Exhibit 4.1

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016570|
003590|127C|RESTRICTED||4|057-423

COMMON STOCK

PAR VALUE $0.001

COMMON STOCK

THIS CERTIFICATE IS TRANSFERABLE IN

CANTON, MA AND NEW YORK, NY

Certificate Number

ZQ 000610

SYCAMORE NETWORKS, INC.

INCORPORATED UNDER THE LAWS OF THE STATE OF DELAWARE

THIS CERTIFIES THAT

** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample ****
Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David
Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample MR. SAMPLE **** Mr. Alexander David Sample ****
Mr. Alexander David &Sample MRS. **** Mr. Alexander David SAMPLE Sample **** Mr. Alexander David Sample **** Mr. & Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample ****
Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David
Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander

David Sample **** Mr. Alexander MR. David Sample SAMPLE **** Mr. Alexander David Sample & **** Mr. Alexander
MRS. David Sample **** SAMPLE Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample
**** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander
David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Sample **** Mr. Sample is the

owner of

**600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares***
 *600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****
600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****6
00620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****60 * * * SIX HUNDRED THOUSAND

0620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600
 620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares***600620**Shares****600620**Shares****60062
0**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620
**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620*
*Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**

SIX HUNDRED AND TWENTY* * *

Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**S
 hares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Shares****600620**Sh

FULLY-PAID AND NON-ASSESSABLE SHARES OF THE COMMON STOCK, PAR VALUE $0.001, OF

SYCAMORE NETWORKS, INC. (hereinafter called the Corporation), transferable on the books of the Corporation by
the holder hereof in person or by duly authorized attorney upon the surrender of this certificate properly endorsed. This certificate and the shares represented hereby are issued and shall be held subject to the laws of the State of Delaware and all
provisions of the Amended and Restated Certificate of Incorporation, and the By-laws of the Corporation all as from time to time amended (copies thereof being on file with the Secretary of the Corporation) and the holder hereof, accepting this
certificate, expressly assents thereto. This Certificate is not valid unless countersigned and registered by the Transfer Agent and Registrar.

Witness the facsimile seal of the Company and the facsimile signatures of its duly authorized officers.

DATED <<Month Day, Year>> COUNTERSIGNED AND REGISTERED:

COMPUTERSHARE TRUST COMPANY, N.A.

TRANSFER AGENT AND REGISTRAR,

President and Chief Executive Officer

Chief Financial Officer, Vice President Finance & Administration

By

AUTHORIZED SIGNATURE

Shares

* * 6 0 0 6 2 0 * * * * * * * * * 6 0 0 6 2 0 * * * * * * * * * 6 0 0 6 2 0 * * * * * * * * * 6 0 0 6 2 0 * * * * * * * *
* 6 0 0 6 2 0 * *

CUSIP 871206 40 5

SEE REVERSE FOR CERTAIN DEFINITIONS

MR A SAMPLE DESIGNATION (IF ANY) ADD 1 ADD 2 ADD 3 ADD 4

!123456564525!

CUSIP XXXXXX XX X Holder ID XXXXXXXXXX

Insurance Value 1,000,000.00 Number of Shares 123456

DTC 12345678 123456789012345

Certificate Numbers Num/No. Denom. Total

1234567890/1234567890 1 1 1 1234567890/1234567890 2 2 2 1234567890/1234567890 3 3 3 1234567890/1234567890 4 4 4
1234567890/1234567890 5 5 5 1234567890/1234567890 6 6 6

Total Transaction 7



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SYCAMORE
NETWORKS, INC.

THE COMPANY WILL FURNISH WITHOUT CHARGE TO EACH SHAREHOLDER WHO SO REQUESTS, A SUMMARY OF THE
POWERS, DESIGNATIONS, PREFERENCES AND RELATIVE, PARTICIPATING, OPTIONAL OR OTHER SPECIAL RIGHTS OF EACH CLASS OF STOCK OF THE COMPANY AND THE QUALIFICATIONS, LIMITATIONS OR RESTRICTIONS OF SUCH PREFERENCES AND RIGHTS, AND THE VARIATIONS IN RIGHTS,
PREFERENCES AND LIMITATIONS DETERMINED FOR EACH SERIES, WHICH ARE FIXED BY THE ARTICLES OF INCORPORATION OF THE COMPANY, AS AMENDED, AND THE RESOLUTIONS OF THE BOARD OF DIRECTORS OF THE COMPANY, AND THE AUTHORITY OF THE BOARD OF DIRECTORS TO
DETERMINE VARIATIONS FOR FUTURE SERIES. SUCH REQUEST MAY BE MADE TO THE OFFICE OF THE SECRETARY OF THE COMPANY OR TO THE TRANSFER AGENT. THE BOARD OF DIRECTORS MAY REQUIRE THE OWNER OF A LOST OR DESTROYED STOCK CERTIFICATE, OR HIS LEGAL
REPRESENTATIVES, TO GIVE THE COMPANY A BOND TO INDEMNIFY IT AND ITS TRANSFER AGENTS AND REGISTRARS AGAINST ANY CLAIM THAT MAY BE MADE AGAINST THEM ON ACCOUNT OF THE ALLEGED LOSS OR DESTRUCTION OF ANY SUCH CERTIFICATE.

The following abbreviations, when used in the inscription on the face of this certificate, shall be construed as though
they were written out in full according to applicable laws or regulations: TEN COMas tenants in common UNIF GIFT MIN ACT- . . . . . . . . . .Custodian . . . . . . . . . . . . . . .

(Cust) (Minor)

TEN ENTas tenants by the entireties under Uniform Gifts to Minors Act . . . . . . . . . . . . .

(State)

JT TENas joint tenants with right of survivorship UNIF TRF MIN ACT . . . . . . . . . . . . . . .Custodian (until
age. . . ). . . . . . . . . . . and not as tenants in common (Cust) (Minor) under Uniform Transfers to Minors Act. . . . . . . . . .

(State)

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

PLEASE INSERT SOCIAL SECURITY OR OTHER IDENTIFYING NUMBER OF ASSIGNEE

For value received, hereby sell, assign and transfer unto

(PLEASE PRINT OR TYPEWRITE NAME AND ADDRESS, INCLUDING POSTAL ZIP CODE, OF ASSIGNEE)

Shares of the common stock represented by the within Certificate, and do hereby irrevocably constitute and appoint

Attorney to transfer the said stock on the books of the within-named Corporation with full power of
substitution in the premises.

Dated: 20

Signature:

Signature: Notice: The signature to this assignment must correspond with the name as written upon the face of the
certificate, in every particular, without alteration or enlargement, or any change whatever.

Signature(s)
Guaranteed: Medallion Guarantee Stamp

THE SIGNATURE(S) SHOULD BE GUARANTEED BY AN ELIGIBLE GUARANTOR
INSTITUTION (Banks, Stockbrokers, Savings and Loan Associations and Credit Unions) WITH MEMBERSHIP IN AN APPROVED SIGNATURE GUARANTEE MEDALLION PROGRAM, PURSUANT TO S.E.C. RULE 17Ad-15.