitted hereunder shall mean such accounting
principles as are generally accepted at the date of such computation; and

        (3)     the words "herein", "hereof" and "hereunder" and other words of
similar import refer to this Indenture as a whole and not to any particular
Article, Section or other subdivision.

<PAGE>   7

        "Act", when used with respect to any Holder of a Security, has the
meaning specified in Section 1.4.

        "Affiliate" of any specified Person means any other Person directly or
indirectly controlling or controlled by or under direct or indirect common
control with such specified Person. For the purposes of this definition,
"control", when used with respect to any specified Person, means the power to
direct the management and policies of such Person, directly or indirectly,
whether through the ownership of voting securities, by contract or otherwise;
and the terms "controlling" and "controlled" have meanings correlative to the
foregoing.

        "Agent Member" means any member of, or participant in, the Depositary.

        "Applicable Procedures" means, with respect to any transfer or
transaction involving a Global Security or beneficial interest therein, the
rules and procedures of The Depository Trust Company or any successor
Depositary, in each case to the extent applicable to such transaction and as in
effect from time to time.

        "Authenticating Agent" means any Person authorized pursuant to Section
6.12 to act on behalf of the Trustee to authenticate Securities.

        "Board of Directors" means either the board of directors of the Company
or any duly authorized committee of that board.

        "Board Resolution" means a resolution duly adopted by the Board of
Directors, a copy of which, certified by the Secretary or an Assistant Secretary
of the Company to have been duly adopted by the Board of Directors and to be in
full force and effect on the date of such certification, shall have been
delivered to the Trustee.

        "Business Day", when used with respect to any Place of Payment, Place of
Conversion or any other place, as the case may be, means each Monday, Tuesday,
Wednesday, Thursday and Friday which is not a day on which banking institutions
in such Place of Payment, Place of Conversion or other place, as the case may
be, are authorized or obligated by law or executive order to close.

        "Change in Control" has the meaning specified in Section 14.4(2).

        "Closing Price Per Share" means, with respect to the Common Stock, for
any day, (i) the last reported sale price regular way on the Nasdaq National
Market or, (ii) if the Common Stock is not quoted on the Nasdaq National Market,
the last reported sale price regular way per share or, in case no such reported
sale takes place on such day, the average of the reported closing bid and asked
prices regular way, in either case, on the principal national securities
exchange on which the Common Stock is listed or admitted to trading, or (iii) if
the Common Stock is not quoted on the Nasdaq National Market or listed or
admitted to trading on any national securities exchange, the average of the
closing bid prices in the over-the-counter market as furnished by any New York
Stock Exchange member firm selected from time to time by the Company for that
purpose.

        "Code" has the meaning specified in Section 2.l.


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        "Commission" means the United States Securities and Exchange Commission,
as from time to time constituted, created under the Exchange Act, or, if at any
time after the execution of this instrument such Commission is not existing and
performing the duties now assigned to it under the Trust Indenture Act, then the
body performing such duties at such time.

        "Common Stock" means the Common Stock, par value $0.01 per share, of the
Company authorized at the date of this instrument as originally executed.
Subject to the provisions of Section 12.11, shares issuable on conversion or
repurchase of Securities shall include only shares of Common Stock or shares of
any class or classes of common stock resulting from any reclassification or
reclassifications thereof; provided, however, that if at any time there shall be
more than one such resulting class, the shares so issuable on conversion of
Securities shall include shares of all such classes, and the shares of each such
class then so issuable shall be substantially in the proportion which the total
number of shares of such class resulting from all such reclassifications bears
to the total number of shares of all such classes resulting from all such
reclassifications.

        "common stock" includes any stock of any class of capital stock which
has no preference in respect of dividends or of amounts payable in the event of
any voluntary or involuntary liquidation, dissolution or winding up of the
issuer thereof and which is not subject to redemption by the issuer thereof.

        "Company" means the Person named as the "Company" in the first paragraph
of this instrument until a successor Person shall have become such pursuant to
the applicable provisions of this Indenture, and thereafter "Company" shall mean
such successor Person.

        "Company Notice" has the meaning specified in Section 14.3.

        "Company Request" or "Company Order" means a written request or order
signed in the name of the Company by its (i) Chairman of the Board, its Vice
Chairman of the Board, its Chief Executive Officer, its President, an Executive
Vice President, a Senior Vice President or a Vice President, and by its (ii)
Principal financial officer, Treasurer, an Assistant Treasurer, its Controller,
its Secretary or an Assistant Secretary, and delivered to the Trustee.

        "Constituent Person" has the meaning specified in Section 12.11.

        "Conversion Agent" means any Person authorized by the Company to convert
Securities in accordance with Article XII. The Company has initially appointed
the Trustee as its Conversion Agent pursuant to Section 10.2 hereof.

        "Conversion Price" has the meaning specified in Section 14.4(3).

        "Conversion Rate" has the meaning specified in Section 12.1.

        "Corporate Trust Office" means the office of the Trustee at which at any
particular time the trust created by this Indenture shall be principally
administered, which may be designated from time to time by notice from the
Trustee to the Company (which at the date of this Indenture is located at 800
East Main Street -- LM, Richmond, Virginia 23219).


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<PAGE>   9

        "corporation" means a corporation, company, association, joint-stock
company or business trust.

        "Defaulted Interest" has the meaning specified in Section 3.7.

        "Depositary" means, with respect to any Securities (including any Global
Securities), a clearing agency that is registered as such under the Exchange Act
and is designated by the Company to act as Depositary for such Securities (or
any successor securities clearing agency so registered).

        "Dollar" or "U.S. $" means a dollar or other equivalent unit in such
coin or currency of the United States as at the time shall be legal tender for
the payment of public and private debts.

        "DTC" means The Depository Trust Company, a New York corporation.

        "Event of Default" has the meaning specified in Section 5.1.

        "Exchange Act" means the United States Securities Exchange Act of 1934
(or any successor statute), as amended from time to time.

        "Global Security" means a Security that is registered in the Security
Register in the name of a Depositary or a nominee thereof.

        "Holder" means the Person in whose name the Security is registered in
the Security Register.

        "Indenture" means this instrument as originally executed or as it may
from time to time be supplemented or amended by one or more indentures
supplemental hereto entered into pursuant to the applicable provisions hereof,
including, for all purposes of this instrument and any such supplemental
indenture, the provisions of the Trust Indenture Act that are deemed to be a
part of and govern this instrument and any such supplemental indenture,
respectively.

        "Interest Payment Date" means the Stated Maturity of an installment of
interest on the Securities.

        "Issue Date" means February 9, 2001.

        "Maturity", when used with respect to any Security, means the date on
which the principal of such Security becomes due and payable as therein or
herein provided, whether at the Stated Maturity or by declaration of
acceleration, call for redemption, exercise of the repurchase right set forth in
Article XIV or otherwise.

        "Non-electing Share" has the meaning specified in Section 12.11.

        "Notice of Default" has the meaning specified in Section 5.1.

        "Officers' Certificate" means a certificate signed by (i) the Chairman
of the Board, a Vice Chairman of the Board, the Chief Executive Officer, the
President, an Executive Vice President,


                                      -4-
<PAGE>   10

a Senior Vice President or a Vice President and by (ii) the principal financial
officer, the Treasurer, an Assistant Treasurer, the Controller, the Secretary or
an Assistant Secretary of the Company, and delivered to the Trustee. One of the
Officers signing an Officers' Certificate given pursuant to Section 10.8 shall
be the principal executive, financial or accounting officer of the Company.

        "Opinion of Counsel" means a written opinion of counsel, who may be
counsel for the Company and who shall be acceptable to the Trustee.

        "Outstanding", when used with respect to Securities, means, as of the
date of determination, all Securities theretofore authenticated and delivered
under this Indenture, except:

                (i)     Securities theretofore canceled by the Trustee or
                        delivered to the Trustee for cancellation;

                (ii)    Securities for the payment or redemption of which money
                        in the necessary amount has been theretofore deposited
                        with the Trustee or any Paying Agent (other than the
                        Company) in trust or set aside and segregated in trust
                        by the Company (if the Company shall act as its own
                        Paying Agent) for the Holders of such Securities,
                        provided that if such Securities are to be redeemed,
                        notice of such redemption has been duly given pursuant
                        to this Indenture or provision therefor satisfactory to
                        the Trustee has been made;

                (iii)   Securities which have been paid pursuant to Section 3.6
                        or in exchange for or in lieu of which other Securities
                        have been authenticated and delivered pursuant to this
                        Indenture, other than any such Securities in respect of
                        which there shall have been presented to the Trustee
                        proof satisfactory to it that such Securities are held
                        by a bona fide purchaser in whose hands such Securities
                        are valid obligations of the Company; and

                (iv)    Securities converted into Common Stock pursuant to
                        Article XII;

provided, however, that in determining whether the Holders of the requisite
principal amount of Outstanding Securities are present at a meeting of Holders
of Securities for quorum purposes or have given any request, demand,
authorization, direction, notice, consent or waiver hereunder, Securities owned
by the Company or any other obligor upon the Securities or any Affiliate of the
Company or such other obligor shall be disregarded and deemed not to be
Outstanding, except that, in determining whether the Trustee shall be protected
in relying upon any such determination as to the presence of a quorum or upon
any such request, demand, authorization, direction, notice, consent or waiver,
only Securities which a Responsible Officer of the Trustee has been notified in
writing to be so owned shall be so disregarded. Securities so owned which have
been pledged in good faith may be regarded as Outstanding if the pledgee is not
the Company or any other obligor upon the Securities or any Affiliate of the
Company or such other obligor, and the Trustee shall be protected in relying
upon an Officer's Certificate to such effect.

        "Over-allotment Option" has the meaning specified in Section 3.1.


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        "Paying Agent" means any Person authorized by the Company to pay the
principal of or interest on any Securities on behalf of the Company and, except
as otherwise specifically set forth herein, such term shall include the Company
if it shall act as its own Paying Agent. The Company has initially appointed the
Trustee as its Paying Agent pursuant to Section 10.2 hereof.

        "Person" means any individual, corporation, limited liability company,
partnership, joint venture, trust, estate, unincorporated organization or
government or any agency or political subdivision thereof.

        "Place of Conversion" has the meaning specified in Section 3.1.

        "Place of Payment" has the meaning specified in Section 3.1.

        "Predecessor Security" of any particular Security means every previous
Security evidencing all or a portion of the same debt as that evidenced by such
particular Security; and, for the purposes of this definition, any Security
authenticated and delivered under Section 3.6 in exchange for or in lieu of a
mutilated, destroyed, lost or stolen Security shall be deemed to evidence the
same debt as the mutilated, destroyed, lost or stolen Security.

        "Press Release" means any press release issued by the Company.

        "Record Date" means any Regular Record Date or Special Record Date.

        "Record Date Period" means the period from the close of business of any
Regular Record Date next preceding any Interest Payment Date to the opening of
business on such Interest Payment Date.

        "Redemption Date", when used with respect to any Security to be
redeemed, means the date fixed for such redemption by or pursuant to this
Indenture.

        "Redemption Price", when used with respect to any Security to be
redeemed, means the price at which it is to be redeemed pursuant to this
Indenture.

        "Regular Record Date" for interest payable in respect of any Security on
any Interest Payment Date means the January 15 or July 15 (whether or not a
Business Day), as the case may be, next preceding such Interest Payment Date.

        "Repurchase Date" has the meaning specified in Section 14.1.

        "Repurchase Price" has the meaning specified in Section 14.1.

        "Responsible Officer", when used with respect to the Trustee, means any
officer within the Corporate Trust Office of the Trustee with direct
responsibility for the administration of this Indenture and also means, with
respect to a particular corporate trust matter, any other officer to whom such
matter is referred because of his knowledge and familiarity with the particular
subject.


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        "Securities" has the meaning ascribed to it in the first paragraph under
the caption "Recitals of the Company".

        "Securities Act" means the United States Securities Act of 1933 (or any
successor statute), as amended from time to time.

        "Security Register" and "Security Registrar" have the respective
meanings specified in Section 3.5.

        "Significant Subsidiary" means, with respect to any Person, a Subsidiary
of such Person that would constitute a "significant subsidiary" as such term is
defined under Rule 1-02 of Regulation S-X under the Securities Act and the
Exchange Act.

        "Special Record Date" for the payment of any Defaulted Interest means a
date fixed by the Company pursuant to Section 3.7.

        "Stated Maturity", when used with respect to any Security or any
installment of interest thereon, means the date specified in such Security as
the fixed date on which the principal of such Security or such installment of
interest is due and payable.

        "Subsidiary" means a corporation more than 50% of the outstanding voting
stock of which is owned, directly or indirectly, by the Company or by one or
more other Subsidiaries, or by the Company and one or more other Subsidiaries.
For the purposes of this definition, "voting stock" means stock or other similar
interests in the corporation which ordinarily has or have voting power for the
election of directors, or persons performing similar functions, whether at all
times or only so long as no senior class of stock or other interests has or have
such voting power by reason of any contingency.

        "Successor Security" of any particular Security means every Security
issued after, and evidencing all or a portion of the same debt as that evidenced
by, such particular Security; and, for the purposes of this definition, any
Security authenticated and delivered under Section 3.6 in exchange for or in
lieu of a mutilated, destroyed, lost or stolen Security shall be deemed to
evidence the same debt as the mutilated, destroyed, lost or stolen Security.

        "Trading Day" means (i) if the Common Stock is quoted on the Nasdaq
National Market or any other system of automated dissemination of quotations of
securities prices, days on which trades may be effected through such system,
(ii) if the Common Stock is listed or admitted for trading on any national or
regional securities exchange, days on which such national or regional securities
exchange is open for business, or (iii) if the Common Stock is not listed on a
national or regional securities exchange or quoted on the Nasdaq National Market
or any other system of automated dissemination of quotation of securities
prices, days on which the Common Stock is traded regular way in the
over-the-counter market and for which a closing bid and a closing asked price
for the Common Stock are available.

        "Trust Indenture Act" means the Trust Indenture Act of 1939, and the
rules and regulations thereunder, as in force at the date as of which this
instrument was executed, provided, however, that in the event the Trust
Indenture Act of 1939 is amended after such date, "Trust


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<PAGE>   13

Indenture Act" means, to the extent required by any such amendment, the Trust
Indenture Act of 1939, and the rules and regulations thereunder, as so amended.

        "Trustee" means the Person named as the "Trustee" in the first paragraph
of this instrument until a successor Trustee shall have become such pursuant to
the applicable provisions of this Indenture, and thereafter "Trustee" shall mean
such successor Trustee.

        "Underwriting Agreement" means the Underwriting Agreement, dated
February 5, 2001, among the Company, Goldman, Sachs & Co., Morgan Stanley & Co.
Incorporated, Banc of America Securities LLC and Robertson Stephens, Inc., as
underwriters, relating to the offering and sale of the Securities.

        "United States" means the United States of America (including the States
and the District of Columbia), its territories, its possessions and other areas
subject to its jurisdiction (its "possessions" including Puerto Rico, the U.S.
Virgin Islands, Guam, American Samoa, Wake Island and the Northern Mariana
Islands).

SECTION 1.2     Compliance Certificates and Opinions.

        Upon any application or request by the Company to the Trustee to take
any action under any provision of this Indenture, the Company shall furnish to
the Trustee an Officers' Certificate stating that all conditions precedent, if
any, provided for in this Indenture relating to the proposed action have been
complied with and an Opinion of Counsel stating that in the opinion of such
counsel all such conditions precedent, if any, have been complied with, except
that in the case of any such application or request as to which the furnishing
of such documents is specifically required by any provision of this Indenture
relating to such particular application or request, no additional certificate or
opinion need be furnished.

        Every certificate or opinion with respect to compliance with a condition
or covenant provided for in this Indenture (including certificates provided for
in Section 10.8) shall include:

        (1)     a statement that each individual signing such certificate or
opinion has read such covenant or condition and the definitions herein relating
thereto;

        (2)     a brief statement as to the nature and scope of the examination
or investigation upon which the statements or opinions contained in such
certificate or opinion are based;

        (3)     a statement that, in the opinion of such individual, he has made
such examination or investigation as is necessary to enable him to express an
informed opinion as to whether or not such covenant or condition has been
complied with; and

        (4)     a statement as to whether, in the opinion of each such
individual, such condition or covenant has been complied with.

SECTION 1.3     Form of Documents Delivered to the Trustee.

        In any case where several matters are required to be certified by, or
covered by an opinion of, any specified Person, it is not necessary that all
such matters be certified by, or


                                      -8-
<PAGE>   14

covered by the opinion of, only one such Person, or that they be so certified or
covered by only one document, but one such Person may certify or give an opinion
with respect to some matters and one or more other such Persons as to other
matters, and any such Person may certify or give an opinion as to such matters
in one or several documents.

        Any certificate or opinion of an officer of the Company may be based,
insofar as it relates to legal matters, upon a certificate or opinion of, or
representations by, counsel, unless such officer knows, or in the exercise of
reasonable care should know, that the certificate or opinion or representations
with respect to the matters upon which such certificate or opinion is based are
erroneous. Any such certificate or opinion of counsel may be based, insofar as
it relates to factual matters, upon a certificate or opinion of, or
representations by, an officer or officers of the Company or any other Person
stating that the information with respect to such factual matters is in the
possession of the Company or such other Person, unless such counsel knows, or in
the exercise of reasonable care should know, that the certificate or opinion or
representations with respect to such matters are erroneous.

        Where any Person is required to make, give or execute two or more
applications, requests, consents, certificates, statements, opinions or other
instruments under this Indenture, they may, but need not, be consolidated and
form one instrument.

SECTION 1.4     Acts of Holders of Securities.

        (1)     Any request, demand, authorization, direction, notice, consent,
waiver or other action provided or permitted by this Indenture to be given or
taken by Holders of Securities may be embodied in and evidenced by (A) one or
more instruments of substantially similar tenor signed by such Holders in person
or by an agent or proxy duly appointed in writing by such Holders or (B) the
record of Holders of Securities voting in favor thereof, either in person or by
proxies duly appointed in writing, at any meeting of Holders of Securities duly
called and held in accordance with the provisions of Article IX. Such action
shall become effective when such instrument or instruments or record is
delivered to the Trustee and, where it is hereby expressly required, to the
Company. The Trustee shall promptly deliver to the Company copies of all such
instruments and records delivered to the Trustee. Such instrument or instruments
and records (and the action embodied therein and evidenced thereby) are herein
sometimes referred to as the "Act" of the Holders of Securities signing such
instrument or instruments and so voting at such meeting. Proof of execution of
any such instrument or of a writing appointing any such agent or proxy, or of
the holding by any Person of a Security, shall be sufficient for any purpose of
this Indenture and (subject to Section 6.1) conclusive in favor of the Trustee
and the Company if made in the manner provided in this Section. The record of
any meeting of Holders of Securities shall be proved in the manner provided in
Section 9.6.

        (2)     The fact and date of the execution by any Person of any such
instrument or writing may be proved by the affidavit of a witness of such
execution or by a certificate of a notary public or other officer authorized by
law to take acknowledgments of deeds, certifying that the individual signing
such instrument or writing acknowledged to him the execution thereof. Where such
execution is by a signer acting in a capacity other than his individual
capacity, such certificate or affidavit shall also constitute sufficient proof
of his authority.


                                      -9-
<PAGE>   15

        (3)     The principal amount and serial number of any Security held by
any Person, and the date of his holding the same, shall be proved by the
Security Register.

        (4)     The fact and date of execution of any such instrument or writing
and the authority of the Person executing the same may also be proved in any
other manner which the Trustee deems sufficient; and the Trustee may in any
instance require further proof with respect to any of the matters referred to in
this Section 1.4.


        (5)     The Company may set any day as the record date for the purpose
of determining the Holders entitled to give or take any request, demand,
authorization, direction, notice, consent, waiver or other action, or to vote on
any action, authorized or permitted by this Indenture to be given or taken by
Holders. Promptly and in any case not later than ten days after setting a record
date, the Company shall notify the Trustee and the Holders of such record date.
If not set by the Company prior to the first solicitation of a Holder made by
any Person in respect of any such action, or, in the case of any such vote,
prior to such vote, the record date for any such action or vote shall be the
30th day (or, if later, the date of the most recent list of Holders required to
be provided pursuant to Section 15.1) prior to such first solicitation or vote,
as the case may be. With regard to any record date, the Holders on such date (or
their duly appointed agents or proxies), and only such Persons, shall be
entitled to give or take, or vote on, the relevant action, whether or not such
Holders remain Holders after such record date. Notwithstanding the foregoing,
the Company shall not set a record date for, and the provisions of this
paragraph shall not apply with respect to, any notice, declaration or direction
referred to in the next paragraph.

        Upon receipt by the Trustee from any Holder of (i) any notice of default
or breach referred to in Section 5.1(4), if such default or breach has occurred
and is continuing and the Trustee shall not have given such a notice to the
Company, (ii) any declaration of acceleration referred to in Section 5.2, if an
Event of Default has occurred and is continuing and the Trustee shall not have
given such a declaration to the Company, or (iii) any direction referred to in
Section 5.12, if the Trustee shall not have taken the action specified in such
direction, then, with respect to clauses (ii) and (iii), a record date shall
automatically and without any action by the Company or the Trustee be set for
determining the Holders entitled to join in such declaration or direction, which
record date shall be the close of business on the tenth day (or, if such day is
not a Business Day, the first Business Day thereafter) following the day on
which the Trustee receives such declaration or direction, and, with respect to
clause (i), the Trustee may set any day as a record date for the purpose of
determining the Holders entitled to join in such notice of default. Promptly
after such receipt by the Trustee of any such declaration or direction referred
to in clause (ii) or (iii), and promptly after setting any record date with
respect to clause (i), and as soon as practicable thereafter, the Trustee shall
notify the Company and the Holders of any such record date so fixed. The Holders
on such record date (or their duly appointed agents or proxies), and only such
Persons, shall be entitled to join in such notice, declaration or direction,
whether or not such Holders remain Holders after such record date; provided
that, unless such notice, declaration or direction shall have become effective
by virtue of Holders of the requisite principal amount of Securities on such
record date (or their duly appointed agents or proxies) having joined therein on
or prior to the 90th day after such record date, such notice, declaration or
direction shall automatically and without any action by any Person be canceled
and of no further effect. Nothing in this paragraph shall be construed to
prevent a Holder (or a duly appointed agent or proxy thereof) from giving,
before or after the expiration of such 90-day


                                      -10-
<PAGE>   16

period, a notice, declaration or direction contrary to or different from, or,
after the expiration of such period, identical to, the notice, declaration or
direction to which such record date relates, in which event a new record date in
respect thereof shall be set pursuant to this paragraph. In addition, nothing in
this paragraph shall be construed to render ineffective any notice, declaration
or direction of the type referred to in this paragraph given at any time to the
Trustee and the Company by Holders (or their duly appointed agents or proxies)
of the requisite principal amount of Securities on the date such notice,
declaration or direction is so given.

        (6)     Except as provided in Sections 5.12 and 5.13, any request,
demand, authorization, direction, notice, consent, election, waiver or other Act
of the Holder of any Security shall bind every future Holder of the same
Security and the Holder of every Security issued upon the registration of
transfer thereof or in exchange therefor or in lieu thereof in respect of
anything done, omitted or suffered to be done by the Trustee or the Company in
reliance thereon, whether or not notation of such action is made upon such
Security.

        (7)     The provisions of this Section 1.4 are subject to the provisions
of Section 9.5.

SECTION 1.5     Notices, Etc to the Trustee and Company.

        Any request, demand, authorization, direction, notice, consent,
election, waiver or other Act of Holders of Securities or other document
provided or permitted by this Indenture to be made upon, given or furnished to,
or filed with,

        (1)     the Trustee by any Holder of Securities or by the Company shall
be sufficient for every purpose hereunder if made, given, furnished or filed in
writing to or with a Responsible Officer of the Trustee and received at its
Corporate Trust Office, Attention: Corporate Trust Department.

        (2)     the Company by the Trustee or by any Holder of Securities shall
be sufficient for every purpose hereunder (unless otherwise herein expressly
provided) if in writing, mailed, first-class postage prepaid, or telecopied and
confirmed by mail, first-class postage prepaid, or delivered by hand or
overnight courier, addressed to the Company at 1201 Winterson Road, Linthicum,
Maryland 21090, Attention: Chief Financial Officer, or at any other address
previously furnished in writing to the Trustee by the Company.

SECTION 1.6     Notice to Holders of Securities; Waiver.

        Except as otherwise expressly provided herein, where this Indenture
provides for notice to Holders of Securities of any event, such notice shall be
sufficiently given to Holders if in writing and mailed, first-class postage
prepaid or delivered by an overnight delivery service, to each Holder of a
Security affected by such event, at the address of such Holder as it appears in
the Security Register, not earlier than the earliest date and not later than the
latest date prescribed for the giving of such notice.

        Neither the failure to mail such notice, nor any defect in any notice so
mailed, to any particular Holder of a Security shall affect the sufficiency of
such notice with respect to other Holders of Securities. In case by reason of
the suspension of regular mail service or by reason of any other cause it shall
be impracticable to give such notice by mail, then such notification to


                                      -11-
<PAGE>   17

Holders of Securities as shall be made with the approval of the Trustee, which
approval shall not be unreasonably withheld, shall constitute a sufficient
notification to such Holders for every purpose hereunder.

        Such notice shall be deemed to have been given when such notice is
mailed.

        Where this Indenture provides for notice in any manner, such notice may
be waived in writing by the Person entitled to receive such notice, either
before or after the event, and such waiver shall be the equivalent of such
notice. Waivers of notice by Holders of Securities shall be filed with the
Trustee, but such filing shall not be a condition precedent to the validity of
any action taken in reliance upon such waiver.

SECTION 1.7     Effect of Headings and Table of Contents.

        The Article and Section headings herein and the Table of Contents are
for convenience only and shall not affect the construction hereof.

SECTION 1.8     Successors and Assigns.

        All covenants and agreements in this Indenture by the Company shall bind
its successors and assigns, whether so expressed or not.

SECTION 1.9     Separability Clause.

        In case any provision in this Indenture or the Securities shall be
invalid, illegal or unenforceable, the validity, legality and enforceability of
the remaining provisions shall not in anyway be affected or impaired thereby.

SECTION 1.10    Benefits of Indenture.

        Nothing in this Indenture or in the Securities, express or implied,
shall give to any Person, other than the parties hereto and their successors
assigns hereunder and the Holders of Securities, any benefit or legal or
equitable right, remedy or claim under this Indenture.

SECTION 1.11    Governing Law.

        THIS INDENTURE AND THE SECURITIES SHALL BE GOVERNED BY AND CONSTRUED IN
ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK, THE UNITED STATES OF AMERICA.

SECTION 1.12    Legal Holidays.

        In any case where any Interest Payment Date, Redemption Date, Repurchase
Date or Stated Maturity of any Security or the last day on which a Holder of a
Security has a right to convert his Security shall not be a Business Day at a
Place of Payment or Place of Conversion, as the case may be, then
(notwithstanding any other provision of this Indenture or of the Securities)
payment of principal of, premium, if any, or interest on, or the payment of the
Redemption Price or Repurchase Price (whether the same is payable in cash or in
shares of Common Stock in the


                                      -12-
<PAGE>   18

case of the Repurchase Price) with respect to, or delivery for conversion of,
such Security need not be made at such Place of Payment or Place of Conversion,
as the case may be, on or by such day, but may be made on or by the next
succeeding Business Day at such Place of Payment or Place of Conversion, as the
case may be, with the same force and effect as if made on the Interest Payment
Date, Redemption Date or Repurchase Date, or at the Stated Maturity or by such
last day for conversion; provided, however, that in the case that payment is
made on such succeeding Business Day, no interest shall accrue on the amount so
payable for the period from and after such Interest Payment Date, Redemption
Date, Repurchase Date, Stated Maturity or last day for conversion, as the case
may be.

SECTION 1.13    Conflict With Trust Indenture Act.

        If any provision hereof limits, qualifies or conflicts with a provision
of the Trust Indenture Act that is required under such Act to be a part of and
govern this Indenture, the latter provision shall control. If any provision of
this Indenture modifies or excludes any provision of the Trust Indenture Act
that may be so modified or excluded, the latter provision shall be deemed to
apply to this Indenture as so modified or to be excluded, as the case may be.

                                   ARTICLE II
                                 SECURITY FORMS

SECTION 2.1     Form Generally.

        The Securities shall be in substantially the form set forth in this
Article, with such appropriate insertions, omissions, substitutions and other
variations as are required or permitted by this Indenture, and may have such
letters, numbers or other marks of identification and such legends or
endorsements placed thereon as may be required to comply with the rules of any
securities exchange, the Internal Revenue Code of 1986, as amended, and
regulations thereunder (the "Code"), or as may, consistent herewith, be
determined by the officers executing such Securities, as evidenced by their
execution thereof. All Securities shall be in fully registered form.

        The Trustee's certificates of authentication shall be in substantially
the form set forth in Section 2.3.

        Conversion notices shall be in substantially the form set forth in
Section 2.4.

        Repurchase notices shall be substantially in the form set forth in
Section 2.2.

        The Securities shall be printed, lithographed, typewritten or engraved
or produced by any combination of these methods or may be produced in any other
manner permitted by the rules of any automated quotation system or securities
exchange (including on steel engraved borders if so required by any securities
exchange upon which the Securities may be listed) on which the Securities may be
quoted or listed, as the case may be, all as determined by the officers
executing such Securities, as evidenced by their execution thereof.

        Upon their original issuance, Securities shall be issued in the form of
one or more Global Securities in definitive, fully registered form without
interest coupons and shall be registered in


                                      -13-
<PAGE>   19

the name of DTC, as Depositary, or its nominee, and deposited with the Trustee,
as custodian for DTC, for credit by DTC to the respective accounts of beneficial
owners of the Securities represented thereby (or such other accounts as they may
direct).

SECTION 2.2     Form of Security.

                                 [FORM OF FACE]

        [THE FOLLOWING LEGEND SHALL APPEAR ON THE FACE OF EACH GLOBAL SECURITY:

THIS SECURITY IS A GLOBAL SECURITY WITHIN THE MEANING OF THE INDENTURE
HEREINAFTER REFERRED TO AND IS REGISTERED IN THE NAME OF THE DEPOSITARY OR A
NOMINEE OF THE DEPOSITARY, WHICH MAY BE TREATED BY THE COMPANY, THE TRUSTEE AND
ANY AGENT THEREOF AS OWNER AND HOLDER OF THIS SECURITY FOR ALL PURPOSES.

UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE
DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION ("DTC"), TO THE COMPANY OR ITS
AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY CERTIFICATE
ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR IN SUCH OTHER NAME AS IS
REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC (AND ANY PAYMENT IS MADE TO
CEDE & CO. OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED
REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR
OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE REGISTERED OWNER
HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

UNLESS AND UNTIL IT IS EXCHANGED IN WHOLE OR IN PART FOR SECURITIES IN
DEFINITIVE REGISTERED FORM IN THE LIMITED CIRCUMSTANCES REFERRED TO IN THE
INDENTURE, THIS GLOBAL SECURITY MAY NOT BE TRANSFERRED EXCEPT AS A WHOLE BY THE
DEPOSITARY TO A NOMINEE OF THE DEPOSITARY OR BY A NOMINEE OF THE DEPOSITARY TO
THE DEPOSITARY OR ANOTHER NOMINEE OF THE DEPOSITARY OR BY THE DEPOSITARY OR ANY
SUCH NOMINEE TO A SUCCESSOR DEPOSITARY OR A NOMINEE OF SUCH SUCCESSOR
DEPOSITARY.]


                                      -14-
<PAGE>   20

                                CIENA CORPORATION

                   3.75% CONVERTIBLE NOTE DUE FEBRUARY 1, 2008

No.                                                               $
    ------------------                                             -------------


CUSIP NO. 171779-AA-9

                CIENA CORPORATION, a corporation duly organized and existing
under the laws of the State of Delaware (herein called the "Company", which term
includes any successor Person under the Indenture referred to on the reverse
hereof), for value received, hereby promises to pay to _________________, or
registered assigns, the principal sum of ________ United States Dollars
(U.S.$______ ) [IF THIS SECURITY IS A GLOBAL SECURITY, THEN INSERT -- (which
principal amount may from time to time be increased or decreased to such other
principal amounts (which, taken together with the principal amounts of all other
Outstanding Securities, shall not exceed $600,000,000.00 (or $690,000,000.00 if
the Over-allotment Option is exercised in full) by adjustments made on the
records of the Trustee hereinafter referred to in accordance with the
Indenture)] on February 1, 2008 and to pay interest thereon, from February 9,
2001, or from the most recent Interest Payment Date (as defined below) to which
interest has been paid or duly provided for, semi-annually in arrears on
February 1 and August 1 in each year (each, an "Interest Payment Date"),
commencing August 1, 2001, at the rate of 3.75% per annum, until the principal
hereof is due, and at the rate of 3.75% per annum on any overdue principal and
premium, if any, and, to the extent permitted by law, on any overdue interest.
The interest so payable, and punctually paid or duly provided for, on any
Interest Payment Date will, as provided in the Indenture, be paid to the Person
in whose name this Security (or one or more Predecessor Securities) is
registered at the close of business on the Regular Record Date for such
interest, which shall be the January 15 or July 15 (whether or not a Business
Day), as the case may be, next preceding such Interest Payment Date. Except as
otherwise provided in the Indenture, any such interest not so punctually paid or
duly provided for will forthwith cease to be payable to the Holder on such
Regular Record Date and may either be paid to the Person in whose name this
Security (or one or more Predecessor Securities) is registered at the close of
business on a Special Record Date for the payment of such Defaulted Interest to
be fixed by the Company, notice whereof shall be given to Holders of Securities
not less than 10 days prior to the Special Record Date, or be paid at any time
in any other lawful manner not inconsistent with the requirements of any
automated quotation system or securities exchange on which the Securities may be
quoted or listed, and upon such notice as may be required by such exchange, all
as more fully provided in the Indenture. Payments of principal shall be made
upon the surrender of this Security at the option of the Holder at the Corporate
Trust Office of the Trustee, or at such other office or agency of the Company as
may be designated by it for such purpose in the Borough of Manhattan, The City
of New York, in such lawful monies of the United States of America as at the
time of payment shall be legal tender for the payment of public and private
debts, or at such other offices or agencies as the Company may designate, by
United States Dollar check drawn on, or wire transfer to, a United States Dollar
account (such a transfer to be made only to a Holder of an aggregate principal
amount of Securities in excess of U.S.$2,000,000 and only if such Holder shall
have furnished wire instructions in writing to the


                                      -15-
<PAGE>   21

Trustee no later than 15 days prior to the relevant payment date). Payment of
interest on this Security may be made by United States Dollar check mailed to
the address of the Person entitled thereto as such address shall appear in the
Security Register, or, upon written application by the Holder to the Security
Registrar setting forth wire instructions not later than the relevant Record
Date, by transfer to a United States Dollar account (such a transfer to be made
only to a Holder of an aggregate principal amount of Securities in excess of
U.S. $2,000,000 and only if such Holder shall have furnished wire instructions
in writing to the Trustee no later than 15 days prior to the relevant payment
date).

        Except as specifically provided herein and in the Indenture, the Company
shall not be required to make any payment with respect to any tax, assessment or
other governmental charge imposed by any government or any political subdivision
or taxing authority thereof or therein.

        Reference is hereby made to the further provisions of this Security set
forth on the reverse hereof, which further provisions shall for all purposes
have the same effect as if set forth at this place.

        Unless the certificate of authentication hereon has been executed by the
Trustee referred to on the reverse hereof or an Authenticating Agent by the
manual signature of one of their respective authorized signatories, this
Security shall not be entitled to any benefit under the Indenture or be valid or
obligatory for any purpose.


                                      -16-
<PAGE>   22

        IN WITNESS WHEREOF, the Company has caused this Security to be duly
executed.



                                              CIENA CORPORATION

                                              By:
                                                  --------------------------
                                                  Name:
                                                  Title:

Attest:


By:
    ---------------------------
    Name:
    Title:



TRUSTEE'S CERTIFICATE OF AUTHENTICATION

This is one of the Securities referred to in the within-mentioned Indenture.

Dated:


FIRST UNION NATIONAL BANK, as Trustee


By:
    ------------------------------
         Authorized Signatory



                                      -17-
<PAGE>   23

                                [FORM OF REVERSE]

        This Security is one of a duly authorized issue of securities of the
Company designated as its "3.75% Convertible Notes due February 1, 2008 (herein
called the "Securities"), limited in aggregate principal amount to U.S.
$600,000,000.00 (or $690,000,000.00 if the Over-allotment Option is exercised in
full), issued and to be issued under an Indenture, dated as of February 9, 2001
(herein called the "Indenture"), between the Company and First Union National
Bank, as Trustee (herein called the "Trustee", which term includes any successor
trustee under the Indenture), to which Indenture and all indentures supplemental
thereto reference is hereby made for a statement of the respective rights,
limitations of rights, duties and immunities thereunder of the Company, the
Trustee and the Holders of the Securities and of the terms upon which the
Securities are, and are to be, authenticated and delivered. As provided in the
Indenture and subject to certain limitations therein set forth, Securities are
exchangeable for a like aggregate principal amount of Securities of any
authorized denominations as requested by the Holder surrendering the same upon
surrender of the Security or Securities to be exchanged, at the Corporate Trust
Office of the Trustee. The Trustee upon such surrender by the Holder will issue
the new Securities in the requested denominations.

        No sinking fund is provided for the Securities. The Securities will not
be subject to redemption until on or after the third Business Day after February
1, 2004 and will be redeemable on and after that date at the option of the
Company, in whole or in part, upon not less than 30 nor more than 60 days notice
to the Holders prior to the Redemption Date at the Redemption Prices (expressed
as percentages of the principal amount) set forth below.

        The following table sets forth the Redemption Prices (expressed as
percentages of the principal amount) if such Security is redeemed during the
12-month period beginning February 1 (beginning the third Business Day after
February 1, 2004 through January 31, 2005, in the case of the first such
period):

<TABLE>
<CAPTION>

                    YEAR                  REDEMPTION PRICE
                    ----                  ----------------
                    <S>                   <C>
                    2004                      102.143%
                    2005                      101.607%
                    2006                      101.071%
                    2007                      100.536%
</TABLE>

and thereafter at a Redemption Price equal to 100% of the principal amount,
together, in each case, with accrued interest to the Redemption Date; provided,
however, that interest installments on Securities whose Stated Maturity is on or
prior to such Redemption Date will be payable to the Holders of such Securities,
or one or more Predecessor Securities, of record at the close of business on the
relevant Record Dates referred to on the face hereof, all as provided in the
Indenture.

        In the event of a redemption of the Securities, the Company will not be
required (a) to register the transfer or exchange of Securities for a period of
15 days immediately preceding the


                                      -18-
<PAGE>   24

date notice is given identifying the serial numbers of the Securities called for
such redemption or (b) to register the transfer or exchange of any Security, or
portion thereof, called for redemption.

        In any case where the due date for the payment of the principal of,
premium, if any, or interest on any Security or the last day on which a Holder
of a Security has a right to convert his Security shall be, at any Place of
Payment or Place of Conversion as the case may be, a day on which banking
institutions at such Place of Payment or Place of Conversion are authorized or
obligated by law or executive order to close, then payment of principal,
premium, if any, or interest or delivery for conversion of such Security need
not be made on or by such date at such place but may be made on or by the next
succeeding day at such place which is not a day on which banking institutions
are authorized or obligated by law or executive order to close, with the same
force and effect as if made on the date for such payment or the date fixed for
redemption or repurchase, or by such last day for conversion, and no interest
shall accrue on the amount so payable for the period after such date.

        Subject to and upon compliance with the provisions of the Indenture, the
Holder of this Security is entitled, at his option, at any time on or before the
close of business on the date of Maturity, or in case this Security or a portion
hereof is called for redemption or the Holder hereof has exercised his right to
require the Company to repurchase this Security or such portion hereof, then in
respect of this Security until the Business Day immediately preceding, but
(unless the Company defaults in making the payment due upon redemption or
repurchase, as the case may be) not after, the close of business on the Business
Day immediately preceding the Redemption Date or the Repurchase Date, as the
case may be, to convert this Security (or any portion of the principal amount
hereof that is an integral multiple of U.S.$1,000, provided that the unconverted
portion of such principal amount is U.S.$1,000 or any integral multiple of
U.S.$1,000 in excess thereof) into fully paid and nonassessable shares of Common
Stock of the Company at an initial Conversion Rate of 9.5808 shares of Common
Stock for each U.S.$1,000 principal amount of Securities (or at the current
adjusted Conversion Rate if an adjustment has been made as provided in the
Indenture) by surrender of this Security, duly endorsed or assigned to the
Company or in blank and, in case such surrender shall be made during the period
from the close of business on any Regular Record Date next preceding any
Interest Payment Date to the opening of business on such Interest Payment Date
(except if this Security or portion thereof has been called for redemption on a
Redemption Date or is repurchasable on a Repurchase Date occurring, in either
case, during such period and, as a result, the right to convert this Security
would otherwise terminate in such period if not exercised), also accompanied by
payment in New York Clearing House or other funds acceptable to the Company of
an amount equal to the interest payable on such Interest Payment Date on the
principal amount of this Security then being converted, and also the conversion
notice hereon duly executed, to the Company at the Corporate Trust Office of the
Trustee, or at such other office or agency of the Company, subject to any laws
or regulations applicable thereto and subject to the right of the Company to
terminate the appointment of any Conversion Agent (as defined below) as may be
designated by it for such purpose in the Borough of Manhattan, The City of New
York, or at such other offices or agencies as the Company may designate (each a
"Conversion Agent"), provided, further, that if this Security or portion hereof
has been called for redemption on a Redemption Date or is repurchasable on a
Repurchase Date occurring, in either case, during the period from the close of
business on any Regular Record Date next preceding any Interest Payment Date to
the opening of business on such succeeding Interest Payment Date, and as a
result, the right to convert this


                                      -19-
<PAGE>   25

Security would otherwise terminate in such period if not exercised and this
Security is surrendered for conversion during such period, then the Holder of
this Security on such Regular Record Date will be entitled to receive the
interest accruing hereon from the Interest Payment Date next preceding the date
of such conversion to such succeeding Interest Payment Date and the Holder of
this Security who converts this Security or a portion hereof during such period
shall not be required to pay such interest upon surrender of this Security for
conversion. Subject to the provisions of the preceding sentence and, in the case
of a conversion after the close of business on the Regular Record Date next
preceding any Interest Payment Date and on or before the close of business on
such Interest Payment Date, to the right of the Holder of this Security (or any
Predecessor Security of record as of such Regular Record Date) to receive the
related installment of interest to the extent and under the circumstances
provided in the Indenture, no cash payment or adjustment is to be made on
conversion for interest accrued hereon from the Interest Payment Date next
preceding the day of conversion, or for dividends on the Common Stock issued on
conversion hereof. The Company shall thereafter deliver to the Holder the fixed
number of shares of Common Stock (together with any cash adjustment, as provided
in the Indenture) into which this Security is convertible and such delivery will
be deemed to satisfy the Company's obligation to pay the principal amount of
this Security. No fractions of shares or scrip representing fractions of shares
will be issued on conversion, but instead of any fractional interest (calculated
to the nearest 1/100th of a share) the Company shall pay a cash adjustment as
provided in the Indenture. The Conversion Rate is subject to adjustment as
provided in the Indenture. In addition, the Indenture provides that in case of
certain consolidations or mergers to which the Company is a party (other than a
consolidation or merger that does not result in any reclassification,
conversion, exchange or cancellation of the Common Stock) or the conveyance,
transfer, sale or lease of all or substantially all of the property and assets
of the Company, the Indenture shall be amended, without the consent of any
Holders of Securities, so that this Security, if then Outstanding, will be
convertible thereafter, during the period this Security shall be convertible as
specified above, only into the kind and amount of securities, cash and other
property receivable upon such consolidation, merger, conveyance, transfer, sale
or lease by a holder of the number of shares of Common Stock of the Company into
which this Security could have been converted immediately prior to such
consolidation, merger, conveyance, transfer, sale or lease (assuming such holder
of Common Stock is not a Constituent Person or an Affiliate of a Constituent
Person, failed to exercise any rights of election and received per share the
kind and amount received per share by a plurality of Non-electing Shares). No
adjustment in the Conversion Rate will be made until such adjustment would
require an increase or decrease of at least one percent of such rate, provided
that any adjustment that would otherwise be made will be carried forward and
taken into account in the computation of any subsequent adjustment.

        If a Change in Control occurs, the Holder of this Security, at the
Holder's option, shall have the right, in accordance with the provisions of the
Indenture, to require the Company to repurchase this Security (or any portion of
the principal amount hereof that is at least $1,000 or an integral multiple of
$1,000 in excess thereof, provided that the portion of the principal amount of
this Security to be Outstanding after such repurchase is at least equal to
U.S.$1,000) for cash at a Repurchase Price equal to 100% of the principal amount
thereof plus interest accrued to the Repurchase Date. At the option of the
Company, the Repurchase Price may be paid in cash or, subject to the conditions
provided in the Indenture, by delivery of shares of Common Stock having a fair
market value equal to the Repurchase Price. For purposes of this paragraph, the
fair market value of shares of Common Stock shall be determined by the Company
and shall be equal


                                      -20-
<PAGE>   26

to 95% of the average of the Closing Prices Per Share for the five consecutive
Trading Days immediately preceding and including the third Trading Day prior to
the Repurchase Date. Whenever in this Security there is a reference, in any
context, to the principal of any Security as of any time, such reference shall
be deemed to include reference to the Repurchase Price payable in respect of
such Security to the extent that such Repurchase Price is, was or would be so
payable at such time, and express mention of the Repurchase Price in any
provision of this Security shall not be construed as excluding the Repurchase
Price so payable in those provisions of this Security when such express mention
is not made; provided, however, that, for the purposes of the second succeeding
paragraph, such reference shall be deemed to include reference to the Repurchase
Price only to the extent the Repurchase Price is payable in cash.

        [THE FOLLOWING PARAGRAPH SHALL APPEAR IN EACH GLOBAL SECURITY:

        In the event of a deposit or withdrawal of an interest in this Security,
including an exchange, transfer, redemption, repurchase or conversion of this
Security in part only, the Trustee, as custodian of the Depositary, shall make
an adjustment on its records to reflect such deposit or withdrawal in accordance
with the Applicable Procedures.]

        [THE FOLLOWING PARAGRAPH SHALL APPEAR IN EACH SECURITY THAT IS NOT A
GLOBAL SECURITY:

        In the event of redemption, repurchase or conversion of this Security in
part only, a new Security or Securities for the unredeemed, unrepurchased or
unconverted portion hereof will be issued in the name of the Holder hereof.]

        If an Event of Default shall occur and be continuing, the principal of
all the Securities, together with accrued interest to the date of declaration,
may be declared due and payable in the manner and with the effect provided in
the Indenture. Upon payment (i) of the amount of principal so declared due and
payable, together with accrued interest to the date of declaration, and (ii) of
interest on any overdue principal and, to the extent permitted by applicable
law, overdue interest, all of the Company's obligations in respect of the
payment of the principal of and interest on the Securities shall terminate.

        The Indenture permits, with certain exceptions as therein provided, the
amendment thereof and the modification of the rights and obligations of the
Company and the rights of the Holders of the Securities under the Indenture at
any time by the Company and the Trustee with either (a) the written consent of
the Holders of not less than a majority in principal amount of the Securities at
the time Outstanding, or (b) by the adoption of a resolution, at a meeting of
Holders of the Outstanding Securities at which a quorum is present, by the
Holders of at least 66-2/3% in aggregate principal amount of the Outstanding
Securities represented and entitled to vote at such meeting. The Indenture also
contains provisions permitting the Holders of specified percentages in principal
amount of the Securities at the time Outstanding, on behalf of the Holders of
all the Securities, to waive compliance by the Company with certain provisions
of the Indenture and certain past defaults under the Indenture and their
consequences. Any such consent or waiver by the Holder of this Security shall be
conclusive and binding upon such Holder and upon all future Holders of this
Security and of any Security issued upon the registration of transfer hereof or
in


                                      -21-
<PAGE>   27

exchange herefor or in lieu hereof whether or not notation of such consent or
waiver is made upon this Security or such other Security.

        As provided in and subject to the provisions of the Indenture, the
Holder of this Security shall not have the right to institute any proceeding
with respect to the Indenture or for the appointment of a receiver or trustee or
for any other remedy thereunder, unless such Holder shall have previously given
the Trustee written notice of a continuing Event of Default, the Holders of not
less than 25% in principal amount of the Outstanding Securities shall have made
written request to the Trustee to institute proceedings in respect of such Event
of Default as Trustee and offered the Trustee reasonable indemnity and the
Trustee shall not have received from the Holders of a majority in principal
amount of the Securities Outstanding a direction inconsistent with such request,
and shall have failed to institute any such proceeding, for 60 days after
receipt of such notice, request and offer of indemnity. The foregoing shall not
apply to any suit instituted by the Holder of this Security for the enforcement
of any payment of principal hereof, premium if any, or interest hereon on or
after the respective due dates expressed herein or for the enforcement of the
right to convert this Security as provided in the Indenture.

        No reference herein to the Indenture and no provision of this Security
or of the Indenture shall alter or impair the obligation of the Company, which
is absolute and unconditional, to pay the principal of, premium, if any, and
interest on this Security at the times, places and rate, and in the coin or
currency, herein prescribed or to convert this Security as provided in the
Indenture.

        As provided in the Indenture and subject to certain limitations therein
set forth, the transfer of this Security is registrable on the Security Register
upon surrender of this Security for registration of transfer at the Corporate
Trust Office of the Trustee or at such other office or agency of the Company as
may be designated by it for such purpose in the Borough of Manhattan, The City
of New York (which shall initially be an office or agency of the Trustee), or at
such other offices or agencies as the Company may designate, duly endorsed by,
or accompanied by a written instrument of transfer in form satisfactory to the
Company and the Security Registrar duly executed by, the Holder thereof or his
attorney duly authorized in writing, and thereupon one or more new Securities,
of authorized denominations and for the same aggregate principal amount, will be
issued to the designated transferee or transferees by the Registrar. No service
charge shall be made for any such registration of transfer or exchange, but the
Company may require payment of a sum sufficient to recover any tax or other
governmental charge payable in connection therewith.

        Prior to due presentation of this Security for registration of transfer,
the Company, the Trustee and any agent of the Company or the Trustee may treat
the Person in whose name this Security is registered, as the owner hereof for
all purposes, whether or not this Security be overdue, and neither the Company,
the Trustee nor any such agent shall be affected by notice to the contrary.

        No recourse for the payment of the principal (and premium, if any) or
interest on this Security and no recourse under or upon any obligation, covenant
or agreement of the Company in the Indenture or any indenture supplemental
thereto or in any Security, or because of the creation of any indebtedness
represented thereby, shall be had against any incorporator, stockholder,
employee, agent, officer or director or subsidiary, as such, past, present or
future, of


                                      -22-
<PAGE>   28

the Company or of any successor corporation, either directly or through the
Company or any successor corporation, whether by virtue of any constitution,
statute or rule of law or by the enforcement of any assessment or penalty or
otherwise, all such liability being, by the acceptance hereof and as part of
consideration for the issue hereof, expressly waived and released.

        Interest on this Security shall be computed on the basis of a 360-day
year of twelve 30-day months.

        THE INDENTURE AND THIS SECURITY SHALL BE GOVERNED BY AND CONSTRUED IN
ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK, UNITED STATES OF AMERICA.

        All terms used in this Security which are defined in the Indenture shall
have the meanings assigned to them in the Indenture.

                                  ABBREVIATIONS

        The following abbreviations, when used in the inscription of the face of
this Security, shall be construed as though they were written out in full
according to applicable laws or regulations:

<TABLE>
<CAPTION>
<S>           <C>                                         <C>                     <C>
TEN COM       as tenant in common                         UNIF GIFT MIN ACT       ____ Custodian ____
TEN ENT       as tenants by the entireties (Cust)                                   (Cust)        (Minor)
JT TEN        as joint tenants with right of survivorship                         under Uniform Gifts to
              and not as tenants in common                                        Minors Act _____
                                                                                            (State)
</TABLE>

        Additional abbreviations may also be used though not in the above list.

                    ELECTION OF HOLDER TO REQUIRE REPURCHASE

        (1)     Pursuant to Section 14.1 of the Indenture, the undersigned
hereby elects to have this Security repurchased by the Company.

        (2)     The undersigned hereby directs the Trustee or the Company to pay
it or ______________ an amount in cash or, at the Company's election, Common
Stock valued as set forth in the Indenture, equal to 100% of the principal
amount to be repurchased (as set forth below), plus interest accrued to the
Repurchase Date, as provided in the Indenture.

Dated:

----------------------------

----------------------------
Signature(s)

Signature(s) must be guaranteed by an Eligible Guarantor Institution with
membership in an approved signature guarantee program pursuant


                                      -23-
<PAGE>   29

to Rule 17Ad-15 under the Securities Exchange Act of 1934.


----------------------------
Signature Guaranteed

Principal amount to be repurchased (at least U.S. $1,000 or an integral multiple
of $1,000 in excess thereof):______________________

Remaining principal amount following such repurchase (not less than U.S.
$1,000):______________

NOTICE: The signature to the foregoing Election must correspond to the Name as
written upon the face of this Security in every particular, without alteration
or any change whatsoever.

SECTION 2.3     Form of Certificate of Authentication.

        The Trustee's certificate of authentication shall be in substantially
the following form:

        This is one of the Securities referred to in the within-mentioned
Indenture.

Dated:
      ----------------------

                      FIRST UNION NATIONAL BANK
                      as Trustee

                      By:
                         --------------------------------
                          Authorized Signatory

SECTION 2.4     Form of Conversion Notice.

                                CONVERSION NOTICE

        The undersigned Holder of this Security hereby irrevocably exercises the
option to convert this Security, or any portion of the principal amount hereof
(which is U.S. $1,000 or an integral multiple of U.S. $1,000 in excess thereof,
provided that the unconverted portion of such principal amount is U.S. $1,000 or
any integral multiple of U.S. $1,000 in excess thereof) below designated, into
shares of Common Stock in accordance with the terms of the Indenture referred to
in this Security, and directs that such shares, together with a check in payment
for any fractional share and any Securities representing any unconverted
principal amount hereof, be delivered to and be registered in the name of the
undersigned unless a different name has been indicated below. If shares of
Common Stock or Securities are to be registered in the name of a Person other
than the undersigned, (a) the undersigned will pay all transfer taxes payable
with respect thereto and (b) signature(s) must be guaranteed by an Eligible
Guarantor Institution with membership in an approved signature guarantee program
pursuant to Rule 17Ad-15 under the


                                      -24-
<PAGE>   30

Securities Exchange Act of 1934. Any amount required to be paid by the
undersigned on account of interest accompanies this Security.

Dated:
      ------------    ---------------------------------------------------------
                                           Signature(s)

                      ---------------------------------------------------------
                                             Name(s)

If shares or Securities are to be registered in the name of a Person other than
the Holder, please print such Person's name and address:


---------------------------
(Name)

---------------------------

---------------------------
(Address)

---------------------------

Social Security or other Identification Number, if any

---------------------------
[Signature Guaranteed]

If only a portion of the Securities is to be converted, please indicate:

1.      Principal amount to be converted: U.S. $ ___________

2.      Principal amount and denomination of Securities representing unconverted
        principal amount to be issued:

        Amount: U.S. $___________           Denominations: U.S. $____________

(U.S.$1,000 or any integral multiple of U.S.$1,000 in excess thereof, provided
that the unconverted portion of such principal amount is U.S. $1,000 or any
integral multiple of U.S. $1,000 in excess thereof)


                                      -25-
<PAGE>   31

SECTION 2.5     Form of Assignment.

        For value received ________________ hereby sell(s), assign(s) and
transfer(s) unto ________________ (Please insert social security or other
identifying number of assignee) the within Security, and hereby irrevocably
constitutes and appoints ____________________as attorney to transfer the said
Security on the books of the Company, with full power of substitution in the
premises.

Dated:
       -----------    ----------------------------------------------------------

                                                   -----------------------------
                                                   Signature(s)

                                                   Signature(s) must be
                                                   guaranteed by an Eligible
                                                   Guarantor Institution with
                                                   membership in an approved
                                                   signature guarantee program
                                                   pursuant to Rule 17Ad - 15
                                                   under the Securities Exchange
                                                   Act of 1934.

                                                   -----------------------------
                                                   Signature Guaranteed

                                  ARTICLE III
                                 THE SECURITIES

SECTION 3.1     Title and Terms.

        The aggregate principal amount of Securities which may be authenticated
and delivered under this Indenture is limited to U.S. $600,000,000.00 (or
$690,000,000.00 if the Over-allotment Option set forth in Section 2 of the
Underwriting Agreement is exercised in full (the "Over-allotment Option")),
except for Securities authenticated and delivered pursuant to Section 3.4, 3.5,
3.6, 8.5, 12.2 or 14.3(5) in exchange for, or in lieu of, other Securities
previously authenticated and delivered under this Indenture.

        (1)     The Securities shall be known and designated as the "3.75%
Convertible Notes due February 1, 2008" of the Company. Their Stated Maturity
shall be February 1, 2008 and they shall bear interest on their principal amount
from February 9, 2001, payable semi-annually in arrears on February 1 and August
1 in each year, commencing August 1, 2001, at the rate of 3.75% per annum until
the principal thereof is due and at the rate of 3.75% per annum on any overdue
principal and, to the extent permitted by law, on any overdue interest;
provided, however, that payments shall only be made on a Business Day as
provided in Section 1.12.

        The principal of, premium, if any, and interest on the Securities shall
be payable as provided in the form of Securities set forth in Section 2.2, and
the Repurchase Price, whether payable in cash or in shares of Common Stock,
shall be payable at such places as are identified


                                      -26-
<PAGE>   32

in the Company Notice given pursuant to Section 14.3 (any city in which any
Paying Agent is located being herein called a "Place of Payment").

        The Securities shall be redeemable at the option of the Company at any
time on or after the third Business Day after February 1, 2004, in whole or in
part, subject to the conditions and as otherwise provided in Article XI and in
the form of Security set forth in Section 2.2.

        The Securities shall be convertible as provided in Article XII (any city
in which any Conversion Agent is located being herein called a "Place of
Conversion").

        The Securities shall be subject to repurchase by the Company at the
option of the Holders as provided in Article XIV.

SECTION 3.2     Denominations.

        The Securities shall be issuable only in registered form, without
coupons, in denominations of U.S.$1,000 and integral multiples of U.S.$1,000 in
excess thereof.

SECTION 3.3     Execution, Authentication, Delivery and Dating.

        The Securities shall be executed on behalf of the Company by its
Chairman of the Board, its Vice Chairman of the Board, its Chief Executive
Officer, its President, one of its Executive Vice Presidents, one of its Senior
Vice Presidents or one of its Vice Presidents, and attested by its Chief
Financial Officer, Secretary or one of its Assistant Secretaries. Any such
signature may be manual or facsimile.

        Securities bearing the manual or facsimile signature of individuals who
were at any time the proper officers of the Company shall bind the Company,
notwithstanding that such individuals or any of them have ceased to hold such
offices prior to the authentication and delivery of such Securities or did not
hold such offices at the date of such Securities.

        At any time and from time to time after the execution and delivery of
this Indenture, the Company may deliver Securities executed by the Company to
the Trustee or to its order for authentication, together with a Company Order
for the authentication and delivery of such Securities, and the Trustee in
accordance with such Company Order shall authenticate and make available for
delivery such Securities as in this Indenture provided.

        Each Security shall be dated the date of its authentication.

        No Security shall be entitled to any benefit under this Indenture or be
valid or obligatory for any purpose unless there appears on such Security a
certificate of authentication substantially in the form provided for herein
executed by the Trustee by manual signature of an authorized signatory, and such
certificate upon any Security shall be conclusive evidence, and the only
evidence, that such Security has been duly authenticated and delivered
hereunder.

SECTION 3.4     Global Securities; Non-global Securities; Book-entry Provisions.

        (1)     Global Securities


                                      -27-
<PAGE>   33

                (i)     Each Global Security authenticated under this Indenture
shall be registered in the name of the Depositary designated by the Company for
such Global Security or a nominee thereof and delivered to such Depositary or a
nominee thereof or custodian therefor, and each such Global Security shall
constitute a single Security for all purposes of this Indenture.

                (ii)    Except for exchanges of Global Securities for
definitive, Non-global Securities at the sole discretion of the Company, no
Global Security may be exchanged in whole or in part for Securities registered,
and no transfer of a Global Security in whole or in part may be registered, in
the name of any Person other than the Depositary for such Global Security or a
nominee thereof unless (A) such Depositary (i) has notified the Company that it
is unwilling or unable to continue as Depositary for such Global Security or
(ii) has ceased to be a clearing agency registered as such under the Exchange
Act or announces an intention permanently to cease business or does in fact do
so or (B) there shall have occurred and be continuing an Event of Default with
respect to such Global Security. In such event, if a successor Depositary for
such Global Security is not appointed by the Company within 90 days after the
Company receives such notice or becomes aware of such ineligibility, the Company
will execute, and the Trustee, upon receipt of an Officers' Certificate
directing the authentication and delivery of Securities, will authenticate and
deliver, Securities, in any authorized denominations in an aggregate principal
amount equal to the principal amount of such Global Security in exchange for
such Global Security.

                (iii)   If any Global Security is to be exchanged for other
Securities or canceled in whole, it shall be surrendered by or on behalf of the
Depositary or its nominee to the Trustee, as Security Registrar, for exchange or
cancellation, as provided in this Article III. If any Global Security is to be
exchanged for other Securities or canceled in part, or if another Security is to
be exchanged in whole or in part for a beneficial interest in any Global
Security, in each case, as provided in Section 3.5, then either (A) such Global
Security shall be so surrendered for exchange or cancellation, as provided in
this Article III, or (B) the principal amount thereof shall be reduced or
increased by an amount equal to the portion thereof to be so exchanged or
canceled, or equal to the principal amount of such other Security to be so
exchanged for a beneficial interest therein, as the case may be, by means of an
appropriate adjustment made on the records of the Trustee, as Security
Registrar, whereupon the Trustee, in accordance with the Applicable Procedures,
shall instruct the Depositary or its authorized representative to make a
corresponding adjustment to its records. Upon any such surrender or adjustment
of a Global Security, the Trustee shall, as otherwise provided in this Article
III, authenticate and deliver any Securities issuable in exchange for such
Global Security (or any portion thereof) to or upon the order of, and registered
in such names as may be directed by, the Depositary or its authorized
representative. Upon the request of the Trustee in connection with the
occurrence of any of the events specified in the preceding paragraph, the
Company shall promptly make available to the Trustee a reasonable supply of
Securities that are not in the form of Global Securities. The Trustee shall be
entitled to rely upon any order, direction or request of the Depositary or its
authorized representative which is given or made pursuant to this Article III if
such order, direction or request is given or made in accordance with the
Applicable Procedures.

                (iv)    Every Security authenticated and delivered upon
registration of transfer of, or in exchange for or in lieu of, a Global Security
or any portion thereof, whether pursuant to this Article III or otherwise, shall
be authenticated and delivered in the form of, and shall be, a


                                      -28-
<PAGE>   34

registered Global Security, unless such Security is registered in the name of a
Person other than the Depositary for such Global Security or a nominee thereof,
in which case such Security shall be authenticated and delivered in definitive,
fully registered form, without interest coupons.

                (v)     The Depositary or its nominee, as registered owner of a
Global Security, shall be the Holder of such Global Security for all purposes
under the Indenture and the Securities, and owners of beneficial interests in a
Global Security shall hold such interests pursuant to the Applicable Procedures.
Accordingly, any such owner's beneficial interest in a Global Security will be
shown only on, and the transfer of such interest shall be effected only through,
records maintained by the Depositary or its nominee or its Agent Members and
such owners of beneficial interests in a Global Security will not be considered
the owners or holders thereof.

        (2)     Non-global Securities. Securities issued upon the events
described in Section 3.4(l)(ii) shall be in definitive, fully registered form,
without interest coupons.

SECTION 3.5     Registration; Registration of Transfer and Exchange;
                Restrictions on

        (1)     The Company shall cause to be kept at the Corporate Trust Office
of the Trustee a register (the register maintained in such office referred to as
the "Security Register") in which, subject to such reasonable regulations as it
may prescribe, the Company shall provide for the registration of Securities and
of transfers of Securities. The Trustee is hereby appointed "Security Registrar"
for the purpose of registering Securities and transfers and exchanges of
Securities as herein provided.

        Upon surrender for registration of transfer of any Security at an office
or agency of the Company designated pursuant to Section 10.2 for such purpose,
the Company shall execute, and the Trustee shall authenticate and deliver, in
the name of the designated transferee or transferees, one or more new Securities
of any authorized denominations and of a like aggregate principal amount.

        At the option of the Holder, and subject to the other provisions of this
Section 3.5, Securities may be exchanged for other Securities of any authorized
denomination and of a like aggregate principal amount, upon surrender of the
Securities to be exchanged at any such office or agency. Whenever any Securities
are so surrendered for exchange, and subject to the other provisions of this
Section 3.5, the Company shall execute, and the Trustee shall authenticate and
deliver, the Securities that the Holder making the exchange is entitled to
receive. Every Security presented or surrendered for registration of transfer or
for exchange shall (if so required by the Company or the Security Registrar) be
duly endorsed, or be accompanied by a written instrument of transfer in form
satisfactory to the Company, the Trustee and the Security Registrar duly
executed, by the Holder thereof or his attorney duly authorized in writing.

        All Securities issued upon any registration of transfer or exchange of
Securities shall be the valid obligations of the Company, evidencing the same
debt and entitled to the same benefits under this Indenture as the Securities
surrendered upon such registration of transfer or exchange.


                                      -29-
<PAGE>   35

        No service charge shall be made to a Holder for any registration of
transfer or exchange of Securities except as provided in Section 3.6, but the
Company may require payment of a sum sufficient to cover any tax or other
governmental charge that may be imposed in connection with any registration of
transfer or exchange of Securities, other than exchanges pursuant to Section
3.4, 8.5, 12.2 or 14.3 (other than where the shares of Common Stock are to be
issued or delivered in a name other than that of the Holder of the Security) not
involving any transfer and other than any stamp and other duties, if any, which
may be imposed in connection with any such transfer or exchange by the United
States or any political subdivision thereof or therein, which shall be paid by
the Company.

        In the event of a redemption of the Securities, neither the Company nor
the Securities Registrar will be required (a) to register the transfer of or
exchange Securities for a period of 15 days immediately preceding the date
notice is given identifying the serial numbers of the Securities called for such
redemption or (b) to register the transfer of or exchange any Security, or
portion thereof, called for redemption.

        (2)     Neither the Trustee, the Paying Agent nor any of their agents
shall (i) have any duty to monitor compliance with or with respect to any
federal or state or other securities or tax laws or (ii) have any duty to obtain
documentation on any transfers or exchanges other than as specifically required
hereunder.

SECTION 3.6     Mutilated, Destroyed, Lost or Stolen Securities.

        If any mutilated Security is surrendered to the Trustee, the Company
shall execute and the Trustee shall authenticate and deliver in exchange
therefor a new Security of like tenor and principal amount and bearing a number
not contemporaneously outstanding.

        If there be delivered to the Company and to the Trustee:

        (1)     evidence to their satisfaction of the destruction, loss or theft
of any Security, and

        (2)     such security or indemnity as may be satisfactory to the Company
and the Trustee to save each of them and any agent of either of them harmless,
then, in the absence of actual notice to the Company or the Trustee that such
Security has been acquired by a bona fide purchaser, the Company shall execute
and the Trustee shall authenticate and deliver, in lieu of any such destroyed,
lost or stolen Security, a new Security of like tenor and principal amount and
bearing a number not contemporaneously outstanding.

        In case any such mutilated, destroyed, lost or stolen Security has
become or is about to become due and payable, the Company in its discretion, but
subject to any conversion rights, may, instead of issuing a new Security, pay
such Security, upon satisfaction of the conditions set forth in the preceding
paragraph.

        Upon the issuance of any new Security under this Section 3.6, the
Company may require the payment of a sum sufficient to cover any tax or other
governmental charge that may be imposed in relation thereto (other than any
stamp and other duties, if any, which may be imposed in connection therewith by
the United States or any political subdivision thereof or therein,



                                      -30-
<PAGE>   36

which shall be paid by the Company) and any other expenses (including the fees
and expenses of the Trustee) connected therewith.

        Every new Security issued pursuant to this Section 3.6 in lieu of any
mutilated, destroyed, lost or stolen Security shall constitute an original
additional contractual obligation of the Company, whether or not the mutilated,
destroyed, lost or stolen Security shall be at any time enforceable by anyone,
and such new Security shall be entitled to all the benefits of this Indenture
equally and proportionately with any and all other Securities duly issued
hereunder.

        The provisions of this Section 3.6 are exclusive and shall preclude (to
the extent lawful) all other rights and remedies of any Holder with respect to
the replacement or payment of mutilated, destroyed, lost or stolen Securities.

SECTION 3.7     Payment of Interest; Interest Rights Preserved.

        Interest on any Security that is payable, and is punctually paid or duly
provided for, on any Interest Payment Date shall be paid to the Person in whose
name that Security (or one or more Predecessor Securities) is registered at the
close of business on the Regular Record Date for such interest.

        Any interest on any Security that is payable, but is not punctually paid
or duly provided for, on any Interest Payment Date (herein called "Defaulted
Interest") shall forthwith cease to be payable to the Holder on the relevant
Regular Record Date by virtue of having been such Holder, and such Defaulted
Interest may be paid by the Company, at its election in each case, as provided
in Clause (1) or (2) below:

        (1)     The Company may elect to make payment of any Defaulted Interest
to the Persons in whose names the Securities (or their respective Predecessor
Securities) are registered at the close of business on a Special Record Date for
the payment of such Defaulted Interest, which shall be fixed in the following
manner. The Company shall notify the Trustee in writing of the amount of
Defaulted Interest proposed to be paid on each Security, the date of the
proposed payment and the Special Record Date, and at the same time the Company
shall deposit with the Trustee an amount of money equal to the aggregate amount
proposed to be paid in respect of such Defaulted Interest or shall make
arrangements satisfactory to the Trustee for such deposit prior to the date of
the proposed payment, such money when deposited to be held in trust for the
benefit of the Persons entitled to such Defaulted Interest as in this Clause
provided. The Special Record Date for the payment of such Defaulted Interest
shall be not more than 15 days and not less than 10 days prior to the date of
the proposed payment and not less than 10 days after the receipt by the Trustee
of the notice of the proposed payment. The Trustee, in the name and at the
expense of the Company, shall cause notice of the proposed payment of such
Defaulted Interest and the Special Record Date therefor to be mailed,
first-class postage prepaid, to each Holder at such Holder's address as it
appears in the Security Register, not less than 10 days prior to such Special
Record Date. Notice of the proposed payment of such Defaulted Interest and the
Special Record Date therefor having been so mailed, such Defaulted Interest
shall be paid to the Persons in whose names the Securities (or their respective
Predecessor Securities) are registered at the close of business on such Special
Record Date and shall no longer be payable pursuant to the following Clause (2).


                                      -31-
<PAGE>   37

        (2)     The Company may make payment of any Defaulted Interest in any
other lawful manner not inconsistent with the requirements of any securities
exchange on which the Securities may be listed, and upon such notice as may be
required by such exchange, if, after notice given by the Company to the Trustee
of the proposed payment pursuant to this Clause, such manner of payment shall be
deemed practicable by the Trustee.

        Subject to the foregoing provisions of this Section and Section 3.5,
each Security delivered under this Indenture upon registration of transfer of or
in exchange for or in lieu of any other Security shall carry the rights to
interest accrued and unpaid, and to accrue, which were carried by such other
Security.

        Interest on any Security that is converted in accordance with Section
12.2 during a Record Date Period shall be payable in accordance with the
provisions of Section 12.2.

SECTION 3.8     Persons Deemed Owners.

        Prior to due presentment of a Security for registration of transfer, the
Company, the Trustee, any Paying Agent and any agent of the Company, the Trustee
or any Paying Agent may treat the Person in whose name such Security is
registered as the owner of such Security for the purpose of receiving payment of
principal of, premium, if any, and (subject to Section 3.7) interest on such
Security and for all other purposes whatsoever, whether or not such Security be
overdue, and neither the Company, the Trustee, any Paying Agent nor any agent of
the Company, the Trustee or any Paying Agent shall be affected by notice to the
contrary.

SECTION 3.9     Cancellation.

        All Securities surrendered for payment, redemption, repurchase,
registration of transfer or exchange or conversion shall, if surrendered to any
Person other than the Trustee, be delivered to the Trustee. All Securities so
delivered to the Trustee shall be canceled promptly by the Trustee (or its
agent). No Securities shall be authenticated in lieu of or in exchange for any
Securities canceled as provided in this Section 3.9. The Trustee shall dispose
of all canceled Securities in accordance with applicable law and its customary
practices in effect from time to time.

SECTION 3.10    Computation of Interest.

        Interest on the Securities shall be computed on the basis of a 360-day
year of twelve 30-day months.

SECTION 3.11    CUSIP Numbers.

        The Company in issuing Securities may use "CUSIP" numbers (if then
generally in use) in addition to serial numbers; if so, the Trustee shall use
such CUSIP numbers in addition to serial numbers in notices of redemption and
repurchase as a convenience to Holders; provided that any such notice may state
that no representation is made as to the correctness of such CUSIP numbers
either as printed on the Securities or as contained in any notice of a
redemption or repurchase and that reliance may be placed only on the serial or
other identification numbers printed on the Securities, and any such redemption
or repurchase shall not be affected by any


                                      -32-
<PAGE>   38

defect in or omission of such CUSIP numbers. The Company shall promptly notify
the Trustee in writing of any change in any such CUSIP number.

                                   ARTICLE IV
                           SATISFACTION AND DISCHARGE

SECTION 4.1     Satisfaction And Discharge of Indenture.

        This Indenture shall upon Company Request cease to be of further effect
(except as to any surviving rights of conversion, or registration of transfer or
exchange, or replacement of Securities herein expressly provided for and the
Company's obligations to the Trustee pursuant to Section 6.7), and the Trustee,
at the expense of the Company, shall execute proper instruments in form and
substance satisfactory to the Trustee acknowledging satisfaction and discharge
of this Indenture, when

        (1)     either

                (i)     all Securities theretofore authenticated and delivered
(other than (A) Securities which have been destroyed, lost or stolen and that
have been replaced or paid as provided in Section 3.6 and (B) Securities for
whose payment money has theretofore been deposited in trust or segregated and
held in trust by the Company and thereafter repaid to the Company or discharged
from such trust, as provided in Section 10.3) have been delivered to the Trustee
for cancellation; or

                (ii)    all such Securities not theretofore delivered to the
Trustee or its agent for cancellation (other than Securities referred to in
clauses (A) and (B) of clause (1)(i) above)

                        (a) have become due and payable, or

                        (b) will have become due and payable at their Stated
Maturity within one year, or

                        (c) are to be called for redemption within one year
under arrangements satisfactory to the Trustee for the giving of notice of
redemption by the Trustee in the name, and at the expense, of the Company, and
the Company, in the case of clause (a), (b) or (c) above, has deposited or
caused to be deposited with the Trustee as trust funds (immediately available to
the Holders in the case of clause (a)) in trust for the purpose an amount in
cash sufficient to pay and discharge the entire indebtedness on such Securities
not theretofore delivered to the Trustee for cancellation, for principal,
premium, if any, and interest to the date of such deposit (in the case of
Securities which have become due and payable) or to the Stated Maturity or
Redemption Date, as the case may be;

        (2)     the Company has paid or caused to be paid all other sums payable
hereunder by the Company; and

        (3)     the Company has delivered to the Trustee an Officers'
Certificate and an Opinion of Counsel, each stating that all conditions
precedent herein provided for relating to the satisfaction and discharge of this
Indenture have been complied with.


                                      -33-
<PAGE>   39

        Notwithstanding the satisfaction and discharge of this Indenture, the
obligations of the Company to the Trustee under Section 6.7, the obligations of
the Company to any Authenticating Agent under Section 6.12, the obligations of
the Trustee under Section 4.2 and the last paragraph of Section 10.3 and the
obligations of the Company and the Trustee under Section 3.5 and Article XII
shall survive.

SECTION 4.2     Application of Trust Money.

        Subject to the provisions of the last paragraph of Section 10.3, all
money deposited with the Trustee pursuant to Section 4.1 shall be held in trust
for the sole benefit of the Holders, and such monies shall be applied by the
Trustee, in accordance with the provisions of the Securities and this Indenture,
to the payment, either directly or through any Paying Agent, to the Persons
entitled thereto, of the principal, premium, if any, and interest for whose
payment such money has been deposited with the Trustee.

        All moneys deposited with the Trustee pursuant to Section 4.1 (and held
by it or any Paying Agent) for the payment of Securities subsequently converted
shall be returned to the Company upon Company Request.

        The Company shall pay and indemnify the Trustee against any tax, fee or
other charge imposed or assessed against all money deposited with the Trustee
pursuant to Section 4.1 (other than income taxes and franchise taxes incurred or
payable by the Trustee and such other taxes, fees or charges incurred or payable
by the Trustee that are not directly the result of the deposit of such money
with the Trustee).

                                    ARTICLE V
                                    REMEDIES

SECTION 5.1     Events of Default.

        "Event of Default", wherever used herein, means any one of the following
events (whatever the reason for such Event of Default and whether it shall be
voluntary or involuntary or be effected by operation of law or pursuant to any
judgment, decree or order of any court or any order, rule or regulation of any
administrative or governmental body):

        (1)     default in the payment of the principal of or premium, if any,
on any Security at its Maturity; or

        (2)     default in the payment of any interest upon any Security when it
becomes due and payable, and continuance of such default for a period of 30
days; or

        (3)     failure by the Company to give a Company Notice in accordance
with Section 14.3; or

        (4)     default in the performance, or breach, of any covenant or
warranty of the Company in this Indenture (other than a covenant or warranty a
default in the performance or breach of which is specifically dealt with
elsewhere in this Section), and continuance of such default or breach for a
period of 60 days after there has been given, by registered or certified


                                      -34-
<PAGE>   40

mail, to the Company by the Trustee or to the Company and the Trustee by the
Holders of at least 25% in principal amount of the Outstanding Securities a
written notice specifying such default or breach and requiring it to be remedied
and stating that such notice is a "Notice of Default" hereunder; or

        (5)     any indebtedness under any bonds, debentures, notes or other
evidences of indebtedness for money borrowed (or guarantee thereof) by the
Company or any Significant Subsidiary or under any mortgage, indenture or
instrument under which there may be issued or by which there may be secured or
evidenced any indebtedness for money borrowed by the Company or any Significant
Subsidiary (an "Instrument") with an aggregate principal amount in excess of
U.S. $25 million, whether such indebtedness now exists or shall hereafter be
created, is not paid at final maturity of any Instrument (either at its stated
maturity or upon acceleration thereof), and such indebtedness is not discharged,
or such acceleration is not rescinded or annulled, within a period of 30 days
after there shall have been given, by registered or certified mail, to the
Company by the Trustee or to the Company and the Trustee by the Holders of at
least 25% in principal amount of the Outstanding Securities a written notice
specifying such default and requiring the Company to cause such indebtedness to
be discharged or cause such default to be cured or waived or such acceleration
to be rescinded or annulled and stating that such notice is a "Notice of
Default" hereunder; or

        (6)     the entry by a court having jurisdiction in the premises of (A)
a decree or order for relief in respect of the Company or any Significant
Subsidiary in an involuntary case or proceeding under any applicable Federal or
State bankruptcy, insolvency, reorganization or other similar law or (B) a
decree or order adjudging the Company or any Significant Subsidiary a bankrupt
or insolvent, or approving as properly filed a petition seeking reorganization,
arrangement, adjustment or composition of or in respect of the Company or any
Significant Subsidiary under any applicable Federal or State law, or appointing
a custodian, receiver, liquidator, assignee, trustee, sequestrator or other
similar official of the Company or any Significant Subsidiary or of any
substantial part of the property of either, or ordering the winding up or
liquidation of its affairs, and the continuance of any such decree or order for
relief or any such other decree or order unstayed and in effect for a period of
60 consecutive days; or

        (7)     the commencement by the Company or any Significant Subsidiary of
a voluntary case or proceeding under any applicable Federal or State bankruptcy,
insolvency, reorganization or other similar law or of any other case or
proceeding to be adjudicated a bankrupt or insolvent, or the consent by either
to the entry of a decree or order for relief in respect of the Company or any
Significant Subsidiary in an involuntary case or proceeding under any applicable
Federal or State bankruptcy, insolvency, reorganization or other similar law or
to the commencement of any bankruptcy or insolvency case or proceeding against
either, or the filing by either of a petition or answer or consent seeking
reorganization or similar relief under any applicable Federal or State law, or
the consent by either to the filing of such petition or to the appointment of or
taking possession by a custodian, receiver, liquidator, assignee, trustee,
sequestrator or other similar official of the Company or any Significant
Subsidiary or of any substantial part of the property of either, or the making
by either of an assignment for the benefit of creditors, or the admission by
either in writing of its inability to pay its debts generally as they become
due, or the taking of corporate action by the Company or any Significant
Subsidiary in furtherance of any such action.


                                      -35-
<PAGE>   41

SECTION 5.2     Acceleration of Maturity; Rescission and Annulment.

        If an Event of Default (other than an Event of Default specified in
Section 5.1(6) or 5.1(7) with respect to the Company) occurs and is continuing,
then in every such case the Trustee or the Holders of not less than 25% in
principal amount of the Outstanding Securities may declare the principal of all
the Securities to be due and payable immediately, by a notice in writing to the
Company (and to the Trustee if given by the Holders), and upon any such
declaration such principal and all accrued interest thereon shall become
immediately due and payable. If an Event of Default specified in Section 5.1(6)
or 5.1(7) with respect to the Company occurs, the principal of, and accrued
interest on, all the Securities shall ipso facto become immediately due and
payable without any declaration or other Act of the Holders or any act on the
part of the Trustee.

        At any time after such declaration of acceleration has been made and
before a judgment or decree for payment of the money due has been obtained by
the Trustee as hereinafter in this Article V provided, the Holders of a majority
in principal amount of the Outstanding Securities, by written notice to the
Company and the Trustee, may, on behalf of all Holders, rescind and annul such
declaration and its consequences if:

        (1)     the Company has paid or deposited with the Trustee a sum
sufficient to pay

                (i)     all overdue interest on all Securities,

                (ii)    the principal of and premium, if any, on any Securities
that have become due otherwise than by such declaration of acceleration and any
interest thereon at the rate borne by the Securities,

                (iii)   to the extent permitted by applicable law, interest upon
overdue interest at a rate of 3.75% per annum, and

                (iv)    all sums paid or advanced by the Trustee hereunder and
the reasonable compensation, expenses, disbursements and advances of the
Trustee, its agents and counsel;

        (2)     all Events of Default, other than the nonpayment of the
principal of and any premium and interest on, Securities which have become due
solely by such declaration of acceleration, have been cured or waived as
provided in Section 5.13; and

        (3)     such rescission and annulment would not conflict with any
judgment or decree issued in appropriate judicial proceedings regarding the
payment by the Trustee to the Holders of the amounts referred to in 5.2(1).

        No rescission or annulment referred to above shall affect any subsequent
default or impair any right consequent thereon.

SECTION 5.3     Collection of Indebtedness and Suits for Enforcement by Trustee.

        The Company covenants that if:


                                      -36-
<PAGE>   42

        (1)     default is made in the payment of any interest on any Security
when it becomes due and payable and such default continues for a period of 30
days, or

        (2)     default is made in the payment of the principal of or premium,
if any, on any Security at the Maturity thereof,

the Company will, upon demand of the Trustee pay to it, for the benefit of the
Holders of such Securities the whole amount then due and payable on such
Securities for principal and interest and interest on any overdue principal and
premium, if any, and, to the extent permitted by applicable law, on any overdue
interest, at a rate of 3.75% per annum, and in addition thereto, such further
amount as shall be sufficient to cover the reasonable costs and expenses of
collection, including the reasonable compensation, expenses, disbursements and
advances of the Trustee, its agents and counsel.

        If the Company fails to pay such amounts forthwith upon such demand, the
Trustee, in its own name and as trustee of an express trust, may institute a
judicial proceeding for the collection of the sums so due and unpaid, may
prosecute such proceeding to judgment or final decree and may enforce the same
against the Company or any other obligor upon the Securities and collect the
moneys adjudged or decreed to be payable in the manner provided by law out of
the property of the Company or any other obligor upon the Securities, wherever
situated.

        If an Event of Default occurs and is continuing, the Trustee may in its
discretion proceed to protect and enforce its rights and the rights of the
Holders of Securities by such appropriate judicial proceedings as the Trustee
shall deem most effectual to protect and enforce any such rights, whether for
the specific enforcement of any covenant or agreement in this Indenture or in
aid of the exercise of any power granted herein, or to enforce any other proper
remedy.

SECTION 5.4     Trustee May File Proofs of Claim.

        In case of the pendency of any receivership, insolvency, liquidation,
bankruptcy, reorganization, arrangement, adjustment, composition or other
judicial proceeding relative to the Company or any other obligor upon the
Securities or the property of the Company or of such other obligor or the
creditors of either, the Trustee (irrespective of whether the principal of, and
any interest on, the Securities shall then be due and payable as therein
expressed or by declaration or otherwise and irrespective of whether the Trustee
shall have made any demand on the Company for the payment of overdue principal
or interest) shall be entitled and empowered, by intervention in such proceeding
or otherwise,

        (1)     to file and prove a claim for the whole amount of principal,
premium, if any, and interest owing and unpaid in respect of the Securities and
take such other actions, including participating as a member, voting or
otherwise, of any official committee of creditors appointed in such matter, and
to file such other papers or documents, in each of the foregoing cases, as may
be necessary or advisable in order to have the claims of the Trustee (including
any claim for the reasonable compensation, expenses, disbursements and advances
of the Trustee, its agents and counsel) and of the Holders of Securities allowed
in such judicial proceeding, and

        (2)     to collect and receive any moneys or other property payable or
deliverable on any such claim and to distribute the same; and any custodian,
receiver, assignee, trustee, liquidator,


                                      -37-
<PAGE>   43

sequestrator or other similar official in any such judicial proceeding is hereby
authorized by each Holder of Securities to make such payments to the Trustee
and, in the event that the Trustee shall consent to the making of such payments
directly to the Holders of Securities to pay to the Trustee any amount due to it
for the reasonable compensation, expenses, disbursements and advances of the
Trustee, its agents and counsel and any other amounts due the Trustee under
Section 6.7.

        Nothing herein contained shall be deemed to authorize the Trustee to
authorize or consent to or accept or adopt on behalf of any Holder of a Security
any plan of reorganization, arrangement, adjustment or composition affecting the
Securities or the rights of any Holder thereof or to authorize the Trustee to
vote in respect of the claim of any Holder of a Security in any such proceeding;
provided, however, that the Trustee may, on behalf of such Holders, vote for the
election of a trustee in bankruptcy or similar official.

SECTION 5.5     Trustee May Enforce Claims Without Possession of Securities.

        All rights of action and claims under this Indenture or the Securities
may be prosecuted and enforced by the Trustee without the possession of any of
the Securities or the production thereof in any proceeding relating thereto, and
any such proceeding instituted by the Trustee shall be brought in its own name
as trustee of an express trust, and any recovery of judgment shall, after
provision for the payment of the reasonable compensation, expenses,
disbursements and advances of the Trustee, its agents and counsel, be for the
ratable benefit of the Holders of the Securities in respect of which judgment
has been recovered.

SECTION 5.6     Application of Money Collected.

        Any money collected by the Trustee pursuant to this Article V shall be
applied in the following order, at the date or dates fixed by the Trustee and,
in case of the distribution of such money on account of principal, premium, if
any, or interest, upon presentation of the Securities and the notation thereon
of the payment if only partially paid and upon surrender thereof if fully paid:

        FIRST: To the payment of all amounts due the Trustee under Section 6.7;

        SECOND: To the payment of the amounts then due and unpaid for principal
of, premium, if any, or interest on, the Securities in respect of which or for
the benefit of which such money has been collected, ratably, without preference
or priority of any kind, according to the amounts due and payable on such
Securities for principal, premium, if any, and interest, respectively;

        THIRD: To such other Person or Persons, if any, to the extent entitled
thereto; and

        FOURTH: Any remaining amounts shall be repaid to the Company.


                                      -38-
<PAGE>   44

SECTION 5.7     Limitation on Suits.

        No Holder of any Security shall have any right to institute any
proceeding, judicial or otherwise, with respect to this Indenture, or for the
appointment of a receiver or trustee, or for any other remedy hereunder, unless:

        (1)     such Holder has previously given written notice to the Trustee
of a continuing Event of Default;

        (2)     the Holders of not less than 25% in principal amount of the
Outstanding Securities shall have made written request to the Trustee to
institute proceedings in respect of such Event of Default in its own name as
Trustee hereunder;

        (3)     such Holder or Holders have offered to the Trustee, and if
requested, shall have provided, reasonable indemnity against the costs, expenses
and liabilities to be incurred in compliance with such request;


        (4)     the Trustee for 60 days after its receipt of such notice,
request and offer of indemnity (or if requested, receipt of indemnity) has
failed to institute any such proceeding; and

        (5)     no direction inconsistent with such written request has been
given to the Trustee during such 60 day period by the Holders of a majority in
principal amount of the Outstanding Securities, it being understood and intended
that no one or more of such Holders shall have any right in any manner whatever
by virtue of, or by availing of, any provision of this Indenture to affect,
disturb or prejudice the rights of any other of such Holders, or to obtain or
seek to obtain priority or preference over any other of such Holders or to
enforce any right under this Indenture, except in the manner herein provided and
for the equal and ratable benefit of all such Holders.

SECTION 5.8     Unconditional Right of Holders to Receive Principal, Premium and
                Interest and to Convert.

        Notwithstanding any other provision in this Indenture, the Holder of any
Security shall have the right, which is absolute and unconditional, to receive
payment of the principal of, premium, if any, and (subject to Section 3.7)
interest on such Security on the respective Stated Maturities expressed in such
Security (or, in the case of redemption or repurchase, on the Redemption Date or
Repurchase Date, as the case may be), and to convert such Security in accordance
with Article XII, and to institute suit for the enforcement of any such payment
and right to convert, and such rights shall not be impaired without the consent
of such Holder.

SECTION 5.9     Restoration of Rights and Remedies.

        If the Trustee or any Holder of a Security has instituted any proceeding
to enforce any right or remedy under this Indenture and such proceeding has been
discontinued or abandoned for any reason, or has been determined adversely to
the Trustee or to such Holder, then and in every such case, subject to any
determination in such proceeding, the Company, the Trustee and the Holders of
Securities shall be restored severally and respectively to their former
positions hereunder and thereafter all rights and remedies of the Trustee and
such Holders shall continue as though no such proceeding had been instituted.


                                      -39-
<PAGE>   45

SECTION 5.10    Rights and Remedies Cumulative.

        Except as otherwise provided with respect to the replacement or payment
of mutilated, destroyed, lost or stolen Securities in the last paragraph of
Section 3.6, no right or remedy herein conferred upon or reserved to the Trustee
or to the Holders of Securities is intended to be exclusive of any other right
or remedy, and every right and remedy shall, to the extent permitted by law, be
cumulative and in addition to every other right and remedy given hereunder or
now or hereafter existing at law or in equity or otherwise. The assertion or
employment of any right or remedy hereunder, or otherwise, shall not prevent the
concurrent assertion or employment of any other appropriate right or remedy.

SECTION 5.11    Delay or Omission Not Waiver.

        No delay or omission of the Trustee or of any Holder of any Security to
exercise any right or remedy accruing upon any Event of Default shall impair any
such right or remedy or constitute a waiver of any such Event of Default or any
acquiescence therein. Every right and remedy given by this Article V or by law
to the Trustee or to the Holders of Securities may be exercised from time to
time, and as often as may be deemed expedient, by the Trustee or (subject to the
limitations contained in this Indenture) by the Holders of Securities as the
case may be.

SECTION 5.12    Control by Holders of Securities.

        Subject to Section 6.3, the Holders of a majority in principal amount of
the Outstanding Securities shall have the right to direct the time, method and
place of conducting any proceeding for any remedy available to the Trustee or
exercising any trust or power conferred on the Trustee, provided that

        (1)     such direction shall not be in conflict with any rule of law or
with this Indenture, and

        (2)     the Trustee may take any other action deemed proper by the
Trustee which is not inconsistent with such direction, and

        (3)     the Trustee need not take any action that might involve it in
personal liability or be unjustly prejudicial to the Holders of Securities not
consenting.

SECTION 5.13    Waiver of Past Defaults.

        The Holders, either (i) through the written consent of not less than a
majority in principal amount of the Outstanding Securities or (ii) by the
adoption of a resolution, at a meeting of Holders of the Outstanding Securities
at which a quorum is present, by the Holders of at least 66-2/3% in principal
amount of the Outstanding Securities represented at such meeting, may on behalf
of the Holders of all the Securities waive any past default hereunder and its
consequences, except a default (A) in the payment of the principal of, premium,
if any, or interest on any Security, or (B) in respect of a covenant or
provision hereof which under Article VIII cannot be modified or amended without
the consent of the Holder of each Outstanding Security affected.


                                      -40-
<PAGE>   46

        Upon any such waiver, such default shall cease to exist, and any Event
of Default arising therefrom shall be deemed to have been cured, for every
purpose of this Indenture; but no such waiver shall extend to any subsequent or
other default or impair any right consequent thereon.

SECTION 5.14    Undertaking for Costs.

        All parties to this Indenture agree, and each Holder of any Security by
his acceptance thereof shall be deemed to have agreed, that any court may in its
discretion require, in any suit for the enforcement of any right or remedy under
this Indenture, or any suit against the Trustee for any action taken, suffered
or omitted by it as Trustee, the filing by any party litigant in such suit of an
undertaking to pay the costs of such suit, and that such court may in its
discretion assess reasonable costs, including reasonable attorneys' fees,
against any party litigant in such suit, having due regard to the merits and
good faith of the claims or defenses made by such party litigant; but the
provisions of this Section 5.14 shall not apply to any suit instituted by the
Company, to any suit instituted by the Trustee, to any suit instituted by any
Holder, or group of Holders, holding in the aggregate more than 10% in principal
amount of the Outstanding Securities, or to any suit instituted by any Holder of
any Security for the enforcement of the payment of the principal of, premium, if
any, or interest on any Security on or after the respective Stated Maturity or
Maturities expressed in such Security (or, in the case of redemption or
repurchase, on or after the Redemption Date or Repurchase Date, as the case may
be) or for the enforcement of the right to convert any Security in accordance
with Article XII.

SECTION 5.15    Waiver of Stay, Usury or Extension Laws.

        The Company covenants (to the extent that it may lawfully do so) that it
will not at any time insist upon, or plead, or in any manner whatsoever claim or
take the benefit or advantage of, any stay, usury or extension law wherever
enacted, now or at any time hereafter in force, that may affect the covenants or
the performance of this Indenture; and the Company (to the extent that it may
lawfully do so) hereby expressly waives all benefit or advantage of any such law
and covenants that it will not hinder, delay or impede by reason of such law the
execution of any power herein granted to the Trustee, but will suffer and permit
the execution of every such power as though no such law had been enacted.

                                   ARTICLE VI
                                  THE TRUSTEE

SECTION 6.1     Certain Duties and Responsibilities.

        (1)     Except during the continuance of an Event of Default,

                (i)     the Trustee undertakes to perform such duties and only
such duties as are specifically set forth in this Indenture, and no implied
covenants or obligations shall be read into this Indenture against the Trustee;
and

                (ii)    in the absence of bad faith on its part, the Trustee may
conclusively rely, as to the truth of the statements and the correctness of the
opinions expressed therein, upon certificates or opinions furnished to the
Trustee and conforming to the requirements of this Indenture, but in the case of
any such certificates or opinions which by any provision hereof are


                                      -41-
<PAGE>   47

specifically required to be furnished to the Trustee, the Trustee shall be under
a duty to examine the same to determine whether or not they conform to the
requirements of this Indenture, but not to verify the contents thereof.

        (2)     In case an Event of Default has occurred and is continuing, the
Trustee shall exercise such of the rights and powers vested in it by this
Indenture, and use the same degree of care and skill in their exercise, as a
prudent man would exercise or use under the circumstances in the conduct of his
own affairs.

        (3)     No provision of this Indenture shall be construed to relieve the
Trustee from liability for its own negligent action, its own negligent failure
to act, or its own willful misconduct, except that

                (i)     this paragraph (3) shall not be construed to limit the
effect of paragraph (1) of this Section;

                (ii)    the Trustee shall not be liable for any error of
judgment made in good faith by a Responsible Officer, unless it shall be proved
that the Trustee was negligent in ascertaining the pertinent facts;

                (iii)   the Trustee shall not be liable with respect to any
action taken or omitted to be taken by it in good faith in accordance with the
direction of the Holders of a majority in principal amount of the Outstanding
Securities relating to the time, method and place of conducting any proceeding
for any remedy available to the Trustee, or exercising any trust or power
conferred upon the Trustee, under this Indenture; and

                (iv)    no provision of this Indenture shall require the Trustee
to expend or risk its own funds or otherwise incur any financial liability in
the performance of any of its duties hereunder, or in the exercise of any of its
rights or powers, if it shall have reasonable grounds for believing that
repayment of such funds or adequate indemnity against such risk or liability is
not reasonably assured to it.

        (4)     Whether or not therein expressly so provided, every provision of
this Indenture relating to the conduct or affecting the liability of or
affording protection to the Trustee shall be subject to the provisions of this
Section.

SECTION 6.2     Notice of Defaults.

        Within 90 days after the occurrence of any default hereunder as to which
a Responsible Officer of the Trustee has received written notice, the Trustee
shall give to all Holders of Securities, in the manner provided in Section 1.6,
notice of such default, unless such default shall have been cured or waived;
provided, however, that, except in the case of a default in the payment of the
principal of, premium, if any, or interest on any Security the Trustee shall be
protected in withholding such notice if and so long as the board of directors,
the executive committee or a trust committee of directors or Responsible
Officers of the Trustee in good faith determines that the withholding of such
notice is in the interest of the Holders; and provided, further, that in the
case of any default of the character specified in Section 5.1(4), no such notice
to Holders of Securities shall be given until at least 60 days after the
occurrence thereof or, if


                                      -42-
<PAGE>   48

applicable, the cure period specified therein. For the purpose of this Section,
the term "default" means any event which is, or after notice or lapse of time or
both would become, an Event of Default.

SECTION 6.3     Certain Rights of Trustee.

        Subject to the provisions of Section 6.1:

        (1)     the Trustee may rely, and shall be protected in acting or
refraining from acting, upon any resolution, Officers' Certificate, other
certificate, statement, instrument, opinion, report, notice, request, direction,
consent, order, bond, debenture, note, coupon, other evidence of indebtedness or
other paper or document (collectively, the "Documents") believed by it to be
genuine and to have been signed or presented by the proper party or parties, and
the Trustee need not investigate any fact or matter stated in such Documents;

        (2)     any request or direction of the Company mentioned herein shall
be sufficiently evidenced by a Company Request or Company Order and any
resolution of the Board of Directors shall be sufficiently evidenced by a Board
Resolution;

        (3)     whenever in the administration of this Indenture the Trustee
shall deem it desirable that a matter be proved or established prior to taking,
suffering or omitting any action hereunder, the Trustee (unless other evidence
be the one specifically prescribed) may, in the absence of bad faith on its
part, request and rely upon an Officers' Certificate or Opinion of Counsel;

        (4)     the Trustee may consult with counsel of its selection and the
advice of such counsel or any Opinion of Counsel shall be full and complete
authorization and protection in respect of any action taken, suffered or omitted
by it hereunder in good faith and in reliance thereon;

        (5)     the Trustee shall be under no obligation to exercise any of the
rights or powers vested in it by this Indenture at the request or direction of
any of the Holders of Securities pursuant to this Indenture, unless such Holders
shall have offered, and, if requested by the Trustee, delivered to the Trustee
reasonable security or indemnity against the costs, expenses and liabilities
which might be incurred by it in compliance with such request or direction;

        (6)     the Trustee shall not be bound to make any investigation into
the facts or matters stated in any resolution, certificate, statement,
instrument, opinion, report, notice, request, direction, consent, order, bond,
debenture, note, coupon, other evidence of indebtedness or other paper or
document, but the Trustee may make such further inquiry or investigation into
such facts or matters as it may see fit, and, if the Trustee shall determine to
make such further inquiry or investigation, it shall be entitled to examine the
books, records and premises of the Company, personally or by agent or attorney;
and

        (7)     the Trustee may execute any of the trusts or powers hereunder or
perform any duties hereunder either directly or by or through agents or
attorneys and the Trustee shall not be responsible for any misconduct or
negligence on the part of any agent or attorney appointed with due care by it
hereunder.


                                      -43-
<PAGE>   49

        (8)     the Trustee shall not be liable for any action it takes or omits
to take in good faith which it believes to be authorized or within its rights or
powers conferred upon it by this Indenture.

SECTION 6.4     Not Responsible for Recitals or Issuance of Securities.

        The recitals contained herein and in the Securities (except the
Trustee's certificates of authentication) shall be taken as the statements of
the Company, and the Trustee assumes no responsibility for their correctness.
The Trustee makes no representations as to the validity or sufficiency of this
Indenture, of the Securities or of the Common Stock issuable upon the conversion
of the Securities. The Trustee shall not be accountable for the use or
application by the Company of Securities or the proceeds thereof.

SECTION 6.5     May Hold Securities, Act as Trustee under Other Indentures.

        The Trustee, any Authenticating Agent, any Paying Agent, any Conversion
Agent or any other agent of the Company or the Trustee, in its individual or any
other capacity, may become the owner or pledgee of Securities and may otherwise
deal with the Company with the same rights it would have if it were not Trustee,
Authenticating Agent, Paying Agent, Conversion Agent or such other agent.

        The Trustee may become and act as trustee under other indentures under
which other securities, or certificates of interest or participation in other
securities, of the Company are outstanding in the same manner as if it were not
Trustee hereunder.

SECTION 6.6     Money Held in Trust.

        Money held by the Trustee in trust hereunder need not be segregated from
other funds except to the extent required by law. The Trustee shall be under no
liability for interest on any money received by it hereunder except as otherwise
agreed in writing with the Company.

SECTION 6.7     Compensation and Reimbursement.

        The Company agrees

        (1)     to pay to the Trustee from time to time such reasonable
compensation as the Company and the Trustee shall from time to time agree in
writing for its acceptance of this Indenture and for all services rendered by it
hereunder (which compensation shall not be limited by any provision of law in
regard to the compensation of a trustee of an express trust);

        (2)     except as otherwise expressly provided herein, to reimburse the
Trustee upon its request for all reasonable expenses, disbursements and advances
incurred or made by the Trustee (including costs and expenses of enforcing this
Indenture and defending itself against any claim (whether asserted by the
Company, any Holder of Securities or any other Person) or liability in
connection with the exercise of any of its powers or duties hereunder) in
accordance with any provision of this Indenture (including the reasonable
compensation and the expenses and disbursements of its agents and counsel),
except any such expense, disbursement or advance as may be attributable to its
negligence or bad faith; and



                                      -44-
<PAGE>   50

        (3)     to indemnify the Trustee (and its directors, officers, employees
and agents) for, and to hold it harmless against, any loss, liability or expense
incurred without negligence or bad faith on its part, arising out of or in
connection with the acceptance or administration of this trust, including the
reasonable costs, expenses and reasonable attorneys' fees of defending itself
against any claim or liability in connection with the exercise or performance of
any of its powers or duties hereunder.

        The Trustee shall have a lien prior to the Securities on all money or
property held or controlled by the Trustee to secure the Company's payment
obligations in this Section 6.7, except that held in trust to pay principal and
interest on the Securities.

        When the Trustee incurs expenses or renders services in connection with
an Event of Default specified in Section 5.1(6) or Section 5.1(7), the expenses
(including the reasonable charges of its counsel) and the compensation for the
services are intended to constitute expenses of the administration under any
applicable Federal or state bankruptcy, insolvency or other similar law.

        The provisions of this Section shall survive the termination of this
Indenture and the resignation or removal of the Trustee.

SECTION 6.8     Corporate Trustee Required; Eligibility.

        There shall at all times be a Trustee hereunder which shall be a Person
that is eligible pursuant to the Trust Indenture Act to act as such, having (or
be part of a holding company group with) a combined capital and surplus of at
least U.S. $50,000,000, subject to supervision or examination by federal or
state authority, and in good standing. The Trustee or an Affiliate of the
Trustee shall maintain an established place of business in the Borough of
Manhattan, The City of New York. If such corporation publishes reports of
condition at least annually, pursuant to law or to the requirements of said
supervising or examining authority, then for the purposes of this Section, the
combined capital and surplus of such corporation shall be deemed to be its
combined capital and surplus as set forth in its most recent report of condition
so published. If at any time the Trustee shall cease to be eligible in
accordance with the provisions of this Section, it shall resign immediately in
the manner and with the effect hereinafter specified in this Article and a
successor shall be appointed pursuant to Section 6.9.

SECTION 6.9     Resignation and Removal; Appointment of Successor.

        (1)     No resignation or removal of the Trustee and no appointment of a
successor Trustee pursuant to this Article shall become effective until the
acceptance of appointment by the successor Trustee in accordance with the
applicable requirements of Section 6.10.

        (2)     The Trustee may resign at any time by giving written notice
thereof to the Company. If the instrument of acceptance by a successor Trustee
required by Section 6.10 shall not have been delivered to the Trustee within 30
days after the giving of such notice of resignation, the resigning Trustee may
petition any court of competent jurisdiction for the appointment of a successor
Trustee.


                                      -45-
<PAGE>   51

        (3)     The Trustee may be removed at any time by an Act of the Holders
of a majority in principal amount of the Outstanding Securities, delivered to
the Trustee and the Company. If the instrument of acceptance by a successor
Trustee required by Section 6.10 shall not have been delivered to the Trustee
within 30 days after the giving of such notice of removal, the removed Trustee
may petition any court of competent jurisdiction for the appointment of a
successor Trustee.

        (4)     If at any time:

                (i)     the Trustee shall cease to be eligible under Section 6.8
and shall fail to resign after written request therefor by the Company or by any
Holder of a Security who has been a bona fide Holder of a Security for at least
six months, or

                (ii)    the Trustee shall become incapable of acting or shall be
adjudged a bankrupt or insolvent or a receiver of the Trustee or of its property
shall be appointed or any public officer shall take charge or control of the
Trustee or of its property or affairs for the purpose of rehabilitation,
conservation or liquidation,

then, in any such case (i) the Company by a Board Resolution may remove the
Trustee, or (ii) subject to Section 5.14, any Holder of a Security who has been
a bona fide Holder of a Security for at least six months may, on behalf of
himself and all others similarly situated, petition any court of competent
jurisdiction for the removal of the Trustee and the appointment of a successor
Trustee.

        (5)     If the Trustee shall resign, be removed or become incapable of
acting, or if a vacancy shall occur in the office of Trustee for any cause, the
Company, by a Board Resolution, shall promptly appoint a successor Trustee and
shall comply with the applicable requirements of this Section and Section 6.10.
If, within one year after such resignation, removal or incapability, or the
occurrence of such vacancy, a successor Trustee shall be appointed by Act of the
Holders of a majority in principal amount of the Outstanding Securities
delivered to the Company and the retiring Trustee, the successor Trustee so
appointed shall, forthwith upon its acceptance of such appointment in accordance
with the applicable requirements of Section 6.10, become the successor Trustee
and supersede the successor Trustee appointed by the Company. If no successor
Trustee shall have been so appointed by the Company or the Holders of Securities
and accepted appointment in the manner required by this Section and Section
6.10, any Holder of a Security who has been a bona fide Holder of a Security for
at least six months may, on behalf of himself and all others similarly situated,
petition any court of competent jurisdiction for the appointment of a successor
Trustee.

        (6)     The Company shall give notice of each resignation and each
removal of the Trustee and each appointment of a successor Trustee to all
Holders of Securities in the manner provided in Section 1.6. Each notice shall
include the name of the successor Trustee and the address of its Corporate Trust
Office.

SECTION 6.10    Acceptance of Appointment by Successor.

        Every successor Trustee appointed hereunder shall execute, acknowledge
and deliver to the Company and to the retiring Trustee an instrument accepting
such appointment, and


                                      -46-
<PAGE>   52

thereupon the resignation or removal of the retiring Trustee shall become
effective and such successor Trustee, without any further act, deed or
conveyance, shall become vested with all the rights, powers, trusts and duties
of the retiring Trustee; but, on the request of the Company or the successor
Trustee, such retiring Trustee shall, upon payment of its charges, execute and
deliver an instrument transferring to such successor Trustee all the rights,
powers and trusts of the retiring Trustee and shall duly assign, transfer and
deliver to such successor Trustee all property and money held by such retiring
Trustee hereunder. Upon request of any such successor Trustee, the Company shall
execute any and all instruments for more fully and certainly vesting in and
confirming to such successor Trustee all such rights, powers and trusts.

        No successor Trustee shall accept its appointment unless at the time of
such acceptance such successor Trustee shall be eligible under this Article.

SECTION 6.11    Merger, Conversion, Consolidation or Succession to Business.

        Any corporation into which the Trustee may be merged or converted or
with which it may be consolidated, or any corporation resulting from any merger,
conversion or consolidation to which the Trustee shall be a party, or any
corporation succeeding to all or substantially all of the corporate trust
business of the Trustee (including the trust created by this Indenture), shall
be the successor of the Trustee hereunder, provided such corporation shall be
otherwise eligible under this Article, without the execution or filing of any
paper or any further act on the part of any of the parties hereto. In case any
Securities shall have been authenticated, but not delivered, by the Trustee then
in office, any successor by merger, conversion or consolidation to such
authenticating Trustee may adopt such authentication and deliver the Securities
so authenticated with the same effect as if such successor Trustee had itself
authenticated such Securities.

SECTION 6.12    Authenticating Agents.

        The Trustee may appoint an Authenticating Agent or Agents reasonably
acceptable to the Company with respect to the Securities, which Authenticating
Agent shall be authorized to act on behalf of the Trustee to authenticate
Securities issued upon exchange or substitution pursuant to this Indenture.

        Securities authenticated by an Authenticating Agent shall be entitled to
the benefits of this Indenture and shall be valid and obligatory for all
purposes as if authenticated by the Trustee hereunder, and every reference in
this Indenture to the authentication and delivery of Securities by the Trustee
or the Trustee's certificate of authentication shall be deemed to include
authentication and delivery on behalf of the Trustee by an Authenticating Agent
and a certificate of authentication executed on behalf of the Trustee by an
Authenticating Agent. Each Authenticating Agent shall be subject to acceptance
by the Company and shall at all times be a corporation organized and doing
business under the laws of the United States of America, any State thereof or
the District of Columbia, authorized under such laws to act as Authenticating
Agent and subject to supervision or examination by government or other fiscal
authority. If at any time an Authenticating Agent shall cease to be eligible in
accordance with the provisions of this Section 6.12, such Authenticating Agent
shall resign immediately in the manner and with the effect specified in this
Section 6.12.




                                      -47-
<PAGE>   53

        Any corporation into which an Authenticating Agent may be merged or
converted or with which it may be consolidated, or any corporation resulting
from any merger, conversion or consolidation to which such Authenticating Agent
shall be a party, or any corporation succeeding to the corporate agency or
corporate trust business of an Authenticating Agent, shall continue to be an
Authenticating Agent, provided such corporation shall be otherwise eligible
under this Section 6.12, without the execution or filing of any paper or any
further act on the part of the Trustee or the Authenticating Agent.

        An Authenticating Agent may resign at any time by giving written notice
thereof to the Trustee and to the Company. The Trustee may at any time terminate
the agency of an Authenticating Agent by giving written notice thereof to such
Authenticating Agent and to the Company. Upon receiving such a notice of
resignation or upon such a termination, or in case at any time such
Authenticating Agent shall cease to be eligible in accordance with the
provisions of this Section 6.12, the Trustee may appoint a successor
Authenticating Agent which shall be subject to acceptance by the Company. Any
successor Authenticating Agent upon acceptance of its appointment hereunder
shall become vested with all the rights, powers and duties of its predecessor
hereunder, with like effect as if originally named as an Authenticating Agent.
No successor Authenticating Agent shall be appointed unless eligible under the
provisions of this Section 6.12.

        The Company agrees to pay to each Authenticating Agent from time to time
reasonable compensation for its services under this Section 6.12.

        If an Authenticating Agent is appointed with respect to the Securities
pursuant to this Section 6.12, the Securities may have endorsed thereon, in
addition to or in lieu of the Trustee's certification of authentication, an
alternative certificate of authentication in the following form:

        This is one of the Securities referred to in the within-mentioned
Indenture.

                                          FIRST UNION NATIONAL BANK as Trustee

                                          By:


                                          ------------------------------
                                          As Authenticating Agent


                                          By:

                                          ------------------------------
                                          Authorized Signatory

SECTION 6.13    Disqualification; Conflicting Interests.

        If the Trustee has or shall acquire a conflicting interest within the
meaning of the Trust Indenture Act, the Trustee shall either eliminate such
interest or resign, to the extent and in the manner provided by, and subject to
the provisions of, the Trust Indenture Act and this Indenture.


                                      -48-
<PAGE>   54

SECTION 6.14    Preferential Collection of Claims Against Company.

        If and when the Trustee shall be or become a creditor of the Company (or
any other obligor upon the Securities), the Trustee shall be subject to the
provisions of the Trust Indenture Act regarding the collection of claims against
the Company (or any such other obligor).

                                  ARTICLE VII
              CONSOLIDATION, MERGER, CONVEYANCE, TRANSFER OR LEASE

SECTION 7.1     Company May Consolidate, Etc. Only on Certain Terms.

        The Company shall not consolidate with or merge into any other Person or
convey, transfer or lease all its properties and assets substantially as an
entirety to any Person, and the Company shall not permit any Person to
consolidate with or merge into the Company or convey, transfer, sell or lease
such Person's properties and assets substantially as an entirety to the Company
unless:

        (1)     the Person formed by such consolidation or into or with which
the Company is merged or the Person to which the properties and assets of the
Company are so conveyed, transferred, sold or leased shall be a corporation,
limited liability company, partnership or trust organized and validly existing
under the laws of the United States of America, any State thereof or the
District of Columbia and, if other than the Company, shall expressly assume, by
an indenture supplemental hereto, executed and delivered to the Trustee, in form
satisfactory to the Trustee, the due and punctual payment of the principal of,
premium, if any, and interest on all of the Securities as applicable, and the
performance or observance of every covenant of this Indenture on the part of the
Company to be performed or observed and shall have provided for conversion
rights in accordance with Article XII;

        (2)     immediately after giving effect to such transaction, no Event of
Default, and no event that after notice or lapse of time or both, would become
an Event of Default, shall have occurred and be continuing; and

        (3)     the Company has delivered to the Trustee an Officers'
Certificate and an Opinion of Counsel, each stating that such consolidation,
merger, conveyance, transfer or lease and, if a supplemental indenture is
required in connection with such transaction, such supplemental indenture comply
with this Article and that all conditions precedent herein provided for relating
to such transaction have been complied with, together with any documents
required under Section 8.3.

SECTION 7.2     Successor Substituted.

        Upon any consolidation of the Company with, or merger of the Company
into any other Person or any conveyance, transfer or lease of all or
substantially all the properties and assets of the Company in accordance with
Section 7.1, the successor Person formed by such consolidation or into or with
which the Company is merged or to which such conveyance, transfer or lease is
made shall succeed to, and be substituted for, and may exercise every right and
power of, the Company under this Indenture with the same effect as if such
successor Person had been named


                                      -49-
<PAGE>   55

as the Company herein, and thereafter, except in the case of a lease, the
predecessor Person shall be relieved of all obligations and covenants under this
Indenture and the Securities.

                                  ARTICLE VIII
                            SUPPLEMENTAL INDENTURES

SECTION 8.1     Supplemental Indentures Without Consent of Holders of
                Securities.

        Without the consent of any Holders of Securities the Company, when
authorized by a Board Resolution, and the Trustee, at any time and from time to
time, may enter into one or more indentures supplemental hereto for any of the
following purposes:

        (1)     to evidence the succession of another Person to the Company and
the assumption by any such successor of the covenants and obligations of the
Company herein and in the Securities as permitted by Article VII of this
Indenture; or

        (2)     to add to the covenants of the Company for the benefit of the
Holders of Securities or to surrender any right or power herein conferred upon
the Company; or

        (3)     to secure the Securities; or

        (4)     to make provision with respect to the conversion rights of
Holders of Securities pursuant to Section 12.11 or to make provision with
respect to the repurchase rights of Holders of Securities pursuant to Section
14.5; or

        (5)     to comply with the requirements of the Trust Indenture Act or
the rules and regulations of the Commission thereunder in order to effect or
maintain the qualification of this Indenture under the Trust Indenture Act, as
contemplated by this Indenture or otherwise; or

        (6)     to evidence and provide for the acceptance of appointment
hereunder by a successor Trustee; or

        (7)     to cure any ambiguity, to correct or supplement any provision
herein that may be inconsistent with any other provision herein or that is
otherwise defective, or to make any other provisions with respect to matters or
questions arising under this Indenture as the Company and the Trustee may deem
necessary or desirable, provided such action pursuant to this clause (7) shall
not adversely affect the interests of the Holders of Securities in any material
respect.

        Upon Company Request, accompanied by a Board Resolution authorizing the
execution of any such supplemental indenture, and subject to and upon receipt by
the Trustee of the documents described in Section 8.3 hereof, the Trustee shall
join with the Company in the execution of any supplemental indenture authorized
or permitted by the terms of this Indenture and to make any further appropriate
agreements and stipulations that may be therein contained.

SECTION 8.2     Supplemental Indentures with Consent of Holders of Securities.

        With either (i) the written consent of the Holders of not less than a
majority in principal amount of the Outstanding Securities, by the Act of said
Holders delivered to the Company and


                                      -50-
<PAGE>   56

the Trustee, or (ii) by the adoption of a resolution, at a meeting of Holders of
the Outstanding Securities at which a quorum is present, by the Holders of at
least 66-2/3% in principal amount of the Outstanding Securities represented at
such meeting, the Company, when authorized by a Board Resolution, and the
Trustee may enter into an indenture or indentures supplemental hereto for the
purpose of adding any provisions to or changing in any manner or eliminating any
of the provisions of this Indenture or of modifying in any manner the rights of
the Holders of Securities under this Indenture; provided, however, that no such
supplemental indenture shall, without the consent or affirmative vote of the
Holder of each Outstanding Security affected thereby,

        (1)     change the Stated Maturity of the principal of, or any
installment of interest on, any Security, or reduce the principal amount of, or
the premium, if any, or the rate of interest payable thereon, or reduce the
amount payable upon a redemption or mandatory repurchase, or change the place or
currency of payment of the principal of, premium, if any, or interest on any
Security (including any payment of Redemption Price or Repurchase Price in
respect of such Security) or impair the right to institute suit for the
enforcement of any payment in respect of any Security on or after the Stated
Maturity thereof (or, in the case of redemption or any repurchase, on or after
the Redemption Date or Repurchase Date, as the case may be) or, except as
permitted by Section 12.11, adversely affect the right of Holders to convert any
Security as provided in Article XII; or

        (2)     reduce the requirements of Section 9.4 for quorum or voting, or
reduce the percentage in principal amount of the Outstanding Securities the
consent of whose Holders is required for any such supplemental indenture or the
consent of whose Holders is required for any waiver (of compliance with certain
provisions of this Indenture or certain defaults hereunder and their
consequences) provided for in this Indenture; or

        (3)     modify the obligation of the Company to maintain an office or
agency in the Borough of Manhattan, The City of New York, pursuant to Section
10.2; or

        (4)     modify any of the provisions of this Section or Section 5.13 or
10.12, except to increase any percentage contained herein or therein or to
provide that certain other provisions of this Indenture cannot be modified or
waived without the consent of the Holder of each Outstanding Security affected
thereby; or

        (5)     modify the provisions of Article XIV in a manner adverse to the
Holders.

        It shall not be necessary for any Act of Holders of Securities under
this Section to approve the particular form of any proposed supplemental
indenture, but it shall be sufficient if such Act shall approve the substance
thereof.

SECTION 8.3     Execution of Supplemental Indentures.

        In executing, or accepting the additional trusts created by, any
supplemental indenture permitted by this Article or the modifications thereby of
the trusts created by this Indenture, the Trustee shall be entitled to receive,
and (subject to Sections 6.1 and 6.3) shall be fully protected in relying upon,
an Opinion of Counsel stating that the execution of such supplemental indenture
is authorized or permitted by this Indenture, and that such supplemental
indenture has been duly authorized, executed and delivered by the Company and
constitutes a valid and legally binding


                                      -51-
<PAGE>   57

obligation of the Company enforceable against the Company in accordance with its
terms. The Trustee may, but shall not be obligated to, enter into any such
supplemental indenture which affects the Trustee's own rights, duties or
immunities under this Indenture or otherwise.

SECTION 8.4     Effect of Supplemental Indentures.

        Upon the execution of any supplemental indenture under this Article,
this Indenture shall be modified in accordance therewith, and such supplemental
indenture shall form a part of this Indenture for all purposes; and every Holder
of Securities theretofore or thereafter authenticated and delivered hereunder
appertaining thereto shall be bound thereby.

SECTION 8.5     Reference in Securities to Supplemental Indentures.

        Securities authenticated and delivered after the execution of any
supplemental indenture pursuant to this Article may, and shall if required by
the Trustee, bear a notation in form approved by the Trustee as to any matter
provided for in such supplemental indenture. If the Company shall so determine,
new Securities so modified as to conform, in the opinion of the Company and the
Trustee, to any such supplemental indenture may be prepared and executed by the
Company and authenticated and delivered by the Trustee in exchange for
Outstanding Securities.

SECTION 8.6     Notice of Supplemental Indentures.

        Promptly after the execution by the Company and the Trustee of any
supplemental indenture pursuant to the provisions of Section 8.2, the Company
shall give notice to all Holders of Securities of such fact, setting forth in
general terms the substance of such supplemental indenture, in the manner
provided in Section 1.6. Any failure of the Company to give such notice, or any
defect therein, shall not in any way impair or affect the validity of any such
supplemental indenture.

SECTION 8.7     Conformity with Trust Indenture Act.

        Every supplemental indenture executed pursuant to this Article shall
conform to the requirements of the Trust Indenture Act.

                                   ARTICLE IX
                        MEETINGS OF HOLDERS OF SECURITIES

SECTION 9.1     Purposes for Which Meetings May Be Called.

        A meeting of Holders of Securities may be called at any time and from
time to time pursuant to this Article to make, give or take any request, demand,
authorization, direction, notice, consent, waiver or other action provided by
this Indenture to be made, given or taken by Holders of Securities.


                                      -52-
<PAGE>   58

SECTION 9.2     Call, Notice and Place of Meetings.

        (1)     The Trustee may at any time call a meeting of Holders of
Securities for any purpose specified in Section 9.1, to be held at such time and
at such place in the Borough of Manhattan, The City of New York, as the Trustee
shall determine. Notice of every meeting of Holders of Securities, setting forth
the time and the place of such meeting and in general terms the action proposed
to be taken at such meeting, shall be given, in the manner provided in Section
1.6, not less than 21 nor more than 180 days prior to the date fixed for the
meeting.

        (2)     In case at any time the Company, pursuant to a Board Resolution,
or the Holders of at least 10% in principal amount of the Outstanding Securities
shall have requested the Trustee to call a meeting of the Holders of Securities
for any purpose specified in Section 9.1, by written request setting forth in
reasonable detail the action proposed to be taken at the meeting, and the
Trustee shall not have mailed the notice of such meeting within 21 days after
receipt of such request or shall not thereafter proceed to cause the meeting to
be held as provided herein, then the Company or the Holders of Securities in the
amount specified, as the case may be, may determine the time and the place in
the Borough of Manhattan, The City of New York, for such meeting and may call
such meeting for such purposes by giving notice thereof as provided in paragraph
(1) of this Section.

SECTION 9.3     Persons Entitled to Vote at Meetings.

        To be entitled to vote at any meeting of Holders of Securities, a Person
shall be (i) a Holder of one or more Outstanding Securities, or (ii) a Person
appointed by an instrument in writing as proxy for a Holder or Holders of one or
more Outstanding Securities by such Holder or Holders. The only Persons who
shall be entitled to be present or to speak at any meeting of Holders shall be
the Persons entitled to vote at such meeting and their counsel, any
representatives of the Trustee and its counsel and any representatives of the
Company and its counsel.

SECTION 9.4     Quorum; Action.

        The Persons entitled to vote a majority in principal amount of the
Outstanding Securities shall constitute a quorum. In the absence of a quorum
within 30 minutes of the time appointed for any such meeting, the meeting shall,
if convened at the request of Holders of Securities, be dissolved. In any other
case, the meeting may be adjourned for a period of not less than 10 days as
determined by the chairman of the meeting prior to the adjournment of such
meeting. In the absence of a quorum at any such adjourned meeting, such
adjourned meeting may be further adjourned for a period not less than 10 days as
determined by the chairman of the meeting prior to the adjournment of such
adjourned meeting (subject to repeated applications of this sentence). Notice of
the reconvening of any adjourned meeting shall be given as provided in Section
9.2(1), except that such notice need be given only once not less than five days
prior to the date on which the meeting is scheduled to be reconvened. Notice of
the reconvening of an adjourned meeting shall state expressly the percentage of
the principal amount of the Outstanding Securities that shall constitute a
quorum.


                                      -53-
<PAGE>   59

        Subject to the foregoing, at the reconvening of any meeting adjourned
for a lack of a quorum, the Persons entitled to vote 25% in principal amount of
the Outstanding Securities at the time shall constitute a quorum for the taking
of any action set forth in the notice of the original meeting.

        At a meeting or an adjourned meeting duly reconvened and at which a
quorum is present as aforesaid, any resolution and all matters (except as
limited by the proviso to Section 8.2 and except to the extent Section 10.12
requires a different vote) shall be effectively passed and decided if passed or
decided by the lesser of (i) the Holders of not less than a majority in
principal amount of Outstanding Securities and (ii) the Persons entitled to vote
not less than 66-2/3% in principal amount of Outstanding Securities represented
and entitled to vote at such meeting.

        Any resolution passed or decisions taken at any meeting of Holders of
Securities duly held in accordance with this Section shall be binding on all the
Holders of Securities whether or not present or represented at the meeting. The
Trustee shall, in the name and at the expense of the Company, notify all the
Holders of Securities of any such resolutions or decisions pursuant to Section
1.6.

SECTION 9.5     Determination of Voting Rights; Conduct and Adjournment of
                Meetings.

        (1)     Notwithstanding any other provisions of this Indenture, the
Trustee may make such reasonable regulations as it may deem advisable for any
meeting of Holders of Securities in regard to proof of the holding of Securities
and of the appointment of proxies and in regard to the appointment and duties of
inspectors of votes, the submission and examination of proxies, certificates and
other evidence of the right to vote, and such other matters concerning the
conduct of the meeting as it shall deem appropriate. Except as otherwise
permitted or required by any such regulations, the holding of Securities shall
be proved in the manner specified in Section 1.4 and the appointment of any
proxy shall be proved in the manner specified in Section 1.4 or by having the
signature of the Person executing the proxy guaranteed by any bank, broker or
other eligible institution participating in a recognized medallion signature
guarantee program.

        (2)     The Trustee shall, by an instrument in writing, appoint a
temporary chairman (which may be the Trustee) of the meeting, unless the meeting
shall have been called by the Company or by Holders of Securities as provided in
Section 9.2(1), in which case the Company or the Holders of Securities calling
the meeting, as the case may be, shall in like manner appoint a temporary
chairman. A permanent chairman and a permanent secretary of the meeting shall be
elected by vote of the Persons entitled to vote a majority in principal amount
of the Outstanding Securities represented at the meeting.

        (3)     At any meeting, each Holder of a Security or proxy shall be
entitled to one vote for each U.S. $1,000 principal amount of Securities held or
represented by him; provided, however, that no vote shall be cast or counted at
any meeting in respect of any Security challenged as not Outstanding and ruled
by the chairman of the meeting to be not Outstanding. The chairman of the
meeting shall have no right to vote, except as a Holder of a Security or proxy.


                                      -54-
<PAGE>   60

        (4)     Any meeting of Holders of Securities duly called pursuant to
Section 9.2 at which a quorum is present may be adjourned from time to time by
Persons entitled to vote a majority in principal amount of the Outstanding
Securities represented at the meeting, and the meeting may be held as so
adjourned without further notice.

SECTION 9.6     Counting Votes and Recording Action of Meetings.

        The vote upon any resolution submitted to any meeting of Holders of
Securities shall be by written ballots on which shall be subscribed the
signatures of the Holders of Securities or of their representatives by proxy and
the principal amounts at Stated Maturity and serial numbers of the Outstanding
Securities held or represented by them. The permanent chairman of the meeting
shall appoint two inspectors of votes who shall count all votes cast at the
meeting for or against any resolution and who shall make and file with the
secretary of the meeting their verified written reports in duplicate of all
votes cast at the meeting. A record, at least in duplicate, of the proceedings
of each meeting of Holders of Securities shall be prepared by the secretary of
the meeting and there shall be attached to said record the original reports of
the inspectors of votes on any vote by ballot taken thereat and affidavits by
one or more Persons having knowledge of the facts setting forth a copy of the
notice of the meeting and showing that said notice was given as provided in
Section 9.2 and, if applicable, Section 9.4. Each copy shall be signed and
verified by the affidavits of the permanent chairman and secretary of the
meeting and one such copy shall be delivered to the Company and another to the
Trustee to be preserved by the Trustee, the latter to have attached thereto the
ballots voted at the meeting. Any record so signed and verified shall be
conclusive evidence of the matters therein stated.

                                    ARTICLE X
                                    COVENANTS

SECTION 10.1    Payment of Principal, Premium and Interest.

        The Company covenants and agrees that it will duly and punctually pay
the principal of and premium, if any, and interest on the Securities in
accordance with the terms of the Securities and this Indenture. The Company will
deposit or cause to be deposited with the Trustee, no later than the opening of
business on the date of the Stated Maturity of any Security or no later than the
opening of business on the due date for any installment of interest, all
payments so due, which payments shall be in immediately available funds on the
date of such Stated Maturity or due date, as the case may be.

SECTION 10.2    Maintenance of Offices or Agencies.

        The Company will maintain in the Borough of Manhattan, The City of New
York, an office or agency where the Securities may be surrendered for
registration of transfer or exchange or for presentation for payment or for
conversion, redemption or repurchase and where notices and demands to or upon
the Company in respect of the Securities and this Indenture may be served. The
Company will give prompt written notice to the Trustee of the location, and any
change in the location, of such office or agency not designated or appointed by
the Trustee. If at any time the Company shall fail to maintain any such required
office or agency or shall fail to furnish the Trustee with the address thereof,
such presentations, surrenders, notices and demands


                                      -55-
<PAGE>   61

may be made or served at the Corporate Trust Office or the office or agency of
the Trustee in the Borough of Manhattan, The City of New York.

        The Company may at any time and from time to time vary or terminate the
appointment of any such agent or appoint any additional agents for any or all of
such purposes; provided, however, that until all of the Securities have been
delivered to the Trustee for cancellation, or moneys sufficient to pay the
principal of, premium, if any, and interest on the Securities have been made
available for payment and either paid or returned to the Company pursuant to the
provisions of Section 10.3, the Company will maintain in the Borough of
Manhattan, The City of New York, an office or agency where Securities may be
presented or surrendered for payment and conversion, which shall initially be
the Trustee, where Securities may be surrendered for registration of transfer or
exchange and where notices and demands to or upon the Company in respect of the
Securities and this Indenture may be served. The Company will give prompt
written notice to the Trustee, and notice to the Holders in accordance with
Section 1.6, of the appointment or termination of any such agents and of the
location and any change in the location of any such office or agency.

        The Company hereby initially designates the Trustee as Paying Agent,
Security Registrar and Conversion Agent, and each of the Corporate Trust Office
of the Trustee and the office or agency of the Trustee in the Borough of
Manhattan, The City of New York, located at 40 Broad Street, 5th Floor, Suite
550, New York, New York 10004 as one such office or agency of the Company for
each of the aforesaid purposes.

SECTION 10.3    Money for Security Payments to Be Held in Trust.

        If the Company shall act as its own Paying Agent, it will, on or before
each due date of the principal of, premium, if any, or interest on any of the
Securities, segregate and hold in trust for the benefit of the Persons entitled
thereto a sum sufficient to pay the principal, premium, if any, or interest so
becoming due until such sums shall be paid to such Persons or otherwise disposed
of as herein provided and the Company will promptly notify the Trustee of its
action or failure so to act.

        Whenever the Company shall have one or more Paying Agents, it will, no
later than the opening of business on each due date of the principal of,
premium, if any, or interest on any Securities, deposit with the Trustee a sum
in funds immediately payable on the payment date sufficient to pay the
principal, premium, if any, or interest so becoming due, such sum to be held for
the benefit of the Persons entitled to such principal, premium, if any, or
interest, and (unless such Paying Agent is the Trustee) the Company will
promptly notify the Trustee of any failure so to act.

        The Company will cause each Paying Agent other than the Trustee to
execute and deliver to the Trustee an instrument in which such Paying Agent
shall agree with the Trustee, subject to the provisions of this Section, that
such Paying Agent will:

        (1)     hold all sums held by it for the payment of the principal of,
premium, if any, or interest on Securities for the benefit of the Persons
entitled thereto until such sums shall be paid to such Persons or otherwise
disposed of as herein provided;


                                      -56-
<PAGE>   62

        (2)     give the Trustee notice of any default by the Company (or any
other obligor upon the Securities) in the making of any payment of principal,
premium, if any, or interest; and

        (3)     at any time during the continuance of any such default, upon the
written request of the Trustee, forthwith pay to the Trustee all sums so held by
such Paying Agent.

        The Company may at any time, for the purpose of obtaining the
satisfaction and discharge of this Indenture or for any other purpose, pay, or
by Company Order direct any Paying Agent to pay, to the Trustee all sums held in
trust by the Company or such Paying Agent, such sums to be held by the Trustee
upon the same trusts as those upon which such sums were held by the Company or
such Paying Agent; and, upon such payment by any Paying Agent to the Trustee,
such Paying Agent shall be released from all further liability with respect to
such money.

        Any money deposited with the Trustee or any Paying Agent, or then held
by the Company, in trust for the payment of the principal of, premium, if any,
or interest on any Security and remaining unclaimed for two years after such
principal, premium, if any, or interest has become due and payable shall be paid
to the Company on Company Request, or (if then held by the Company) shall be
discharged from such trust; and the Holder of such Security shall thereafter, as
an unsecured general creditor, look only to the Company for payment thereof, and
all liability of the Trustee or such Paying Agent with respect to such trust
money, and all liability of the Company as trustee thereof, shall thereupon
cease.

SECTION 10.4    Existence.

        Subject to Article VII, the Company will do or cause to be done all
things necessary to preserve and keep in full force and effect its existence,
rights (charter and statutory) and franchises; provided, however, that the
Company shall not be required to preserve any such right or franchise if the
Company shall determine that the preservation thereof is no longer desirable in
the conduct of the business of the Company and that the loss thereof is not
disadvantageous in any material respect to the Holders.

SECTION 10.5    Maintenance of Properties.

        The Company will cause all properties used or useful in the conduct of
its business or the business of any Significant Subsidiary to be maintained and
kept in good condition, repair and working order and supplied with all necessary
equipment and will cause to be made all necessary repairs, renewals,
replacements, betterments and improvements thereof, all as in the judgment of
the Company may be necessary so that the business carried on in connection
therewith may be properly and advantageously conducted at all times; provided,
however, that nothing in this Section shall prevent the Company from
discontinuing the operation or maintenance of any of such properties if such
discontinuance is, in the judgment of the Company, desirable in the conduct of
its business or the business of any Significant Subsidiary and not
disadvantageous in any material respect to the Holders.


                                      -57-
<PAGE>   63

SECTION 10.6    Payment of Taxes and Other Claims.

        The Company will pay or discharge, or cause to be paid or discharged,
before the same may become delinquent, (i) all taxes, assessments and
governmental charges levied or imposed upon the Company or any Significant
Subsidiary or upon the income, profits or property of the Company or any
Significant Subsidiary, (ii) all claims for labor, materials and supplies which,
if unpaid, might by law become a lien or charge upon the property of the Company
or any Significant Subsidiary, and (iii) all stamps and other duties, if any,
which may be imposed by the United States or any political subdivision thereof
or therein in connection with the issuance, transfer, exchange or conversion of
any Securities or with respect to this Indenture; provided, however, that, in
the case of clauses (i) and (ii), the Company shall not be required to pay or
discharge or cause to be paid or discharged any such tax, assessment, charge or
claim (A) if the failure to do so will not, in the aggregate, have a material
adverse impact on the Company, or (B) if the amount, applicability or validity
is being contested in good faith by appropriate proceedings.

SECTION 10.7    Reserved.

SECTION 10.8    Statement by Officers as to Default.

        The Company shall deliver to the Trustee, within 120 days after the end
of each fiscal year of the Company ending after the date hereof, an Officers'
Certificate, stating whether or not to the best knowledge of the signers thereof
the Company is in default in the performance and observance of any of the terms,
provisions and conditions of this Indenture (without regard to any period of
grace or requirement of notice provided hereunder) and, if the Company shall be
in default, specifying all such defaults and the nature and status thereof of
which they may have knowledge.

        The Company will deliver to the Trustee, forthwith upon becoming aware
of any default or any Event of Default under the Indenture, an Officers'
Certificate specifying with particularity such default or Event of Default and
further stating what action the Company has taken, is taking or proposes to take
with respect thereto. For the purpose of this Section, the term "default" means
any event which is, or after notice or lapse of time or both would become, an
Event of Default.

        Any notice required to be given under this Section 10.8 shall be
delivered to the Trustee at its Corporate Trust Office.

SECTION 10.9    Reserved.

SECTION 10.10   Reserved.

SECTION 10.11   Reserved.

SECTION 10.12   Waiver of Certain Covenants.

        The Company may omit in any particular instance to comply with any
covenant or condition set forth in Sections 10.4 (other than with respect to the
existence of the Company


                                      -58-
<PAGE>   64

(subject to Article VII)), 10.5 and 10. 6, inclusive (other than a covenant or
condition which under Article VIII cannot be modified or amended without the
consent of the Holder of each Outstanding Security affected), if before the time
for such compliance the Holders shall, through (i) the written consent of not
less than a majority in principal amount of the Outstanding Securities or (ii)
the adoption of a resolution at a meeting of Holders of the Outstanding
Securities at which a quorum is present by the Holders of not less than 66-2/3%
in principal amount of the Outstanding Securities represented at such meeting,
either waive such compliance in such instance or generally waive compliance with
such covenant or condition, but no such waiver shall extend to or affect such
covenant or condition except to the extent so expressly waived, and, until such
waiver shall become effective, the obligations of the Company and the duties of
the Trustee or any Paying or Conversion Agent in respect of any such covenant or
condition shall remain in full force and effect.

                                   ARTICLE XI
                            REDEMPTION OF SECURITIES

SECTION 11.1    Right of Redemption.

        The Securities may be redeemed in accordance with the provisions of the
form of Securities set forth in Section 2.2.

SECTION 11.2    Applicability of Article.

        Redemption of Securities at the election of the Company or otherwise, as
permitted or required by any provision of the Securities or this Indenture,
shall be made in accordance with such provision and this Article XI.

SECTION 11.3    Election to Redeem; Notice to Trustee.

        The election of the Company to redeem any Securities shall be evidenced
by a Board Resolution. In case of any redemption at the election of the Company
of any of the Securities, the Company shall, at least 45 days prior to the
Redemption Date fixed by the Company (unless a shorter notice shall be
satisfactory to the Trustee), notify the Trustee in writing of such Redemption
Date.

SECTION 11.4    Selection by Trustee of Securities to Be Redeemed.

        If less than all the Securities are to be redeemed, the particular
Securities to be redeemed shall be selected by the Trustee within five Business
Days after it receives the notice described in 11.3, from the Outstanding
Securities not previously called for redemption, by lot or by such other method
as the Trustee may deem fair and appropriate.

        If any Security selected for partial redemption is converted in part
before termination of the conversion right with respect to the portion of the
Security so selected, the converted portion of such Security shall be deemed (so
far as may be) to be the portion selected for redemption. Securities which have
been converted during a selection of Securities to be redeemed may be treated by
the Trustee as Outstanding for the purpose of such selection. The Trustee shall
promptly notify the Company and each Security Registrar in writing of the
securities selected for


                                      -59-
<PAGE>   65

redemption and, in the case of any Securities selected for partial redemption,
the principal amount thereof to be redeemed.

        For all purposes of this Indenture, unless the context otherwise
requires, all provisions relating to the redemption of Securities shall relate,
in the case of any Securities redeemed or to be redeemed only in part, to the
portion of the principal amount of such Securities which has been or is to be
redeemed.

SECTION 11.5    Notice of Redemption.

        Notice of redemption shall be given in the manner provided in Section
1.6 to the Holders of Securities to be redeemed not less than 30 nor more than
60 days prior to the Redemption Date, and such notice shall be irrevocable. The
Company shall, concurrently with the giving of such notice, publish a Press
Release including the information required to be included in such notice of
redemption hereunder.

        All notices of redemption shall state:

        (1)     the Redemption Date,

        (2)     the Redemption Price, and accrued interest, if any, to the
Redemption Date,

        (3)     if less than all Outstanding Securities are to be redeemed, the
aggregate principal amount of Securities to be redeemed and the aggregate
principal amount of Securities which will be outstanding after such partial
redemption,

        (4)     that on the Redemption Date the Redemption Price, and accrued
interest, if any, to the Redemption Date, will become due and payable upon each
such Security to be redeemed, and that interest thereon shall cease to accrue on
and after said date,

        (5)     the Conversion Rate, the date on which the right to convert the
Securities to be redeemed will terminate and the places where such Securities
may be surrendered for conversion, and

        (6)     the place or places where such Securities are to be surrendered
for payment of the Redemption Price and accrued interest, if any, to the
Redemption Date.

        In case of a partial redemption, the notice shall specify the serial and
CUSIP numbers (if any) and the portions thereof called for redemption and that
transfers and exchanges may occur on or prior to the Redemption Date.

        Notice of redemption of Securities to be redeemed at the election of the
Company shall be given by the Company or, at the Company's written request, by
the Trustee in the name of and at the expense of the Company. Notice of
redemption of Securities to be redeemed at the election of the Company received
by the Trustee shall be given by the Trustee to each Paying Agent in the name of
and at the expense of the Company.


                                      -60-
<PAGE>   66

SECTION 11.6    Deposit of Redemption Price.

        On or prior to the Redemption Date, the Company shall deposit with the
Trustee (or, if the Company is acting as its own Paying Agent, segregate and
hold in trust as provided in Section 10.3) an amount of money (which shall be in
immediately available funds on such Redemption Date) sufficient to pay the
Redemption Price of, and (except if the Redemption Date shall be an Interest
Payment Date) accrued interest to the Redemption Date on, all the Securities
which are to be redeemed on that date other than any Securities called for
redemption on that date which have been converted prior to the date of such
deposit.

        If any Security called for redemption is converted, any money deposited
with the Trustee or so segregated and held in trust for the redemption of such
Security shall (subject to any right of the Holder of such Security or any
Predecessor Security to receive interest as provided in the last paragraph of
Section 3.7) be paid to the Company on Company Request or, if then held by the
Company, shall be discharged from such trust.

SECTION 11.7    Securities Payable on Redemption Date.

        Notice of redemption having been given as aforesaid, the Securities so
to be redeemed shall, on the Redemption Date, become due and payable at the
Redemption Price therein specified and from and after such date (unless the
Company shall default in the payment of the Redemption Price, including accrued
interest) such Securities shall cease to bear interest. Upon surrender of any
Security for redemption in accordance with said notice such Security shall be
paid by the Company at the Redemption Price together with accrued and unpaid
interest to the Redemption Date; provided, however, that installments of
interest on Securities whose Stated Maturity is on or prior to the Redemption
Date shall be payable to the Holders of such Securities, or one or more
Predecessor Securities, registered as such on the relevant Record Date according
to their terms and the provisions of Section 3.7.

        If any Security called for redemption shall not be so paid upon
surrender thereof for redemption, the principal amount of, premium, if any, and,
to the extent permitted by applicable law, accrued interest on such Security
shall, until paid, bear interest from the Redemption Date at a rate of 3.75% per
annum and such Security shall remain convertible until the Redemption Price of
such Security (or portion thereof, as the case may be) shall have been paid or
duly provided for.

        Any Security that is to be redeemed only in part shall be surrendered at
the Corporate Trust Office or an office or agency of the Company designated for
that purpose pursuant to Section 10.2 (with, if the Company or the Trustee so
requires, due endorsement by, or a written instrument of transfer in form
satisfactory to the Company and the Trustee duly executed by, the Holder thereof
or his attorney duly authorized in writing), and the Company shall execute, and
the Trustee shall authenticate and make available for delivery to the Holder of
such Security without service charge, a new Security or Securities, of any
authorized denomination as requested by such Holder, in aggregate principal
amount equal to and in exchange for the unredeemed portion of the principal of
the Security so surrendered.


                                      -61-
<PAGE>   67

SECTION 11.8    Conversion Arrangement on Call for Redemption.

        In connection with any redemption of Securities, the Company may arrange
for the purchase and conversion of any Securities by an agreement with one or
more investment bankers or other purchasers (the "Purchasers") to purchase such
securities by paying to the Trustee in trust for the Holders, on or before the
Redemption Date, an amount not less than the applicable Redemption Price,
together with interest accrued to the Redemption Date, of such Securities.
Notwithstanding anything to the contrary contained in this Article XI, the
obligation of the Company to pay the Redemption Price, together with interest
accrued to the Redemption Date, shall be deemed to be satisfied and discharged
to the extent such amount is so paid by such Purchasers. If such an agreement is
entered into (a copy of which shall be filed with the Trustee prior to the close
of business on the Business Day immediately prior to the Redemption Date), any
Securities called for redemption that are not duly surrendered for conversion by
the Holders thereof may, at the option of the Company, be deemed, to the fullest
extent permitted by law, and consistent with any agreement or agreements with
such Purchasers, to be acquired by such Purchasers from such Holders and
(notwithstanding anything to the contrary contained in Article XII) surrendered
by such Purchasers for conversion, all as of immediately prior to the close of
business on the Redemption Date (and the right to convert any such Securities
shall be extended through such time), subject to payment of the above amount as
aforesaid. At the direction of the Company, the Trustee shall hold and dispose
of any such amount paid to it by the Purchasers to the Holders in the same
manner as it would monies deposited with it by the Company for the redemption of
Securities. Without the Trustee's prior written consent, no arrangement between
the Company and such Purchasers for the purchase and conversion of any
Securities shall increase or otherwise affect any of the powers, duties,
responsibilities or obligations of the Trustee as set forth in this Indenture,
and the Company agrees to indemnify the Trustee from, and hold it harmless
against, any loss, liability or expense arising out of or in connection with any
such arrangement for the purchase and conversion of any Securities between the
Company and such Purchasers, including the costs and expenses, including
reasonable legal fees, incurred by the Trustee in the defense of any claim or
liability arising out of or in connection with the exercise or performance of
any of its powers, duties, responsibilities or obligations under this Indenture.

                                  ARTICLE XII
                            CONVERSION OF SECURITIES

SECTION 12.1    Conversion Privilege and Conversion Rate.

        Subject to and upon compliance with the provisions of this Article, at
the option of the Holder thereof, any Security may be converted into fully paid
and nonassessable shares (calculated as to each conversion to the nearest
1/100th of a share) of Common Stock of the Company at the Conversion Rate,
determined as hereinafter provided, in effect at the time of conversion. Such
conversion right shall commence on the initial issuance date of the Securities
and expire at the close of business on the date of Maturity, subject, in the
case of conversion of any Global Security, to any Applicable Procedures. In case
a Security or portion thereof is called for redemption at the election of the
Company or the Holder thereof exercises his right to require the Company to
repurchase the Security, such conversion right in respect of the Security, or
portion thereof so called, shall expire at the close of business on the Business
Day immediately


                                      -62-
<PAGE>   68

preceding the Redemption Date or the Repurchase Date, as the case may be, unless
the Company defaults in making the payment due upon redemption or repurchase, as
the case may be (in each case subject as aforesaid to any Applicable Procedures
with respect to any Global Security).

        The rate at which shares of Common Stock shall be delivered upon
conversion (herein called the "Conversion Rate") shall be initially 9.5808
shares of Common Stock for each U.S.$1,000 principal amount of Securities. The
Conversion Rate shall be adjusted in certain instances as provided in this
Article XII.

SECTION 12.2    Exercise of Conversion Privilege.

        In order to exercise the conversion privilege, the Holder of any
Security to be converted shall surrender such Security, duly endorsed in blank,
at any office or agency of the Company maintained for that purpose pursuant to
Section 10.2, accompanied by a duly signed conversion notice substantially in
the form set forth in Section 2.4 stating that the Holder elects to convert such
Security or, if less than the entire principal amount thereof is to be
converted, the portion thereof to be converted. Each Security surrendered for
conversion (in whole or in part) during the Record Date Period shall (except in
the case of any Security or portion thereof which has been called for redemption
on a Redemption Date, or is repurchasable on a Repurchase Date, occurring, in
either case, within such Record Date Period and, as a result, the right to
convert such Security would otherwise terminate in such period if not exercised)
be accompanied by payment in New York Clearing House funds or other funds
acceptable to the Company of an amount equal to the interest payable on such
Interest Payment Date on the principal amount of such Security (or part thereof,
as the case may be) being surrendered for conversion. The interest so payable on
such Interest Payment Date with respect to any Security (or portion thereof, if
applicable) that is surrendered for conversion during the Record Date Period
shall be paid to the Holder of such Security as of such Regular Record Date in
an amount equal to the interest that would have been payable on such Security if
such Security had been converted as of the close of business on such Interest
Payment Date. Interest payable on any Interest Payment Date in respect of any
Security surrendered for conversion on or after such Interest Payment Date shall
be paid to the Holder of such Security as of the Regular Record Date next
preceding such Interest Payment Date, notwithstanding the exercise of the right
of conversion. Except as provided in this paragraph and subject to the last
paragraph of Section 3.7, no cash payment or adjustment shall be made upon any
conversion on account of any interest accrued from the Interest Payment Date
next preceding the conversion date, in respect of any Security (or part thereof,
as the case may be) surrendered for conversion, or on account of any dividends
on the Common Stock issued upon conversion. The Company's delivery to the Holder
of the number of shares of Common Stock (and cash in lieu of fractions thereof,
as provided in this Indenture) into which a Security is convertible will be
deemed to satisfy the Company's obligation to pay the principal amount of the
Security.

        Securities shall be deemed to have been converted immediately prior to
the close of business on the day of surrender of such Securities for conversion
in accordance with the foregoing provisions, and at such time the rights of the
Holders of such Securities as Holders shall cease, and the Person or Persons
entitled to receive the Common Stock issuable upon conversion shall be treated
for all purposes as the record holder or holders of such Common Stock at such
time. As promptly as practicable on or after the conversion date, the Company



                                      -63-
<PAGE>   69

shall issue and deliver to the Trustee, for delivery to the Holder, a
certificate or certificates for the number of full shares of Common Stock
issuable upon conversion, together with payment in lieu of any fraction of a
share, as provided in Section 12.3.

        In the case of any Security which is converted in part only, upon such
conversion the Company shall execute and the Trustee shall authenticate and
deliver to the Holder thereof, at the expense of the Company, a new Security or
Securities of authorized denominations in an aggregate principal amount equal to
the unconverted portion of the principal amount of such Security. A Security may
be converted in part, but only if the principal amount of such Security to be
converted is any integral multiple of U.S. $1,000 and the principal amount of
such security to remain Outstanding after such conversion is equal to U.S.
$1,000 or any integral multiple of $1,000 in excess thereof.

SECTION 12.3    Fractions of Shares.

        No fractional shares of Common Stock shall be issued upon conversion of
any Security or Securities. If more than one Security shall be surrendered for
conversion at one time by the same Holder, the number of full shares which shall
be issuable upon conversion thereof shall be computed on the basis of the
aggregate principal amount of the Securities (or specified portions thereof) so
surrendered. Instead of any fractional share of Common Stock that would
otherwise be issuable upon conversion of any Security or Securities (or
specified portions thereof), the Company shall calculate and pay a cash
adjustment in respect of such fraction (calculated to the nearest 1/100th of a
share) in an amount equal to the same fraction of the Closing Price Per Share at
the close of business on the day of conversion.

SECTION 12.4    Adjustment of Conversion Rate.

        The Conversion Rate shall be subject to adjustments from time to time as
follows:

        (1)     In case the Company shall pay or make a dividend or other
distribution on shares of any class of capital stock payable in shares of Common
Stock, the Conversion Rate in effect at the opening of business on the day
following the date fixed for the determination of shareholders entitled to
receive such dividend or other distribution shall be increased by dividing such
Conversion Rate by a fraction of which the numerator shall be the number of
shares of Common Stock outstanding at the close of business on the date fixed
for such determination and the denominator shall be the sum of such number of
shares and the total number of shares constituting such dividend or other
distribution, such increase to become effective immediately after the opening of
business on the day following the date fixed for such determination. If, after
any such date fixed for determination, any dividend or distribution is not in
fact paid, the Conversion Rate shall be immediately readjusted, effective as of
the date the Board of Directors determines not to pay such dividend or
distribution, to the Conversion Rate that would have been in effect if such
determination date had not been fixed. For the purposes of this paragraph (1),
the number of shares of Common Stock at any time outstanding shall not include
shares held in the treasury of the Company but shall include shares issuable in
respect of scrip certificates issued in lieu of fractions of shares of Common
Stock. The Company will not pay any dividend or make any distribution on shares
of Common Stock held in the treasury of the Company.


                                      -64-
<PAGE>   70

        (2)     In case the Company shall issue rights, options or warrants to
all holders of its Common Stock entitling them to subscribe for or purchase
shares of Common Stock at a price per share less than the current market price
per share (determined as provided in paragraph (8) of this Section 12.4) of the
Common Stock on the date fixed for the determination of stockholders entitled to
receive such rights, options or warrants (other than any rights, options or
warrants that by their terms will also be issued to any Holder upon conversion
of a Security into shares of Common Stock without any action required by the
Company or any other Person), the Conversion Rate in effect at the opening of
business on the day following the date fixed for such determination shall be
increased by dividing such Conversion Rate by a fraction of which the numerator
shall be the number of shares of Common Stock outstanding at the close of
business on the date fixed for such determination plus the number of shares of
Common Stock that the aggregate of the offering price of the total number of
shares of Common Stock so offered for subscription or purchase would purchase at
such current market price and the denominator shall be the number of shares of
Common Stock outstanding at the close of business on the date fixed for such
determination plus the number of shares of Common Stock so offered for
subscription or purchase, such increase to become effective immediately after
the opening of business on the day following the date fixed for such
determination. If, after any such date fixed for determination, any such rights,
options or warrants are not in fact issued, or are not exercised prior to the
expiration thereof, the Conversion Rate shall be immediately readjusted,
effective as of the date such rights, options or warrants expire, or the date
the Board of Directors determines not to issue such rights, options or warrants,
to the Conversion Rate that would have been in effect if the unexercised rights,
options or warrants had never been granted or such determination date had not
been fixed, as the case may be. For the purposes of this paragraph (2), the
number of shares of Common Stock at any time outstanding shall not include
shares held in the treasury of the Company but shall include shares issuable in
respect of scrip certificates issued in lieu of fractions of shares of Common
Stock. The Company will not issue any rights, options or warrants in respect of
shares of Common Stock held in the treasury of the Company.

        (3)     In case outstanding shares of Common Stock shall be subdivided
into a greater number of shares of Common Stock, the Conversion Rate in effect
at the opening of business on the day following the day upon which such
subdivision becomes effective shall be proportionately increased, and,
conversely, in case outstanding shares of Common Stock shall be combined into a
smaller number of shares of Common Stock, the Conversion Rate in effect at the
opening of business on the day following the day upon which such subdivision or
combination becomes effective shall be proportionately reduced, such increase or
reduction, as the case may be, to become effective immediately after the opening
of business on the day following the day upon which such subdivision or
combination becomes effective.

        (4)     In case the Company shall, by dividend or otherwise, distribute
to all holders of its Common Stock evidences of its indebtedness, shares of any
class of capital stock or other property (including cash or assets or
securities, but excluding (i) any rights, options or warrants referred to in
paragraph (2) of this Section, (ii) any dividend or distribution paid
exclusively in cash, (iii) any dividend or distribution referred to in paragraph
(1) of this Section and (iv) any consideration distributed in any merger or
consolidation to which Section 12.11 applies), the Conversion Rate shall be
adjusted so that the same shall equal the rate determined by dividing the
Conversion Rate in effect immediately prior to the close of business on the date
fixed for the determination of stockholders entitled to receive such
distribution by a fraction of which the


                                      -65-
<PAGE>   71

numerator shall be the current market price per share (determined as provided in
paragraph (8) of this Section 12.4) of the Common Stock on the date fixed for
such determination less the then fair market value (as determined by the Board
of directors, whose determination shall be conclusive and described in a Board
Resolution filed with the Trustee) of the portion of the assets, shares or
evidences of indebtedness so distributed applicable to one share of Common Stock
and the denominator shall be such current market price per share of the Common
Stock, such adjustment to become effective immediately prior to the opening of
business on the day following the date fixed for the determination of
stockholders entitled to receive such distribution. If after any such date fixed
for determination, any such distribution is not in fact made, the Conversion
Rate shall be immediately readjusted, effective as of the date of the Board of
Directors determines not to make such distribution, to the Conversion Rate that
would have been in effect if such determination date had not been fixed.

        (5)     In case the Company shall, by dividend or otherwise, distribute
to all holders of its Common Stock cash (excluding any cash that is distributed
as part of a distribution referred to in paragraph (4) of this Section or cash
distributed upon a merger or consolidation to which Section 12.11 applies) in an
aggregate amount that, combined together with (I) the aggregate amount of any
other all-cash distributions to all holders of its Common Stock made exclusively
in cash within the 365-day period preceding the date of payment of such
distribution and in respect of which no adjustment pursuant to this paragraph
(5) has been made and (II) the aggregate of any cash plus the fair market value
(as determined by the Board of Directors, whose determination shall be
conclusive and described in a Board Resolution) of consideration payable in
respect of any tender offer by the Company or any of its Subsidiaries for all or
any portion of the Common Stock concluded within the 365-day period preceding
the date of payment of such distribution and in respect of which no adjustment
pursuant to paragraph (6) of this Section 12.4 has been made (the "combined cash
and tender amount") exceeds 10% of the product of the current market price per
share (determined as provided in paragraph (8) of this Section 12.4) of the
Common Stock on the date for the determination of holders of shares of Common
Stock entitled to receive such distribution times the number of shares of Common
Stock outstanding on such date (the "aggregate current market price"), then, and
in each such case, immediately after the close of business on such date for
determination, the Conversion Rate shall be adjusted so that the same shall
equal the rate determined by dividing the Conversion Rate in effect immediately
prior to the close of business on the date fixed for determination of the
stockholders entitled to receive such distribution by a fraction (i) the
numerator of which shall be equal to the current market price per share
(determined as provided in paragraph (8) of this Section) of the Common Stock on
the date fixed for such determination less an amount equal to the quotient of
(x) the excess of such combined cash and tender amount over 10% of such
aggregate current market price divided by (y) the number of shares of Common
Stock outstanding on such date for determination and (ii) the denominator of
which shall be equal to the current market price per share (determined as
provided in paragraph (8) of this Section 12.4) of the Common Stock on such date
fixed for determination.

        (6)     In case a tender offer made by the Company or any Subsidiary for
all or any portion of the Common Stock shall expire and such tender offer (as
amended upon the expiration thereof) shall require the payment to stockholders
(based on the acceptance (up to any maximum specified in the terms of the tender
offer) of Purchased Shares (as defined below)) of an aggregate consideration
having a fair market value (as determined by the Board of Directors,


                                      -66-
<PAGE>   72

whose determination shall be conclusive and described in a Board Resolution)
that combined together with (I) the aggregate of the cash plus the fair market
value (as determined by the Board of Directors, whose determination shall be
conclusive and described in a Board Resolution), as of the expiration of such
tender offer, of consideration payable in respect of any other tender offer by
the Company or any Subsidiary for all or any portion of the Common Stock
expiring within the 365-day period preceding the expiration of such tender offer
and in respect of which no adjustment pursuant to this paragraph (6) has been
made and (II) the aggregate amount of any cash distributions to all holders of
the Common Stock within 365-day period preceding the expiration of such tender
offer and in respect of which no adjustment pursuant to paragraph (5) of this
Section has been made (the "combined tender and cash amount") exceeds 10% of the
product of the current market price per share of the Common Stock (determined as
provided in paragraph (8) of this Section 12.4) as of the last time (the
"Expiration Time") tenders could have been made pursuant to such tender offer
(as it may be amended) times the number of shares of Common Stock outstanding
(including any tendered shares) as of the Expiration Time, then, and in each
such case immediately prior to the opening of business on the day after the date
of the Expiration Time, the Conversion Rate shall be adjusted so that the same
shall equal the rate determined by dividing the Conversion Rate immediately
prior to close of business on the date of the Expiration Time by a fraction (i)
the numerator of which shall be equal to (A) the product of (I) the current
market price per share of the Common Stock (determined as provided in paragraph
(8) of this Section 12.4) on the date of the Expiration Time multiplied by (II)
the number of shares of Common Stock outstanding (including any tendered shares)
on the Expiration Time less (B) the combined tender and cash amount, and (ii)
the denominator of which shall be equal to the product of (A) the current market
price per share of the Common Stock (determined as provided in paragraph (8) of
this Section 12.4) as of the Expiration Time multiplied by (B) the number of
shares of Common Stock outstanding (including any tendered shares) as of the
Expiration Time less the number of all shares validly tendered and not withdrawn
as of the Expiration Time (the shares deemed so accepted up to any such maximum,
being referred to as the "Purchased Shares").

        (7)     The reclassification of Common Stock into securities other than
Common Stock (other than any reclassification upon a consolidation or merger to
which Section 12.11 applies) shall be deemed to involve (a) a distribution of
such securities other than Common Stock to all holders of Common Stock (and the
effective date of such reclassification shall be deemed to be "the date fixed
for the determination of stockholders entitled to receive such distribution" and
"the date fixed for such determination" within the meaning of paragraph (4) of
this Section), and (b) a subdivision or combination, as the case may be, of the
number of shares of Common Stock outstanding immediately prior to such
reclassification into the number of shares of Common Stock outstanding
immediately thereafter (and the effective date of such reclassification shall be
deemed to be "the day upon which such subdivision becomes effective" or "the day
upon which such combination becomes effective", as the case may be, and "the day
upon which such subdivision or combination becomes effective" within the meaning
of paragraph (3) of this Section 12.4).

        (8)     For the purpose of any computation under paragraphs (2), (4),
(5) or (6) of this Section 12.4, the current market price per share of Common
Stock on any date shall be calculated by the Company and be the average of the
daily Closing Prices Per Share for the five consecutive Trading Days selected by
the Company commencing not more than 10 Trading Days


                                      -67-
<PAGE>   73

before, and ending not later than the earlier of the day in question and the day
before the "ex" date with respect to the issuance or distribution requiring such
computation. For purposes of this paragraph, the term "'ex' date", when used
with respect to any issuance or distribution, means the first date on which the
Common Stock trades regular way in the applicable securities market or on the
applicable securities exchange without the right to receive such issuance or
distribution.

        (9)     No adjustment in the Conversion Rate shall be required unless
such adjustment (plus any adjustments not previously made by reason of this
paragraph (9)) would require an increase or decrease of at least one percent in
such rate; provided, however, that any adjustments which by reason of this
paragraph (9) are not required to be made shall be carried forward and taken
into account in any subsequent adjustment. All calculations under this Article
shall be made to the nearest cent or to the nearest one-hundredth of a share, as
the case may be.

        (10)    The Company may make such increases in the Conversion Rate, for
the remaining term of the Securities or any shorter term, in addition to those
required by paragraphs (1), (2), (3), (4), (5) and (6) of this Section 12.4, as
it considers to be advisable in order to avoid or diminish any income tax to any
holders of shares of Common Stock resulting from any dividend or distribution of
stock or issuance of rights or warrants to purchase or subscribe for stock or
from any event treated as such for income tax purposes. The Company shall have
the power to resolve any ambiguity or correct any error in this paragraph (10)
and its actions in so doing shall, absent manifest error, be final and
conclusive.

        (11)    Notwithstanding the foregoing provisions of this Section, no
adjustment of the Conversion Rate shall be required to be made (a) upon the
issuance of shares of Common Stock pursuant to any present or future plan for
the reinvestment of dividends or (b) because of a tender or exchange offer of
the character described in Rule 13e-4(h)(5) under the Exchange Act or any
successor rule thereto.

        (12)    To the extent permitted by applicable law, the Company from time
to time may increase the Conversion Rate by any amount for any period of time if
the period is at least twenty (20) days, the increase is irrevocable during such
period, and the Board of Directors shall have made a determination that such
increase would be in the best interests of the Company, which determination
shall be conclusive; provided, however, that no such increase shall be taken
into account for purposes of determining whether the Closing Price Per Share of
the Common Stock equals or exceeds 105% of the Conversion Price in connection
with an event which would otherwise be a Change of Control pursuant to Section
14.4. Whenever the Conversion Rate is increased pursuant to the preceding
sentence, the Company shall give notice of the increase to the Holders in the
manner provided in Section 1.6 at least fifteen (15) days prior to the date the
increased Conversion Rate takes effect, and such notice shall state the
increased Conversion Rate and the period during which it will be in effect.

SECTION 12.5    Notice of Adjustments of Conversion Rate.

        Whenever the Conversion Rate is adjusted as herein provided:

        (1)     the Company shall compute the adjusted Conversion Rate in
accordance with Section 12.4 and shall prepare a certificate signed by the Chief
Financial Officer of the Company


                                      -68-
<PAGE>   74

setting forth the adjusted Conversion Rate and showing in reasonable detail the
facts upon which such adjustment is based, and such certificate shall promptly
be filed with the Trustee and with each Conversion Agent; and

        (2)     upon each such adjustment, a notice stating that the Conversion
Rate has been adjusted and setting forth the adjusted Conversion Rate shall be
required, and as soon as practicable after it is required, such notice shall be
provided by the Company to all Holders in accordance with Section 1.6.

        Neither the Trustee nor any Conversion Agent shall be under any duty or
responsibility with respect to any such certificate or the information and
calculations contained therein, except to exhibit the same to any Holder of
Securities desiring inspection thereof at its office during normal business
hours, and shall not be deemed to have knowledge of any adjustment in the
Conversion Rate unless and until a Responsible Officer of the Trustee shall have
received such a certificate. Until a Responsible Officer of the Trustee receives
such a certificate, the Trustee and each Conversion Agent may assume without
inquiry that the last Conversion Rate of which the Trustee has knowledge of
remains in effect.

SECTION 12.6    Notice of Certain Corporate Action.

        In case:

        (1)     the Company shall declare a dividend (or any other distribution)
on its Common Stock payable (i) otherwise than exclusively in cash or (ii)
exclusively in cash in an amount that would require any adjustment pursuant to
Section 12.4; or

        (2)     the Company shall authorize the granting to all or substantially
all of the holders of its Common Stock of rights, options or warrants to
subscribe for or purchase any shares of capital stock of any class or of any
other rights; or

        (3)     of any reclassification of the Common Stock, or of any
consolidation, merger or share exchange to which the Company is a party and for
which approval of any stockholders of the Company is required, or of the
conveyance, sale, transfer or lease of all or substantially all of the assets of
the Company; or

        (4)     of the voluntary or involuntary dissolution, liquidation or
winding up of the Company,

then the Company shall cause to be filed at each office or agency maintained for
the purpose of conversion of Securities pursuant to Section 10.2, and shall
cause to be provided to all Holders in accordance with Section 1.6, at least 10
days prior to the applicable record or effective date hereinafter specified, a
notice stating (x) the date on which a record is to be taken for the purpose of
such dividend, distribution, rights, options or warrants, or, if a record is not
to be taken, the date as of which the holders of Common Stock of record to be
entitled to such dividend, distribution, rights, options or warrants are to be
determined or (y) the date on which such reclassification, consolidation,
merger, conveyance, transfer, sale, lease, dissolution, liquidation or winding
up is expected to become effective, and the date as of which it is expected that
holders of Common Stock of record shall be entitled to exchange their shares of
Common Stock


                                      -69-
<PAGE>   75

for securities, cash or other property deliverable upon such reclassification,
consolidation, merger, conveyance, transfer, sale, lease, dissolution,
liquidation or winding up. Neither the failure to give such notice or the notice
referred to in the following paragraph nor any defect therein shall affect the
legality or validity of the proceedings described in clauses (1) through (4) of
this Section 12.6. If at the time the Trustee shall not be the Conversion Agent,
a copy of such notice shall also forthwith be filed by the Company with the
Trustee.

        The Company shall cause to be filed at the Corporate Trust Office and
each office or agency maintained for the purpose of conversion of Securities
pursuant to Section 10.2, and shall cause to be provided to all Holders in
accordance with Section 1.6, notice of any tender offer by the Company or any
Subsidiary for all or any portion of the Common Stock at or about the time that
such notice of tender offer is provided to the public generally.

SECTION 12.7    Company to Reserve Common Stock.

        The Company shall at all times reserve and keep available, free from
preemptive rights, out of its authorized but unissued Common Stock, for the
purpose of effecting the conversion of Securities, the full number of shares of
Common Stock then issuable upon the conversion of all Outstanding Securities.

SECTION 12.8    Taxes on Conversions.

        Except as provided in the next sentence, the Company will pay any and
all taxes and duties (other than income taxes) that may be payable in respect of
the issue or delivery of shares of Common Stock on conversion of Securities
pursuant hereto. The Company shall not, however, be required to pay any tax or
duty that may be payable in respect of any transfer involved in the issue and
delivery of shares of Common Stock in a name other than that of the Holder of
the Security or Securities to be converted, and no such issue or delivery shall
be made unless and until the Person requesting such issue has paid to the
Company the amount of any such tax or duty, or has established to the
satisfaction of the Company that such tax or duty has been paid.

SECTION 12.9    Covenant as to Common Stock.

        The Company agrees that all shares of Common Stock that may be delivered
upon conversion of Securities, upon such delivery, will have been duly
authorized and validly issued and will be fully paid and nonassessable and,
except as provided in Section 12.8, the Company will pay all taxes, liens and
charges with respect to the issue thereof.

SECTION 12.10   Cancellation of Converted Securities.

        All Securities delivered for conversion shall be delivered to the
Trustee or its agent to be canceled by or at the direction of the Trustee, which
shall dispose of the same as provided in Section 3.9.

SECTION 12.11   Provision in Case of Consolidation, Merger or Sale of Assets.

        In case of any consolidation or merger of the Company with or into any
other Person, any merger of another Person with or into the Company (other than
a merger that does not result in



                                      -70-
<PAGE>   76

any reclassification, conversion, exchange or cancellation of outstanding shares
of Common Stock of the Company) or any conveyance, sale, transfer or lease of
all or substantially all of the assets of the Company, the Person formed by such
consolidation or resulting from such merger or which acquires such assets, as
the case may be, shall execute and deliver to the Trustee a supplemental
indenture providing that the Holder of each Security then Outstanding shall have
the right thereafter, during the period such Security shall be convertible as
specified in Section 12.1, to convert such Security only into the kind and
amount of securities, cash and other property receivable upon such
consolidation, merger, conveyance, sale, transfer or lease by a holder of the
number of shares of Common Stock of the Company into which such Security might
have been converted immediately prior to such consolidation, merger, conveyance,
sale, transfer or lease, assuming such holder of Common Stock of the Company (i)
is not (A) a Person with which the Company consolidated or merged with or into
or which merged into or with the Company or to which such conveyance, sale,
transfer or lease was made, as the case may be (a "Constituent Person"), or (B)
an Affiliate of a Constituent Person and (ii) failed to exercise his rights of
election, if any, as to the kind or amount of securities, cash and other
property receivable upon such consolidation, merger, conveyance, sale, transfer
or lease (provided that if the kind or amount of securities, cash and other
property receivable upon such consolidation, merger, conveyance, sale, transfer,
or lease is not the same for each share of Common Stock of the Company held
immediately prior to such consolidation, merger, conveyance, sale, transfer or
lease by others than a Constituent Person or an Affiliate thereof and in respect
of which such rights of election shall not have been exercised ("Non-electing
Share"), then for the purpose of this Section 12.11 the kind and amount of
securities, cash and other property receivable upon such consolidation, merger,
conveyance, sale, transfer or lease by the holders of each Non-electing Share
shall be deemed to be the kind and amount so receivable per share by a plurality
of the Non-electing Shares). Such supplemental indenture shall provide for
adjustments that, for events subsequent to the effective date of such
supplemental indenture, shall be as nearly equivalent as may be practicable to
the adjustments provided for in this Article. The above provisions of this
Section 12.11 shall similarly apply to successive consolidations, mergers,
conveyances, sales, transfers or leases. Notice of the execution of such a
supplemental indenture shall be given by the Company to the Holder of each
Security as provided in Section 1.6 promptly upon such execution.

        Neither the Trustee nor any Conversion Agent shall be under any
responsibility to determine the correctness of any provisions contained in any
such supplemental indenture relating either to the kind or amount of shares of
stock or other securities or property or cash receivable by Holders of
Securities upon the conversion of their Securities after any such consolidation,
merger, conveyance, transfer, sale or lease or to any such adjustment, but may
accept as conclusive evidence of the correctness of any such provisions, and
shall be protected in relying upon, an Opinion of Counsel with respect thereto,
which the Company shall cause to be furnished to the Trustee upon request.

SECTION 12.12   Rights Issued in Respect of Common Stock.

        Rights or warrants distributed by the Company to all holders of Common
Stock entitling the holders thereof to subscribe for or purchase shares of the
Company's capital stock (either initially or under certain circumstances), which
rights or warrants, until the occurrence of a specified event or events
("Trigger Event"):


                                      -71-
<PAGE>   77

                (i)     are deemed to be transferred with such shares of Common
Stock,

                (ii)    are not exercisable, and

                (iii)   are also issued in respect of future issuances of Common
Stock

shall not be deemed distributed for purposes of Section 12.4(2) until the
occurrence of the earliest Trigger Event. In addition, in the event of any
distribution of rights or warrants, or any Trigger Event with respect thereto,
that shall have resulted in an adjustment to the Conversion Rate under Section
12.4(2), (1) in the case of any such rights or warrants that shall all have been
redeemed or repurchased without exercise by any holders thereof, the Conversion
Rate shall be readjusted upon such final redemption or repurchase to give effect
to such distribution or Trigger Event, as the case may be, as though it were a
cash distribution, equal to the per share redemption or repurchase price
received by a holder of Common Stock with respect to such rights or warrants
(assuming such holder had retained such rights or warrants), made to all holders
of Common Stock as of the date of such redemption or repurchase, and (2) in the
case of any such rights or warrants all of which shall have expired without
exercise by any holder thereof, the Conversion Price shall be readjusted as if
such issuance had not occurred.

SECTION 12.13   Responsibility of Trustee for Conversion Provisions.

        The Trustee, subject to the provisions of Section 6.1, and any
Conversion Agent shall not at any time be under any duty or responsibility to
any Holder of Securities to determine whether any facts exist which may require
any adjustment of the Conversion Rate, or with respect to the nature or extent
of any such adjustment when made, or with respect to the method employed, herein
or in any supplemental indenture provided to be employed, in making the same, or
whether a supplemental indenture need be entered into. Neither the Trustee,
subject to the provisions of Section 6.1, nor any Conversion Agent shall be
accountable with respect to the validity or value (or the kind or amount) of any
Common Stock, or of any other securities or property or cash, which may at any
time be issued or delivered upon the conversion of any Security; and it or they
do not make any representation with respect thereto. Neither the Trustee,
subject to the provisions of Section 6.1, nor any Conversion Agent shall be
responsible for any failure of the Company to make or calculate any cash payment
or to issue, transfer or deliver any shares of Common Stock or share
certificates or other securities or property or cash upon the surrender of any
Security for the purpose of conversion; and the Trustee, subject to the
provisions of Section 6.1, and any Conversion Agent shall not be responsible for
any failure of the Company to comply with any of the covenants of the Company
contained in this Article.

                                  ARTICLE XIII
                                   [RESERVED]


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<PAGE>   78

                                  ARTICLE XIV
                 REPURCHASE OF SECURITIES AT THE OPTION OF THE
                        HOLDER UPON A CHANGE IN CONTROL

SECTION 14.1    Right to Require Repurchase.

        In the event that a Change in Control (as hereinafter defined) shall
occur, then each Holder shall have the right, at the Holder's option, but
subject to the provisions of Section 14.2, to require the Company to repurchase,
and upon the exercise of such right the Company shall repurchase, all of such
Holder's Securities not theretofore called for redemption, or any portion of the
principal amount thereof that is equal to U.S. $1,000 or any integral multiple
of U.S. $1,000 in excess thereof (provided that no single Security may be
repurchased in part unless the portion of the principal amount of such Security
to be Outstanding after such repurchase is equal to U.S. $1,000 or integral
multiples of U.S. $1,000 in excess thereof), on the date (the "Repurchase Date")
that is 45 days after the date of the Company Notice (as defined in Section
14.3) at a purchase price equal to 100% of the principal amount of the
Securities to be repurchased plus interest accrued to the Repurchase Date (the
"Repurchase Price"); provided, however, that installments of interest on
Securities whose Stated Maturity is on or prior to the Repurchase Date shall be
payable to the Holders of such Securities, or one or more Predecessor
Securities, registered as such on the relevant Record Date according to their
terms and the provisions of Section 3.7. Such right to require the repurchase of
the Securities shall not continue after a discharge of the Company from its
obligations with respect to the Securities in accordance with Article IV, unless
a Change in Control shall have occurred prior to such discharge. At the option
of the Company, the Repurchase Price may be paid in cash or, subject to the
fulfillment by the Company of the conditions set forth Section 14.2, by delivery
of shares of Common Stock having a fair market value equal to the Repurchase
Price. Whenever in this Indenture (including Sections 2.2, 3.1, 5.1(1) and 5.8)
there is a reference, in any context, to the principal of any Security as of any
time, such reference shall be deemed to include reference to the Repurchase
Price payable in respect of such Security to the extent that such Repurchase
Price is, was or would be so payable at such time, and express mention of the
Repurchase Price in any provision of this Indenture shall not be construed as
excluding the Repurchase Price in those provisions of this Indenture when such
express mention is not made.

SECTION 14.2    Conditions to the Company's Election to Pay the Repurchase Price
                in Common Stock.

        The Company may elect to pay the Repurchase Price by delivery of shares
of Common Stock pursuant to Section 14.1 if and only if the following conditions
shall have been satisfied:

        (1)     The shares of Common Stock deliverable in payment of the
Repurchase Price shall have a fair market value as of the Repurchase Date of not
less than the Repurchase Price. For purposes of Section 14.1 and this Section
14.2, the fair market value of shares of Common Stock shall be determined by the
Company and shall be equal to 95% of the average of the Closing Prices Per Share
of the Common Stock for the five consecutive Trading Days immediately preceding
and including the third Trading Day prior to the Repurchase Date;


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<PAGE>   79

        (2)     The Repurchase Price shall be paid only in cash in the event any
shares of Common Stock to be issued upon repurchase of Securities hereunder (i)
require registration under any federal securities law before such shares may be
freely transferable without being subject to any transfer restrictions under the
Securities Act upon repurchase and if such registration is not completed or does
not become effective prior to the Repurchase Date, and/or (ii) require
registration with or approval of any governmental authority under any state law
or any other federal law before such shares may be validly issued or delivered
upon repurchase and if such registration is not completed or does not become
effective or such approval is not obtained prior to the Repurchase Date;

        (3)     Payment of the Repurchase Price may not be made in Common Stock
unless such stock is, or shall have been, approved for quotation on the Nasdaq
National Market or listed on a national securities exchange, in either case,
prior to the Repurchase Date; and

        (4)     All shares of Common Stock that may be issued upon repurchase of
Securities will be issued out of the Company's authorized but unissued Common
Stock and, will upon issue, be duly and validly issued and fully paid and
non-assessable and free of any preemptive or similar rights.

        If all of the conditions set forth in this Section 14.2 are not
satisfied in accordance with the terms thereof, the Repurchase Price shall be
paid by the Company only in cash.

SECTION 14.3    Notices; Method of Exercising Repurchase Right, Etc.

        (1)     Unless the Company shall have theretofore called for redemption
all of the Outstanding Securities, on or before the 30th day after the
occurrence of a Change in Control, the Company or, at the request and expense of
the Company on or before the 15th day after such occurrence, the Trustee, shall
give to all Holders of Securities, in the manner provided in Section 1.6, notice
(the "Company Notice") of the occurrence of the Change of Control and of the
repurchase right set forth herein arising as a result thereof and the Company
shall issue a Press Release including the information required to be included in
such Company Notice hereunder. The Company shall also deliver a copy of such
Company Notice to the Trustee.

        Each Company Notice shall state:

                (i)     the Repurchase Date,

                (ii)    the date by which the repurchase right must be
exercised,

                (iii)   the Repurchase Price, and whether the Repurchase Price
shall be paid by the Company in cash or by delivery of shares of Common Stock,

                (iv)    a description of the procedure that a Holder must follow
to exercise a repurchase right, and the place or places where such Securities
are to be surrendered for payment of the Repurchase Price and accrued interest,
if any to the Repurchase Date,

                (v)     that on the Repurchase Date the Repurchase Price, and
accrued interest, if any to the Repurchase Date, will become due and payable
upon each such Security designated by


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<PAGE>   80

the Holder to be repurchased, and that interest thereon shall cease to accrue on
and after said date,

                (vi)    the Conversion Rate then in effect, the date on which
the right to convert the principal amount of the Securities to be repurchased
will terminate and the place or places where such Securities may be surrendered
for conversion, and

                (vii)   the place or places that the Security certificate with
the Election of Holder to Require Repurchase as specified in Section 2.2 shall
be delivered.

        No failure of the Company to give the foregoing notices or defect
therein shall limit any Holder' s right to exercise a repurchase right or affect
the validity of the proceedings for the repurchase of Securities.

        If any of the foregoing provisions or other provisions of this Article
XIV are inconsistent with applicable law, such law shall govern.

        (2)     To exercise a repurchase right, a Holder shall deliver to the
Trustee on or before the 30th day after the date of the Company Notice (i)
irrevocable written notice of the Holder's exercise of such right, which notice
shall set forth the name of the Holder, the principal amount of the Securities
to be repurchased (and, if any Security is to repurchased in part, the serial
number thereof, the portion of the principal amount thereof to be repurchased
and the name of the Person in which the portion thereof to remain Outstanding
after such repurchase is to be registered) and a statement that an election to
exercise the repurchase right is being made thereby, and, in the event that the
Repurchase Price shall be paid in shares of Common Stock, the name or names
(with addresses) in which the certificate or certificates for shares of Common
Stock shall be issued, and (ii) the Securities with respect to which the
repurchase right is being exercised. Such written notice shall be irrevocable,
except that the right of the Holder to convert the Securities with respect to
which the repurchase right is being exercised shall continue until the close of
business on the Business Day immediately preceding the Repurchase Date.

        (3)     In the event a repurchase right shall be exercised in accordance
with the terms hereof, the Company shall pay or cause to be paid to the Trustee
the Repurchase Price in cash or shares of Common Stock, as provided above, for
payment to the Holder on the Repurchase Date or, if shares of Common Stock are
to be paid, as promptly after the Repurchase Date as practicable, together with
accrued and unpaid interest to the Repurchase Date payable with respect to the
Securities as to which the repurchase right has been exercised; provided,
however, that installments of interest that mature on or prior to the Repurchase
Date shall be payable in cash to the Holders of such Securities, or one or more
Predecessor Securities, registered as such at the close of business on the
relevant Regular Record Date.

        (4)     If any Security (or portion thereof) surrendered for repurchase
shall not be so paid on the Repurchase Date, the principal amount of such
Security (or portion thereof, as the case may be) shall, until paid, bear
interest to the extent permitted by applicable law from the Repurchase Date at
the rate of 3.75% per annum, and each Security shall remain convertible into
Common Stock until the principal of such Security (or portion thereof, as the
case may be) shall have been paid or duly provided for.


                                      -75-
<PAGE>   81

        (5)     Any Security that is to be repurchased only in part shall be
surrendered to the Trustee (with, if the Company or the Trustee so requires, due
endorsement by, or a written instrument of transfer in form satisfactory to the
Company and the Trustee duly executed by, the Holder thereof or his attorney
duly authorized in writing), and the Company shall execute, and the Trustee
shall authenticate and make available for delivery to the Holder of such
Security without service charge, a new Security or Securities, containing
identical terms and conditions, each in an authorized denomination in aggregate
principal amount equal to and in exchange for the unrepurchased portion of the
principal of the Security so surrendered.

        (6)     Any issuance of shares of Common Stock in respect of the
Repurchase Price shall be deemed to have been effected immediately prior to the
close of business on the Repurchase Date and the Person or Persons in whose name
or names any certificate or certificates for shares of Common Stock shall be
issuable upon such repurchase shall be deemed to have become on the Repurchase
Date the holder or holders of record of the shares represented thereby;
provided, however, that any surrender for repurchase on a date when the stock
transfer books of the Company shall be closed shall constitute the Person or
Persons in whose name or names the certificate or certificates for such shares
are to be issued as the record holder or holders thereof for all purposes at the
opening of business on the next succeeding day on which such stock transfer
books are open. No payment or adjustment shall be made for dividends or
distributions on any Common Stock issued upon repurchase of any Security
declared prior to the Repurchase Date.

        (7)     No fractions of shares shall be issued upon repurchase of
Securities. If more than one Security shall be repurchased from the same Holder
and the Repurchase Price shall be payable in shares of Common Stock, the number
of full shares that shall be issuable upon such repurchase shall be computed on
the basis of the aggregate principal amount of the Securities so repurchased.
Instead of any fractional share of Common Stock that would otherwise be issuable
on the repurchase of any Security or Securities, the Company will deliver to the
applicable Holder its check for the current market value of such fractional
share. The current market value of a fraction of a share is determined by
multiplying the current market price of a full share by the fraction, and
rounding the result to the nearest cent. For purposes of this Section, the
current market price of a share of Common Stock is the Closing Price Per Share
of the Common Stock on the Trading Day immediately preceding the Repurchase
Date.

        (8)     Any issuance and delivery of certificates for shares of Common
Stock on repurchase of Securities shall be made without charge to the Holder of
Securities being repurchased for such certificates or for any tax or duty in
respect of the issuance or delivery of such certificates or the securities
represented thereby; provided, however, that the Company shall not be required
to pay any tax or duty that may be payable in respect of (i) income of the
Holder or (ii) any transfer involved in the issuance or delivery of certificates
for shares of Common Stock in a name other than that of the Holder of the
Securities being repurchased, and no such issuance or delivery shall be made
unless and until the Person requesting such issuance or delivery has paid to the
Company the amount of any such tax or duty or has established, to the
satisfaction of the Company, that such tax or duty has been paid.


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<PAGE>   82

        (9)     All Securities delivered for repurchase shall be delivered to
the Trustee to be canceled at the direction of the Trustee, which shall dispose
of the same as provided in Section 3.9.

SECTION 14.4    Certain Definitions.

        For purposes of this Article XIV,

        (1)     the term "beneficial owner" shall be determined in accordance
with Rule 13d-3, as in effect on the date of the original execution of this
Indenture, promulgated by the Commission pursuant to the Exchange Act;

        (2)     a "Change in Control" shall be deemed to have occurred at the
time, after the original issuance of the Securities, of:

                (i)     the acquisition by any Person (including any syndicate
or group deemed to be a "person" under Section 13(d)(3) of the Exchange Act) of
beneficial ownership, directly or indirectly, through a purchase, merger or
other acquisition transaction or series of transactions, of shares of capital
stock of the Company entitling such person to exercise 50% or more of the total
voting power of all shares of capital stock of the Company entitled to vote
generally in the elections of directors, other than any such acquisition by the
Company, any subsidiary of the Company or any employee benefit plan of the
Company; or

                (ii)    any consolidation of the Company with, or merger of the
Company into, any other Person, any merger of another Person into the Company,
or any conveyance, sale, transfer or lease of all or substantially all of the
assets of the Company to another Person (other than any such transaction (x)
that does not result in any reclassification, conversion, exchange or
cancellation of outstanding shares of capital stock of the Company, (y) pursuant
to which the holders of 50% or more of the total voting power of all shares of
the Company's capital stock entitled to vote generally in the election of
directors immediately prior to such transaction have the entitlement to
exercise, directly or indirectly, 50% or more of the total voting power of all
shares of capital stock entitled to vote generally in the election of directors
of the continuing or surviving corporation immediately after such transaction or
(z) which is effected solely to change the jurisdiction of incorporation of the
Company and results in a reclassification, conversion or exchange of outstanding
shares of Common Stock into solely shares of common stock); provided, however,
that a Change in Control shall not be deemed to have occurred if (I) the Closing
Price Per Share of the Common Stock for any five Trading Days within the period
of 10 consecutive Trading Days ending immediately after the later of the Change
in Control or the public announcement of the Change in Control (in the case of a
Change in Control under clause (i) above) or the period of 10 consecutive
Trading Days ending immediately before the Change in Control (in the case of a
Change in Control under clause (ii) above) shall, in the case of each of such
five Trading Days, equal or exceed 105% of the Conversion Price of the
Securities in effect on each of such five Trading Days or (II) all of the
consideration (excluding cash payments for fractional shares and cash payments
made pursuant to dissenters' appraisal rights) in a merger or consolidation
otherwise constituting a Change of Control under clause (i) and/or clause (ii)
above consists of shares of common stock traded on a national securities
exchange or quoted on the Nasdaq National Market (or will be so traded or quoted
immediately following


                                      -77-
<PAGE>   83

such merger or consolidation) and as a result of such merger or consolidation
the notes become convertible into such common stock;

        (3)     the term "Conversion Price" shall equal U.S.$1,000 divided by
the Conversion Rate (rounded to the nearest cent); and

        (4)     for purposes of Section 14.4(2)(i), the term "person" shall
include any syndicate or group which would be deemed to be a "person" under
Section 13(d)(3) of the Exchange Act, as in effect on the date of the original
execution of this Indenture.

SECTION 14.5    Consolidation, Merger, etc.

        In the case of any merger, consolidation, conveyance, sale, transfer or
lease of all or substantially all of the assets of the Company to which Section
12.11 applies, in which the Common Stock of the Company is changed or exchanged
as a result into the right to receive shares of stock and other securities or
property or assets (including cash) which includes shares of Common Stock of the
Company or common stock of another Person that are, or upon issuance will be,
traded on a United States national securities exchange or approved for trading
on an established automated over-the-counter trading market in the United States
and such shares constitute at the time such change or exchange becomes effective
in excess of 50% of the aggregate fair market value of such shares of stock and
other securities, property and assets (including cash) (as determined by the
Company, which determination shall be conclusive and binding), then the Person
formed by such consolidation or resulting from such merger or combination or
which acquires the properties or assets (including cash) of the Company, as the
case may be, shall execute and deliver to the Trustee a supplemental indenture
(which shall comply with the Trust Indenture Act as in force at the date of
execution of such supplemental indenture) modifying the provisions of this
Indenture relating to the right of Holders to cause the Company to repurchase
the Securities following a Change in Control, including without limitation the
applicable provisions of this Article XIV and the definitions of the Common
Stock and Change in Control, as appropriate, and such other related definitions
set forth herein as determined in good faith by the Company (which determination
shall be conclusive and binding), to make such provisions apply in the event of
a subsequent Change in Control to the common stock and the issuer thereof if
different from the Company and Common Stock of the Company (in lieu of the
Company and the Common Stock of the Company).

                                   ARTICLE XV
         HOLDERS LISTS AND REPORTS BY TRUSTEE AND COMPANY; NON-RECOURSE

SECTION 15.1    Company to Furnish Trustee Names and Addresses of Holders.

        The Company will furnish or cause to be furnished to the Trustee:

        (1)     semi-annually, not more than 15 days after the Regular Record
Date, a list, in such form as the Trustee may reasonably require, of the names
and addresses of the Holders of Securities as of such Regular Record Date, and


                                      -78-
<PAGE>   84

        (2)     at such other times as the Trustee may reasonably request in
writing, within 30 days after the receipt by the Company of any such request, a
list of similar form and content as of a date not more than 15 days prior to the
time such list is furnished;

        provided, however, that no such list need be furnished so long as the
Trustee is acting as Security Registrar.

SECTION 15.2    Preservation of Information.

        (1)     The Trustee shall preserve, in as current a form as is
reasonably practicable, the names and addresses of Holders contained in the most
recent list furnished to the Trustee as provided in Section 15.1 and the names
and addresses of Holders received by the Trustee in its capacity as Security
Registrar. The Trustee may destroy any list, if any, furnished to it as provided
in Section 15.1 upon receipt of a new list so furnished.

        (2)     The rights of Holders to communicate with other Holders with
respect to their rights under this Indenture or under the Securities, and the
corresponding rights, and duties of the Trustee, shall be as provided by the
Trust Indenture Act.

        (3)     Every Holder of Securities, by receiving and holding the same,
agrees with the Company and the Trustee that neither the Company nor the Trustee
nor any agent of either of them shall be held accountable by reason of any
disclosure of information as to names and addresses of Holders made pursuant to
the Trust Indenture Act.

SECTION 15.3    Reserved.

SECTION 15.4    Reports by Trustee.

        (1)     The Trustee shall transmit to Holders such reports concerning
the Trustee and its actions under this Indenture as may be required pursuant to
the Trust Indenture Act at the times and in the manner provided pursuant
thereto.

        (2)     A copy of each such report shall, at the time of such
transmission to Holders, be filed by the Trustee with each stock exchange upon
which the Securities are listed, with the Commission and with the Company. The
Company will notify the Trustee when the Securities are listed on any stock
exchange.

SECTION 15.5    Reports by Company.

        The Company shall file with the Trustee and the Commission, and transmit
to Holders, such information, documents and other reports, and such summaries
thereof, as may be required pursuant to the Trust Indenture Act at the times and
in the manner provided pursuant to such Act; provided that any such information,
documents or reports required to be filed with the Commission pursuant to
Section 13 or 15(d) of the Exchange Act shall be filed with the Trustee within
15 days after the same is so required to be filed with the Commission.


                                      -79-
<PAGE>   85

                                  ARTICLE XVI
        IMMUNITY OF INCORPORATORS, STOCKHOLDERS, OFFICERS AND DIRECTORS

SECTION 16.1    Indenture and Securities Solely Corporate Obligations.

        No recourse for the payment of the principal of or premium, if any, or
interest on any Security and no recourse under or upon any obligation, covenant
or agreement of the Company in this Indenture or in any supplemental indenture
or in any Security, or because of the creation of any indebtedness represented
thereby, shall be had against any incorporator, stockholder, employee, agent,
officer, or director or subsidiary, as such, past, present or future, of the
Company or of any successor corporation, whether by virtue of any constitution,
statute or rule of law, or by the enforcement of any assessment or penalty or
otherwise; it being expressly understood that all such liability is hereby
waived and released as a condition of, and as a consideration for, the execution
of this Indenture and the issue of the Securities.


                             ----------------------

        This instrument may be executed in any number of counterparts, each of
which so executed shall be deemed to be an original, but all such counterparts
shall together constitute but one and the same instrument.

            [THE REMAINDER OF THIS PAGE IS INTENTIONALLY LEFT BLANK]



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<PAGE>   86


        IN WITNESS WHEREOF, the parties hereto have caused this Indenture to be
duly executed all as of the day and year first above written.

                              CIENA CORPORATION

                              By:    /s/ Michael O. McCarthy
                                 -----------------------------------------------
                                 Name: Michael O. McCarthy
                                 Title: Senior Vice President & General Counsel






                              FIRST UNION NATIONAL BANK
                              as Trustee


                              By:    /s/ Monique L. Green
                                 -----------------------------------------------
                                 Name: Monique L. Green
                                 Title: Vice President




                                      -81-