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                                                                     EXHIBIT 4.3

THIS WARRANT AND THE SHARES ISSUABLE HEREUNDER HAVE NOT BEEN REGISTERED UNDER
THE SECURITIES ACT OF 1933, AS AMENDED, AND MAY NOT BE SOLD, PLEDGED, OR OTHER
WISE TRANSFERRED WITHOUT AN EFFECTIVE REGISTRATION THEREOF UNDER SUCH ACT OR
PURSUANT TO RULE 144 OR AN OPINION OF COUNSEL REASONABLY SATISFACTORY TO THE
CORPORATION AND ITS COUNSEL, THAT SUCH REGISTRATION IS NOT REQUIRED.

                            WARRANT TO PURCHASE STOCK

Corporation:                 Avanex Corporation, a California corporation
Number of Shares:            [see below]
Class of Stock:              Series D Preferred
Initial Exercise Price:      [see below]
Issue Date:                  July 8, 1999
Expiration Date:             July 8, 2004

        THIS WARRANT CERTIFIES THAT, for the agreed upon value of $1.00 and for
other good and valuable consideration, COMERICA INCORPORATED ("Holder") is
entitled to purchase the number of fully paid and nonassessable shares of the
class of securities (the "Shares") of the corporation (the "Company") at the
initial exercise price per Share (the "Warrant Price") all as set forth above
and as adjusted pursuant to Article 2 of this Warrant, subject to the provisions
and upon the terms and conditions set forth of this Warrant.

The Warrant price shall be equal to the price per share at which the company
after the date hereof sells its equity securities in an offering or series of
related offerings in which the net proceeds to the company is not less than Five
Million Dollars ($5,000,000.00) (such offering being the "Series D Round", and
the price per share at which the company sells such securities being the "Series
D Round Price"); provided that if the Series D Round is not completed on or
before November 30, 1999, the Warrant Price shall be (i) the Series D Round
price (if known upon exercise hereof) or (ii) the lowest price per share at
which the company has sold any shares of its Series C Preferred Stock ("Series
C"), whichever is less, and the shares shall be Preferred Series C. Holder may
purchase a number of Shares under this Warrant equal to the quotient derived by
dividing $112,500 by the Warrant Price in effect on the date of such purchase.

ARTICLE 1: EXERCISE.

        1.1 Method of Exercise. Holder may exercise this Warrant by delivering a
duly executed Notice of Exercise in substantially the form attached as Appendix
1 to the principal office of the Company. Unless Holder is exercising the
conversion right set forth in Section 1.2, Holder shall also deliver to the
Company a check for the aggregate Warrant Price for the Shares being purchased.

        1.2 Conversion Right. In lieu of exercising this Warrant as specified in
Section 1.1, Holder may from time to time convert this Warrant, in whole or in
part, into a number of Shares determined by dividing (a) the aggregate fair
market value of the Shares or other securities otherwise issuable upon exercise
of this Warrant minus the aggregate Warrant Price of such Shares by (b) the fair
market value of one Share. The fair market value of the Shares shall be
determined pursuant Section 1.4.

        1.3 Alternative Stock Appreciation Right. At Holder's option, the
Company shall pay the fair market value of the Shares issuable upon conversion
of this Warrant pursuant to Section 1.2 in cash in lieu of such Shares.

        1.4 Fair Market Value. If the Shares are traded in a public market, the
fair market value of the Shares shall be the closing price of the Shares (or the
closing price of the Company's stock into which the Shares are convertible)
reported for the business day immediately before Holder delivers its Notice of
Exercise to the Company. If the Shares are not traded in a public market, the
Board of Directors of the Company shall determine fair market value in its
reasonable good faith judgment. The foregoing notwithstanding, if Holder advises
the Board of Directors in writing that Holder disagrees with such determination,
then the Company and Holder shall promptly

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agree upon a reputable investment banking firm to undertake such valuation. If
the valuation of such investment banking firm is greater than that determined by
the Board of Directors, then all fees and expenses of such investment banking
firm shall be paid by the Company. In all other circumstances, such fees and
expenses shall be paid by Holder.

        1.5 Delivery of Certificate and New Warrant. Promptly after Holder
exercises or converts this Warrant, the Company shall deliver to Holder
certificates for the Shares acquired and, if this Warrant has not been fully
exercised or converted and has not expired, a new Warrant representing the
Shares not so acquired.

        1.6 Replacement of Warrants. On receipt of evidence reasonably
satisfactory to the Company of the loss, theft, destruction or mutilation of
this Warrant and, in the case of loss, theft or destruction, on delivery of an
indemnity agreement reasonably satisfactory in form and amount to the Company
or, in the case of mutilation, or surrender and cancellation of this Warrant,
the Company at its expense shall execute and deliver, in lieu of this Warrant, a
new warrant of like tenor.

        1.7 Repurchase on Sale, Merger, or Consolidation of the Company.

        1.7.1 "Acquisition". For the purpose of this Warrant, "Acquisition"
means any sale, license, or other disposition of all or substantially all of the
assets of the Company, or any reorganization, consolidation, or merger of the
Company where the holders of the Company's securities before the transaction
beneficially own less than 50% of the outstanding voting securities of the
surviving entity after the transaction.

        1.7.2 Assumption of Warrant. Upon the closing of any Acquisition the
successor entity shall assume the obligations of this Warrant, and this Warrant
shall be exercisable for the same securities, cash, and property as would be
payable for the Shares issuable upon exercise of the unexercised portion of this
Warrant as if such Shares were outstanding on the record date for the
Acquisition and subsequent closing. The Warrant Price shall be adjusted
accordingly.

        1.7.3 Purchase Right. Notwithstanding the foregoing, at the election of
Holder, the Company shall purchase the unexercised portion of this Warrant for
cash upon the closing of any Acquisition for an amount equal to (a) the fair
market value of any consideration that would have been received by Holder in
consideration of the Shares had Holder exercised the unexercised portion of this
Warrant immediately before the record date for determining the shareholders
entitled to participate in the proceeds of the Acquisition, less (b) the
aggregate Warrant Price of the Shares, but in no event less than zero.

ARTICLE 2: ADJUSTMENTS TO THE SHARES.

        2.1 Stock Dividends, Splits, Etc. If the Company declares or pays a
dividend on its common stock (or the Shares if the Shares are securities other
than common stock) payable in common stock, or other securities, subdivides the
outstanding common stock into a greater amount of common stock, or, if the
Shares are securities other than common stock, subdivides the Shares in a
transaction that increases the amount of common stock into which the Shares are
convertible, then upon exercise of this Warrant, for each Share acquired, Holder
shall receive, without cost to Holder, the total number and kind of securities
to which Holder would have been entitled had Holder owned the Shares of record
as of the date the dividend or subdivision occurred.

        2.2 Reclassification, Exchange or Substitution. Upon any
reclassification, exchange, substitution, or other event that results in a
change of the number and/or class of the securities issuable upon exercise or
conversion of this Warrant, Holder shall be entitled to receive, upon exercise
or conversion of this Warrant, the number and kind of securities and property
that Holder would have received for the Shares if this Warrant had been
exercised immediately before such reclassification, exchange, substitution, or
other event. Such an event shall include any automatic conversion of the
outstanding or issuable securities of the Company of the same class or series as
the Shares to common stock pursuant to the terms of the Company's Articles of
Incorporation upon the closing of a registered public offering of the Company's
common stock. The Company or its successor shall promptly issue to Holder a new
Warrant for such new securities or other property. The new Warrant shall provide
for adjustments which shall be as nearly equivalent as may be practicable to the
adjustments provided for in this Article 2 including,

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without limitation, adjustments to the Warrant Price and to the number of
securities or property issuable upon exercise of the new Warrant. The provisions
of this Section 2.2 shall similarly apply to successive reclassifications.
exchanges, substitutions, or other events.

        2.3 Adjustments for Combinations, Etc. If the outstanding Shares are
combined or consolidated, by reclassification or otherwise, into a lesser number
of shares, the Warrant Price shall be proportionately increased.

        2.4 Adjustments for Diluting Issuances. The Warrant Price and the number
of Shares issuable upon exercise of this Warrant or, if the Shares are Preferred
Stock, the number of shares of common stock issuable upon conversion of the
Shares, shall be subject to adjustment, from time to time in the manner set
forth in the Company's Articles of Incorporation, as amended from time to time.

        2.5 No Impairment. The Company shall not, by amendment of its Articles
of Incorporation or through a reorganization, transfer of assets, consolidation,
merger, dissolution, issue, or sale of securities or any other voluntary action,
avoid or seek to avoid the observance or performance of any of the terms to be
observed or performed under this Warrant by the Company, but shall at all times
in good faith assist in carrying out of all the provisions of this Article 2 and
in taking all such action as may be necessary or appropriate to protect Holder's
rights under this Article against impairment. If the Company takes any action
affecting the Shares or its common stock other than as described above that
adversely affects Holder's rights under this Warrant, the Warrant Price shall be
adjusted downward and the number of Shares issuable upon exercise of this
Warrant shall be adjusted upward in such a manner that the aggregate Warrant
Price of this Warrant is unchanged. Notwithstanding the foregoing, nothing in
this Section 2.5 shall require any adjustment to the Warrant Price or the number
of shares issuable upon exercise of this Warrant beyond that which would be
afforded pursuant to the Articles of Incorporation which, provide for anti
dilution protection for preferred shares.

        2.6 Fractional Shares. No fractional Shares shall be issuable upon
exercise or conversion of the Warrant and the number of Shares to be issued
shall be rounded down to the nearest whole Share. If a fractional share interest
arises upon any exercise or conversion of the Warrant, the Company shall
eliminate such fractional share interest by paying Holder amount computed by
multiplying the fractional interest by the fair market value of a full Share.

        2.7 Certificate as to Adjustments. Upon each adjustment of the Warrant
Price, the Company at its expense shall promptly compute such adjustment, and
furnish Holder with a certificate of its Chief Financial Officer setting forth
such adjustment and the facts upon which such adjustment is based. The Company
shall, upon written request, furnish Holder a certificate setting forth the
Warrant Price in effect upon the date thereof and the series of adjustments
leading to such Warrant Price.

ARTICLE 3: REPRESENTATIONS AND COVENANTS OF THE COMPANY.

        3.1 Representations and Warranties. The Company hereby represents and
warrants to the Holder as follows:

               (a) The initial Warrant Price referenced on the first page of
this Warrant is not greater than the fair market value of the Shares as of the
date of this Warrant.

               (b) All Shares which may be issued upon the exercise of the
purchase right represented by this Warrant, and all securities, if any, issuable
upon conversion of the Shares, shall, upon issuance, be duly authorized, validly
issued, fully paid and nonassessable, and free of any liens and encumbrances
except for restrictions on transfer provided for herein or under applicable
federal and state securities laws.

        3.2 Notice of Certain Events. If the Company proposes at any time (a) to
declare any dividend or distribution upon its common stock, whether in cash,
property, stock, or other securities and whether or not a regular cash dividend;
(b) to offer for subscription pro rata to the holders of any class or series of
its stock any additional shares of stock of any class or series or other rights;
(c) to merge or consolidate with or into any other corporation, or sell, lease,
license, or convey all or substantially all of its assets, or to liquidate,
dissolve or wind up; or (d) offer

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holders of registration rights the opportunity to participate in an underwritten
public offering of the company's. securities for cash, then, in connection with
each such event, the Company shall give Holder (1) at least 10 days prior
written notice of the date on which a record will be taken for such dividend,
distribution, or subscription rights (and specifying the date on which the
holders of common stock will be entitled thereto) or for determining rights to
vote, if any, in respect of the matters referred to in (c) above; (2) in the
case of the matters referred to in (c) above at least 10 days prior written
notice of the date when the same will take place (and specifying the date on
which the holders of common stock will be entitled to exchange their common
stock for securities or other property deliverable upon the occurrence of such
event); and (3) in the case of the matter referred to in (d) above, the same
notice as is given to the holders of such registration rights.

        3.3 Information Rights. So long as the Holder holds this Warrant and/or
any of the Shares, the Company shall deliver to the Holder (a) promptly after
mailing, copies of all notices or other written communications to the
shareholders of the Company.

        3.4 Registration Under Securities Act of 1933, as amended. The Company
agrees that the Shares or, if the Shares are convertible into common stock of
the Company, such common stock, shall be subject to the registration rights of
"Registrable Securities" set forth in the First Amended and Restated Shareholder
Rights Agreement dated February 19, 1999, as may be amended from time to time.

ARTICLE 4: MISCELLANEOUS.

        4.1 Term. This Warrant is exercisable, in whole or in part, at any time
and from time to time on or before the Expiration Date set forth above.

        4.2 Legends. This Warrant and the Shares (and the securities issuable,
directly or indirectly, upon conversion of the Shares, if any) shall be
imprinted with a legend in substantially the following form:

                THIS SECURITY HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT
                OF 1933, AS AMENDED, AND MAY NOT BE SOLD, PLEDGED OR OTHERWISE
                TRANSFERRED WITHOUT AN EFFECTIVE REGISTRATION THEREOF UNDER SUCH
                ACT OR PURSUANT TO RULE 144 OR AN OPINION OF COUNSEL REASONABLY
                SATISFACTORY TO THE CORPORATION AND ITS COUNSEL THAT SUCH
                REGISTRATION IS NOT REQUIRED.

        4.3 Compliance with Securities Laws on Transfer. This Warrant and the
Shares issuable upon exercise this Warrant (and the securities issuable,
directly or indirectly, upon conversion of the Shares, if any) may not be
transferred or assigned in whole or in part without compliance with applicable
federal and state securities laws by the transferor and the transferee
(including, without limitation, the delivery of investment representation
letters and legal opinions reasonably satisfactory to the Company, as reasonably
requested by the Company). The Company shall not require Holder to provide an
opinion of counsel if the transfer is to an affiliate of Holder or if there is
no material question as to the availability of current information as referenced
in Rule 144(c), Holder represents that it has complied with Rule 144(d) and (e)
in reasonable detail, the selling broker represents that it has complied with
Rule 144(f), and the Company is provided with a copy of Holder's notice of
proposed sale.

        4.4 Transfer Procedure. Subject to the provisions of Section 4.2, Holder
may transfer all or part of this Warrant or the Shares issuable upon exercise of
this Warrant (or the securities issuable, directly or indirectly, upon
conversion of the Shares, if any) by giving the Company notice of the portion of
the Warrant being transferred setting forth the name, address and taxpayer
identification number of the transferee and surrendering this Warrant to the
Company for reissuance to the transferee(s) (and Holder if applicable). Unless
the Company is filing financial information with the SEC pursuant to the
Securities Exchange Act of 1934, the Company shall have the right to refuse to
transfer any portion of this Warrant to any person who directly competes with
the Company.

        4.5 Notices. All notices and other communications from the Company to
the Holder, or vice versa, shall be deemed delivered and effective when given
personally or mailed by first class registered or certified mail,

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postage prepaid, at such address as may have been furnished to the Company or
the Holder, as the case may be, in writing by the Company or such holder from
time to time. Notice to Holder pursuant to this Section 4.5 shall be deemed to
be effective notice to any assignee or transferee of Holder pursuant to any
assignment or transfer of this Warrant for which the Company's prior written
consent was not obtained.

        4.6 Waiver. This Warrant and any term hereof may be changed, waived,
discharged or terminated only by an instrument in writing signed by the party
against which enforcement of such change, waiver, discharge or termination is
sought.

        4.7 Attorneys Fees. In the event of any dispute between the parties
concerning the terms and provisions of this Warrant, the party prevailing in
such dispute shall be entitled to collect from the other party all costs
incurred in such dispute, including reasonable attorneys' fees.

        4.8 Governing Law. This Warrant shall be governed by and construed in
accordance with the laws of the State of California, without giving effect to
its principles regarding conflicts of law.

                                        "COMPANY"

                                     By: /s/ WALTER ALESSANDRINI
                                        -------------------------------

                                     Name: WALTER ALESSANDRINI
                                          -----------------------------

                                     Title: CEO
                                           ----------------------------

                                     By: /s/ JESSY CHAO
                                        -------------------------------

                                     Name: JESSY CHAO
                                          -----------------------------

                                     Title: DIRECTOR OF FINANCE
                                           ----------------------------
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                                   APPENDIX I

                               NOTICE OF EXERCISE

        1. The undersigned hereby irrevocably elects to purchase _____ shares of
the Series D Preferred Stock of Avanex Corporation pursuant to the terms of the
attached Warrant, and tenders herewith payment of the purchase price of such
shares in full.

        1. The undersigned hereby elects to convert the attached Warrant into
Shares/cash [strike one] in the manner specified in the Warrant. This conversion
is exercised with respect to _________________ of the Shares covered by the
Warrant.

        [Strike paragraph that does not apply.]

        2. Please issue a certificate or certificates representing said shares
in the name of the undersigned or in such other name as is specified below:

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

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

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

        3. The undersigned represents it is acquiring the shares solely for its
own account and not as a nominee for any other party and not with a view toward
the resale or distribution thereof except in compliance with applicable
securities laws.

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

                                              ----------------------------------
                                              (Date)

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