EXHIBIT 4.6 AMENDMENT NO. 4 TO SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT This Agreement, dated as of February 11, 2000, is entered into by and among Sycamore Networks, Inc., a Delaware corporation ( the "Company"), the Investors (as defined below) and the Founders (as defined below). WHEREAS, the Company has entered into a Second Amended and Restated Investor Rights Agreement (the "Agreement") dated as of February 26, 1999, with the persons and entities listed on Schedule I thereto under the heading "Investors" (individually, an "Investor" and collectively, the "Investors") and the persons listed on Schedule II thereto under the heading "Founders" (individually, a "Founder" and collectively, the "Founders"), which Agreement was amended by Amendment No. 1 thereto dated as of July 23, 1999 by and among the Company, Siemens Information and Communication Networks, Inc., a Delaware corporation, the Investors and the Founders, and further amended by Amendment No. 2 thereto and Amendment No. 3 thereto dated as of August 5, 1999, and September 20, 1999, respectively, by and among the Company, the Investors and the Founders (the Agreement, as so amended being referred to herein as the "Second Restated Agreement"); and WHEREAS, the Second Restated Agreement provides, among other things, that it may be amended at any time by a written instrument signed by the Company and Investors holding at least a majority of the shares of the common stock $.001 par value, of the Company issued or issuable upon conversion of the Shares (as defined in the Second Restated Agreement); and WHEREAS, the Investors parties hereto hold shares of Common Stock representing at least a majority of the shares of Common Stock issued upon conversion of the Shares; and WHEREAS, the parties hereto wish to amend the Second Restated Agreement as set forth herein; NOW, THEREFORE, in consideration of the mutual promises and covenants contained herein, and for other good and valuable consideration, the receipt of which is hereby acknowledged, the parties hereto agree as follows: 1. Paragraph (a) of Section 2 of Article III of the Second Restated Agreement shall be deleted in its entirety and the following substituted in its place: a. Whenever the Company proposes to file a Registration Statement at any time and from time to time, it will, prior to such filing, give written notice to all Stockholders of its intention to do so and, upon the written request of a Stockholder or Stockholders, given within 10 business days after the Company provides such notice (which request shall state the intended method of disposition of such Registrable Shares), the Company shall use its reasonable best efforts to cause all Registrable Shares which the Company has been requested by such Stockholder or Stockholders to register, to be registered under the Securities Act to the extent necessary to permit their sale or other disposition in accordance with the intended methods of distribution specified in the request of such Stockholder or Stockholders; provided, -------- however, that the provisions of this Section 2 shall ------- not apply to any Registration Statement filed by the Company prior to January 1, 2001; provided, further, -------- ------- however, that the Company shall have the right to ------- postpone or withdraw any registration effected pursuant to this Section 2 without obligation to any Stockholder. 2. The Second Restated Agreement, as supplemented and modified by this Amendment together with the other writings referred to in the Second Restated Agreement or delivered pursuant thereto which form a part thereof, contains the entire agreement among the parties with respect to the subject matter thereof and amends, restates and supersedes all prior and contemporaneous arrangements or understandings with respect thereto. 3. Upon the effectiveness of this Agreement, on and after the date hereof, each reference in the Second Restated Agreement to "this Agreement," "hereunder," "hereof," "herein" or words of like import, and each reference in the other documents entered into in connection with the Second Restated Agreement, shall mean and be a reference to the Second Restated Agreement, as amended hereby. Except as specifically amended above, the Second Restated Agreement shall remain in full force and effect and is hereby ratified and confirmed. 2 4. This Amendment shall be governed by the laws of the State of Delaware, notwithstanding the conflict-of-law doctrines of Delaware or any other jurisdiction to the contrary. 5. This Amendment may be executed in any number of counterparts, and each such counterpart shall be deemed to be an original instrument, but all such counterparts together shall constitute but one agreement. 6. This Amendment shall be binding on all parties to the Second Restated Agreement as and when executed by the Company and Investors holding at least a majority of the shares of Common Stock issued upon conversion of the Shares. IN WITNESS WHEREOF the parties hereto have executed this Amendment on the date first above written. COMPANY: SYCAMORE NETWORKS, INC. By: /s/ Daniel Smith ----------------------------------- Daniel Smith President INVESTORS SIEMENS INFORMATION AND COMMUNICATION NETWORKS, INC. By:___________________________________ Address: 900 Broken Sound Parkway Boca Raton, FL 33487 For Notices: P.O. Box 58075 Santa Clara, CA 95052-8075 Attn: Bjoern Christensen Fax: (408) 492-4821 3 With Copies to: Siemens Corporation 1301 Avenue of Americas New York, NY 10019 Attn: General Counsel Fax: (212) 258-4490 MATRIX PARTNERS V, L.P. Bay Colony Corporate Center 1000 Winter Street, Suite 4500 Waltham, MA 02154 By: Matrix V Management Co., L.L.C., its General Partner By: /s/ Timothy Barrows ------------------------------------------ MATRIX V ENTREPRENEURS FUND, L.P. Bay Colony Corporate Center 1000 Winter Street, Suite 4500 Waltham, MA 02154 By: Matrix V Management Co., L.L.C., its General Partner By: /s/ Timothy Barrows ------------------------------------------ NORTH BRIDGE VENTURE PARTNERS II, L.P. 404 Wyman Street, Suite 365 Waltham, MA 02154 By: North Bridge Ventures Partners II, L.P. its General Partner By:_________________________________________ 4 INTEGRAL CAPITAL PARTNERS IV, L.P. 2750 Sand Hill Road Menlo Park, CA 94025-7020 By: Integral Capital Management IV, LLC its General Partner By:__________________________________________ Pamela K. Hagenah a Manager INTEGRAL CAPITAL PARTNERS IV MS SIDE FUND, L.P. 2750 Sand Hill Road Menlo Park, CA 94025-7020 By: ICP MS Management, LLC its General Partner By:__________________________________________ Pamela K. Hagenah a Manager PEQUOT PRIVATE EQUITY FUND, L.P. 500 Nyala Farm Road Westport, CT 06880 By:_________________________________________ PEQUOT OFFSHORE PRIVATE EQUITY FUND, INC. 500 Nyala Farm Road Westport, CT 06880 By:_________________________________________ PEQUOT VENTURE PARTNERS, L.P. 500 Nyala Farm Road Westport, CT 06880 By:_________________________________________ 5 SPINNAKER FOUNDERS FUND, L.P. 1875 South Grant Street San Mateo, CA 94402 By: Bowman Capital Management, L.L.C. its General Partner By:_________________________________________ William J. Haggerty, Managing Director of Operations of Bowman Capital Management, L.L.C. SPINNAKER OFFSHORE FOUNDERS FUND, CAYMAN LIMITED 1875 South Grant Street San Mateo, CA 94402 By: Bowman Capital Management, L.L.C., its Investment Adviser and Attorney-in-Fact By:_________________________________________ William J. Haggerty, Managing Director of Operations of Bowman Capital Management, L.L.C. SPINNAKER CLIPPER FUND, L.P. 1875 South Grant Street San Mateo, CA 94402 By: Bowman Capital Management, L.L.C., its General Partner By:_______________________________________ William J. Haggerty, Managing Director of Operations of Bowman Capital Management, L.L.C. 6 ATGF II, a Panamanian corporation SUCRE Building Calle 48 Este Bella Vista, P.O. Box 5168 Panama S, Panama By:_________________________________________ Director The Ralph H. Cechettini 1995 Trust By:_________________________________________ ____________________________________________ James Stableford ____________________________________________ Anthony Ciulla ____________________________________________ William Slattery ____________________________________________ Marc Weiss ____________________________________________ Chikong Shue ____________________________________________ Siu Wing Li 7 ____________________________________________ Michael Viren ____________________________________________ Steven Finn ____________________________________________ Eric MacDonald ____________________________________________ John Dowling ____________________________________________ Leaf Uptegrove ____________________________________________ Scott Baker ____________________________________________ Jeanette Slaff 8 /s/ Gururaj Deshpande -------------------------------------------- Gururaj Deshpande /s/ Daniel Smith -------------------------------------------- Daniel Smith FOUNDERS: /s/ Gururaj Deshpande -------------------------------------------- Gururaj Deshpande Address: 9 Sparta Way Andover, MA 01810 ____________________________________________ Richard Barry Address: 1284 Beacon Street, #815 Brookline, MA 02138 9 Schedule I ---------- Investors --------- Matrix Partners V, L.P. Matrix V Entrepreneurs Fund, L.P. North Bridge Venture Partners II, L.P. Integral Capital Partners IV, L.P. Integral Capital Partners IV MS Side Fund, L.P. Pequot Private Equity Fund, L.P. Pequot Venture Partners, L.P. Pequot Offshore Private Equity Fund, Inc. ATGF II, a Panamanian corporation The Ralph H. Cechettini 1995 Trust James Stableford Anthony Ciulla William Slattery Marc Weiss Spinnaker Founders Fund, L.P. Spinnaker Offshore Founders Fund, Cayman Limited Spinnaker Clipper Fund, L.P. Gururaj Deshpande Daniel Smith Chikong Shue Siu Wing Li Michael Viren Steven Finn Eric MacDonald John Dowling Leaf Uptegrove Scott Baker Jeannette Slaff Siemens Information and Communication Networks, Inc.