Filed Pursuant to Rule 424(b)(3)
Registration No. 333-229052

MERGER PROPOSED — YOUR VOTE IS VERY IMPORTANT

February 7, 2019

Dear Shareholders of II-VI Incorporated and Stockholders of Finisar Corporation:

II-VI Incorporated (“II-VI”) and Finisar Corporation (“Finisar”) have entered into an Agreement and Plan of Merger, dated as of November 8, 2018 (the “Merger Agreement”). Pursuant to the terms of the Merger Agreement, Mutation Merger Sub Inc., a Delaware corporation and wholly owned subsidiary of II-VI, will be merged with and into Finisar, and Finisar will continue as the surviving corporation in the merger and a wholly owned subsidiary of II-VI (the “Merger”).

If the Merger is consummated as described in the accompanying joint proxy statement/prospectus, Finisar stockholders will be entitled to receive, at their election, consideration per share of common stock of Finisar (the “Finisar Common Stock”) consisting of (i) $26.00 in cash, without interest (subject to the proration adjustment procedures described in the accompanying joint proxy statement/prospectus, the “Cash Election Consideration”), (ii) 0.5546 validly issued, fully paid and nonassessable shares of II-VI common stock (the shares, the “II-VI Common Stock,” and the consideration, subject to the proration adjustment procedures described in the accompanying joint proxy statement/prospectus, the “Stock Election Consideration,” respectively), or (iii) a combination of $15.60 in cash, without interest, and 0.2218 validly issued, fully paid and nonassessable shares of II-VI Common Stock (the “Mixed Election Consideration,” and, together with the Cash Election Consideration and the Stock Election Consideration, the “Merger Consideration”). If no election is made as to a share of Finisar Common Stock, the holder of that share will receive the Mixed Election Consideration. The Cash Election Consideration and the Stock Election Consideration are subject to proration adjustment pursuant to the terms of the Merger Agreement such that the aggregate Merger Consideration will consist of approximately 60% cash and approximately 40% II-VI Common Stock (with the II-VI Common Stock valued at the closing price as of November 8, 2018), as further described under the heading “The Merger Agreement — Merger Consideration” beginning on page 140 of the accompanying joint proxy statement/prospectus.

Based on the closing price for II-VI Common Stock on the Nasdaq Global Select Market on February 7, 2019, the most recent practicable date for which such information was available, the Stock Election Consideration represented approximately $20.26 in value per share of Finisar Common Stock (before giving effect to any proration adjustment), and the Mixed Election Consideration represented approximately $23.70 in value per share of Finisar Common Stock. The Cash Election Consideration represents a premium of approximately 37.7% over the closing price for Finisar Common Stock on the Nasdaq Global Select Market on November 8, 2018 (before giving effect to any proration adjustment). The value of the Stock Election Consideration and Mixed Election Consideration will fluctuate based on the market price of II-VI Common Stock until the completion of the Merger. Shares of II-VI Common Stock are traded on the Nasdaq Global Select Market under the ticker symbol “IIVI,” and shares of Finisar Common Stock are traded on the Nasdaq Global Select Market under the ticker symbol “FNSR.” We urge you to obtain current market quotations for the shares of II-VI Common Stock and Finisar Common Stock.

Based on the number of shares of Finisar Common Stock outstanding as of February 5, 2019, and the treatment of shares of Finisar Common Stock and Finisar equity awards in the Merger, and assuming no conversions of the Finisar Convertible Notes, II-VI expects to issue approximately 26.38 million shares of II-VI Common Stock to holders of Finisar Common Stock and Finisar equity awards upon completion of the Merger. The actual number of shares of II-VI Common Stock to be issued upon completion of the Merger will be determined at the completion of the Merger based on, among other things, the number of shares of Finisar

Common Stock outstanding at that time. Based on the number of shares of Finisar Common Stock outstanding as of February 5, 2019, and the number of shares of II-VI Common Stock outstanding as of February 5, 2019, it is expected that, immediately after completion of the Merger, former holders of Finisar Common Stock and Finisar equity awards will own approximately 29.27% of the outstanding shares of II-VI Common Stock.

At the special meeting of II-VI shareholders described in the accompanying joint proxy statement/prospectus (the “II-VI Special Meeting”), II-VI shareholders will be asked to consider and vote on the following matters:

Approval of the Share Issuance Proposal requires the affirmative vote of at least a majority of the votes that all II-VI shareholders present at the II-VI Special Meeting, in person or by proxy, are entitled to cast (assuming a quorum is present). This vote will satisfy the vote requirements of Listing Rule 5635(d) of the Nasdaq Stock Market with respect to the Share Issuance Proposal. Approval of the II-VI Adjournment Proposal requires the affirmative vote of at least a majority of the votes that all II-VI shareholders present at the II-VI Special Meeting, in person or by proxy, are entitled to cast, whether or not a quorum is present.

At the special meeting of Finisar stockholders described in the accompanying joint proxy statement/prospectus (the “Finisar Special Meeting”), Finisar stockholders will be asked to consider and vote on the following matters:

Approval of the Merger Proposal requires the affirmative vote of holders of a majority of the outstanding shares of Finisar Common Stock. Approval of the Finisar Adjournment Proposal requires the affirmative vote of a majority of the votes cast on such proposal at the Finisar Special Meeting. Approval of the Compensation Proposal requires the affirmative vote of a majority of the votes cast on such proposal at the Finisar Special Meeting.

The Merger cannot be completed unless, among other things, II-VI shareholders approve the Share Issuance Proposal and Finisar stockholders approve the Merger Proposal. Your vote is very important, regardless of the number of shares you own. Even if you plan to attend the II-VI Special Meeting or the Finisar Special Meeting, as applicable, in person, please complete, sign, date and return, as promptly as possible, the enclosed proxy or voting instruction card in the accompanying prepaid reply envelope or submit your proxy by telephone or the Internet prior to the II-VI Special Meeting or Finisar Special Meeting, as applicable, to ensure that your shares will be represented at the II-VI Special Meeting or the Finisar Special Meeting, as applicable, if you are unable to attend. If you hold your shares in “street name” through a bank, brokerage firm or other nominee, you should follow the procedures provided by your bank, brokerage firm or other nominee to vote your shares.

After careful consideration, the II-VI board of directors unanimously approved and declared advisable the Merger Agreement and the other transactions contemplated thereby, including the Merger

and the issuance of shares of II-VI Common Stock issuable in connection with the Merger, and determined that the terms of the Merger Agreement, the Merger and the other transactions contemplated thereby are fair to and in the best interests of II-VI and its shareholders. The II-VI board of directors accordingly unanimously recommends that II-VI shareholders vote “FOR” each of the Share Issuance Proposal and the II-VI Adjournment Proposal.

After careful consideration, the Finisar board of directors, by unanimous vote, approved and declared advisable the Merger Agreement and the other transactions contemplated thereby, including the Merger, and determined that the terms of the Merger Agreement, the Merger and the other transactions contemplated thereby are fair to and in the best interests of Finisar and its stockholders. The Finisar board of directors accordingly recommends that Finisar stockholders vote “FOR” each of the Merger Proposal, the Finisar Adjournment Proposal and the Compensation Proposal. In considering the recommendation of the Finisar board of directors, you should be aware that directors and executive officers of Finisar have certain interests in the Merger that may be different from, or in addition to, the interests of Finisar stockholders generally. See the sections entitled “Finisar Proposal No. 3 — Non-Binding, Advisory Vote on Merger-Related Compensation for Finisar’s Named Executive Officers” beginning on page 189 of the accompanying joint proxy statement/prospectus and “Interests of Finisar’s Directors and Executive Officers in the Merger” beginning on page 166 of the accompanying joint proxy statement/prospectus for a more detailed description of these interests.

We urge you to read the accompanying joint proxy statement/prospectus, including the annexes and the documents incorporated by reference, carefully and in its entirety. In particular, we urge you to read carefully the section entitled “Risk Factors” beginning on page 48 of the accompanying joint proxy statement/prospectus.

On behalf of the respective boards of directors of II-VI and Finisar, thank you for your consideration and continued support.

Sincerely,

NEITHER THE SECURITIES AND EXCHANGE COMMISSION NOR ANY STATE SECURITIES COMMISSION HAS APPROVED OR DISAPPROVED THE TRANSACTIONS DESCRIBED IN THE ATTACHED JOINT PROXY STATEMENT/PROSPECTUS OR THE SECURITIES TO BE ISSUED IN CONNECTION WITH THE MERGER DESCRIBED UNDER THE ATTACHED JOINT PROXY STATEMENT/PROSPECTUS NOR HAVE THEY DETERMINED IF THE ATTACHED JOINT PROXY STATEMENT/PROSPECTUS IS ACCURATE OR ADEQUATE. ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.

The accompanying joint proxy statement/prospectus is dated February 7, 2019 and is first being mailed to II-VI shareholders and Finisar stockholders on or about February 14, 2019.

NOTICE OF SPECIAL MEETING OF SHAREHOLDERS

Dear Shareholders of II-VI Incorporated:

You are cordially invited to attend a special meeting of II-VI Incorporated (“II-VI”) shareholders. The special meeting, as described in the accompanying joint proxy statement/prospectus (the “II-VI Special Meeting”), will be held on March 26, 2019, at 2:00 p.m. local time, at 5000 Ericsson Drive, Warrendale, Pennsylvania 15086, to consider and vote on the following matters:

The record date for the II-VI Special Meeting is February 5, 2019 (the “II-VI Record Date”). Only shareholders of record of II-VI as of the close of business on the II-VI Record Date are entitled to notice of, and to vote at, the II-VI Special Meeting and any adjournments or postponements thereof. The merger contemplated by the Merger Agreement (the “Merger”) cannot be completed unless the Share Issuance Proposal receives the affirmative vote of at least a majority of the votes that all II-VI shareholders present at the II-VI Special Meeting, in person or by proxy, are entitled to cast (assuming a quorum is present). Approval of the II-VI Adjournment Proposal requires the affirmative vote of at least a majority of the votes that all II-VI shareholders present at the II-VI Special Meeting, in person or by proxy, are entitled to cast, whether or not a quorum is present. Your vote is very important, regardless of the number of shares of II-VI Common Stock that you own.

The II-VI board of directors unanimously recommends that you vote “FOR” each of the Share Issuance Proposal and the II-VI Adjournment Proposal.

EVEN IF YOU PLAN TO ATTEND THE II-VI SPECIAL MEETING IN PERSON, PLEASE COMPLETE, DATE, SIGN AND RETURN, AS PROMPTLY AS POSSIBLE, THE ENCLOSED PROXY CARD OR VOTING INSTRUCTION CARD IN THE ACCOMPANYING PREPAID REPLY ENVELOPE, OR SUBMIT YOUR PROXY BY TELEPHONE OR THE INTERNET PRIOR TO THE II-VI SPECIAL MEETING TO ENSURE THAT YOUR SHARES OF II-VI COMMON STOCK WILL BE REPRESENTED AT THE II-VI SPECIAL MEETING IF YOU ARE UNABLE TO ATTEND. IF YOU HOLD YOUR SHARES IN “STREET NAME” THROUGH A BANK, BROKERAGE FIRM OR OTHER NOMINEE, YOU SHOULD FOLLOW THE PROCEDURES PROVIDED BY YOUR BANK, BROKERAGE FIRM OR OTHER NOMINEE TO VOTE YOUR SHARES. IF YOU ATTEND THE II-VI SPECIAL MEETING AND VOTE IN PERSON, YOUR VOTE BY BALLOT WILL REVOKE ANY PROXY PREVIOUSLY SUBMITTED.

We urge you to read the accompanying joint proxy statement/prospectus, including all documents incorporated by reference into the accompanying joint proxy statement/prospectus, and its annexes carefully and in their entirety. If you have any questions concerning the Merger Agreement, the Merger or the other transactions contemplated thereby, the II-VI Special Meeting or the accompanying joint proxy statement/prospectus, would like additional copies of the accompanying joint proxy statement/prospectus, or need help submitting a proxy to vote, please contact II-VI:

II-VI Incorporated

375 Saxonburg Boulevard

Saxonburg, PA 16056

Attention: Mark Lourie

(724) 352-4455

February 7, 2019

FINISAR CORPORATION

1389 Moffett Park Drive

Sunnyvale, California 94089

NOTICE OF SPECIAL MEETING OF STOCKHOLDERS

Dear Stockholders of Finisar Corporation:

You are cordially invited to attend a special meeting of Finisar Corporation (“Finisar”) stockholders. The special meeting, as described in the accompanying joint proxy statement/prospectus (the “Finisar Special Meeting”), will be held on March 26, 2019, at 11:00 a.m. local time, at 2765 Sand Hill Road, Menlo Park, California 94025, to consider and vote on the following matters:

The record date for the Finisar Special Meeting is February 5, 2019 (the “Finisar Record Date”). Only stockholders of record of Finisar as of the close of business on the Finisar Record Date are entitled to notice of, and to vote at, the Finisar Special Meeting and any adjournments or postponements thereof. The merger contemplated by the Merger Agreement (the “Merger”) cannot be completed unless the Merger Proposal receives the affirmative vote of holders of a majority of the outstanding shares of Finisar common stock. Approval of the Finisar Adjournment Proposal requires the affirmative vote of a majority of the votes cast on such proposal at the Finisar Special Meeting. Approval of the Compensation Proposal requires the affirmative vote of a majority of the votes cast on such proposal at the Finisar Special Meeting. Your vote is very important, regardless of the number of shares of Finisar common stock that you own.

The Finisar board of directors unanimously recommends that you vote “FOR” each of the Merger Proposal, the Finisar Adjournment Proposal and the Compensation Proposal. In considering the recommendation of the Finisar board of directors, you should be aware that directors and executive officers of Finisar have certain interests in the Merger that may be different from, or in addition to, the interests of Finisar stockholders generally. See the sections entitled “Finisar Proposal No. 3 — Non-Binding, Advisory Vote on Merger-Related Compensation for Finisar’s Named Executive Officers” beginning on page 189 of the accompanying joint proxy statement/prospectus and “Interests of Finisar’s Directors and Executive Officers in the Merger” beginning on page 166 of the accompanying joint proxy statement/prospectus for a more detailed description of these interests.

EVEN IF YOU PLAN TO ATTEND THE FINISAR SPECIAL MEETING IN PERSON, PLEASE COMPLETE, DATE, SIGN AND RETURN, AS PROMPTLY AS POSSIBLE, THE ENCLOSED PROXY CARD OR VOTING INSTRUCTION CARD IN THE ACCOMPANYING PREPAID REPLY ENVELOPE, OR SUBMIT YOUR PROXY BY TELEPHONE OR THE INTERNET PRIOR TO THE FINISAR SPECIAL MEETING TO ENSURE THAT YOUR SHARES OF FINISAR COMMON STOCK

WILL BE REPRESENTED AT THE FINISAR SPECIAL MEETING IF YOU ARE UNABLE TO ATTEND. IF YOU HOLD YOUR SHARES IN “STREET NAME” THROUGH A BANK, BROKERAGE FIRM OR OTHER NOMINEE, YOU SHOULD FOLLOW THE PROCEDURES PROVIDED BY YOUR BANK, BROKERAGE FIRM OR OTHER NOMINEE TO VOTE YOUR SHARES. IF YOU ATTEND THE FINISAR SPECIAL MEETING AND VOTE IN PERSON, YOUR VOTE BY BALLOT WILL REVOKE ANY PROXY PREVIOUSLY SUBMITTED.

We urge you to read the accompanying joint proxy statement/prospectus, including all documents incorporated by reference into the accompanying joint proxy statement/prospectus, and its annexes carefully and in their entirety. If you have any questions concerning the Merger Agreement, the Merger or the other transactions contemplated thereby, the Finisar Special Meeting or the accompanying joint proxy statement/prospectus, would like additional copies of the accompanying joint proxy statement/prospectus, or need help submitting a proxy to vote, please contact:

Finisar Corporation

1389 Moffett Park Drive

Sunnyvale, CA 94089

Attention: Investor Relations

(408) 548-1000

OR

D.F. King & Co., Inc.

48 Wall Street, 22nd Floor

New York, NY 10005

Banks and Brokers, call collect: (212) 269-5550

All others, call toll free: (866) 356-7813

Email: FNSR@dfking.com

February 7, 2019

REFERENCES TO ADDITIONAL INFORMATION

The accompanying joint proxy statement/prospectus incorporates important business and financial information about II-VI and Finisar from other documents that II-VI Incorporated (“II-VI”) and Finisar Corporation (“Finisar”) have filed with the U.S. Securities and Exchange Commission (the “SEC”) that are not included in or delivered with the accompanying joint proxy statement/prospectus. For a listing of documents incorporated by reference into the accompanying joint proxy statement/prospectus, please see the section entitled “Where You Can Find More Information” beginning on page 223 of the accompanying joint proxy statement/prospectus. This information is available for you to review through the SEC’s website at www.sec.gov.

You may request copies of the accompanying joint proxy statement/prospectus and any of the documents incorporated by reference into the accompanying joint proxy statement/prospectus or other information concerning II-VI, without charge, by written or telephonic request directed to II-VI Incorporated, 375 Saxonburg Boulevard, Saxonburg, PA 16056, Attention: Mark Lourie, Telephone (724) 352-4455.

You may also request a copy of the accompanying joint proxy statement/prospectus and any of the documents incorporated by reference into the accompanying joint proxy statement/prospectus or other information concerning Finisar, without charge, by written or telephonic request directed to Finisar Corporation, 1389 Moffett Park Drive, Sunnyvale, CA 94089, Attention: Investor Relations, Telephone (408) 548-1000.

In order for you to receive timely delivery of the documents in advance of the special meeting of II-VI shareholders or Finisar stockholders, as applicable, you must request the information no later than five business days prior to the date of the applicable special meeting (i.e., by March 19, 2019).

ABOUT THE ACCOMPANYING JOINT PROXY STATEMENT/PROSPECTUS

The accompanying document, which forms part of a registration statement on Form S-4 filed with the SEC by II-VI (File No. 333-229052), constitutes a prospectus of II-VI under Section 5 of the Securities Act of 1933, as amended (the “Securities Act”), with respect to the shares of common stock, no par value, of II-VI (“II-VI Common Stock”) to be issued pursuant to the Agreement and Plan of Merger, dated as of November 8, 2018, as it may be amended from time to time (the “Merger Agreement”), by and among II-VI, Mutation Merger Sub Inc. (“Merger Sub”) and Finisar. The accompanying document also constitutes a joint proxy statement under Section 14(a) of the Securities Exchange Act of 1934, as amended. It also constitutes a notice of meeting with respect to the special meeting of II-VI shareholders described in the accompanying joint proxy statement/prospectus and a notice of meeting with respect to the special meeting of Finisar stockholders described in the accompanying joint proxy statement/prospectus.

II-VI has supplied all information contained or incorporated by reference into the accompanying joint proxy statement/prospectus relating to II-VI and Merger Sub, as well as all pro forma financial information, and Finisar has supplied all such information relating to Finisar.

II-VI and Finisar have not authorized anyone to provide you with information other than the information that is contained in, or incorporated by reference into, the accompanying joint proxy statement/prospectus. II-VI and Finisar take no responsibility for, and can provide no assurances as to the reliability of, any other information that others may give you. The accompanying joint proxy statement/prospectus is dated February 7, 2019, and you should not assume that the information contained in the accompanying joint proxy statement/prospectus is accurate as of any date other than such date. Further, you should not assume that the information incorporated by reference into the accompanying joint proxy statement/prospectus is accurate as of any date other than the date of the incorporated document. Neither the mailing of this joint proxy statement/prospectus to II-VI shareholders or Finisar stockholders, nor the issuance by II-VI of shares of II-VI Common Stock in connection with the Merger Agreement will create any implication to the contrary.

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Unless otherwise indicated or as the context otherwise requires, all references in the accompanying joint proxy statement/prospectus to:

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TABLE OF CONTENTS

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QUESTIONS AND ANSWERS ABOUT THE MERGER AND THE SPECIAL MEETINGS

The following questions and answers are intended to briefly address some commonly asked questions regarding the Merger and matters to be addressed at the Special Meetings. These questions and answers may not address all questions that may be important to II-VI shareholders and Finisar stockholders. Please refer to the section entitled “Summary” beginning on page 20 of this joint proxy statement/prospectus and the more detailed information contained elsewhere in this joint proxy statement/prospectus, the annexes to this joint proxy statement/prospectus and the documents referred to in this joint proxy statement/prospectus, which you should read carefully and in their entirety. You may obtain the information incorporated by reference into this joint proxy statement/prospectus without charge by following the instructions under the section entitled “Where You Can Find More Information” beginning on page 223 of this joint proxy statement/prospectus.

II-VI is holding the II-VI Special Meeting to obtain the requisite approval of its shareholders for the Share Issuance Proposal. The Merger cannot be completed unless, among other things, the Share Issuance Proposal receives the affirmative vote of at least a majority of the votes that all II-VI shareholders present at the II-VI Special Meeting, in person or by proxy, are entitled to cast (assuming a quorum is present). In addition, II-VI shareholders also will be asked to approve the II-VI Adjournment Proposal.

Finisar is holding the Finisar Special Meeting to obtain the requisite approval of its stockholders for the Merger Proposal. The Merger cannot be completed unless, among other things, the Merger Proposal receives the affirmative vote of holders of a majority of the outstanding shares of Finisar Common Stock. In addition, Finisar stockholders also will be asked to approve the Finisar Adjournment Proposal and the Compensation Proposal.

This joint proxy statement/prospectus serves as a proxy statement of II-VI, a proxy statement of Finisar and a prospectus of II-VI in connection with the issuance of shares of II-VI Common Stock as part of the aggregate Merger Consideration (as defined below).

Your vote is very important. We encourage you to complete, sign, date and submit a proxy card to vote your shares of II-VI Common Stock or Finisar Common Stock, as applicable, as soon as possible.

For more information regarding the II-VI Special Meeting, the Share Issuance Proposal, and the II-VI Adjournment Proposal, see the section entitled “Information About the II-VI Special Meeting” beginning on page 71 of this joint proxy statement/prospectus. For more information regarding the Finisar Special Meeting, the Merger Proposal, the Finisar Adjournment Proposal, and the Compensation Proposal, see the section entitled “Information About the Finisar Special Meeting” beginning on page 65 of this joint proxy statement/prospectus.

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If you otherwise would be entitled to receive a fractional share of II-VI Common Stock as part of your Merger Consideration, you will receive cash in lieu of the fractional share of II-VI Common Stock to which you would otherwise be entitled, and you will not be entitled to dividends, voting rights or any other rights in respect of such fractional share. For more information regarding allocation and proration procedures, see the section entitled “The Merger Agreement — Merger Consideration” beginning on page 140 of this joint proxy statement/prospectus.

Because the exchange ratios for the shares of II-VI Common Stock that will be issued in the Merger as part of the Stock Election Consideration and the Mixed Election Consideration are fixed and there will be no adjustment to such exchange ratios, the aggregate value of the Merger Consideration received by Finisar stockholders who receive II-VI Common Stock as Merger Consideration will depend on the then-current market price of shares of II-VI Common Stock at the Effective Time. As a result, the value of the Merger Consideration that Finisar stockholders will receive in the Merger could be greater than, less than, or the same as, the value of such Merger Consideration on the date of this joint proxy statement/prospectus or at the time of the Finisar Special Meeting.

For more information regarding the Stock Election Consideration, Cash Election Consideration, or Mixed Election Consideration, as applicable, to be provided to Finisar stockholders, see the section entitled “The Merger Agreement — Merger Consideration” beginning on page 140 of this joint proxy statement/prospectus. For more information regarding election mechanics, see the sections entitled “The Merger Agreement — Election Procedures” beginning on page 142 of this joint proxy statement/prospectus and “The Merger Agreement — Exchange Procedures” beginning on page 143 of this joint proxy statement/prospectus.

For more information regarding the treatment of holders of Finisar Stock Options, see the section entitled “The Merger Agreement — Treatment of Finisar Employee Stock Plans — Stock Options” beginning on page 144 of this joint proxy statement/prospectus.

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As of the Effective Time, each Finisar Restricted Stock Unit (or portion thereof) that is subject to a performance-based vesting condition that relates solely to the value of Finisar Common Stock but does not vest in accordance with its terms in connection with the Merger will be cancelled and extinguished without any right to receive the Merger Consideration or any other payment.

At the Effective Time, each Finisar Restricted Stock Unit (or portion thereof) that is outstanding and unvested and does not vest in accordance with its terms in connection with the Merger and is either (x) subject to time-based vesting requirements only or (y) subject to a performance-based vesting condition other than the value of Finisar Common Stock will be assumed by II-VI (each, an “Assumed RSU”). Each Assumed RSU will be subject to substantially the same terms and conditions as applied to the related Finisar Restricted Stock Unit immediately prior to the Effective Time, except that the number of shares of II-VI Common Stock subject to such Assumed RSU will be adjusted as described below under “The Merger Agreement — Treatment of Finisar Employee Stock Plans — Restricted Stock Units.”

For more information regarding the treatment of holders of Finisar Restricted Stock Units, see the section entitled “The Merger Agreement — Treatment of Finisar Employee Stock Plans — Restricted Stock Units” beginning on page 144 of this joint proxy statement/prospectus.

Elections to receive Cash Election Consideration (each, a “Cash Election”) and elections to receive Stock Election Consideration (each, a “Stock Election”) are subject to the proration adjustment procedures set forth in the Merger Agreement to ensure that the aggregate Merger Consideration will consist of approximately 60% cash and approximately 40% II-VI Common Stock (with the II-VI Common Stock valued at the closing price as of November 8, 2018).

For more information regarding the election procedures, see the section entitled “The Merger Agreement — Election Procedures” beginning on page 142 of this joint proxy statement/prospectus.

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If you make a Stock Election, the Merger Consideration that you will receive will be adjusted if the Available Cash Election Amount exceeds the Cash Election Amount. If the Available Cash Election

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Amount exceeds the Cash Election Amount, then the following Merger Consideration will be paid in respect of each share of Finisar Common Stock with respect to which a Stock Election was made and not revoked or lost in accordance with the terms of the Merger Agreement (each, and as applicable with each Stock Election RSU, a “Stock Electing Share”):

The “Available Cash Election Amount” means (i) the product of $15.60 multiplied by the number of total outstanding shares of Finisar Common Stock as of the Effective Time (excluding the Excluded Shares, but including the number of Dissenting Stockholder Shares, Net Option Shares, and Participating RSUs) minus (ii) the aggregate amount of cash to be paid in respect of all shares of Finisar Common Stock with respect to which either a Mixed Election was made and not revoked or with respect to which no election was made (together with the Mixed Election RSUs, the “Mixed Consideration Shares”) (assuming that all Dissenting Stockholder Shares and all Net Option Shares are Mixed Consideration Shares).

The “Available Stock Election Amount” means (i) the product of 0.2218 multiplied by the number of total outstanding shares of Finisar Common Stock as of the Effective Time (excluding the Excluded Shares, but including the number of Dissenting Stockholder Shares, Net Option Shares, and Participating RSUs) minus (ii) the aggregate number of shares of II-VI Common Stock to be paid in respect of all Mixed Consideration Shares (assuming that all Dissenting Stockholder Shares and all Net Option Shares are Mixed Consideration Shares).

The “Cash Election Amount” means the product of (i) the number of Cash Electing Shares multiplied by (ii) the Cash Election Consideration (before giving effect to any proration adjustment).

The “Stock Election Amount” means the product of (i) the number of Stock Electing Shares multiplied by (ii) the Stock Election Consideration (before giving effect to any proration adjustment).

For more information regarding the proration adjustments, see the section entitled “The Merger Agreement — Merger Consideration” beginning on page 140 of this joint proxy statement/prospectus.

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The Finisar Special Meeting will be held on March 26, 2019, at 11:00 a.m. local time, at 2765 Sand Hill Road, Menlo Park, California 94025.

If you are a II-VI shareholder of record or a Finisar stockholder of record and plan to attend the II-VI Special Meeting or the Finisar Special Meeting, as applicable, in person, please mark the appropriate box on the enclosed proxy card, or enter that information when submitting your voting instructions by telephone or Internet prior to the II-VI Special Meeting or the Finisar Special Meeting, as applicable. II-VI and Finisar would like to know by March 19, 2019 if you plan to attend the II-VI Special Meeting or the Finisar Special Meeting, as applicable, in person. If your shares are held through an intermediary, such as a broker or a bank, you will need to present proof of your ownership as of the close of business on the II-VI Record Date or the Finisar Record Date for admission to the II-VI Special Meeting location or the Finisar Special Meeting location, respectively. Proof of ownership could include a voting instruction form from your bank or broker, or a copy of your account statement. All in-person attendees will need to present valid photo identification for admission. If you are the representative of a corporate or institutional shareholder or stockholder, as applicable, you must present valid photo identification along with proof that you are the

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representative of such shareholder or stockholder, as applicable. The use of recording devices and other electronic devices will not be permitted during the II-VI Special Meeting and the Finisar Special Meeting. For additional information about the II-VI Special Meeting, see the section entitled “Information About the II-VI Special Meeting” beginning on page 71 of this joint proxy statement/prospectus. For additional information about the Finisar Special Meeting, see the section entitled “Information About the Finisar Special Meeting” beginning on page 65 of this joint proxy statement/prospectus.

The approval by II-VI shareholders of the Share Issuance Proposal is a condition to the obligations of II-VI and Finisar to complete the Merger. The approval of the II-VI Adjournment Proposal is not a condition to the obligations of II-VI or Finisar to complete the Merger.

Under Pennsylvania law, II-VI shareholders are not required to consider and vote to adopt the Merger Agreement.

The approval by Finisar stockholders of the Merger Proposal is a condition to the obligations of II-VI and Finisar to complete the Merger. The approval of the Finisar Adjournment Proposal and the Compensation Proposal are not conditions to the obligations of II-VI or Finisar to complete the Merger.

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If you are a beneficial owner, please refer to the instructions provided by your bank, brokerage firm or other nominee to see which of the above choices are available to you. Please note that if you are a beneficial owner and wish to vote in person at the applicable special meeting, you must obtain a legal proxy from your bank, brokerage firm or other nominee.

See the sections entitled “Information About the II-VI Special Meeting — Voting of Shares, Proxies and Revocation” beginning on page 73 of this joint proxy statement/prospectus and “Information About the Finisar Special Meeting — Voting of Shares, Proxies and Revocation” beginning on page 67 of this joint proxy statement/prospectus.

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There must be a quorum for the vote on the Share Issuance Proposal to be taken at the II-VI Special Meeting. If there is no quorum, the II-VI Special Meeting may be adjourned or postponed to another date if the II-VI Adjournment Proposal is approved, which may subject II-VI to additional expense and delay or prevent the completion of the Merger.

See the section entitled “Information About the II-VI Special Meeting — Record Date, Outstanding Shares and Quorum” beginning on page 71 of this joint proxy statement/prospectus.

There must be a quorum for votes on the Merger Proposal, the Finisar Adjournment Proposal and the Compensation Proposal to be taken at the Finisar Special Meeting. If there is no quorum, the Finisar Special Meeting may be adjourned or postponed to another date, which may subject Finisar to additional expense and delay or prevent the completion of the Merger. If a quorum shall fail to attend the Finisar Special Meeting, the chairman of the meeting or the holders of a majority of the shares of Finisar Common Stock entitled to vote who are present, in person or by proxy, may adjourn the meeting to another place, date, or time.

See the section entitled “Information About the Finisar Special Meeting — Record Date, Outstanding Shares and Quorum” beginning on page 66 of this joint proxy statement/prospectus.

Approval of the II-VI Adjournment Proposal requires the affirmative vote of at least a majority of the votes that all II-VI shareholders present at the II-VI Special Meeting, in person or by proxy, are entitled to cast,

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whether or not a quorum is present. Accordingly, abstentions will have the same effect as a vote “AGAINST” the II-VI Adjournment Proposal, but shares deemed not in attendance at the meeting, whether due to a record holder’s failure to vote or a “street name” holder’s failure to provide any voting instructions to such holder’s nominee or intermediary will have no effect on the II-VI Adjournment Proposal.

See the section entitled “Information About the II-VI Special Meeting — Vote Required” beginning on page 72 of this joint proxy statement/prospectus.

Assuming that a quorum is present, approval of the Finisar Adjournment Proposal requires the affirmative vote of a majority of the votes cast on such proposal at the Finisar Special Meeting. If your shares of Finisar Common Stock are not voted on the Finisar Adjournment Proposal, whether due to a record holder’s failure to vote or a “street name” holder’s failure to provide any voting instructions to such holder’s nominee or intermediary, or if you abstain on the Finisar Adjournment Proposal, your shares will have no effect on the Finisar Adjournment Proposal.

Assuming that a quorum is present, approval of the Compensation Proposal requires the affirmative vote of a majority of the votes cast on such proposal at the Finisar Special Meeting. If your shares of Finisar Common Stock are not voted on the Compensation Proposal, whether due to a record holder’s failure to vote or a “street name” holder’s failure to provide any voting instructions to such holder’s nominee or intermediary, or if you abstain on the Compensation Proposal, your shares will have no effect on the Compensation Proposal.

See the section entitled “Information About the Finisar Special Meeting — Vote Required” beginning on page 66 of this joint proxy statement/prospectus.

If your shares are held by a bank, brokerage firm or other nominee, you are considered the beneficial owner of shares held in “street name,” and your bank, brokerage firm or other nominee is considered the holder of record with respect to those shares. Your bank, brokerage firm or other nominee will send to you, as the beneficial owner, a package describing the procedure for voting your shares. You should follow the instructions provided by them to vote your shares. You are invited to attend the applicable special meeting; however, you may not vote these shares in person at the applicable special meeting unless you obtain a “legal proxy” from your bank, brokerage firm or other nominee that holds your shares, giving you the right to vote the shares at the applicable special meeting.

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Unless your bank, brokerage firm or other nominee has discretionary authority to vote your shares, your bank, brokerage firm or other nominee may not vote your shares without voting instructions from you. In accordance with applicable stock exchange rules, if your shares are held in “street name” through a brokerage firm, your broker has authority to vote on “routine” proposals if you have not provided voting instructions. However, your broker is precluded from exercising voting discretion with respect to non-routine matters. All of the proposals to be voted on by II-VI shareholders at the II-VI Special Meeting and Finisar stockholders at the Finisar Special Meeting are non-routine matters. As a result, if your shares are held in “street name” through a brokerage firm and you do not provide voting instructions, your broker will not have discretionary authority to vote your shares at the II-VI Special Meeting or the Finisar Special Meeting, as applicable, and, accordingly, II-VI and Finisar do not expect any broker non-votes on any of the proposals at the Special Meetings. A broker non-vote occurs on an item when (i) a broker has discretionary authority to vote on at least one routine proposal at a meeting, but under stock exchange rules is not permitted to vote on other non-routine proposals without instructions from the beneficial owner of the shares and (ii) that broker exercises its discretionary authority on the routine proposal after the beneficial owner fails to provide such instructions, resulting in broker non-votes on each of the non-routine proposals.

If you are a Finisar stockholder and you fail to instruct your bank, brokerage firm or other nominee how to vote your shares, your shares will have the same effect as a vote “AGAINST” the Merger Proposal. Your shares will not be counted, and therefore will have no effect, on any of the other proposals voted on at the Special Meetings if you fail to instruct your bank, brokerage firm or other nominee how to vote your shares.

You should therefore provide your bank, brokerage firm or other nominee with instructions as to how to vote your shares of II-VI Common Stock or Finisar Common Stock, as applicable.

Please follow the voting instructions provided by your bank, brokerage firm or other nominee so that it may vote your shares on your behalf. Please note that you may not vote shares held in street name by returning a proxy card directly to II-VI or Finisar or by voting in person at your special meeting unless you first obtain a proxy from your bank, brokerage firm or other nominee.

See the sections entitled “Information About the II-VI Special Meeting — Vote Required” beginning on page 72 of this joint proxy statement/prospectus and “Information About the Finisar Special Meeting — Vote Required” beginning on page 66 of this joint proxy statement/prospectus.

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If you are a II-VI shareholder and you properly sign your proxy card but do not mark the boxes showing how your shares of II-VI Common Stock should be voted on a matter, the shares represented by your properly signed proxy will be voted “FOR” the Share Issuance Proposal and “FOR” the II-VI Adjournment Proposal, as applicable.

If you are a Finisar stockholder and you properly sign your proxy card but do not mark the boxes showing how your shares of Finisar Common Stock should be voted on a matter, the shares represented by your properly signed proxy will be voted “FOR” the Merger Proposal, “FOR” the Finisar Adjournment Proposal and “FOR” the Compensation Proposal, as applicable.

If you fail to submit a valid proxy and to attend the applicable special meeting, or if your shares are held through a bank, brokerage firm or other nominee and you do not instruct your bank, brokerage firm or other nominee to vote your shares, your shares will not be voted on any of the matters being considered at the applicable Special Meeting and, if you are a Finisar stockholder, will have the effect of a vote “AGAINST” the Merger Proposal.

See the sections entitled “Information About the II-VI Special Meeting — Voting of Shares, Proxies and Revocation” beginning on page 73 of this joint proxy statement/prospectus and “Information About the Finisar Special Meeting — Voting of Shares, Proxies and Revocation” beginning on page 67 of this joint proxy statement/prospectus.

If you are a holder of record of II-VI Common Stock as of the II-VI Record Date, you can revoke your proxy or change your vote by:

If you are a holder of record of Finisar Common Stock as of the Finisar Record Date, you can revoke your proxy or change your vote by:

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In either case, if you hold your shares in street name, you must contact your nominee or intermediary to change your vote or obtain a legal proxy to vote your shares if you wish to cast your vote in person at the II-VI Special Meeting or the Finisar Special Meeting.

See the sections entitled “Information About the II-VI Special Meeting — Voting of Shares, Proxies and Revocation” beginning on page 73 of this joint proxy statement/prospectus and “Information About the Finisar Special Meeting — Voting of Shares, Proxies and Revocation” beginning on page 67 of this joint proxy statement/prospectus.

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Under Delaware law, record holders of Finisar Common Stock who choose the Stock Election Consideration for their shares of Finisar Common Stock, but receive a mix of cash and II-VI Common Stock for such shares through the proration adjustment mechanism in connection with an oversubscription of the Stock Election Consideration, will be entitled to appraisal rights for such shares if such stockholders have otherwise complied with the requirements of Section 262 of the DGCL. Appraisal rights will not be available to Finisar stockholders who fail to make an election and receive the Mixed Election Consideration or to Finisar stockholders who choose the Cash Election Consideration or the Mixed Election Consideration.

In addition, a stockholder who desires to exercise appraisal rights must neither vote in favor of the Merger Proposal nor consent thereto in writing, must continuously hold his, her or its shares of Finisar Common Stock through the effective date of the Merger, must deliver to Finisar a written demand for appraisal prior to the date of the Finisar Special Meeting and must otherwise comply with the procedures set forth in Section 262 of the DGCL.

If the Merger is completed, subject to the provisions of Section 262 of the DGCL, Finisar stockholders who are entitled to, and properly perfect, their appraisal rights will obtain payment in cash of the fair value of their shares of Finisar Common Stock as determined by the Delaware Court of Chancery, instead of receiving the Merger Consideration for their shares. The “fair value” of shares of Finisar Common Stock as determined by the Delaware Court of Chancery could be greater than, the same as, or less than the value of the Merger Consideration that Finisar stockholders would otherwise be entitled to receive under the terms of the Merger Agreement.

However, notwithstanding a Finisar stockholder’s compliance with the DGCL in perfecting appraisal rights, under Section 262 of the DGCL, assuming Finisar Common Stock remains listed on a national securities exchange immediately prior to the Effective Time, the Delaware Court of Chancery will dismiss any appraisal proceedings as to all Finisar stockholders who are otherwise entitled to appraisal rights unless (i) the total number of shares entitled to appraisal exceeds 1% of the outstanding shares of Finisar Common Stock, or (ii) the value of the consideration provided in the Merger for such total number of shares entitled to appraisal exceeds $1 million. To exercise appraisal rights, Finisar stockholders must comply with the procedures prescribed by Section 262 of the DGCL. These procedures are summarized in the section entitled “Appraisal Rights” beginning on page 215 of this joint proxy statement/prospectus. In addition, a copy of the full text of Section 262 of the DGCL is included as Annex D to this joint proxy statement/prospectus. Failure to comply with these provisions may result in a loss of the right of appraisal.

As described in the sections entitled “The Merger Agreement — Conditions to Completion of the Merger” and “The Merger — Regulatory Approvals” beginning on pages 160 and 129, respectively, of this joint proxy statement/prospectus, completion of the Merger is conditioned on, among other things, (i) the expiration or early termination of the applicable waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended (the “HSR Act”), and (ii) receipt of all other consents under certain specified federal, state, local or foreign antitrust, competition, premerger notification or trade regulation laws, regulations or orders.

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The exchange of Finisar Common Stock for cash, II-VI Common Stock or both in the Merger generally will be a taxable transaction for U.S. holders of Finisar Common Stock for U.S. federal income tax purposes and may also be taxable under state, local or other tax laws. You should read the section entitled “The Merger — Material U.S. Federal Income Tax Consequences” beginning on page 132 of this joint proxy statement/prospectus for more information.

Tax matters can be complicated and the tax consequences of the Merger to you will depend on your particular circumstances. You are urged to consult your tax advisor regarding the U.S. federal income tax consequences of the Merger to you in your particular circumstances, as well as tax consequences arising under the laws of any state, local or foreign taxing jurisdiction.

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Finisar will bear the entire cost of proxy solicitation, including preparation, assembly, printing and mailing of the notice of Finisar Special Meeting, proxy card, this joint proxy statement/prospectus and any additional materials furnished to Finisar stockholders. Copies of these materials will be furnished to brokerage houses, fiduciaries and custodians holding shares in their names that are beneficially owned by others to forward to those beneficial owners. In addition, Finisar may reimburse the costs of forwarding these materials to those beneficial owners. Finisar also may reimburse banks, brokerage firms, other nominees or their respective agents for their expenses in forwarding proxy materials to beneficial owners of Finisar Common Stock. Finisar’s directors, officers and employees also may solicit proxies by telephone, by

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facsimile, by mail, on the Internet or in person. They will not be paid any additional amounts for soliciting proxies. Finisar has engaged D.F. King & Co., Inc. to aid in the solicitation of proxies from brokers, bank nominees and other institutional owners for approximately $12,500, plus reimbursement of related expenses.

On November 8, 2018, in connection with its entry into the Merger Agreement, II-VI entered into a commitment letter (together with a related fee letter) with Bank of America, N.A. (“Bank of America”), which was subsequently amended and restated on December 7, 2018 and on December 14, 2018 (together with one or more related fee letters, the “Commitment Letter”). Subject to the terms and conditions set forth in the Commitment Letter, Bank of America and the other lender parties thereto (the “Lending Parties”) have severally committed to provide 100% of up to $2.425 billion in aggregate principal amount of senior secured credit facilities of II-VI (the “II-VI Senior Credit Facilities”) comprised of (i) a “term a” loan facility of up to $1.0 billion, a portion of which will be available after the closing of the Merger on a delayed draw basis, (ii) a “term b” loan facility of up to $975.0 million and (iii) a revolving credit facility of up to $450.0 million. The obligation of Bank of America and the other lead arranger parties thereto (the “Lead Arrangers”) to provide the debt financing under the Commitment Letter is subject to a number of conditions. II-VI currently intends to pay the cash portion of the aggregate Merger Consideration and pay related fees and expenses in connection with the Merger using the proceeds of draws under the II-VI Senior Credit Facilities and cash and short-term investments of II-VI and Finisar. II-VI currently does not intend to draw on the revolving credit facility in order to fund the cash portion of the aggregate Merger Consideration.

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For more information on the II-VI Senior Credit Facilities, see the section entitled “The Merger — Description of Debt Financing” beginning on page 135 of this joint proxy statement/prospectus.

At the consummation of the Merger and pursuant to the Indentures (as defined below), II-VI, the Surviving Corporation and Wells Fargo Bank, National Association, as trustee (the “Trustee”), will enter into supplemental indentures to (i) the Indenture, dated as of December 16, 2013 (the “2033 Notes Indenture”), by and between Finisar and the Trustee, governing the 2033 Notes and (ii) the Indenture, dated as of December 21, 2016 (the “2036 Notes Indenture” and, together with the 2033 Notes Indenture, the “Indentures”), by and between Finisar and the Trustee, governing the 2036 Notes. The respective supplemental indentures will comply with the applicable terms of the Indentures and will, among other things, provide that (y) at and after the Effective Time, the right to convert each $1,000 principal amount of the applicable Finisar Convertible Notes will be changed into a right to convert such principal amount of the applicable Finisar Convertible Notes into the weighted average of the types and amounts of consideration received by holders of Finisar Common Stock that affirmatively make an election to receive Cash Election Consideration, Stock Election Consideration or Mixed Election Consideration that a holder of a number of shares of Finisar Common Stock equal to the applicable conversion rate immediately prior to the consummation of the Merger would have owned or been entitled to receive in connection with the Merger (the “Reference Property”) and (z) II-VI fully and unconditionally guarantees, on a senior unsecured basis, the Finisar Convertible Notes.

Pursuant to the terms of the Indentures, consummation of the Merger will constitute a “Fundamental Change” and a “Make Whole Fundamental Change.” As a result, holders of the Finisar Convertible Notes will be permitted to choose, pursuant, and subject, to the terms and conditions of the Indentures (i) to convert their Finisar Convertible Notes, (ii) to require Finisar to repurchase their Finisar Convertible Notes for a price equal to 100% of their principal amount, together with accrued and unpaid interest to, but excluding, the repurchase date, or (iii) to continue holding their Finisar Convertible Notes until maturity or until they are otherwise redeemed, repurchased, or converted pursuant to the terms of the applicable Indenture. Neither II-VI, Merger Sub, Finisar nor any of their respective affiliates or representatives have made, or intend to make, any recommendation to any holder of Finisar Convertible Notes regarding this election.

See the section entitled “The Merger — Treatment of Finisar Convertible Notes” beginning on page 136 of this joint proxy statement/prospectus.

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RISK FACTORS

In deciding how and whether to vote, you should carefully consider the following risk factors and all of the information contained in or incorporated by reference into this joint proxy statement/prospectus, including but not limited to, the matters addressed in the section entitled “Cautionary Statement Regarding Forward-Looking Statements” beginning on page 62 of this joint proxy statement/prospectus and the matters discussed under “Item 1A. Risk Factors” of II-VI’s Annual Report on Form 10-K for the fiscal year ended June 30, 2018, as updated from time to time in II-VI’s subsequent filings with the SEC, which are incorporated by reference into this joint proxy statement/prospectus, and Finisar’s Annual Report on Form 10-K for the fiscal year ended April 29, 2018, as updated from time to time in Finisar’s subsequent filings with the SEC, which are incorporated by reference into this joint proxy statement/prospectus. See the section entitled “Where You Can Find More Information” of this joint proxy statement/prospectus.

Risks Relating to the Merger

The Merger is subject to approval by the shareholders of II-VI and the stockholders of Finisar.

In order for the Merger to be completed, among other things, II-VI shareholders must approve the Share Issuance Proposal, which requires the affirmative vote of at least a majority of the votes that all II-VI shareholders present at the II-VI Special Meeting, in person or by proxy, are entitled to cast (assuming a quorum is present), and Finisar stockholders must approve the Merger Proposal, which requires the affirmative vote of holders of a majority of the outstanding shares of Finisar Common Stock at the Finisar Special Meeting. There can be no assurance that either approval will be obtained.

II-VI’s stock price may be negatively impacted by risks, conditions and developments that apply to II-VI, some of which are different from the risks, conditions and developments applicable to Finisar.

Upon completion of the Merger, Finisar stockholders who elect to receive Stock Election Consideration or Mixed Election Consideration will become holders of II-VI Common Stock, and Finisar stockholders who elect to receive Cash Election Consideration may become holders of II-VI Common Stock. See “— Finisar stockholders may not receive all consideration in the form they elect.” The businesses and markets of II-VI are different from those of Finisar in some respects. There is a risk that various factors, conditions and developments that would not affect the price of Finisar Common Stock could negatively affect the price of II-VI Common Stock. The issuance of shares of II-VI Common Stock in the Merger could on its own have the effect of depressing the market price for II-VI Common Stock. In addition, many Finisar stockholders may decide not to hold the shares of II-VI Common Stock they receive as a result of the Merger. Other Finisar stockholders, such as funds with limitations on their permitted holdings of stock in individual issuers, may be required to sell the shares of II-VI Common Stock they receive as a result of the Merger. Any such sales of II-VI Common Stock could have the effect of depressing the market price for II-VI Common Stock.

Finisar stockholders may not receive all consideration in the form they elect.

Finisar stockholders that elect to receive Cash Election Consideration or Stock Election Consideration will be subject to proration if holders of Finisar Common Stock, in the aggregate, elect to receive more or less than the aggregate amount of cash consideration or II-VI Common Stock to be paid in the Merger. Accordingly, Finisar stockholders who elect to receive Cash Election Consideration or Stock Election Consideration may instead receive a combination of cash and shares of II-VI Common Stock if necessary to maintain the aggregate mix of consideration described above. The relative proportion of stock and cash that a Finisar stockholder receives may also have a value that is higher or lower than the relative proportion of stock and cash that the Finisar stockholder elected to receive. A discussion of the proration mechanism can be found under the heading “The Merger Agreement — Merger Consideration” beginning on page 140 of this joint proxy statement/prospectus.

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II-VI and Finisar may have difficulty attracting, motivating and retaining executives and other employees in light of the Merger.

Uncertainty about the effect of the Merger on II-VI and Finisar employees may have an adverse effect on II-VI and Finisar and consequently the combined company. This uncertainty may impair II-VI’s and Finisar’s ability to attract, retain and motivate personnel both before and after completion of the Merger. II-VI and Finisar are dependent on the experience and industry knowledge of their officers and other key employees to execute their business plans. The combined company’s success after the Merger will depend in part upon its ability to retain key management personnel and other key employees of II-VI and Finisar. Employee retention may be particularly challenging during the pendency of the Merger, as employees may feel uncertain about their future roles with the combined company. In addition, II-VI and Finisar may have to provide additional compensation in order to retain employees.

If employees of II-VI or Finisar depart because of issues relating to the uncertainty and difficulty of integration or a desire not to become employees of the combined company, the combined company’s ability to realize the anticipated benefits of the Merger could be reduced. II-VI may have to incur significant costs in retaining such individuals or in identifying, hiring and retaining replacements for departing employees and may lose significant expertise and talent relating to the business of Finisar, and II-VI’s ability to realize the anticipated benefits of the Merger may be materially and adversely affected. Accordingly, no assurance can be given that II-VI will be able to attract or retain key employees following the completion of the Merger to the same extent that II-VI or Finisar has been able to attract or retain employees in the past.

II-VI and Finisar will incur significant transaction-related costs in connection with the Merger.

II-VI and Finisar expect to incur a number of non-recurring transaction-related costs associated with completing the Merger, combining the operations of the two companies and achieving desired synergies. These fees and costs will be significant. Non-recurring transaction costs include, but are not limited to, fees paid to legal, financial and accounting advisors, filing fees and printing costs. II-VI will incur significant costs with respect to the financing for the cash consideration to be paid in connection with the Merger. Additional unanticipated costs may be incurred in the integration of the businesses of II-VI and Finisar. There can be no assurance that the elimination of certain duplicative costs, as well as the realization of other efficiencies related to the integration of the two businesses, will offset the incremental transaction-related costs over time. Thus, any net benefit may not be achieved in the near term, the long term or at all.

Failure to successfully combine the businesses of II-VI and Finisar in the expected time frame may adversely affect the future results of the combined company, and, consequently, the value of any II-VI Common Stock that Finisar stockholders receive as part of the Merger Consideration.

The success of the Merger will depend, in part, on the ability of II-VI to realize the anticipated benefits and synergies from combining the businesses of II-VI and Finisar. To realize these anticipated benefits, the businesses must be successfully combined. The combined business’s ability to successfully manage this expanded business will depend, in part, upon management’s ability to implement an effective integration of the two companies and its ability to manage a combined business with significantly larger size and scope with the associated increased costs and complexity. If the combined company is not able to achieve these objectives, or is not able to achieve these objectives on a timely basis, the anticipated benefits of the Merger may not be realized fully or at all. In addition, the actual integration may result in additional and unforeseen expenses, which could reduce the anticipated benefits of the Merger. These integration difficulties could result in declines in the market value of II-VI Common Stock and, consequently, result in declines in the market value of the II-VI Common Stock that Finisar stockholders receive as part of the aggregate Merger Consideration and continue to hold following consummation of the Merger.

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The Merger is subject to conditions, including certain conditions that may not be satisfied, and may not be completed on a timely basis, or at all. Failure to complete the Merger could have material and adverse effects on Finisar and II-VI.

The completion of the Merger is subject to a number of conditions, including the approval of the Share Issuance Proposal by the II-VI shareholders and approval of the Merger Proposal by the Finisar stockholders, which make the completion and timing of the completion of the Merger uncertain. For more information relating to conditions to completion of the Merger, see the section entitled “The Merger Agreement — Conditions to Completion of the Merger” beginning on page 160 of this joint proxy statement/prospectus. Also, either Finisar or II-VI may terminate the Merger Agreement if the Merger has not been completed by November 8, 2019; provided that this termination right is not available to II-VI or Finisar, as applicable, if II-VI’s or Finisar’s, as applicable, failure to comply with the Merger Agreement is a principal cause of or results in the failure of the Merger to occur before November 8, 2019.

If the Merger is not completed on a timely basis, or at all, II-VI’s and Finisar’s respective ongoing businesses may be adversely affected and, without realizing any of the benefits of having completed the Merger, II-VI and Finisar will be subject to a number of risks, including the following:

In addition, if the Merger is not completed, II-VI and/or Finisar may experience negative reactions from the financial markets and from their respective customers and employees. II-VI and/or Finisar could also be subject to litigation related to any failure to complete the Merger or to enforcement proceedings commenced against II-VI or Finisar to perform their respective obligations under the Merger Agreement. If the Merger is not completed, II-VI and Finisar cannot assure their respective security holders that the risks described above will not materialize and will not adversely affect the business, financial results and stock prices of II-VI and/or Finisar.

Lawsuits have been filed against Finisar, the Finisar Board, II-VI, and Merger Sub, and other lawsuits may be filed against Finisar, II-VI, Merger Sub, and/or their respective boards of directors challenging the Merger. An adverse ruling in any such lawsuit may prevent the Merger from being completed.

As of January 17, 2019, six lawsuits have been filed by alleged Finisar stockholders challenging the Merger. The first complaint, a putative class action complaint, was filed by Herbert Hein in the Superior Court of

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California, County of Santa Clara, and is captioned Hein v. Finisar Corporation, et al., 19CV340510. The second complaint, a putative class action complaint, was filed by Pete Tenvold in the United States District Court for the District of Delaware and is captioned Tenvold v. Finisar Corporation, et al., 1:19-cv-00050. The third complaint, a putative class action complaint, was filed by Melvyn Klein in the United States District Court for the Northern District of California and is captioned Klein v. Finisar Corporation, et al., 3:19-cv-00155. The fourth complaint, a putative class action complaint, was filed by Earl Wheby, Jr. in the United States District Court for the District of Delaware and is captioned Wheby v. Finisar Corporation, et al., 1:19-cv-00064. The fifth complaint was filed by Pankaj Sharma individually in the United States District Court for the Northern District of California and is captioned Sharma v. Finisar Corporation, et al., 3:19-cv-00220. The sixth complaint, a putative class action complaint, was filed by William Davis in the United States District Court for the Northern District of California and is captioned Davis v. Finisar Corporation, et al., 3:19-cv-00271.

The complaints name as defendants Finisar and each member of the Finisar Board. In addition, the Hein, Tenvold, and Klein complaints name II-VI and Merger Sub as defendants. The Hein, Tenvold, Klein, Wheby, and Davis complaints seek relief on behalf of a putative class defined as all similarly situated Finisar stockholders.

The Hein complaint alleges that the Finisar Board breached its fiduciary duties to Finisar stockholders by purportedly engaging in an insufficient sales process, obtaining inadequate merger consideration, and filing a materially misleading preliminary proxy statement that does not include, among other things, material information regarding the sales process, financial projections for both Finisar and II-VI, and financial analyses conducted by their financial advisors. The Hein complaint further asserts that II-VI knowingly aided and abetted the Finisar Board in breaching their fiduciary duties to Finisar stockholders by entering into the proposed transaction. The Hein complaint seeks preliminary and permanent injunction of the proposed transaction unless the information requested by the plaintiff is disclosed, rescission and unspecified damages if the Merger is consummated, and attorneys’ fees and expert fees and costs.

The Tenvold, Klein, Wheby, Sharma, and Davis complaints purport to state claims for violations of Section 14(a) and 20(a) of the Exchange Act and Rule 14a-9 and, in the case of the Davis complaint, Regulation G promulgated thereunder. The plaintiffs in these actions generally allege that the preliminary proxy statement omits material information with respect to the proposed transaction which renders the preliminary proxy statement false and misleading. The plaintiffs in these actions seek an order enjoining the defendants from filing a definitive proxy statement with the SEC or otherwise disseminating a definitive proxy statement to Finisar stockholders or proceeding with closing the Merger unless and until the preliminary proxy statement is cured. In the event the Merger is consummated prior to entry of final judgment, the Tenvold, Klein, Wheby, and Sharma complaints seek rescission of the Merger or rescissory damages, and the Tenvold, Klein, Wheby, Sharma, and Davis complaints also seek unspecified damages, attorneys’ and expert fees, and expenses and costs. The defendants believe that the complaints are without merit.

See “The Merger — Litigation Relating to the Merger” beginning on page 137 of this joint proxy statement/prospectus for more information about litigation related to the Merger that has been commenced prior to the date of this joint proxy statement/prospectus. There can be no assurance that additional complaints will not be filed with respect to the Merger.

One of the conditions to completion of the Merger is the absence of any applicable law (including any order) being in effect that prohibits completion of the Merger. Accordingly, if a plaintiff is successful in obtaining an order prohibiting completion of the Merger, then such order may prevent the Merger from being completed, or from being completed within the expected timeframe.

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In order to complete the Merger, II-VI and Finisar must obtain certain governmental authorizations, and if such authorizations are not granted or are granted with conditions that become applicable to the parties, completion of the Merger may be jeopardized or prevented or the anticipated benefits of the Merger could be reduced.

Completion of the Merger is conditioned upon the expiration or early termination of the waiting period relating to the merger under the HSR Act and certain other applicable laws or regulations and the required governmental authorizations having been obtained and being in full force and effect. Although II-VI and Finisar have agreed in the Merger Agreement to use their reasonable best efforts to cause the closing of the Merger to occur, there can be no assurance that the relevant waiting periods will expire or authorizations will be obtained and no assurance that the Merger will be completed.

The Merger Agreement contains provisions that make it difficult for Finisar to pursue alternatives to the Merger.

Under the Merger Agreement, Finisar is subject to certain restrictions with respect to entering into an alternative transaction to the Merger. Unless and until the Merger Agreement is terminated, subject to specified exceptions (which are discussed in more detail in “The Merger Agreement — Termination of the Merger Agreement” beginning on page 161 of this joint proxy statement/prospectus), Finisar has agreed not to, among other things, (i) solicit, initiate or knowingly encourage or facilitate any inquiries, offers or the making of any proposals or announcement that is or would reasonably be excepted to lead to a takeover proposal, (ii) enter into, continue or otherwise participate in any discussions or negotiations with any third party regarding any takeover proposal or any inquiry that would reasonably be excepted to lead to a takeover proposal, (iii) furnish any nonpublic information regarding itself or any of its subsidiaries to any person in connection with a takeover proposal or any inquiry that would reasonably be expected to lead to a takeover proposal, (iv) release or consent to the release of any confidentiality or similar provisions of any agreement that it is a party to, (v) approve any transaction under Section 203 of the DGCL or (vi) enter into a letter of intent, agreement in principle, memorandum of understanding or other agreement contemplating or otherwise relating to a takeover proposal. Additionally, under the Merger Agreement, in the event of a potential change by the Finisar Board of its recommendation with respect to the Merger in light of a superior proposal, Finisar must provide II-VI with three business days’ prior written notice to allow II-VI to propose an adjustment to the terms and conditions of the Merger Agreement. Finisar may terminate the Merger Agreement and enter into an agreement with respect to a superior proposal only if specified conditions have been satisfied, including compliance with the non-solicitation and termination provisions of the Merger Agreement. The parties believe these provisions are reasonable and not preclusive of other offers, but these restrictions might discourage a third party that has an interest in acquiring all or a significant part of Finisar from considering or proposing that acquisition, even if that party were prepared to pay consideration with a higher per share value than the per share Merger Consideration. Furthermore, the termination fees described below may result in a potential competing acquirer proposing to pay a lower per share price to acquire the applicable party than it might otherwise have proposed to pay because of the added expense of the termination fee that may become payable by such party in certain circumstances.

Under the Merger Agreement, Finisar may be required to pay to II-VI a termination fee of $105.2 million if the Merger Agreement is terminated under specified circumstances. If such a termination fee is payable, the payment of this fee could have material and adverse consequences to the financial condition and operations of Finisar. For a discussion of the restrictions on Finisar entering into a takeover proposal or alternative transaction and the Finisar Board’s ability to change its recommendation, see “The Merger Agreement — No Solicitation of Alternative Proposals,” and “The Merger Agreement — Change of Finisar Board Recommendation” beginning on page 151 and page 153 of this joint proxy statement/prospectus, respectively.

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Finisar’s executive officers and directors have interests in the Merger that may be different from, or in addition to, the interests of Finisar’s stockholders generally.

Executive officers of Finisar negotiated the terms of the Merger Agreement with their counterparts at II-VI, and the Finisar Board, by unanimous vote, approved and declared advisable the Merger Agreement and the other transactions contemplated thereby, including the Merger, and determined that the terms of the Merger Agreement, the Merger and the other transactions contemplated thereby are fair to and in the best interests of Finisar and its stockholders. In considering these facts and the other information contained in this joint proxy statement/prospectus, Finisar stockholders should be aware that aside from their interests as stockholders, Finisar’s executive officers and directors may have employment and other compensation arrangements or plans that give them financial interests in the Merger that may be different from, or in addition to, the interests of Finisar stockholders. For a further description of these interests see the section entitled “Interests of Finisar’s Directors and Executive Officers in the Merger” beginning on page 166 of this joint proxy statement/prospectus.

The opinion of Finisar’s financial advisor speaks only as of the date of such opinion and does not reflect changes in events or circumstances that may occur between the original signing of the Merger Agreement and the completion of the Merger.

Consistent with market practices, the Finisar Board has not obtained an updated opinion from its financial advisor as of the date of this joint proxy statement/prospectus and does not expect to receive an updated, revised or reaffirmed opinion prior to the completion of the Merger. The opinion does not speak as of the time the Merger will be completed or as of any date other than the date of such opinion. Changes in the operations and prospects of Finisar or II-VI, general market and economic conditions and other factors which may be beyond the control of Finisar or II-VI and on which Finisar’s financial advisor’s opinion was based, may significantly alter the value of Finisar or II-VI or the price of shares of Finisar Common Stock or shares of II-VI Common Stock by the time the Merger is completed. Because Finisar’s financial advisor will not be updating its opinion, the opinion will not address the fairness of the Merger Consideration from a financial point of view at the time the Merger is completed. For a description of the opinion that Finisar received from its financial advisor, see the section entitled “The Merger — Opinion of Finisar’s Financial Advisor” beginning on page 102 of this joint proxy statement/prospectus.

The opinion rendered to the II-VI Board by its financial advisor, BofA Merrill Lynch, speaks only as of the date of such opinion. BofA Merrill Lynch’s opinion does not reflect changes in events or circumstances after the date of its opinion. II-VI has not obtained, and does not expect to obtain, an updated fairness opinion reflecting changes in circumstances that may have occurred since such date.

On November 8, 2018, at a meeting of the II-VI Board held to evaluate the Merger, BofA Merrill Lynch delivered to the II-VI Board its oral opinion, which was confirmed by delivery of a written opinion dated November 8, 2018, with respect to the fairness, from a financial point of view, of the Merger Consideration to II-VI. Consistent with market practices, the II-VI Board has not obtained an updated opinion from its financial advisor as of the date of this joint proxy statement/prospectus and does not expect to receive an updated, revised or reaffirmed opinion prior to the completion of the Merger. The opinion delivered by BofA Merrill Lynch to the II-VI Board does not speak as of any date other than the date of such opinion. Changes in the operations and prospects of Finisar or II-VI, general market and economic conditions and other factors which may be beyond the control of Finisar or II-VI may have altered since the date of BofA Merrill Lynch’s opinion, and may alter in the future, the values of Finisar or II-VI or the prices of Finisar Common Stock or II-VI Common Stock. BofA Merrill Lynch has no obligation or duty to update its opinion, and II-VI does not expect to obtain an updated fairness opinion, to take into account any such changes. For a summary description of BofA Merrill Lynch’s opinion, see the section entitled “The Merger — Opinion of II-VI’s Financial Advisor” beginning on page 112 of this joint proxy statement/prospectus.

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The closing of the Merger may trigger change in control provisions in certain agreements to which Finisar is a party.

The closing of the Merger may trigger change in control provisions in certain agreements to which Finisar is a party. If Finisar and II-VI are unable to negotiate waivers of those provisions, the counterparties may exercise their rights and remedies under the agreements, potentially terminating the agreements or seeking monetary damages. Even if Finisar and II-VI are able to negotiate waivers, the counterparties may require a fee for such waiver or seek to renegotiate the agreements on terms less favorable to Finisar or the combined company.

Each of Finisar and II-VI is subject to business uncertainties and contractual restrictions while the Merger is pending, which could adversely affect each of Finisar’s and II-VI’s business and operations.

Under the terms of the Merger Agreement, Finisar and II-VI are subject to certain restrictions on the conduct of their respective business prior to completing the Merger, which may adversely affect each party’s ability to execute certain of its business strategies. Such limitations could negatively affect each party’s businesses and operations prior to the completion of the Merger. Furthermore, the process of planning to integrate two businesses and organizations for the post-Merger period can divert management attention and resources and could ultimately have an adverse effect on each of Finisar and II-VI.

In connection with the Merger, parties with which Finisar or II-VI does business may experience uncertainty associated with the Merger, including with respect to current or future business relationships with Finisar, II-VI or the combined business. It is possible that some customers, suppliers and other persons with whom Finisar or II-VI has a business relationship may delay or defer certain business decisions or might decide to seek to terminate, change or renegotiate their relationships with Finisar or II-VI, as applicable, as a result of the Merger, which could negatively affect Finisar’s or II-VI’s revenues, earnings and cash flows, as well as the market price of shares of its common stock, regardless of whether the Merger is completed.

The exchange ratios are fixed and because the market price of II-VI Common Stock and Finisar Common Stock will fluctuate, Finisar stockholders receiving II-VI Common Stock as part of the Merger Consideration cannot be sure of the market value of such Merger Consideration relative to the value of their shares of Finisar Common Stock that they are exchanging.

If the Merger is completed, each share of Finisar Common Stock (other than Dissenting Stockholder Shares and Excluded Shares) will be converted into the right to receive either $26.00 in cash (without any interest thereon), 0.5546 shares of II-VI Common Stock or a combination of $15.60 in cash (without any interest thereon) and 0.2218 shares of II-VI Common Stock (subject to the adjustment and proration procedures described in further detail in the section entitled “The Merger Agreement — Merger Consideration” beginning on page 140 of this joint proxy statement/prospectus). During the pendency of the Merger, the market value of II-VI Common Stock will fluctuate, and decreases in the market value of II-VI Common Stock will negatively affect the value of the Merger Consideration that Finisar stockholders receive. The market value of Finisar Common Stock will also fluctuate during the pendency of the Merger, and increases in the market value of Finisar Common Stock may mean that the Merger Consideration issued to Finisar stockholders will be worth less than the market value of the shares of Finisar Common Stock such stockholders are exchanging. The exchange ratios were fixed at the time the Merger Agreement was executed, and the value of II-VI Common Stock and Finisar Common Stock may vary significantly from their values on the date of the Merger Agreement, the date of this joint proxy statement/prospectus, the date on which II-VI shareholders vote on the Share Issuance Proposal, the date on which Finisar stockholders vote on the Merger Proposal, the date on which Finisar stockholders make their election and the date on which Finisar stockholders receive the applicable Merger Consideration. Neither Finisar nor II-VI is permitted to terminate the Merger Agreement solely due to changes in the market price of either party’s common stock.

There will be a period of time between the date on which Finisar stockholders make an election with respect to the form of Merger Consideration to be received by them in exchange for their Finisar Common Stock and the

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date on which Finisar stockholders actually receive II-VI Common Stock, depending on their election and subject to proration. Fluctuations in the market value of II-VI Common Stock during this time period will also affect the value of the Merger Consideration, once it is actually received.

If a Finisar stockholder elects to receive Stock Election Consideration or Mixed Election Consideration and the market value of II-VI Common Stock falls between the time of the election and the time the applicable Merger Consideration is actually received, the value of the Merger Consideration received may be less than the value of the Merger Consideration such stockholder would have received if they had elected to receive Cash Election Consideration. Conversely, if a Finisar stockholder elects to receive Cash Election Consideration and the market value of II-VI Common Stock rises between the time of the election and the time the applicable Merger Consideration is actually received, the value of the Merger Consideration received may be less than the value of the Merger Consideration such stockholder would have received if they had elected to receive Stock Election Consideration or Mixed Election Consideration. Finisar stockholders are urged to obtain current market quotations for II-VI Common Stock when they make their elections.

The unaudited pro forma financial information included in this joint proxy statement/prospectus may not necessarily reflect the combined company’s operating results and financial condition following the Merger.

The unaudited pro forma condensed combined financial information included in this joint proxy statement/prospectus is derived from II-VI’s and Finisar’s separate historical consolidated financial statements. The preparation of this pro forma information is based upon available information and certain assumptions and estimates that II-VI and Finisar currently believe are reasonable. These assumptions and estimates may not prove to be accurate, and this pro forma financial information does not necessarily reflect what the combined company’s results of operations and financial position would have been had the Merger been completed on the relevant dates assumed and the assumptions and estimates were to prove accurate, or what the combined company’s results of operations or financial position will be in the future.

Finisar’s financial estimates are based on various assumptions that may not prove to be correct.

The financial estimates set forth in the forecast included under “The Merger — Unaudited Prospective Financial Information” are based on assumptions of, and information available to, Finisar at the time they were prepared and provided to the Finisar Board and to Barclays, as Finisar’s financial advisor. Finisar does not know whether the assumptions they made will prove correct. Any or all of such estimates may turn out to be wrong. They can be adversely affected by inaccurate assumptions or by known or unknown risks and uncertainties, many of which are beyond Finisar’s control. Many factors mentioned in this joint proxy statement/prospectus and Finisar’s other filings with the SEC incorporated by reference into this joint proxy statement/prospectus, including the risks outlined in this “Risk Factors” section and in Finisar’s public filings and the events and/or circumstances described under “Cautionary Statement Regarding Forward-Looking Statements” will be important in determining Finisar’s future results. See also, “Where You Can Find More Information.” As a result of these contingencies, actual future results may vary materially from Finisar’s estimates. In view of these uncertainties, the inclusion of Finisar’s financial estimates in this joint proxy statement/prospectus is not and should not be viewed as a representation that the forecasted results will be achieved. These financial estimates are Finisar’s internal financial forecasts and were not prepared with a view toward public disclosure or toward compliance with published guidelines of any regulatory or professional body. Further, any forward-looking statement speaks only as of the date on which it is made, and Finisar undertakes no obligation, other than as required by applicable law, to update its financial estimates herein to reflect events or circumstances after the date those financial estimates were prepared or to reflect the occurrence of anticipated or unanticipated events or circumstances. The financial estimates included in this joint proxy statement/prospectus have been prepared by, and are the responsibility of, Finisar. Moreover, Finisar’s independent auditors, BDO USA, LLP, have not compiled, examined or performed any procedures with respect to Finisar’s prospective financial information contained herein, nor have they expressed any opinion or any other form of assurance on such information or its achievability, and, accordingly, BDO USA, LLP assumes no responsibility for, and disclaims any association

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with, Finisar’s prospective financial information. The reports of BDO USA, LLP incorporated by reference relate exclusively to the historical financial information of the entities named in those reports and do not cover any other information in this joint proxy statement/prospectus and should not be read to do so. See “The Merger — Unaudited Prospective Financial Information” for more information.

II-VI’s financial estimates are based on various assumptions that may not prove to be correct.

The financial estimates set forth in the forecast included under “The Merger — Unaudited Prospective Financial Information” are based on assumptions of, and information available to, II-VI at the time they were prepared and provided to the II-VI Board and to BofA Merrill Lynch, as II-VI’s financial advisor. II-VI does not know whether the assumptions they made will prove correct. Any or all of such estimates may turn out to be wrong. They can be adversely affected by inaccurate assumptions or by known or unknown risks and uncertainties, many of which are beyond II-VI’s control. Many factors mentioned in this joint proxy statement/prospectus and II-VI’s other filings with the SEC incorporated by reference into this joint proxy statement/prospectus, including the risks outlined in this “Risk Factors” section and in II-VI’s public filings and the events and/or circumstances described under “Cautionary Statement Regarding Forward-Looking Statements” will be important in determining II-VI’s future results. See also, “Where You Can Find More Information.” As a result of these contingencies, actual future results may vary materially from II-VI’s estimates. In view of these uncertainties, the inclusion of II-VI’s financial estimates in this joint proxy statement/prospectus is not and should not be viewed as a representation that the forecasted results will be achieved. These financial estimates are II-VI’s internal financial forecasts and were not prepared with a view toward public disclosure or toward compliance with published guidelines of any regulatory or professional body. Further, any forward-looking statement speaks only as of the date on which it is made, and II-VI undertakes no obligation, other than as required by applicable law, to update its financial estimates herein to reflect events or circumstances after the date those financial estimates were prepared or to reflect the occurrence of anticipated or unanticipated events or circumstances. The financial estimates included in this joint proxy statement/prospectus have been prepared by, and are the responsibility of, II-VI. Moreover, II-VI’s independent auditors, Ernst & Young LLP, have not compiled, examined or performed any procedures with respect to II-VI’s prospective financial information contained herein, nor have they expressed any opinion or any other form of assurance on such information or its achievability, and, accordingly, Ernst & Young LLP assumes no responsibility for, and disclaims any association with, II-VI’s prospective financial information. The reports of Ernst & Young LLP incorporated by reference relate exclusively to the historical financial information of the entities named in those reports and do not cover any other information in this joint proxy statement/prospectus and should not be read to do so. See “The Merger — Unaudited Prospective Financial Information” for more information.

Current II-VI shareholders and Finisar stockholders will have a reduced ownership and voting interest in II-VI after the Merger.

Upon the completion of the Merger, each Finisar stockholder who receives consideration in the form of II-VI Common Stock and each II-VI shareholder will have a percentage ownership of II-VI that is smaller than such stockholder’s previous percentage ownership of Finisar or II-VI, as applicable. Based on the number of shares of Finisar Common Stock outstanding as of February 5, 2019, and the number of shares of II-VI Common Stock outstanding as of February 5, 2019, and assuming no adjustment in the number of shares of II-VI Common Stock to be issued as aggregate Merger Consideration in connection with the Merger Agreement, and assuming no conversions of the Finisar Convertible Notes, it is expected that, immediately after completion of the Merger, former holders of Finisar Common Stock and Finisar equity awards will own approximately 29.27% of the outstanding shares of II-VI Common Stock. As a result of these reduced ownership percentages, each of II-VI shareholders and Finisar stockholders, as a group, will have less voting power in, and influence on the board of directors, management and policies of, II-VI following the Merger than they now have in their respective companies.

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The shares of II-VI Common Stock to be received by Finisar stockholders upon completion of the Merger will have different rights from shares of Finisar Common Stock.

Upon completion of the Merger, Finisar stockholders will no longer be stockholders of Finisar, a Delaware corporation, but will instead become shareholders of II-VI, a Pennsylvania corporation. As such, their rights as II-VI shareholders will be governed by Pennsylvania law and the terms of the II-VI Charter, as it may be amended from time to time, and the II-VI By-Laws, as they may be amended from time to time. Pennsylvania law and the terms of the II-VI Charter and the II-VI By-Laws are in some respects materially different than Delaware law and the terms of the Finisar Charter and the Finisar Bylaws, as they may be amended from time to time, which currently govern the rights of Finisar Stockholders. See “Comparison of Shareholders’ Rights” beginning on page 196 of this joint proxy statement/prospectus for a discussion of the different rights associated with shares of Finisar Common Stock and shares of II-VI Common Stock.

No assurance can be provided that II-VI will be able to consummate the II-VI Senior Credit Facilities or obtain alternative financing to fund the cash portion of the aggregate Merger Consideration to be paid in connection with the Merger.

The completion of the Merger is not subject to a financing condition. The receipt of any financing by II-VI is not a condition to completion of the Merger and, except in certain limited circumstances in which II-VI or Finisar may be permitted to terminate the Merger Agreement (as more fully described in “The Merger Agreement — Termination of the Merger Agreement” beginning on page 161 of this joint proxy statement/prospectus), II-VI will be required to complete the Merger (assuming that all of the conditions to its obligations to complete the Merger under the Merger Agreement are satisfied or waived) whether or not financing is available on acceptable terms or at all.

On November 8, 2018, in connection with its entry into the Merger Agreement, II-VI entered into the Commitment Letter, which was subsequently amended and restated on December 7, 2018 and on December 14, 2018. Subject to the terms and conditions set forth in the Commitment Letter, the Lending Parties have severally committed to provide 100% of up to $2.425 billion in aggregate principal amount of the II-VI Senior Credit Facilities, comprised of (i) a “term a” loan facility of up to $1.0 billion, a portion of which will be available after the closing of the Merger on a delayed draw basis, (ii) a “term b” loan facility of up to $975.0 million and (iii) a revolving credit facility of up to $450.0 million. II-VI currently intends to pay the cash portion of the aggregate Merger Consideration and pay related fees and expenses in connection with the Merger using the proceeds of draws under the II-VI Senior Credit Facilities and cash and short-term investments of II-VI and Finisar. II-VI currently does not intend to draw on the revolving credit facility in order to fund the cash portion of the aggregate Merger Consideration.

The commitments of the Lead Arrangers with respect to the II-VI Senior Credit Facilities will automatically terminate at 11:59 p.m., New York City time, on the first to occur of (i) November 8, 2019 (unless the Merger occurs on or prior thereto), (ii) the date of closing of the Merger without the use of proceeds from the II-VI Senior Credit Facilities or (iii) the date on which II-VI delivers written notice to terminate its obligations under the Merger Agreement pursuant to the terms thereof or the date that the Merger Agreement is terminated.

The documentation governing the II-VI Senior Credit Facilities has not been finalized and, accordingly, the actual terms of the II-VI Senior Credit Facilities may differ from those described herein or in the Commitment Letter as a result of the syndication process. Although the debt financing described in this joint proxy statement/prospectus is not subject to a due diligence or “market out,” such financing may not be considered assured. The obligation of the Lead Arrangers to provide the debt financing under the Commitment Letter is subject to a number of conditions. There is a risk that these conditions will not be satisfied and the II-VI Senior Credit Facilities may not be funded when required or at all. As of the date of this joint proxy statement/prospectus, no alternative financing arrangements have been made in the event the II-VI Senior Credit Facilities are not available, and any such alternative financing arrangements may not be available on acceptable terms, or at all, if the II-VI Senior Credit Facilities are not consummated.

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See the section entitled “The Merger — Description of Debt Financing” beginning on page 135 of this joint proxy statement/prospectus.

Risk Factors Relating to the Combined Company Following the Merger

Although II-VI expects that its acquisition of Finisar will result in cost savings, synergies and other benefits, the combined company may not realize those benefits because of integration difficulties and other challenges.

The success of II-VI’s acquisition of Finisar will depend in large part on the success of the management of the combined company in integrating the operations, strategies, technologies and personnel of the two companies following the completion of the Merger. The combined company may fail to realize some or all of the anticipated benefits of the Merger if the integration process takes longer than expected or is more costly than expected. The failure of the combined company to meet the challenges involved in successfully integrating the operations of the two companies or to otherwise realize any of the anticipated benefits of the Merger, including additional cost savings and synergies, could impair the operations of the combined company. In addition, II-VI anticipates that the overall integration of Finisar will be a time-consuming and expensive process that, without proper planning and effective and timely implementation, could significantly disrupt the combined company’s business.

Potential difficulties the combined company may encounter in the integration process include the following:

The anticipated cost savings, synergies and other benefits of the Merger assume a successful integration of the companies and are based on projections and other assumptions, which are inherently uncertain. Even if integration is successful, anticipated cost savings, synergies and other benefits may not be achieved.

The market price of II-VI Common Stock may decline in the future as a result of the Merger.

The market price of II-VI Common Stock may decline in the future as a result of the Merger for a number of reasons, including:

These factors are, to some extent, beyond the control of II-VI. As a consequence, current II-VI shareholders and Finisar stockholders who become holders of II-VI Common Stock after completion of the Merger could lose the value of their investment in II-VI Common Stock.

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The Merger may not be accretive and may cause dilution to the combined company’s earnings per share, which may negatively affect the market price of the II-VI Common Stock.

II-VI currently anticipates that the Merger will be accretive to earnings per share (on an adjusted earnings basis) during the first full calendar year after the Merger. This expectation is based on preliminary estimates which may materially change. The combined company could also encounter additional transaction-related costs or other factors such as the failure to realize all of the benefits anticipated in the Merger. All of these factors could cause dilution to the combined company’s earnings per share or decrease or delay the expected accretive effect of the Merger and cause a decrease in the market price of II-VI Common Stock.

The combined company’s future results will suffer if it does not effectively manage its expanded operations following the Merger.

Following the Merger, the size of the business of the combined company will increase significantly beyond the current size of either II-VI’s or Finisar’s current businesses. The combined company’s future success depends, in part, upon its ability to manage this expanded business, which may pose substantial challenges for management, including challenges related to the management and monitoring of new operations and associated increased costs and complexity. There can be no assurance that the combined company will be successful or that it will realize the expected operating efficiencies, cost savings, revenue enhancements and other benefits currently anticipated from the Merger.

II-VI and Finisar face competition, which is expected to intensify and which may reduce the market share and profits of II-VI after consummation of the Merger.

Competition in the industries in which II-VI and Finisar operate is intense. Increased competition could hurt II-VI’s and Finisar’s businesses, hinder their market share expansion and lead to pricing pressures that may adversely impact their margins and revenues. If the combined company is unable to successfully compete following the Merger, its business, prospects, liquidity, financial condition and results of operations could be materially and adversely affected.

Following the consummation of the Merger, the combined company’s competitive position could be weakened by strategic alliances or consolidation within the combined company’s industries or the development of new technologies by competitors. The combined company’s ability to compete successfully will depend on how well it markets its products and services and on its ability to anticipate and respond to various competitive factors affecting its industries, including changes in customer preferences, and changes in the product offerings or pricing strategies of the combined company’s competitors.

After the consummation of the Merger, competition could materially adversely affect the combined company in several ways, including (i) the loss of customers and market share, (ii) the combined company’s need to lower prices or increase expenses to remain competitive and (iii) the loss of business relationships within II-VI’s existing markets.

II-VI is expected to incur substantial expenses related to the Merger and integration.

II-VI is expected to incur substantial expenses in connection with the Merger and the related integration. There are a large number of processes, policies, procedures, operations, technologies and systems that may need to be integrated, including purchasing, accounting and finance, sales, payroll, pricing and benefits.

While II-VI has assumed that a certain level of expenses will be incurred, there are many factors beyond its control that could affect the total amount or the timing of the integration expenses. Moreover, many of the expenses that will be incurred are, by their nature, difficult to estimate accurately. These expenses could, particularly in the near term, exceed the savings that II-VI expects to achieve from the elimination of duplicative expenses and the realization of economies of scale and cost savings. These integration expenses likely will result

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in the combined company taking significant charges against earnings following the completion of the Merger, and the amount and timing of such charges are uncertain at present.

Following the consummation of the Merger, II-VI will be bound by all of the obligations and liabilities of both companies.

Following the consummation of the Merger, the combined company will become bound by all of the obligations and liabilities of Finisar in addition to II-VI’s obligations and liabilities existing prior to the consummation of the Merger. Neither II-VI nor Finisar can predict the financial condition of the combined company at the time of the combination or the ability of the combined company to satisfy its obligations and liabilities.

The Merger may result in a loss of suppliers and strategic alliances and may result in the termination of existing contracts.

Following the Merger, some of the suppliers of II-VI or Finisar, as historical businesses, may terminate or scale back their business relationship with the combined company. II-VI and Finisar have contracts with suppliers, vendors, and other business partners which may require II-VI or Finisar to obtain consents from these other parties in connection with the Merger, which may not be obtained at all or on favorable terms. If supplier relationships or strategic alliances are adversely affected by the Merger, or if the combined company, following the Merger, loses the benefits of the contracts of II-VI or Finisar, the combined company’s business and financial performance could suffer.

Following the Merger, the combined company will have a substantial amount of debt, which could adversely affect its business, financial condition or results of operations and prevent it from fulfilling its debt-related obligations.

Following the Merger, the combined company will have a substantial amount of debt. As of September 30, 2018, on a pro forma basis, the combined company would have had approximately $2.2 billion of outstanding debt (including under its outstanding debt securities and borrowings under II-VI’s credit facilities). The combined company’s substantial debt could have important consequences for the holders of II-VI Common Stock, including:

The combined company may not generate sufficient cash flow from operations, together with any future borrowings, to enable the combined company to pay its indebtedness, or to fund the combined company’s other

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liquidity needs. The combined company may need to refinance all or a portion of its indebtedness, on or before its maturity. The combined company may not be able to refinance any of its indebtedness on commercially reasonable terms or at all. The combined company may not be able to pay the repurchase price on the 2033 Notes and 2036 Notes to the extent holders elect to exercise their repurchase rights in December 2023 and 2028 with respect to the 2033 Notes and December 2026 and 2031 with respect to the 2036 Notes. In addition, the combined company may incur additional indebtedness in order to finance its operations, to fund acquisitions, or to repay existing indebtedness. If the combined company cannot service its indebtedness, it may have to take actions such as selling assets, seeking additional debt or equity or reducing or delaying capital expenditures, strategic acquisitions, investments and alliances. Any such actions, if necessary, may not be able to be effected on commercially reasonable terms or at all, or on terms that would be advantageous to the combined company’s stockholders or on terms that would not require II-VI to breach the terms and conditions of its existing or future debt agreements.

Other Risk Factors Relating to II-VI and Finisar

As a result of entering into the Merger Agreement, II-VI’s and Finisar’s businesses are and will be subject to the risks described above. In addition, II-VI and Finisar are, and following completion of the Merger, the combined company will continue to be, subject to the risks described in II-VI’s Annual Report on Form 10-K for the fiscal year ended June 30, 2018 and Finisar’s Annual Report on Form 10-K for the fiscal year ended April 29, 2018, each as updated by subsequent Quarterly Reports on Form 10-Q and Current Reports on Form 8-K, all of which are filed with the SEC and incorporated by reference into this joint proxy statement/prospectus. For the location of information incorporated by reference, see “Where You Can Find More Information.”

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CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS

Information set forth, and the documents to which Finisar and II-VI refer you, in this registration statement, of which this joint proxy statement/prospectus forms a part, including financial estimates and statements as to the expected timing, completion and effects of the transactions between II-VI and Finisar, constitute “forward-looking statements” within the meaning of the safe harbor provisions of the Private Securities Litigation Reform Act of 1995 and the rules, regulations and releases of the SEC. These forward-looking statements are subject to risks and uncertainties, and actual results might differ materially from those discussed in, or implied by, the forward-looking statements. Such forward-looking statements include, but are not limited to, statements about the benefits of the transactions, including future financial and operating results, the combined company’s plans, objectives, expectations and intentions, and other statements that are not historical facts. Such statements are based on the current beliefs and expectations of the management of Finisar and II-VI and are subject to significant risks and uncertainties outside of our control.

Statements included in or incorporated by reference into this registration statement, of which this joint proxy statement/prospectus forms a part, that are not historical facts, including statements about the beliefs and expectations of the managements of Finisar and II-VI, are forward-looking statements within the meaning of the federal securities laws, including Section 27A of the Securities Act and Section 21E of the Exchange Act. In this context, forward-looking statements often address expected future business and financial performance and financial condition, and often contain words such as “expect,” “anticipate,” “intend,” “plan,” “believe,” “seek,” “see,” “will,” “would,” “target,” similar expressions, and variations or negatives of these words. Forward-looking statements by their nature address matters that are, to different degrees, uncertain, such as statements about the consummation of the proposed transaction and the anticipated benefits thereof. These and other forward-looking statements are not guarantees of future results and are subject to risks, uncertainties and assumptions that could cause actual results to differ materially from those expressed in any forward-looking statements, including the failure to consummate the proposed transaction or to make any filing or take other action required to consummate such transaction in a timely manner or at all, are not guarantees of future results and are subject to risks, uncertainties and assumptions that could cause actual results to differ materially from those expressed in any forward-looking statements. Important factors that may cause such a difference include, but are not limited to: (i) the ability of II-VI and Finisar to complete the proposed transaction on the anticipated terms and timing or at all, (ii) the ability of the parties to satisfy the conditions to the closing of the proposed transaction, including obtaining required regulatory approvals, (iii) potential litigation relating to the proposed transaction, which could be instituted against II-VI, Finisar or their respective directors, (iv) potential adverse reactions or changes to business relationships resulting from the announcement or completion of the transaction, (v) the triggering of any third party contracts containing consent and/or other similar provisions, (vi) any negative effects of the announcement of the transaction on the market price of Finisar Common Stock and/or negative effects of the announcement or commencement of the transaction on the market price of II-VI Common Stock, (vii) the decisions of holders of the Finisar Convertible Notes with respect to whether to convert their notes, require Finisar to repurchase their notes or continue holding their notes until maturity or until they are otherwise redeemed pursuant to the terms of the applicable Indenture, (viii) uncertainty as to the long-term value of II-VI Common Stock, and thus the value of the II-VI shares to be issued in the transaction, (ix) any unexpected impacts from unforeseen liabilities, future capital expenditures, revenues, expenses, earnings, synergies, economic performance, indebtedness, financial condition and losses on the future prospects, business and management strategies for the management, expansion and growth of the combined company’s operations after the consummation of the transaction and on the other conditions to the completion of the Merger, (x) inherent risks, costs and uncertainties associated with integrating the businesses successfully and achieving all or any of the anticipated synergies, (xi) potential disruptions from the proposed transaction that may harm II-VI’s or Finisar’s respective businesses, including current plans and operations, (xii) the ability of II-VI and Finisar to retain and hire key personnel, (xiii) adverse legal and regulatory developments or determinations or adverse changes in, or interpretations of, U.S. or foreign laws, rules or regulations, that could delay or prevent completion of the proposed transaction or cause the terms of the proposed transaction to be modified, (xiv) the ability of II-VI to obtain or consummate financing or refinancing related to the transaction upon acceptable terms or at all,

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