111111
`
`1111111111111111111111111111111111111111111111111111111111111
`US008089683B2
`
`c12) United States Patent
`Holmes
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 8,089,683 B2
`Jan.3,2012
`
`(54) OPTICAL PROCESSING
`
`(75)
`
`Inventor: Melanie Holmes, Consett (GB)
`
`(73) Assignee: Thomas Swan & Co. Ltd., Durham
`(GB)
`
`( *) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 196 days.
`
`(21) Appl. No.: 11/978,258
`
`(22) Filed:
`
`Oct. 29, 2007
`
`(65)
`
`Prior Publication Data
`
`US 2008/0145053 Al
`
`Jun. 19,2008
`
`Related U.S. Application Data
`
`(60)
`
`Continuation of application No. 11/515,389, filed on
`Sep. 1, 2006, now Pat. No. 7,612,930, which is a
`division of application No. 10/487,810, filed as
`application No. PCT/GB02/04011 on Sep. 2, 2002,
`now Pat. No. 7,145,710.
`
`(30)
`
`Foreign Application Priority Data
`
`Sep. 3, 2001
`
`(GB) ................................... 0121308.1
`
`(51)
`
`Int. Cl.
`G02F 1101
`G02B 27110
`G02B 6142
`H04J 14102
`(52) U.S. Cl.
`
`(2006.01)
`(2006.01)
`(2006.01)
`(2006.01)
`359/279; 359/618; 359/9; 359/11;
`398/79; 398/45; 398/82; 398/83; 385/15;
`385/16; 385/18; 385/24; 385/27; 349/196
`
`(58) Field of Classification Search .......... 359/290-295,
`359/22, 279, 341.41, 349, 494, 495, 497,
`359/498, 487, 558, 618, 337.21; 398/43-50,
`398/59,72,79,82,83, 176, 182, 183, 141,
`398/195, 202, 203, 208, 209; 385/15-18,
`385/22, 24, 27, 33, 50, 125; 349/196; 250/227.23;
`372/18, 20, 32
`See application file for complete search history.
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`3,773,401 A
`1111973 Douklias et al.
`(Continued)
`
`EP
`
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`1112000
`(Continued)
`
`OTHER PUBLICATIONS
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`Yamazaki, H., eta!., "4 x 4 Free Space Optical Switching Using
`Real-Time Binary Phase-Only Holograms Generated by a Liquid(cid:173)
`Crystal Display," Optical Society of America, 16(18):1415-1417
`(1991).
`
`(Continued)
`
`Primary Examiner- Loha Ben
`(74) Attorney, Agent, or Firm- Hamilton, Brook, Smith &
`Reynolds, P.C.
`
`ABSTRACT
`(57)
`A modular routing node includes a single input port and a
`plurality of output ports. The modular routing node is
`arranged to produce a plurality of different deflections and
`uses small adjustments to compensate for wavelength differ(cid:173)
`ences and alignment tolerances in an optical system. An opti(cid:173)
`cal device is arranged to receive a multiplex of many optical
`signals at different wavelengths, to separate the optical sig(cid:173)
`nals into at least two groups, and to process at least one of the
`groups adaptively.
`
`44 Claims, 36 Drawing Sheets
`
`FNC 1001
`
`

`

`US 8,089,683 B2
`Page 2
`
`U.S. PATENT DOCUMENTS
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`9/2002 Jenkins et al . .................. 359/11
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`3/2003 Peng eta!.
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`4/2003 Rotolo eta!. ................... 398/68
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`4/2003 Street eta!. ..................... 385/18
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`4/2003 Hare! et al . ..................... 385/18
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`5/2003 Sauer eta!. ..................... 398/79
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`6,577,417 B1 *
`6/2003 Khoury ........................... 398/82
`6,583,901 B1*
`6/2003 Hung .............................. 398/79
`6,594,082 B1
`7/2003 Li eta!.
`6,603,894 B1 *
`8/2003 Pu ................................... 385/18
`6,654,516 B2 * 1112003 So ................................... 385/27
`12/2003 Maromet al.
`6,657,770 B2
`3/2004 Ducellier et al.
`6,707,959 B2
`6,710,292 B2
`3/2004 Fukuchi et a!.
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`5/2004 Mar om
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`6,795,182 B2
`6,804,428 B1
`10/2004 Garrett et a!.
`6,813,408 B2 * 1112004 Bortolini ......................... 385/17
`6,842,549 B2 *
`112005 So ................................... 385/15
`6,879,426 B1
`4/2005 Weiner
`6,920,261 B2 *
`7/2005 Inada et al . ..................... 385/24
`
`6,950,609 B2
`6,954,252 B1
`6,975,786 B1
`6,990,268 B2 *
`7,079,723 B2 *
`7,113,702 B2 *
`7,127,168 B2 *
`7,151,601 B2
`7,177,496 B1
`7,436,588 B2 *
`7,536,108 B2 *
`7,796,319 B2
`200110050787 A1
`2002/0060760 A1
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`2007/0035803 A1
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`
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`1112007 Holmes
`
`EP
`EP
`wo
`wo
`wo
`wo
`wo
`
`FOREIGN PATENT DOCUMENTS
`1 207 418 A1
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`mable Holographic Elements, lEE Colloquim on Multiwavelength
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`1472-1473 .
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`ing Using Real-Time Binary Phase-Only Holograms Generated by a
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`
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`WDM Channels at 50 Ghz Spacing," OFC Postdeadline Paper, pp .
`FB7-1-FB7-3 (Mar. 2002).
`* cited by examiner
`
`

`

`U.S. Patent
`
`Jan.3,2012
`
`Sheet 1 of 36
`
`US 8,089,683 B2
`
`225
`
`223
`222
`
`221
`
`20111
`
`224
`
`230
`
`26~
`
`200/
`
`FIG. 1
`
`

`

`U.S. Patent
`US. Patent
`
`Jan. 3, 2012
`Jan.3,2012
`
`Sheet 2 of 36
`Sheet 2 of 36
`
`US 8,089,683 B2
`US 8,089,683 B2
`
`4
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`3
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`
`FIG. 2
`FIG. 2
`
`

`

`U.S. Patent
`US. Patent
`
`Jan.3,2012
`Jan. 3, 2012
`
`Sheet 3 of 36
`Sheet 3 of 36
`
`US 8,089,683 B2
`US 8,089,683 B2
`
`27
`27
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`
`FIG. 3
`FIG. 3
`
`

`

`U.S. Patent
`US. Patent
`
`Jan. 3, 2012
`Jan.3,2012
`
`Sheet 4 of 36
`Sheet 4 of 36
`
`US 8,089,683 B2
`US 8,089,683 B2
`
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`FIG. 4
`
`

`

`U.S. Patent
`US. Patent
`
`Jan.3,2012
`Jan. 3, 2012
`
`Sheet 5 of 36
`Sheet 5 of 36
`
`US 8,089,683 B2
`US 8,089,683 B2
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`FIG. 5
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`

`

`U.S. Patent
`US. Patent
`
`Jan.3,2012
`Jan. 3, 2012
`
`Sheet 6 of 36
`Sheet 6 of 36
`
`US 8,089,683 B2
`US 8,089,683 B2
`
`48
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`

`

`U.S. Patent
`US. Patent
`
`Jan.3,2012
`Jan. 3, 2012
`
`Sheet 7 of 36
`Sheet 7 of 36
`
`US 8,089,683 B2
`US 8,089,683 B2
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`

`

`U.S. Patent
`
`Jan.3,2012
`
`Sheet 8 of 36
`
`US 8,089,683 B2
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`

`U.S. Patent
`US. Patent
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`Jan.3,2012
`Jan. 3, 2012
`
`Sheet 9 of 36
`Sheet 9 of 36
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`US 8,089,683 B2
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`U.S. Patent
`
`Jan.3,2012
`
`Sheet 10 of 36
`
`US 8,089,683 B2
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`IMAGINARY
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`

`

`U.S. Patent
`US. Patent
`
`Jan.3,2012
`Jan. 3, 2012
`
`Sheet 11 of 36
`Sheet 11 of 36
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`US 8,089,683 B2
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`Jan.3,2012
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`Sheet 12 of 36
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`U.S. Patent
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`Jan.3,2012
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`Sheet 13 of 36
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`US 8,089,683 B2
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`U.S. Patent
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`Jan.3,2012
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`Sheet 14 of 36
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`US 8,089,683 B2
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`U.S. Patent
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`Jan.3,2012
`Jan. 3, 2012
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`Sheet 15 of 36
`Sheet 15 of 36
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`US 8,089,683 B2
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`Jan. 3, 2012
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`Sheet 16 of 36
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`US 8,089,683 B2
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`U.S. Patent
`
`Jan. 3, 2012
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`Sheet 17 of 36
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`

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`U.S. Patent
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`Jan.3,2012
`Jan. 3, 2012
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`U.S. Patent
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`Jan.3,2012
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`Sheet 21 of 36
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`US 8,089,683 B2
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`U.S. Patent
`
`Jan.3,2012
`
`Sheet 22 of 36
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`US 8,089,683 B2
`
`{A-2, A-5, A-13, A-20}
`{A. 1, A-3, A-17}
`
`-"-,
`
`"" -
`
`"" ,..
`
`{A-7, A 19, A-37}
`
`•
`
`• .
`
`. • . . . . .
`
`{A-1, A-2, A-3 ...... . ... A.N}
`,
`
`_.lio.
`
`FIG. 21
`
`

`

`U.S. Patent
`US. Patent
`
`Jan. 3, 2012
`Jan.3,2012
`
`Sheet 23 of 36
`Sheet 23 of 36
`
`US 8,089,683 B2
`US 8,089,683 B2
`
`661
`
`.------. 662
`662
`666
`666
`667
`667
`
`671
`671
`675
`675
`676
`
`677
`
`660
`
`670
`
`663 664 665 672 673 67 4
`663 664 665 672 673 674
`
`FIG. 22
`FIG. 22
`
`

`

`U.S. Patent
`US. Patent
`
`Jan. 3, 2012
`Jan.3,2012
`
`Sheet 24 of 36
`Sheet 24 of 36
`
`US 8,089,683 B2
`US 8,089,683 B2
`
`720 722
`720
`722
`
`733 734
`733 734
`
`730
`730
`
`721
`
`751
`
`724
`
`753
`
`FIG. 23
`
`__)
`
`731
`
`•
`
`732
`
`
`
`

`

`U.S. Patent
`US. Patent
`
`Jan. 3, 2012
`Jan.3,2012
`
`Sheet 25 of 36
`Sheet 25 of 36
`
`US 8,089,683 B2
`US 8,089,683 B2
`
`762
`762
`
`763
`
`764
`
`770
`
`773
`
`768
`
`
`
`774
`
`772
`
`766
`766
`
`765
`765
`
`771
`
`FIG. 24
`FIG. 24
`
`

`

`U.S. Patent
`
`Jan.3,2012
`
`Sheet 26 of 36
`
`US 8,089,683 B2
`
`794
`
`794o
`
`795
`
`795o
`
`796
`
`796o
`
`797
`
`797o
`
`o1 o2
`
`o4
`
`790
`
`790iJ
`
`791
`
`791 i _}
`
`..
`
`..
`
`792 ..
`
`792i.J
`
`793
`
`)lo
`
`793iJ
`
`FIG. 25
`
`

`

`U.S. Patent
`U.S. Patent
`
`Jan. 3, 2012
`Jan.3,2012
`
`Sheet 27 of 36
`Sheet 27 of 36
`
`US 8,089,683 B2
`US 8,089,683 B2
`
`862
`862
`
`
`
`880
`
`881
`
`882
`883
`
`884
`
`861
`
`863
`
`864
`
`865
`
`870
`
`866
`866
`
`FIG. 26
`FIG. 26
`
`

`

`U.S. Patent
`
`Jan.3,2012
`
`Sheet 28 of 36
`
`US 8,089,683 B2
`
`Cr.WHcL
`
`501
`
`500
`
`502
`
`FIG. 27
`
`

`

`620
`
`621
`' 616 617
`
`615
`
`_...-600
`
`623
`
`~
`00
`•
`~
`~
`~
`
`~ = ~
`
`~
`
`~ :=
`
`(.H
`
`~
`
`N
`
`0 ....
`
`N
`
`p---------~--.1~1~ I I ~~t=~~~
`
`611
`
`636
`635
`637
`
`- ---:1 622
`
`('D
`('D
`
`rFJ =(cid:173)
`.....
`N
`\0
`0 .....
`(.H
`0\
`
`ADDRESSING
`OPTICS
`
`1..
`
`.. 1..
`
`ROUTING OPTICS
`
`.. I
`
`FIG. 28
`
`d
`rJl
`
`\C
`0..,
`
`00 = 00
`00 w = N
`
`

`

`1700
`
`1721
`
`:~J 1722
`
`,G---2~1
`1701
`---
`n--- ~
`1712
`-- ---
`1702
`G---~~3-
`1703
`---- _.
`1714
`17040-----~-- -- ,.
`
`I
`
`I
`
`FIG. 29
`
`~
`00
`•
`~
`~
`~
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`~ = ~
`
`~
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`~ :=
`
`(.H
`
`~
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`N
`
`0 ....
`
`N
`
`('D
`('D
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`rFJ =(cid:173)
`.....
`(.H
`0
`0 .....
`(.H
`0\
`
`d
`rJl
`
`\C
`0..,
`
`00 = 00
`00 w = N
`
`

`

`U.S. Patent
`US. Patent
`
`Jan. 3, 2012
`Jan.3,2012
`
`Sheet 31 of 36
`Sheet 31 of 36
`
`US 8,089,683 B2
`US 8,089,683 B2
`
`900-.....,...
`
`928
`928
`(
`
`\
`911
`915
`917
`
`915
`911
`912
`916
`918
`
` 918
`916
`912
`
`923
`919 920
`907
`
`902
`
`901
`
`
`901
`902
`919 920
`907
`923
`
`910
`924
`904
`921 922
`903
`903
`904
`921
`922
`910
`924
`92?-1-- ~
`
`913
`913
`
`914
`914
`
`~ ~ 929
`if
`
`FIG. 30
`FIG. 30
`
`
`
`927
`
`~ ~ ~
`
`
`926
`925
`906
`905
` 906
` 926
` 905
`925
`
`

`

`U.S. Patent
`US. Patent
`
`Jan. 3, 2012
`Jan.3,2012
`
`Sheet 32 of 36
`Sheet 32 of 36
`
`US 8,089,683 B2
`US 8,089,683 B2
`
`
`
`941
`
`942 945
`
`~
`944
`
`FIG. 31
`FIG. 31
`
`

`

`U.S. Patent
`U.S. Patent
`
`Jan. 3, 2012
`Jan.3,2012
`
`Sheet 33 of 36
`Sheet 33 of 36
`
`US 8,089,683 B2
`US 8,089,683 B2
`
`
`
`964
`964
`
`FIG. 32
`FIG. 32
`
`

`

`U.S. Patent
`US. Patent
`
`Jan.3,2012
`Jan. 3, 2012
`
`Sheet 34 of 36
`Sheet 34 of 36
`
`US 8,089,683 B2
`US 8,089,683 B2
`
`975
`
`970
`
`
`
`972
`972
`
`971
`
`973
`
`974:
`974
`
`FIG. 33
`FIG. 33
`
`

`

`U.S. Patent
`US. Patent
`
`Jan.3,2012
`Jan. 3, 2012
`
`Sheet 35 of 36
`Sheet 35 of 36
`
`US 8,089,683 B2
`US 8,089,683 B2
`
`980
`
`985
`
`986
`
`987
`
`982
`
`
`
`983
`
`981
`
`FIG. 34
`FIG. 34
`
`

`

`U.S. Patent
`US. Patent
`
`Jan.3,2012
`Jan. 3, 2012
`
`Sheet 36 of 36
`Sheet 36 of 36
`
`US 8,089,683 B2
`US 8,089,683 B2
`
`990
`990
`. .............................................................................................. .
`1.0 ................................................................
`994
`0.9 ............................................................................................................................................................... .
`0.8 .................................................................................................................................................................. .
`0.7 ............................................................................................................................................................. .
`995
`0.6 ..................................................................................... "" .................................................................. .
`
`
`
`FIG. 35
`FIG. 35
`
`

`

`US 8,089,683 B2
`
`1
`OPTICAL PROCESSING
`
`RELATED APPLICATIONS
`
`This application is a continuation of U.S. application Ser.
`No. 11/515,389, filed Sep. 1, 2006, now issued U.S. Pat. No.
`7,612,930, which is a divisional ofU.S. application Ser. No.
`10/487,810, filed Sep. 10, 2004 now issued U.S. Pat. No.
`7,145,710, which is the U.S. National Stage oflnternational
`Application No. PCT/GB02/04011, filed Sep. 2, 2002, and
`published in English. This application claims priority under
`35 U.S.C. §119 or 365 to Great Britain Application No.
`0121308.1, filed Sep. 3, 2001. The entire teachings of the
`above application(s) are incorporated herein by reference.
`
`FIELD OF THE INVENTION
`
`The present invention relates to an optical device and to a
`method of controlling an optical device.
`More particularly but not exclusively the invention relates
`to the general field of controlling one or more light beams by
`the use of electronically controlled devices. The field of appli(cid:173)
`cation is mainly envisaged as being to fields in which recon(cid:173)
`figuration between inputs and outputs is likely, and stability
`of performance is a significant requirement.
`
`BACKGROUND OF THE INVENTION
`
`It has previously been proposed to use so-called spatial
`light modulators to control the routing oflight beams within 30
`an optical system, for instance from selected ones of a number
`of input optical fibres to selected ones of output fibres.
`Optical systems are subject to performance impairments
`resulting from aberrations, phase distortions and component
`misaligmnent. An example is a multiway fibre connector,
`which although conceptually simple can often be a critical
`source of system failure or insertion loss due to the very tight
`aligmnent tolerances for optical fibres, especially for single(cid:173)
`mode optical fibres. Every time a fibre connector is con(cid:173)
`nected, it may provide a different alignment error. Another
`example is an optical switch in which aberrations, phase
`distortions and component misalignments result in poor opti(cid:173)
`cal coupling efficiency into the intended output optical fibres.
`This in turn may lead to high insertion loss. The aberrated
`propagating waves may diffract into intensity fluctuations
`creating significant unwanted coupling of light into other
`output optical fibres, leading to levels of crosstalk that impede
`operation. In some cases, particularly where long path lengths
`are involved, the component misalignment may occur due to
`ageing or temperature effects.
`Some prior systems seek to meet such problems by use of
`expensive components. For example in a communications
`context, known free-space wavelength multiplexers and
`demultiplexers use expensive thermally stable opto-mechan-
`ics to cope with the problems associated with long path 55
`lengths.
`Certain optical systems have a requirement for reconfig(cid:173)
`include optical
`urability. Such reconfigurable systems
`switches, add/drop multiplexers and other optical routing
`systems where the mapping of signals from input ports to 60
`output ports is dynamic. In such systems the path-dependent
`losses, aberrations and phase distortions encountered by opti-
`cal beams may vary from beam to beam according to the route
`taken by the beam through the system. Therefore the path(cid:173)
`dependent loss, aberrations and phase distortions may vary 65
`for each input beam or as a function of the required output
`port.
`
`2
`The prior art does not adequately address this situation.
`Other optical systems are static in terms of input/output
`configuration. In such systems, effects such as assembly
`errors, manufacturing tolerances in the optics and also
`changes in the system behaviour due to temperature and
`ageing, create the desirability for dynamic direction control,
`aberration correction, phase distortion compensation or mis(cid:173)
`alignment compensation.
`It should be noted that the features of dynamic direction
`10 control, phase distortion compensation and misalignment
`control are not restricted to systems using input beams com(cid:173)
`ing from optical fibres. Such features may also be advanta(cid:173)
`geous in a reconfigurable optical system. Another static sys(cid:173)
`tem in which dynamic control of phase distortion, direction
`15 and (relative) misalignment would be advantageous is one in
`which the quality and/or position of the input beams is time(cid:173)
`varying.
`Often the input and output beams for optical systems con(cid:173)
`tain a multiplex of many optical signals at different wave-
`20 lengths, and these signals may need to be separated and
`adaptively and individually processed inside the system.
`Sometimes, although the net aim of a system is not to separate
`optical signals according to their wavelength and then treat
`them separately, to do so increases the wavelength range of
`25 the system as a whole. Where this separation is effected, it is
`often advantageous for the device used to route each channel
`to have a low insertion loss and to operate quickly.
`It is an aim of some aspects of the present invention at least
`partly to mitigate difficulties of the prior art.
`It is desirable for certain applications that a method or
`device for addressing these issues should be polarisation(cid:173)
`independent, or have low polarisation-dependence.
`SLMs have been proposed for use as adaptive optical com(cid:173)
`ponents in the field of astronomical devices, for example as
`35 wavefront correctors. In this field of activity, the constraints
`are different to the present field-for example in communi(cid:173)
`cation and like devices, the need for consistent performance is
`paramount if data is to be passed without errors. Communi(cid:173)
`cation and like devices are desirably inexpensive, and desir-
`40 ably inhabit and successfully operate in environments that are
`not closely controlled. By contrast, astronomical devices may
`be used in conditions more akin to laboratory conditions, and
`cost constraints are less pressing. Astronomical devices are
`unlikely to need to select successive routings oflight within a
`45 system, and variations in performance may be acceptable.
`
`SUMMARY OF THE INVENTION
`
`According to a first aspect of the invention, there is pro-
`50 vided a method of operating an optical device comprising an
`SLM having a two-dimensional array of controllable phase(cid:173)
`modulating elements, the method comprising
`delineating groups of individual phase-modulating ele(cid:173)
`ments;
`selecting, from stored control data, control data for each
`group of phase-modulating elements;
`generating from the respective selected control data a
`respective hologram at each group of phase-modulating ele(cid:173)
`ments; and
`varying the delineation of the groups and/or the selection of
`control data whereby upon illumination of said groups by
`respective light beams, respective emergent light beams from
`the groups are controllable independently of each other.
`In some embodiments, the variation of the delineation and/
`or control data selection is in response to a signal or signals
`indicating a non-optimal performance of the device. In other
`embodiments, the variation is performed during a set up or
`
`

`

`US 8,089,683 B2
`
`25
`
`3
`training phase of the device. In yet other embodiments, the
`variation is in response to an operating signal, for example a
`signal giving the result of sensing non-performance system
`parameters such as temperature.
`An advantage of the method of this aspect of the invention
`is that stable operation can be achieved in the presence of
`effects such as ageing, temperature, component, change of
`path through the system and assembly tolerances.
`Preferably, control of said light beams is selected from the
`group comprising: control of direction, control of power, 10
`focussing, aberration compensation, sampling and beam
`shaping.
`Clearly in most situations more than one of these control
`types will be needed-for example in a routing device (such as
`a switch, filter or add/drop multiplexer) primary changes of 15
`direction are likely to be needed to cope with changes of
`routing as part of the main system but secondary correction
`will be needed to cope with effects such as temperature and
`ageing. Additionally such systems may also need to control
`power, and to allow sampling (both of which may in some 20
`cases be achieved by direction changes).
`Advantageously, each phase modulating element is
`responsive to a respective applied voltage to provide a corre(cid:173)
`sponding phase shift to emergent light, and the method fur(cid:173)
`ther comprises;
`controlling said phase-modulating elements of the spatial
`light modulator to provide respective actual holograms
`derived from the respective generated holograms, wherein the
`controlling step comprises;
`resolving the respective generated holograms modulo 2 pi. 30
`The preferred SLM uses a liquid crystal material to provide
`phase shift and the liquid crystal material is not capable of
`large phase shifts beyond plus or minus 2Jt. Some liquid
`crystal materials can only provide a smaller range of phase
`shifts, and if such materials are used, the resolution of the 35
`generated hologram is correspondingly smaller.
`Preferably the method comprises:
`providing a discrete number of voltages available for appli(cid:173)
`cation to each phase modulating element;
`on the basis of the respective generated holograms, deter- 40
`mining the desired level of phase modulation at a predeter(cid:173)
`mined point on each phase modulating element and choosing
`for each phase modulating element the available voltage
`which corresponds most closely to the desired level.
`Where a digital control device is used, the resolution of the 45
`digital signal does not provide a continuous spectrum of
`available voltages. One way of coping with this is to deter(cid:173)
`mine the desired modulation for each pixel and to choose the
`individual voltage which will provide the closest modulation
`to the desired level.
`In another embodiment, the method comprises:
`providing a discrete number of voltages available for appli(cid:173)
`cation to each phase modulating element;
`determining a subset of the available voltages which pro(cid:173)
`vides the best fit to the generated hologram.
`Another technique is to look at the pixels of the group as a
`whole and to select from the available voltages those that give
`rise to the nearest phase modulation across the whole group.
`Advantageously, the method further comprises the step of
`storing said control data wherein the step of storing said
`control data comprises calculating an initial hologram using a
`desired direction change of a beam of light, applying said
`initial hologram to a group of phase modulating elements, and
`correcting the initial hologram to obtain an improved result.
`The method may further comprise the step of providing 65
`sensors for detecting temperature change, and performing
`said varying step in response to the outputs of those sensors.
`
`4
`The SLM may be integrated on a substrate and have an
`integral quarter-wave plate whereby it is substantially polari(cid:173)
`sation insensitive.
`Preferably the phase-modulating elements are substan(cid:173)
`tially reflective, whereby emergent beams are deflected from
`the specular reflection direction.
`In some aspects, for at least one said group of pixels, the
`method comprises providing control data indicative of two
`holograms to be displayed by said group and generating a
`combined hologram before said resolving step.
`According to a second aspect of the invention there is
`provided an optical device comprising an SLM and a control
`circuit, the SLM having a two-dimensional array of control(cid:173)
`lable phase-modulating elements and the control circuit hav(cid:173)
`ing a store constructed and arranged to hold plural items of
`control data, the control circuit being constructed and
`arranged to delineate groups of individual phase-modulating
`elements, to select, from stored control data, control data for
`each group of phase-modulating elements, and to generate
`from the respective selected control data a respective holo(cid:173)
`gram at each group of phase-modulating elements,
`wherein the control circuit is further constructed and
`arranged, to vary the delineation of the groups and/or the
`selection of control data
`whereby upon illumination of said groups by respective
`light beams, respective emergent light beams from the groups
`are controllable independently of each other.
`An advantage of the device of this aspect of the invention is
`that stable operation can be achieved in the presence of effects
`such as ageing, temperature, component and assembly toler(cid:173)
`ances. Embodiments of the device can handle many light
`beams simultaneously. Embodiments can be wholly recon(cid:173)
`figurable, for example compensating differently for a number
`of routing configurations.
`Preferably, the optical device has sensor devices arranged
`to detect light emergent from the SLM, the control circuit
`being responsive to signals from the sensors to vary said
`delineation and/or said selection.
`In some embodiments, the optical device has temperature
`responsive devices constructed and arranged to feed signals
`indicative of device temperature to said control circuit,
`whereby said delineation and/or selection is varied.
`In another aspect, the invention provides an optical routing
`device having at least first and second SLMs and a control
`circuit, the first SLM being disposed to receive respective
`light beams from an input fibre array, and the second SLM
`being disposed to receive emergent light from the first SLM
`and to provide light to an output fibre array, the first and
`second SLMs each having a respective two-dimensional
`50 array of controllable phase-modulating elements and the con(cid:173)
`trol circuit having a store constructed and arranged to hold
`plural items of control data, the control circuit being con(cid:173)
`structed and arranged to delineate groups of individual phase(cid:173)
`modulating elements, to select, from stored control data, con-
`55 trol data for each group of phase-modulating elements, and to
`generate from the respective selected control data a respective
`hologram at each group of phase-modulating elements,
`wherein the control circuit is further constructed and
`arranged, to vary the delineation of the groups and/or the
`60 selection of control data
`whereby upon illumination of said groups by respective
`light beams, respective emergent light beams from the groups
`are controllable independently of each other.
`In a further aspect, the invention provides a device for
`shaping one or more light beams in which the or each light
`beam is incident upon a respective group of pixels of a two(cid:173)
`dimensional SLM, and the pixels of the or each respective
`
`

`

`US 8,089,683 B2
`
`5
`group are controlled so that the corresponding beams emerg(cid:173)
`ing from the SLM are shaped as required.
`According to a further aspect of the invention there is
`provided an optical device comprising one or more optical
`inputs at respective locations, a diffraction grating con(cid:173)
`structed and arranged to receive light from the or each optical
`input, a focussing device and a continuous array of phase
`modulating elements, the diffraction grating and the array of
`phase modulating elements being disposed in the focal plane
`of the focussing device whereby diverging light from a single 10
`point on the diffraction grating passes via the focussing
`device to form beams at the array of phase modulating ele(cid:173)
`ments, the device further comprising one or more optical
`output at respective locations spatially separate from the or 15
`each optical input, whereby the diffrac