UNITED STATES 
                  SECURITIES AND EXCHANGE COMMISSION 
                        Washington, D.C. 20549 
                                    
                                    
                             SCHEDULE 13G 
                                    
               Under the Securities Exchange Act of 1934 
                                    
                                    
                          (Amendment No. 1)* 
                                    
                                    
                           Finisar Corporation 
                             (Name of Issuer) 
                                      
                               Common Stock 
                      (Title of Class of Securities) 
                                      
                                31787A507 
                              (CUSIP Number) 
                                    
                            December 29, 2017 
         (Date of Event Which Requires Filing of this Statement) 
                                    
                                    
Check the appropriate box to designate the rule pursuant to which this 
Schedule is filed: 
[X] Rule 13d-1(b) 
[ ] Rule 13d-1(c) 
[ ] Rule 13d-1(d) 
 
 
*The remainder of this cover page shall be filled out for a reporting 
person's initial filing on this form with respect to the subject class 
of securities, and for any subsequent amendment containing information 
which would alter the disclosures provided in a prior cover page. 
 
The information required in the remainder of this cover page shall not 
be deemed to be "filed" for the purpose of Section 18 of the Securities 
Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of 
that section of the Act but shall be subject to all other provisions of 
the Act (however, see the Notes). 
                                    
                                    
                                    















CUSIP: 31787A507                                                Page 1 of 4 
<Page> 

                                    
 1   NAMES OF REPORTING PERSONS 
     I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY) 
     SMALLCAP World Fund, Inc.  
      
      
 2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE          
     INSTRUCTIONS)                                                 (a)     
                                                                      
                                                                    (b)     
 3   SEC USE ONLY 
      
      
 4   CITIZENSHIP OR PLACE OF ORGANIZATION 
      
     Maryland 

             5   SOLE VOTING POWER 
                   
                  NONE 

       
             6   SHARED VOTING POWER 
 NUMBER OF         
   SHARES         NONE 
BENEFICIALL        
 Y OWNED BY 
             7   SOLE DISPOSITIVE POWER 
    EACH           
 REPORTING        NONE 
   PERSON 
   WITH: 
             8   SHARED DISPOSITIVE POWER 
                   
                  NONE 
                   
 9   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 
      
     1,850,500          See Additional information in Item 4.  
     Under certain circumstances, SMALLCAP World Fund, Inc. may vote the 
     shares of the fund.  These shares may also be reflected in a filing 
     made by Capital Research Global Investors, Capital International 
     Investors, and/or Capital World Investors. 
 10  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES 
     (SEE INSTRUCTIONS) 
      
      
 11  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 
      
     1.6%   

 12  TYPE OF REPORTING PERSON (SEE INSTRUCTIONS) 
      
     IV   

 





CUSIP: 31787A507                                                Page 2 of 4 
<Page> 

                  SECURITIES AND EXCHANGE COMMISSION 
                         Washington, DC 20549 
                                    
                             Schedule 13G 
               Under the Securities Exchange Act of 1934 
                                    
Amendment No. 1 
 
Item 1(a)     Name of Issuer: 
       Finisar Corporation 
 
Item 1(b)     Address of Issuer's Principal Executive Offices: 
       1389 Moffett Park Drive 
       Sunnyvale, CA 94089 
        
Item 2(a)     Name of Person(s) Filing: 
       SMALLCAP World Fund, Inc. 
        
Item 2(b)     Address of Principal Business Office or, if none, 
       Residence: 
       6455 Irvine Center Drive 
       Irvine, California 92618-4518 
        
Item 2(c)     Citizenship:   N/A 
        
Item 2(d)     Title of Class of Securities: 
       Common Stock 
        
Item 2(e)     CUSIP Number: 
       31787A507 
        
Item 3     If this statement is filed pursuant to sections 240.13d-1(b) 
       or 240.13d-2(b) or (c), check whether the person filing is a:  
        (d)     [X]     Investment company registered under section 8 
            of the Investment Company Act of 1940 (15 U.S.C. 80a-8). 
        
Item 4     Ownership 
        
       Provide the following information regarding the aggregate 
       number and percentage of the class of securities of the issuer 
       identified in Item 1. 
        
        
       (a)    Amount beneficially owned: 
       (b)    Percent of class: 
       (c)    Number of shares as to which the person has: 
       (i)    Sole power to vote or to direct the vote: 
       (ii)   Shared power to vote or to direct the vote: 
       (iii)  Sole power to dispose or to direct the disposition of: 
       (iv)   Shared power to dispose or to direct the disposition of: 
        
       See page 2  
        
       SMALLCAP World Fund, Inc., an investment company registered 
       under the Investment Company Act of 1940, which is advised by 
       Capital Research and Management Company ("CRMC"), is the 
       beneficial owner of 1,850,500 shares or 1.6% of the 114,024,083 
       shares believed to be outstanding.  CRMC manages equity assets 
       for various investment companies through three divisions, 
       Capital Research Global Investors, Capital World Investors, and 
CUSIP: 31787A507                                                Page 3 of 4 
<Page>        Capital International Investors. These divisions generally 
       function separately from each other with respect to investment 
       research activities and they make investment decisions and 
       proxy voting decisions for the investment companies on a 
       separate basis. 
        
Item 5     Ownership of Five Percent or Less of a Class.  If this 
       statement is being filed to report the fact that as of the date 
       hereof the reporting person has ceased to be the beneficial 
       owner of more than five percent of the class of securities, 
       check the following: [X] 
        
Item 6     Ownership of More than Five Percent on Behalf of Another 
       Person: N/A 
        
Item 7     Identification and Classification of the Subsidiary Which 
       Acquired the Security Being Reported on By the Parent Holding 
       Company or Control Person: N/A 
        
Item 8     Identification and Classification of Members of the Group:  
       N/A 
        
Item 9     Notice of Dissolution of Group:  N/A 
        
Item 10     Certification 
        
       By signing below, I certify that, to the best of my knowledge 
       and belief, the securities referred to above were acquired and 
       are held in the ordinary course of business and were not 
       acquired and are not held for the purpose of or with the effect 
       of changing or influencing the control of the issuer of the 
       securities and were not acquired and are not held in connection 
       with or as a participant in any transaction having that purpose 
       or effect. 
        
     Signature 
        
       After reasonable inquiry and to the best of my knowledge and 
       belief, I certify that the information set forth in this 
       statement is true, complete and correct. 
 
        Date:          February 6, 2018 
                        
        Signature:     /s/ Michael W. Stockton 
        Name/Title:    Michael W. Stockton - Secretary 
                       SMALLCAP World Fund, Inc. 
 
        
        
        
                
                
                
        
           
                
                



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