111111
`
`1111111111111111111111111111111111111111111111111111111111111
`US007664395B2
`
`c12) United States Patent
`Holmes
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 7,664,395 B2
`Feb.16,2010
`
`(54) OPTICAL PROCESSING
`
`(75)
`
`Inventor: Melanie Holmes, Ipswich (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 3 days.
`
`(21) Appl. No.: 11/514,725
`
`(22) Filed:
`
`Sep.1,2006
`
`(65)
`
`Prior Publication Data
`
`US 2007/0035803 Al
`
`Feb. 15, 2007
`
`Related U.S. Application Data
`
`(62) Division of application No. 10/487,810, filed as appli(cid:173)
`cation No. PCT/GB02/04011 on Sep. 2, 2002, now
`Pat. No. 7,145,710.
`
`(30)
`
`Foreign Application Priority Data
`
`4,952,010 A
`5,107,359 A
`5,315,423 A *
`5,428,466 A
`5,526,171 A
`5,539,543 A
`5,589,955 A
`5,629,802 A
`5,938,309 A
`
`8/1990 Healey et a!.
`4/1992 Ohuchida
`5/1994 Hong .......................... 398/79
`6/1995 Rejman-Greene eta!.
`6/1996 Warren
`7/1996 Liu eta!.
`12/1996 Amako eta!.
`511997 Clark
`8/1999 Taylor
`
`(Continued)
`
`FOREIGN PATENT DOCUMENTS
`
`EP
`
`1 050 77 5 A1
`
`1112000
`
`(Continued)
`
`OTHER PUBLICATIONS
`
`Mears, R. J., et a!., "Telecommunications Applications of Fer(cid:173)
`roelectric Liquid-Crystal Smart Pixels," IEEE Journal of Selected
`Topics in Quantum Electronics, vol. 2, No. 1, Apr. 1996, pp. 35-46.
`
`(Continued)
`
`Primary Examiner-Alessandro Amari
`(74) Attorney, Agent, or Firm-Hamilton, Brook, Smith &
`Reynolds, P.C.
`
`Sep.3,2001
`
`(GB)
`
`................................. 0121308.1
`
`(57)
`
`ABSTRACT
`
`(51)
`
`Int. Cl.
`H04J 14100
`(2006.01)
`(52) U.S. Cl. ........................................................ 398/49
`(58) Field of Classification Search ................... 359/15,
`359/19, 9, 569, 566, 572, 571, 244; 349/201,
`349/202; 398/48, 49, 79, 81, 82, 84, 87
`See application file for complete search history.
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`To operate an optical device comprising an SLM with a two(cid:173)
`dimensional array of controllable phase-modulating ele(cid:173)
`ments groups of individual phase-modulating elements are
`delineated, and control data selected from a store for each
`delineated group of phase-modulating elements. The selected
`control data are used to generate holograms at each group and
`one or both of the delineation of the groups and the selection
`of control data is/are varied. In this way upon illumination of
`the groups by light beams, light beams emergent from the
`groups are controllable independently of each other.
`
`3,773,401 A
`
`1111973 Douklias et a!.
`
`27 Claims, 36 Drawing Sheets
`
`300
`
`310
`
`320
`
`320a
`320b
`320c
`
`350
`\_
`
`304
`
`305
`
`FNC 1001
`
`

`
`US 7,664,395 B2
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`5,959,747 A
`5,960,133 A
`5,995,251 A
`6,072,608 A
`6,115,123 A
`6,243,176 B1
`6,529,307 B1
`6,594,082 B1
`6,710,292 B2
`6,714,309 B2
`6,747,774 B2
`6,760,511 B2
`6,954,252 B1 *
`6,975,786 B1
`200110050787 A1 *
`2002/0060760 A1 *
`2004/0126120 A1
`2005/0270616 A1
`2007/0268537 A1
`2008/0145053 A1
`
`9/1999 Psaltis et al.
`9/1999 Tomlinson
`1111999 Hesselink et a!.
`6/2000 Psaltis et al.
`9/2000 Stappaerts eta!.
`6/2001 Ishikawa et a!.
`3/2003 Peng eta!.
`7/2003 Li eta!.
`3/2004 Fukuchi et a!.
`3/2004 May
`6/2004 Kelly et a!.
`7/2004 Garrett et a!.
`10/2005 Crossland eta!. ........... 349/196
`12/2005 Warr eta!.
`12/2001 Crossland eta!. ............. 359/15
`5/2002 Weiner . ... ... .. ... ... ... ... .. . 349/96
`7/2004 Cohen et al.
`12/2005 Weiner
`1112007 Holmes
`6/2008 Holmes
`
`FOREIGN PATENT DOCUMENTS
`
`EP
`
`1 207 418 A1
`
`5/2002
`
`EP
`wo
`wo
`wo
`wo
`wo
`
`1 053 501 B1
`WO 01 25840 A1
`WO 01 25848 A2
`WO 01 90823 A1
`WO 02 079870 A2
`WO 02 101451 A1
`
`7/2003
`4/2001
`4/2001
`1112001
`10/2002
`12/2002
`
`OTHER PUBLICATIONS
`
`Mears, R. J., et al., "WDM Channel Management Using Program(cid:173)
`mable Holographic Elements," lEE Colloquim on Multiwavelength
`Optical Networks: Devices, Systems and Network ImplementatiOns,
`lEE London, GB, Jun. 18, 1998, pp. 11-1-11-6.
`Pan: Ci-Ling, et a!., "Tunable Semiconductor Laser with Liquid
`Crystal Pixel Mirror in Grating-Loaded External Cavity," Electronics
`Letters, lEE Stevenage, GB, vol. 35, No. 17, Aug. 19, 1999, pp.
`1472-1473.
`Marom, D.M., et a!., "Wavelength-Selective 1x4 Switch for 128
`WDM Channels at 50 Ghz Spacing," OFC Postdeadline Paper, pp.
`FB7-1-FB7-3 (2002).
`Yamazaki, H., et al., "4x4 Free Space Optical Switching Using Real(cid:173)
`Time Binary Phase-Only Holograms Generated by a Liquid-Crystal
`Display," Optical Society of America, 16(18): 1415-1417(1991).
`* cited by examiner
`
`

`
`U.S. Patent
`
`Feb.16,2010
`
`Sheet 1 of 36
`
`US 7,664,395 B2
`
`20111
`
`225
`
`223
`222
`
`221
`
`......................................................................................................
`.................................................................................................
`.................................................................................................
`. . . .. . . . . . . . . . . .. . . . . . .. .. . . . . . . . . .. .. . .. . . . . .. . . ~ ....................................................... .
`.............................................................................................
`........................................................................................................
`.........................................................................................................
`:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
`...............................................................................................
`...............................................................................................
`...................................................................................................
`..............................................................................................
`········••+••················· .. ····························································
`.............................................................................................
`
`0 0
`
`-1 I 0 <- <- 0 I I 0 o 0 .. 0 0 0 I I . I I 0 I 0 o o o 0 •
`
`• o o o • • o o • • • o
`
`o • • • o • • o o 0 0 o 0 o • • 0 o 0 0 o o 0 o 0 ~ I 0 o o • o ' .. o • • • o o o • • • o o o • • • • o o ._ • • 0 o o ._ o • o o o o • • o o o o .. o • o o • 0 o 0 0 • • 0 0 0 • o .. 0
`
`0 • I . I • 0 -o 0 • • •
`
`o o- • • o o • o • o o • • 0 o 0 o o o 0. I<- 6 • 0 o 0 <- 0 • ~ 0
`
`230
`
`200/
`
`26_,_d}
`
`FIG. 1
`
`

`
`U.S. Patent
`U.S. Patent
`
`Feb.16,2010
`Feb. 16, 2010
`
`Sheet 2 of 36
`Sheet 2 of 36
`
`US 7,664,395 B2
`US 7,664,395 B2
`
`4
`
`3
`
`2
`
`1
`
`6
`
`5
`
`13 A 14
`10 I
`10
`
`—
`12
`12
`
`11
`11
`
`16
`16
`
`15/
`15/
`
`FIG. 2
`
`

`
`U.S. Patent
`U.S. Patent
`
`Feb. 16, 2010
`Feb. 16, 2010
`
`Sheet 3 of 36
`Sheet 3 of 36
`
`US 7,664,395 B2
`US 7,664,395 B2
`
`27
`27
`26
`26 T 5
`20
`V
`
`6
`5
`
`A
`
`23
`23
`
`Ij
`
`21
`
`24
`
`\25
`'-. 25
`
`FIG. 3
`FIG. 3
`
`1
`
`3
`3
`
`2
`
`4
`
`

`
`U.S. Patent
`U.S. Patent
`
`Feb. 16, 2010
`Feb. 16, 2010
`
`Sheet 4 of 36
`Sheet 4 of 36
`
`US 7,664,395 B2
`US 7,664,395 B2
`
`1
`
`20
`20
`
`123
`123
`
`A
`
`13 - -
`
`125
`
`122
`
`124
`
`FIG. 4
`
`

`
`U.S. Patent
`U.S. Patent
`
`Feb.16,2010
`Feb. 16, 2010
`
`Sheet 5 of 36
`Sheet 5 of 36
`
`US 7,664,395 B2
`US 7,664,395 B2
`
`3
`
`30
`
`31
`
`32
`
`6
`
`'-35
`
`FIG. 5
`
`

`
`U.S. Patent
`U.S. Patent
`
`Feb.16,2010
`Feb. 16, 2010
`
`Sheet 6 of 36
`Sheet 6 of 36
`
`US 7,664,395 B2
`US 7,664,395 B2
`
`48
`
`47
`
`44
`
`45
`
`43
`
`FIG. 6
`
`

`
`U.S. Patent
`U.S. Patent
`
`Feb.16,2010
`Feb. 16, 2010
`
`Sheet 7 of 36
`Sheet 7 of 36
`
`US 7,664,395 B2
`US 7,664,395 B2
`
`~4 50'
`3», V 7/
`3~
`
`I
`
`\ 2
`
`4
`
`5
`
`81
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`
`82
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`
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`I
`
`I
`
`83
`
`84
`
` I
`
`FIG. 7
`FIG. 7
`
`

`
`U.S. Patent
`
`Feb. 16, 2010
`
`Sheet 8 of 36
`
`US 7,664,395 B2
`
`21t ------------- ........ ~
`
`0
`
`Q/m
`
`FIG. 8A
`
`21t
`
`---------------r--~
`
`0
`
`Q/m
`
`FIG. 88
`
`

`
`U.S. Patent
`U.S. Patent
`
`Feb.16,2010
`Feb. 16, 2010
`
`Sheet 9 of 36
`Sheet 9 of 36
`
`US 7,664,395 B2
`US 7,664,395 B2
`
`L()
`
`96
`
`2a
`
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`
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`»—1b
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`0'>
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`
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`FIG.9
`(.9 -LJ_
`
`~
`0'>
`
`9294
`
`N en
`
`

`
`U.S. Patent
`
`Feb.16,2010
`
`Sheet 10 of 36
`
`US 7,664,395 B2
`
`IMAGINARY
`
`+Sine --------------------
`
`~----~--------------------~----READ
`Case
`
`-Sine --------------------
`
`FIG. 10
`
`

`
`U.S. Patent
`U.S. Patent
`
`Feb.16,2010
`Feb. 16,2010
`
`Sheet 11 of 36
`Sheet 11 of 36
`
`US 7,664,395 B2
`US 7,664,395 B2
`
`.....-
`
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`
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`~
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`(9
`-
`u.
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`
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`
`

`
`U.S. Patent
`
`Feb.16,2010
`
`Sheet 12 of 36
`
`US 7,664,395 B2
`
`300
`
`310
`
`320
`
`320a
`320b
`320c
`
`350
`\_
`
`304
`
`305
`
`FIG. 12
`
`

`
`U.S. Patent
`
`Feb. 16, 2010
`
`Sheet 13 of 36
`
`US 7,664,395 B2
`
`140
`
`141
`
`131a
`
`142
`
`132
`
`130a
`
`133
`
`FIG. 13A
`
`

`
`U.S. Patent
`
`Feb.16,2010
`
`Sheet 14 of 36
`
`US 7,664,395 B2
`
`138a
`
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`136a
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`
`139
`
`135
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`134
`
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`
`FIG. 138
`
`

`
`U.S. Patent
`U.S. Patent
`
`Feb. 16, 2010
`Feb.16,2010
`
`Sheet 15 of 36
`Sheet 15 of 36
`
`US 7,664,395 B2
`US 7,664,395 B2
`
` O ' . ' . ' . ' . ' . ' . ' . ‘ . ' . ' . ' . ' . ‘ . ' . ' . ' . ' . ' . ' . ' . ' . ' . ' . ' . ' . ' . ' . ' . ‘ . -.
`<1‘ jjjj
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`

`
`U.S. Patent
`
`Feb. 16, 2010
`
`Sheet 16 of 36
`
`US 7,664,395 B2
`
`153
`
`154
`
`155b
`
`156a
`
`156b
`
`FIG. 15
`
`

`
`U.S. Patent
`
`Feb. 16, 2010
`
`Sheet 17 of 36
`
`US 7,664,395 B2
`
`162a
`
`161a
`
`164a
`
`165b
`
`166a
`166b
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`167a
`167b
`
`163a
`
`165a
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`164b
`
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`
`163b ------i-------- 162b
`
`FIG. 16
`
`

`
`U.S. Patent
`U.S. Patent
`
`Feb. 16, 2010
`Feb.16,2010
`
`Sheet 18 of 36
`Sheet 18 of 36
`
`US 7,664,395 B2
`US 7,664,395 B2
`
`176
`176
`
`174
`
`175
`
` "GROUND"
`
`FIG. 17
`FIG. 17
`
`

`
`U.S. Patent
`
`Feb.16,2010
`
`Sheet 19 of 36
`
`US 7,664,395 B2
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`co
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`U.S. Patent
`U.S. Patent
`
`Feb. 16, 2010
`Feb.16,2010
`
`Sheet 20 of 36
`Sheet 20 of 36
`
`US 7,664,395 B2
`US 7,664,395 B2
`
`-1
`
`-2
`
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`-5
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`FIG. 19
`FIG. 19
`
`

`
`U.S. Patent
`
`Feb.16,2010
`
`Sheet 21 of 36
`
`US 7,664,395 B2
`
`o~--------------------------------~
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`-20
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`1.2
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`FIG. 20
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`

`
`U.S. Patent
`U.S. Patent
`
`Feb. 16,2010
`Feb.16,2010
`
`Sheet 22 of 36
`Sheet 22 of 36
`
`US 7,664,395 B2
`US 7,664,395 B2
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`{A-1, A-2, A-3 ...... . ... A.N}
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`07, 2.19, 1.37}
`
`FIG. 21
`FIG. 21
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`

`
`U.S. Patent
`U.S. Patent
`
`Feb. 16, 2010
`Feb.16,2010
`
`Sheet 23 of 36
`Sheet 23 of 36
`
`US 7,664,395 B2
`US 7,664,395 B2
`
`671
`675
`676
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`666
`667
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`
`
`663 664 665 672 673 67 4
`663 664 665 672 673 674
`
`FIG. 22
`FIG. 22
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`

`
`U.S. Patent
`U.S. Patent
`
`Feb. 16,2010
`Feb.16,2010
`
`Sheet 24 of 36
`Sheet 24 of 36
`
`US 7,664,395 B2
`US 7,664,395 B2
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`720
`720
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`722
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`FIG. 23
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`

`
`U.S. Patent
`U.S. Patent
`
`Feb. 16, 2010
`Feb.16,2010
`
`Sheet 25 of 36
`Sheet 25 of 36
`
`US 7,664,395 B2
`US 7,664,395 B2
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`762
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`FIG. 24
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`

`
`U.S. Patent
`
`Feb.16,2010
`
`Sheet 26 of 36
`
`US 7,664,395 B2
`
`794
`
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`795
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`

`
`U.S. Patent
`U.S. Patent
`
`Feb. 16, 2010
`Feb.16,2010
`
`Sheet 27 of 36
`Sheet 27 of 36
`
`US 7,664,395 B2
`US 7,664,395 B2
`
`862
`
`861
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`863
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`864
`
`865
`
`870
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`880
`
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`
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`883
`
`884
`
`866
`
`FIG. 26
`FIG. 26
`
`

`
`U.S. Patent
`
`Feb. 16, 2010
`
`Sheet 28 of 36
`
`US 7,664,395 B2
`
`Cr.WHCL
`
`501
`
`500
`
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`
`FIG. 27
`
`

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`
`623
`624
`625
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`OPTICS
`
`1..
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`
`ROUTING OPTICS
`
`.. I
`
`FIG. 28
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`U.S. Patent
`U.S. Patent
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`Feb. 16, 2010
`Feb.16,2010
`
`Sheet 30 of 36
`Sheet 30 of 36
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`US 7,664,395 B2
`US 7,664,395 B2
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`U.S. Patent
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`Feb. 16, 2010
`Feb.16,2010
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`Sheet 31 of 36
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`US 7,664,395 B2
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`
`U.S. Patent
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`
`Feb. 16, 2010
`Feb.16,2010
`
`Sheet 32 of 36
`Sheet 32 of 36
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`US 7,664,395 B2
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`U.S. Patent
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`Feb. 16, 2010
`Feb.16,2010
`
`Sheet 33 of 36
`Sheet 33 of 36
`
`US 7,664,395 B2
`US 7,664,395 B2
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`

`
`U.S. Patent
`U.S. Patent
`
`Feb. 16, 2010
`Feb.16,2010
`
`Sheet 34 of 36
`Sheet 34 of 36
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`US 7,664,395 B2
`US 7,664,395 B2
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`

`
`U.S. Patent
`U.S. Patent
`
`Feb. 16, 2010
`Feb.16,2010
`
`Sheet 35 of 36
`Sheet 35 of 36
`
`US 7,664,395 B2
`US 7,664,395 B2
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`

`
`U.S. Patent
`U.S. Patent
`
`Feb.16,2010
`Feb. 16, 2010
`
`Sheet 36 of 36
`Sheet 36 of 36
`
`US 7,664,395 B2
`US 7,664,395 B2
`
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`FIG. 35
`
`

`
`US 7,664,395 B2
`
`1
`OPTICAL PROCESSING
`
`RELATED APPLICATIONS
`
`This application is a divisional ofU.S. application Ser. No.
`10/487,810 now U.S. Pat. No. 7,145,710 filed Sep. 10, 2004,
`which is the U.S. National Stage of International Appl. No.
`PCT/GB02/04011, filed Sep. 2, 2002, and published in
`English. This application claims priority under 35 U.S.C. §
`119 or365 to Great BritainAppl. 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
`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
`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
`output ports is dynamic. In such systems the path-dependent
`losses, aberrations and phase distortions encountered by opti(cid:173)
`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
`for each input beam or as a function of the required output
`port.
`The prior art does not adequately address this situation.
`
`2
`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
`control, phase distortion compensation and misalignment
`10 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
`and (relative) misalignment would be advantageous is one in
`15 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(cid:173)
`lengths, and these signals may need to be separated and
`20 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
`the system as a whole. Where this separation is effected, it is
`25 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
`30 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
`wavefront correctors. In this field of activity, the constraints
`35 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(cid:173)
`ably inhabit and successfully operate in environments that are
`40 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
`system, and variations in performance may be acceptable.
`
`45
`
`SUMMARY OF THE INVENTION
`
`According to a first aspect of the invention, there is pro(cid:173)
`vided a method of operating an optical device comprising an
`50 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
`55 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
`60 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
`65 indicating a non-optimal performance of the device. In other
`embodiments, the variation is performed during a set up or
`training phase of the device. In yet other embodiments, the
`
`

`
`US 7,664,395 B2
`
`3
`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,
`focussing, aberration compensation, sampling and beam 10
`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
`direction are likely to be needed to cope with changes of 15
`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
`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 25
`light modulator to provide respective actual holograms
`derived from the respective generated holograms, wherein the
`controlling step comprises;
`resolving the respective generated holograms modulo 2pi.
`The preferred SLM uses a liquid crystal material to provide 30
`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
`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-
`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
`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
`20 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
`
`35
`
`40
`
`45
`
`

`
`US 7,664,395 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
`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
`each optical input, whereby the diffraction grating is con(cid:173)
`structed and arranged to output light to the or each optical
`output.
`This device allows multiwavelength input light to be dis(cid:173)
`tributed in wavelength terms across different groups of phase(cid:173)
`modulating elements. This allows different processing effects
`to be applied to any desired part or parts of the spectrum.
`According to a still further aspect of the invention there is
`provided a method of filtering light comprising applying a
`beam of said light to a diffraction grating whereby emerging
`light from the grating is angularly dispersed by wavelength,
`forming respective beams from said emerging light by pass(cid:173)
`ing the emerging light to a focussing device having the grating
`at its focal plane, passing the respective beams to an SLM at
`the focal plane of the focussing device, the SLM having a
`two-dimensional array of controllable phase-modulating ele(cid:173)
`ments, selectively reflecting light from different locations of
`said SLM and passing said reflected light to said focussing
`element and then to said grating.
`Preferably the method comprises delineating groups of
`individual phase-modulating elements to receive beams of
`light of differing wavelength;
`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.
`According to a still further aspect of the invention there is 45
`provided an optical add/drop multiplexer having a reflective
`SLM having a two-dimensional array of controllable phase(cid:173)
`modulating elements, a diffraction device and a focussing
`device wherein light beams from a common point on the
`diffraction device are mutually parallel when incident upon 50
`the SLM, and wherein the SLM displays respective holo(cid:173)
`grams at locations of incidence of light to provide emergent
`beams whose direction deviates from the direction of specular
`reflection.
`In a yet further aspect, the invention provides a test or 55
`monitoring device comprising an SLM having a two-dimen(cid:173)
`sional array of pixels, and operable to cause incident light to
`emerge in a direction deviating from the specular direction,
`the device