UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 6)*

EMCORE CORPORATION

(Name of Issuer)

Common Stock

(Title of Class of Securities)

290846203

(CUSIP Number)

Becker Drapkin Management, L.P.

Attn: Steven R. Becker

Attn: Matthew A. Drapkin

500 Crescent Court

Suite 230

Dallas, Texas 75201

(214) 756-6016

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

August 28, 2015

(Date of Event Which Requires Filing of This Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box:  ¨

Note: Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See Rule 240.13d-7 for other parties to whom copies are to be sent.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

SCHEDULE 13D

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This Amendment No. 6 to Schedule 13D amends and supplements the Schedule 13D filed with the Securities and Exchange Commission (the “SEC”) on October 15, 2013 (the “Original Schedule 13D”), Amendment No. 1 thereto, filed with the SEC on October 29, 2013, Amendment No. 2 thereto, filed with the SEC on December 4, 2013, Amendment No. 3 thereto, filed with the SEC on December 6, 2013, Amendment No. 4 thereto, filed with the SEC on September 18, 2014, and Amendment No. 5 thereto, filed with the SEC on August 12, 2015, with respect to the shares of common stock, no par value (the “Common Stock”), of EMCORE Corporation, a New Jersey corporation (the “Issuer”).

Item 3 is amended and supplemented to add the following information for updating as of the date hereof:

The Reporting Persons expended an aggregate amount equal to $10,278,849 (including commissions) to purchase 2,175,522 shares of Common Stock.

Item 5 is amended and supplemented to add the following information for updating as of the date hereof:

(a), (b) The Reporting Persons may be deemed to beneficially own in the aggregate 2,175,522 shares of Common Stock. Based upon a total of 25,563,888 outstanding shares of Common Stock, as reported in the Issuer’s quarterly report on Form 10-Q for the quarterly period ended June 30, 2015, the Reporting Persons’ shares represent approximately 8.510% of the outstanding shares of Common Stock.

Becker Drapkin QP owns 1,413,904 shares of Common Stock (the “Becker Drapkin QP Shares”), which represent approximately 5.531% of the outstanding shares of Common Stock.

Becker Drapkin, L.P. owns 199,203 shares of Common Stock (the “Becker Drapkin, L.P. Shares”), which represent approximately 0.779% of the outstanding shares of Common Stock.

The Becker Drapkin QP Shares and Becker Drapkin, L.P. Shares are collectively referred to herein as the “Becker Drapkin Funds Shares”.

Becker Drapkin QP has the power to vote or to direct the vote of (and the power to dispose or direct the disposition of) the Becker Drapkin QP Shares. Becker Drapkin QP disclaims beneficial ownership of the Becker Drapkin, L.P. Shares.

Becker Drapkin, L.P. has the power to vote or to direct the vote of (and the power to dispose or direct the disposition of) the Becker Drapkin, L.P. Shares. Becker Drapkin, L.P. disclaims the beneficial ownership of the Becker Drapkin QP Shares.

As general partner of the Becker Drapkin Funds, BD Management may be deemed to have the shared power to vote or direct the vote of (and the shared power to dispose or direct the disposition of) the Becker Drapkin Funds Shares. BD Management in its capacity as investment manager for the Managed Account has the sole power to vote or direct the vote of (and the sole power to dispose or direct the disposition of) 562,415 shares held by the Managed Account (the “Managed Account Shares”), which represent approximately 2.200% of the outstanding shares of Common Stock. BD Management disclaims beneficial ownership of the Becker Drapkin Funds Shares.

The Becker Drapkin Funds disclaim beneficial ownership of the Managed Account Shares.

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As general partner of BD Management, BCA may be deemed to have the shared power to vote or direct the vote of (and the shared power to dispose or direct the disposition of) any shares of Common Stock beneficially owned by BCA. Mr. Becker and Mr. Drapkin each disclaim beneficial ownership of any shares of Common Stock beneficially owned by BCA.

As of the date hereof, no Reporting Persons owns any shares of Common Stock other than those set forth in this Item 5.

(c) The trading dates, number of shares of Common Stock purchased or sold, and the price per share of Common Stock for all transactions by the Reporting Persons in shares of Common Stock since the Reporting Persons filed Amendment No. 5 to the Original Schedule 13D are set forth in the chart below.

(d) No person other than the Reporting Persons, and the Managed Account with respect to the Managed Account Shares, has the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the shares of common Stock set forth above.

(e) Not applicable.

Item 6 is amended and supplemented to add the following information for updating as of the date hereof:

On August 28, 2015, each of (i) Becker Drapkin QP, (ii) Becker Drapkin, L.P., and (iii) BD Management entered into Stock Purchase Plans (the “10b5-1 Plans”) with Tourmaline Partners, LLC (“Tourmaline”), pursuant to which Tourmaline may purchase shares of Common Stock on behalf of the applicable Reporting Person for the period beginning September 30, 2015 and ending December 15, 2015. Transactions under the 10b5-1 Plans will be subject to certain price restrictions and termination in accordance with each of their terms and subject to applicable law and regulation. The 10b5-1 Plans are intended to comply with the requirements of Rule 10b5-1(c) promulgated under the Securities Exchange Act of 1934.

The foregoing description of the 10b5-1 Plans is qualified in its entirety by reference to the text of the 10b5-1 Plans, which are attached as Exhibits 99.3, 99.4 and 99.5 hereto and incorporated by reference herein.

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SIGNATURES

After reasonable inquiry and to the best of each of the undersigned’s knowledge and belief, each of the undersigned, severally and not jointly, certifies that the information set forth in this statement is true, complete and correct.

Dated: August 28, 2015

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