Name of Issuer:

The name of the issuer is GSI Group Inc. (the “Company”).

Address of Issuer’s Principal Executive Offices:

The Company’s principal executive offices are located at 125 Middlesex Turnpike, Bedford, Massachusetts, USA.

Name of Person Filing:

This statement is filed by:

The foregoing persons are hereinafter sometimes collectively referred to as the "Reporting Persons."

Address of Principal Business Office or, if None, Residence:

The address of the business office of each of the Reporting Persons is 401 Bay Street, Suite 1900, PO Box 19, Toronto, Ontario M5H 2Y4, Canada.

Citizenship:

The citizenship of each of the Reporting Persons is set forth above.

Title and Class of Securities:

Common stock, no par value

CUSIP No.:

36191C205

Item 3.

If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:

Broker or dealer registered under Section 15 of the Act;

Bank as defined in Section 3(a)(6) of the Act;

Insurance company as defined in Section 3(a)(19) of the Act;

Investment company registered under Section 8 of the Investment Company Act of 1940;

An investment adviser in accordance with Rule 13d-1(b)(1)(ii)(E);

An employee benefit plan or endowment fund in accordance with Rule 13d-1(b)(1)(ii)(F);

A parent holding company or control person in accordance with Rule 13d-1(b)(1)(ii)(G);

A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);

A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940;

A non-U.S. institution in accordance with Rule 240.13d-1(b)(1)(ii)(J);

Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).

If filing as a non-U.S. institution in accordance with Rule 240.13d-1(b)(1)(ii)(J), please specify the type of institution:_____

Ownership

The percentages used herein are calculated based upon 34,406,281 Shares reported to be outstanding as of April 29, 2015 as reported on Form 10-Q filed by the Company on May 7, 2015.

Polar Securities

Amount Beneficially Owned: 1,741,438

Percent of Class: 5.06%

Number of shares as to which such person has:

Sole power to vote or to direct the vote: 0

Shared power to vote or to direct the vote: 1,741,438

Sole power to dispose or to direct the disposition of: 0

Shared power to dispose or to direct the disposition of: 1,741,438

Altairis

Amount Beneficially Owned: 1,741,438

Percent of Class: 5.06%

Number of shares as to which such person has:

Sole power to vote or to direct the vote: 0

Shared power to vote or to direct the vote: 1,741,438

Sole power to dispose or to direct the disposition of: 0

Shared power to dispose or to direct the disposition of: 1,741,438

If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following [   ].

Ownership of more than Five Percent on Behalf of Another Person.

Not Applicable

Identification and classification of the subsidiary which acquired the security being reported on by the parent holding company or control person.

Not Applicable

Identification and classification of members of the group.

Not Applicable

Notice of Dissolution of Group.

Not Applicable

Certifications.

Each of the Reporting Persons hereby makes the following certification:

By signing below each Reporting Person certifies that, to the best of his or its knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect.