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                                                                    Exhibit 10.1

                            SYCAMORE NETWORKS, INC.

                           1998 STOCK INCENTIVE PLAN
                           -------------------------

1.   Purpose
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     The purpose of this 1998 Stock Incentive Plan (the "Plan") of Sycamore
Networks, Inc., a Delaware corporation (the "Company"), is to advance the
interests of the Company's stockholders by enhancing the Company's ability to
attract, retain and motivate persons who make (or are expected to make)
important contributions to the Company by providing such persons with equity
ownership opportunities and performance-based incentives and thereby better
aligning the interests of such persons with those of the Company's stockholders.
Except where the context otherwise requires, the term "Company" shall include
any of the Company's present or future subsidiary corporations of as defined in
Section 424(f) of the Internal Revenue Code of 1986, as amended, and any
regulations promulgated thereunder (the "Code").

2.   Eligibility
     -----------

     All of the Company's employees, officers, directors, consultants and
advisors (and any individuals who have accepted an offer for employment) are
eligible to be granted options, restricted stock awards, or other stock-based
awards (each, an "Award") under the Plan.  Each person who has been granted an
Award under the Plan shall be deemed a "Participant".

3.   Administration, Delegation
     --------------------------

     (a)  Administration by Board of Directors. The Plan will be administered by
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the Board of Directors of the Company (the "Board"). The Board shall have
authority to grant Awards and to adopt, amend and repeal such administrative
rules, guidelines and practices relating to the Plan as it shall deem advisable.
The Board may correct any defect, supply any omission or reconcile any
inconsistency in the Plan or any Award in the manner and to the extent it shall
deem expedient to carry the Plan into effect and it shall be the sole and final
judge of such expediency. All decisions by the Board shall be made in the
Board's sole discretion and shall be final and binding on all persons having or
claiming any interest in the Plan or in any Award. No director or person acting
pursuant to the authority delegated by the Board shall be liable for any action
or determination relating to or under the Plan made in good faith.

     (b)  Delegation to Executive Officers.  To the extent permitted by
          --------------------------------
applicable law, the Board may delegate to one or more executive officers of the
Company the power to make Awards and exercise such other powers under the Plan
as the Board may determine, provided that the Board shall fix the maximum number
of shares
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subject to Awards and the maximum number of shares for any one Participant to be
made by such executive officers.

     (c)  Appointment of Committees.  To the extent permitted by applicable law,
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the Board may delegate any or all of its powers under the Plan to one or more
committees or subcommittees of the Board (a "Committee").  All references in the
Plan to the "Board" shall mean the Board or a Committee of the Board or the
executive officer referred to in Section 3(b) to the extent that the Board's
powers or authority under the Plan have been delegated to such Committee or
executive officer.

4.   Stock Available for Awards
     --------------------------

     (a)  Number of Shares. Subject to adjustment under Section 8, Awards may be
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made under the Plan for up to 509,396 shares of common stock, $.001 par value
per share, of the Company (the "Common Stock"). If any Award expires or is
terminated, surrendered or canceled without having been fully exercised or is
forfeited in whole or in part or results in any Common Stock not being issued,
the unused Common Stock covered by such Award shall again be available for the
grant of Awards under the Plan, subject, however, in the case of Incentive Stock
Options (as hereinafter defined), to any limitation required under the Code.
Shares issued under the Plan may consist in whole or in part of authorized but
unissued shares or treasury shares.

     (b)  Per-Participant Limit.  Subject to adjustment under Section 8, for
          ---------------------
Awards granted after the Common Stock is registered under the Securities
Exchange Act of 1934 (the "Exchange Act"), the maximum number of shares of
Common Stock with respect to which an Award may be granted to any Participant
under the Plan shall be 500,000 per calendar year.   The per-Participant limit
described in this Section 4(b) shall be construed and applied consistently with
Section 162(m) of the Code.

5.   Stock Options
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     (a)  General.  The Board may grant options to purchase Common Stock (each,
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an "Option") and determine the number of shares of Common Stock to be covered by
each Option, the exercise price of each Option and the conditions and
limitations applicable to the exercise of each Option, including conditions
relating to applicable federal or state securities laws, as it considers
necessary or advisable.  An Option which is not intended to be an Incentive
Stock Option (as hereinafter defined) shall be designated a "Nonstatutory Stock
Option".

     (b)  Incentive Stock Options.  An Option that the Board intends to be an
          -----------------------
"incentive stock option" as defined in Section 422 of the Code (an "Incentive
Stock Option") shall only be granted to employees of the Company and shall be
subject to and shall be construed consistently with the requirements of Section
422 of the Code.

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The Company shall have no liability to a Participant, or any other party, if an
Option (or any part thereof) which is intended to be an Incentive Stock Option
is not an Incentive Stock Option.

     (c)  Exercise Price.  The Board shall establish the exercise price at the
          --------------
time each Option is granted and specify it in the applicable option agreement.

     (d)  Duration of Options.  Each Option shall be exercisable at such times
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and subject to such terms and conditions as the Board may specify in the
applicable option agreement.

     (e)  Exercise of Option.  Options may be exercised by delivery to the
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Company of a written notice of exercise signed by the proper person or by any
other form of notice (including electronic notice) approved by the Board
together with payment in full as specified in Section 5(f) for the number of
shares for which the Option is exercised.

     (f)  Payment Upon Exercise.  Common Stock purchased upon the exercise of an
          ----------------------
Option granted under the Plan shall be paid for as follows:

          (1)  in cash or by check, payable to the order of the Company;

          (2)  except as the Board may, in its sole discretion, otherwise
provide in an option agreement, by (i) delivery of an irrevocable and
unconditional undertaking by a creditworthy broker to deliver promptly to the
Company sufficient funds to pay the exercise price or (ii) delivery by the
Participant to the Company of a copy of irrevocable and unconditional
instructions to a creditworthy broker to deliver promptly to the Company cash or
a check sufficient to pay the exercise price;

          (3)  when the Common Stock is registered under the Exchange Act, by
delivery of shares of Common Stock owned by the Participant valued at their fair
market value as determined by (or in a manner approved by) the Board in good
faith ("Fair Market Value"), which Common Stock was owned by the Participant at
least six months prior to such delivery;

          (4)  to the extent permitted by the Board, in its sole discretion by
(i) delivery of a promissory note of the Participant to the Company on terms
determined by the Board, or (ii) payment of such other lawful consideration as
the Board may determine; or

          (5)  by any combination of the above permitted forms of payment.

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6.   Restricted Stock
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     (a)  Grants.  The Board may grant Awards entitling recipients to acquire
          ------
shares of Common Stock, subject to the right of the Company to repurchase all or
part of such shares at their issue price or other stated or formula price (or to
require forfeiture of such shares if issued at no cost) from the recipient in
the event that conditions specified by the Board in the applicable Award are not
satisfied prior to the end of the applicable restriction period or periods
established by the Board for such Award (each, a "Restricted Stock Award").

     (b)  Terms and Conditions.  The Board shall determine the terms and
          --------------------
conditions of any such Restricted Stock Award, including the conditions for
repurchase (or forfeiture) and the issue price, if any.  Any stock certificates
issued in respect of a Restricted Stock Award shall be registered in the name of
the Participant and, unless otherwise determined by the Board, deposited by the
Participant, together with a stock power endorsed in blank, with the Company (or
its designee).  At the expiration of the applicable restriction periods, the
Company (or such designee) shall deliver the certificates no longer subject to
such restrictions to the Participant or if the Participant has died, to the
beneficiary designated, in a manner determined by the Board, by a Participant to
receive amounts due or exercise rights of the Participant in the event of the
Participant's death (the "Designated Beneficiary").  In the absence of an
effective designation by a Participant, Designated Beneficiary shall mean the
Participant's estate.

7.   Other Stock-Based Awards
     ------------------------

     The Board shall have the right to grant other Awards based upon the Common
Stock having such terms and conditions as the Board may determine, including the
grant of shares based upon certain conditions, the grant of securities
convertible into Common Stock and the grant of stock appreciation rights.

8.   Adjustments for Changes in Common Stock and Certain Other Events
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     (a)  Changes in Capitalization.  In the event of any stock split, reverse
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stock split, stock dividend, recapitalization, combination of shares,
reclassification of shares, spin-off or other similar change in capitalization
or event, or any distribution to holders of Common Stock other than a normal
cash dividend, (i) the number and class of securities available under this Plan,
(ii) the per-Participant limit set forth in Section 4(b), (iii) the number and
class of securities and exercise price per share subject to each outstanding
Option, (iv) the repurchase price per share subject to each outstanding
Restricted Stock Award, and (v) the terms of each other outstanding Award shall
be appropriately adjusted by the Company (or substituted Awards may be made, if
applicable) to the extent the Board shall determine, in good faith, that such an
adjustment (or substitution) is necessary and appropriate.  If this Section 8(a)

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applies and Section 8(c) also applies to any event, Section 8(c) shall be
applicable to such event, and this Section 8(a) shall not be applicable.

     (b)  Liquidation or Dissolution.  In the event of a proposed liquidation or
          --------------------------
dissolution of the Company, the Board shall upon written notice to the
Participants provide that all then unexercised Options will (i) become
exercisable in full as of a specified time at least 10 business days prior to
the effective date of such liquidation or dissolution and (ii) terminate
effective upon such liquidation or dissolution, except to the extent exercised
before such effective date.  The Board may specify the effect of a liquidation
or dissolution on any Restricted Stock Award or other Award granted under the
Plan at the time of the grant of such Award.

     (c)  Acquisition Events
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          (1)  Definition.  An "Acquisition Event" shall mean: (a) any merger or
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consolidation of the Company with or into another entity as a result of which
the Common Stock is converted into or exchanged for the right to receive cash,
securities or other property or (b) any exchange of shares of the Company for
cash, securities or other property pursuant to a statutory share exchange
transaction.

          (2)  Consequences of an Acquisition Event on Options.   Upon the
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occurrence of an Acquisition Event, or the execution by the Company of any
agreement with respect to an Acquisition Event, the Board shall provide that all
outstanding Options shall be assumed, or equivalent options shall be
substituted, by the acquiring or succeeding corporation (or an affiliate
thereof).  For purposes hereof, an Option shall be considered to be assumed if,
following consummation of the Acquisition Event, the Option confers the right to
purchase, for each share of Common Stock subject to the Option immediately prior
to the consummation of the Acquisition Event, the consideration (whether cash,
securities or other property) received as a result of the Acquisition Event by
holders of Common Stock for each share of Common Stock held immediately prior to
the consummation of the Acquisition Event (and if holders were offered a choice
of consideration, the type of consideration chosen by the holders of a majority
of the outstanding shares of Common Stock); provided, however, that if the
consideration received as a result of the Acquisition Event is not solely common
stock of the acquiring or succeeding corporation (or an affiliate thereof), the
Company may, with the consent of the acquiring or succeeding corporation,
provide for the consideration to be received upon the exercise of Options to
consist solely of common stock of the acquiring or succeeding corporation (or an
affiliate thereof) equivalent in fair market value to the per share
consideration received by holders of outstanding shares of Common Stock as a
result of the Acquisition Event.

          Notwithstanding the foregoing, if the acquiring or succeeding
corporation (or an affiliate thereof) does not agree to assume, or substitute
for, such

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Options, then the Board shall, upon written notice to the Participants, provide
that all then unexercised Options will become exercisable in full as of a
specified time prior to the Acquisition Event and will terminate immediately
prior to the consummation of such Acquisition Event, except to the extent
exercised by the Participants before the consummation of such Acquisition Event;
provided, however, that in the event of an Acquisition Event under the terms of
which holders of Common Stock will receive upon consummation thereof a cash
payment for each share of Common Stock surrendered pursuant to such Acquisition
Event (the "Acquisition Price"), then the Board may instead provide that all
outstanding Options shall terminate upon consummation of such Acquisition Event
and that each Participant shall receive, in exchange therefor, a cash payment
equal to the amount (if any) by which (A) the Acquisition Price multiplied by
the number of shares of Common Stock subject to such outstanding Options
(whether or not then exercisable), exceeds (B) the aggregate exercise price of
such Options.

          (3)  Consequences of an Acquisition Event on Restricted Stock Awards.
               ---------------------------------------------------------------
Upon the occurrence of an Acquisition Event, the repurchase and other rights of
the Company under each outstanding Restricted Stock Award shall inure to the
benefit of the Company's successor and shall apply to the cash, securities or
other property which the Common Stock was converted into or exchanged for
pursuant to such Acquisition Event in the same manner and to the same extent as
they applied to the Common Stock subject to such Restricted Stock Award.

          (4)  Consequences of an Acquisition Event on Other Awards.  The Board
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shall specify the effect of an Acquisition Event on any other Award granted
under the Plan at the time of the grant of such Award.

9.   General Provisions Applicable to Awards
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     (a)  Transferability of Awards. Except as the Board may otherwise determine
          -------------------------
or provide in an Award, Awards shall not be sold, assigned, transferred, pledged
or otherwise encumbered by the person to whom they are granted, either
voluntarily or by operation of law, except by will or the laws of descent and
distribution, and, during the life of the Participant, shall be exercisable only
by the Participant. References to a Participant, to the extent relevant in the
context, shall include references to authorized transferees.

     (b)  Documentation.  Each Award shall be evidenced by a written instrument
          -------------
in such form as the Board shall determine.  Each Award may contain terms and
conditions in addition to those set forth in the Plan.

     (c)  Board Discretion. Except as otherwise provided by the Plan, each Award
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may be made alone or in addition or in relation to any other Award. The

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terms of each Award need not be identical, and the Board need not treat
Participants uniformly.

     (d)  Termination of Status.  The Board shall determine the effect on an
          ---------------------
Award of the disability, death, retirement, authorized leave of absence or other
change in the employment or other status of a Participant and the extent to
which, and the period during which, the Participant, the Participant's legal
representative, conservator, guardian or Designated Beneficiary may exercise
rights under the Award.

     (e)  Withholding.  Each Participant shall pay to the Company, or make
          -----------
provision satisfactory to the Board for payment of, any taxes required by law to
be withheld in connection with Awards to such Participant no later than the date
of the event creating the tax liability.  Except as the Board may otherwise
provide in an Award, when the Common Stock is registered under the Exchange Act,
Participants may satisfy such tax obligations in whole or in part by delivery of
shares of Common Stock, including shares retained from the Award creating the
tax obligation, valued at their Fair Market Value.  The Company may, to the
extent permitted by law, deduct any such tax obligations from any payment of any
kind otherwise due to a Participant.

     (f)  Amendment of Award.  The Board may amend, modify or terminate any
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outstanding Award, including but not limited to, substituting therefor another
Award of the same or a different type, changing the date of exercise or
realization, and converting an Incentive Stock Option to a Nonstatutory Stock
Option, provided that the Participant's consent to such action shall be required
unless the Board determines that the action, taking into account any related
action, would not materially and adversely affect the Participant.

     (g)  Conditions on Delivery of Stock.  The Company will not be obligated to
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deliver any shares of Common Stock pursuant to the Plan or to remove
restrictions from shares previously delivered under the Plan until (i) all
conditions of the Award have been met or removed to the satisfaction of the
Company, (ii) in the opinion of the Company's counsel, all other legal matters
in connection with the issuance and delivery of such shares have been satisfied,
including any applicable securities laws and any applicable stock exchange or
stock market rules and regulations, and (iii) the Participant has executed and
delivered to the Company such representations or agreements as the Company may
consider appropriate to satisfy the requirements of any applicable laws, rules
or regulations.

     (h)  Acceleration. The Board may at any time provide that any Options shall
          ------------
become immediately exercisable in full or in part, that any Restricted Stock
Awards shall be free of restrictions in full or in part or that any other Awards
may

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become exercisable in full or in part or free of some or all restrictions or
conditions, or otherwise realizable in full or in part, as the case may be.

10.  Miscellaneous
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     (a)  No Right To Employment or Other Status. No person shall have any claim
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or right to be granted an Award, and the grant of an Award shall not be
construed as giving a Participant the right to continued employment or any other
relationship with the Company. The Company expressly reserves the right at any
time to dismiss or otherwise terminate its relationship with a Participant free
from any liability or claim under the Plan, except as expressly provided in the
applicable Award.

     (b) No Rights As Stockholder.  Subject to the provisions of the applicable
         ------------------------
Award, no Participant or Designated Beneficiary shall have any rights as a
stockholder with respect to any shares of Common Stock to be distributed with
respect to an Award until becoming the record holder of such shares.
Notwithstanding the foregoing, in the event the Company effects a split of the
Common Stock by means of a stock dividend and the exercise price of and the
number of shares subject to such Option are adjusted as of the date of the
distribution of the dividend (rather than as of the record date for such
dividend), then an optionee who exercises an Option between the record date and
the distribution date for such stock dividend shall be entitled to receive, on
the distribution date, the stock dividend with respect to the shares of Common
Stock acquired upon such Option exercise, notwithstanding the fact that such
shares were not outstanding as of the close of business on the record date for
such stock dividend.

     (c)  Effective Date and Term of Plan.  The Plan shall become effective on
          -------------------------------
the date on which it is adopted by the Board.  No Awards shall be granted under
the Plan after the completion of ten years from the earlier of (i) the date on
which the Plan was adopted by the Board or (ii) the date the Plan was approved
by the Company's stockholders, but Awards previously granted may extend beyond
that date.

     (d)  Amendment of Plan.  The Board may amend, suspend or terminate the Plan
          -----------------
or any portion thereof at any time.

     (e)  Governing Law.  The provisions of the Plan and all Awards made
          -------------
hereunder shall be governed by and interpreted in accordance with the laws of
the State of Delaware, without regard to any applicable conflicts of law.

                            Adopted by the Board of Directors on August 19, 1998
                                Approved by the Stockholders on October 19, 1998

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                            SYCAMORE NETWORKS, INC.

                                Amendment No. 1
                                      to
                           1998 Stock Incentive Plan



     Subsection 4(a) of the 1998 Stock Incentive Plan (the "Plan) of Sycamore
Networks, Inc. (the "Company), is hereby amended, subject to stockholder
approval, to increase from 509,396 to 2,009,396 the number of shares of the
Company's Common Stock, $0.001 par value per share, authorized for issuance
under the Plan.


                                   Adopted by the Board of Directors
                                   on October 19, 1998


                                   Approved by the Stockholders
                                   on October 19, 1998
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                            SYCAMORE NETWORKS, INC.

                                Amendment No. 2
                                      to
                           1998 Stock Incentive Plan



     Subsection 4(a) of the 1998 Stock Incentive Plan (the "Plan) of Sycamore
Networks, Inc. (the "Company), is hereby amended, subject to stockholder
approval, to increase from 2,009,396 to 2,855,000 the number of shares of the
Company's Common Stock, $0.001 par value per share, authorized for issuance
under the Plan.


                              Adopted by the Board of Directors
                              on February 25, 1999


                              Approved by the Stockholders
                              on May __, 1999