US008335033B2
`
`(12) United States Patent
`Holmes
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`US 8,335,033 B2
`Dec. 18, 2012
`
`(54) OPTICAL PROCESSING
`
`(56)
`
`References Cited
`
`(75) Inventor: Melanie Holmes, Woodbridge (GB)
`
`US PATENT DOCUMENTS
`
`(73) Assignee: Thomas Swan & Co. Ltd., Consett
`(GB)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.: 12/710,913
`(22) Filed:
`Feb. 23, 2010
`
`3,773,401 A 11/1973 Douklias et a1~
`3,917,380 A * 11/1975 Kato et al. .................... .. 359/35
`4,317,610 A *
`3/1982 Breglia et al. ................. .. 359/24
`4’952’010 A
`8/1990 _Hea1ey et a1‘
`(comlnued)
`
`EP
`
`FOREIGN PATENT DOCUMENTS
`1050 775 Al
`110000
`(Continued)
`
`(65)
`
`Prior Publication Data
`
`OTHER PUBLICATIONS
`
`Aug' 19’ 2010
`Us 2010/0209109 A1
`Related U_s_ Application Data
`
`(60) Continuation of application No. 11/978,258, ?led on
`Oct. 29, 2007, Which is a continuation of application
`No. 11/515,389, ?led on Sep. 1, 2006, noW Pat. No.
`7,612,930, Which is a division of application No.
`10/487,810, ?led as applicationNo. PCT/GB02/04011
`on Sep' 2, 2002, HOW Pat‘ NO‘ 7,145,710‘
`
`(30)
`
`Foreign Application Priority Data
`
`Sep. 3, 2001
`
`(GB) ................................. .. 01213081
`
`(51) Int‘ Cl‘
`(200601)
`G02F 1/01
`(200601)
`G03H 1/08
`(52) us. Cl. ............ .. 359/279; 359/9; 359/11; 359/238;
`
`359/615; 369/103; 356/326
`_
`_
`_
`(58) Field of Classi?cation Search ................ .. 359/3, 9,
`359/11, 2374239, 279, 556, 558, 559, 566,
`359/24, 29; 385/l5il8, 22, 31, 43, 129,
`385/133, 146, 147, 901; 356/326, 328; 362/26,
`362/602; 369/103, 44.29, 100; 398/49, 79
`See application ?le for complete search history.
`
`YamaZaki, H., et a1., “4x4 Free Space Optical Switching Using Real
`Time Binary Phase-Only Holograms Generated by a Liquid-Crystal
`D' l ,”O t' [S 't
`A
`' ,161811415-1417 1991.
`lsp ay p [Ca Ocleyof merlca
`(
`)
`<
`)
`(Continued)
`
`Primary ExamineriLOha Ben
`. i .
`.
`5331110412??? Agent, or Fzrm
`Hamllton, Brook, Smlth &
`
`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 de?ections and
`uses small ad'ustments to com ensate for Wavelen th differ
`.J
`p.
`.
`g
`.
`ences and alignment tolerances 1n an optical system. An opt1
`-
`-
`-
`-
`-
`cal devlce is arranged to receive a multiplex of many optical
`signals at different Wavelengths, to separate the optical sig
`nals into at least tWo groups, and to process at least one of the
`groups adaptively.
`
`91 Claims, 36 Drawing Sheets
`
`1711
`o---h----—+
`1701
`1712
`...___':\--__ __'>
`
`1702
`
`1713
`___1'\____..4_
`1714
`17049
`___b_____4—
`
`1703
`
`FNC 1001
`
`

`
`US 8,335,033 B2
`Page 2
`
`US. PATENT DOCUMENTS
`5 107 359 A
`4/1992 Ohuchida
`
`6,879,426 B1
`6,920,261 B2
`
`4/2005 Weiner
`7/2005 Inada et al.
`
`A 5,153,751 A * 10/1992 Ishikawa et al. .............. .. 359/13
`
`5 285 308 A
`21994 Jenkins et 31
`52932038 A *
`3/1994 Kadowaki etal. .......... .. 250/216
`5 315 423 A
`5/l994 Hong
`5:329:384 A *
`7/1994 Setanietal. ................ .. 358/514
`5416616 A
`5/l995 J nk.
`31
`5,428,466 A
`M995 lfejnllgfféreéne etal
`5:461:475 A * 10/1995 Lerner et al. ................ .. 356/300
`5 495 356 A
`21996 Sharony et 31
`5:515:354 A *
`5/1996 Miyake etal. ......... .. 369/112.07
`5 526171 A
`@1996 W
`5,539,543 A
`M996 D3221
`53548418 A *
`8/1996 Gaynor et al. ................ .. 359/20
`5 589 955 A l2/l996 Amak t l
`5,629,802 A
`“997 C1 k0 e a'
`5’66l’577 A
`8/l997 J
`a1
`580222 A
`9/l998 Rea lllllstetl ~
`5,832,155 A “H998 Rasch etal'
`’
`’
`3° 6 a'
`5,856,048 A *
`1/1999 T311313 et a1~ ~~~~~~~~~~~~~~~~~~~ ~~ 430/1
`5,917,625 A
`6/1999 Ogusu et al.
`5938309 A
`8/ 1999 Taylor
`5,953,143 A
`9/1999 Sharony et al.
`5,959,747 A
`9/1999 Psaltisetal.
`5,960,133 A
`9/1999 Tomlinson
`5,995,251 A 11/1999 Hesselink etal.
`6,072,608 A
`6/2000 Psaltisetal.
`6,084,694 A
`7/2000 Milton etal.
`6,097,859 A
`8/2000 Solgaard etal.
`6,115,123 A
`9/2000 Stappaertsetal.
`6,130,872 A * 10/2000 Sugiura et al. ......... .. 369/112.04
`6,141,361 A 10/2000 Mears et al.
`6175432 B1
`M2001 Wu et a1
`6’l95’l84 Bl * 20001 Chao et 51
`’
`’
`-
`' """""""""" "
`6,243,176 B1
`6/2001 Ish1kawa et al.
`6,263,123 B1
`7/2001 Bishop et a1‘
`6,275,623 B1
`8/2001 Brophy et a1,
`6,445,470 B1
`9/ 2002 Jenkins et 31.
`6,504,976 B1
`1/2003 Polynkin et al.
`6,507,685 B1
`V2003 Polynkin et 61.
`6,529,307 B1
`3/2003 Peng et a1~
`6,542,268 B1
`4/2003 R°t°1° et a1~
`
`359/32
`
`7222; 500% 8:52;; 31'
`
`232228151 6’559’986 B1
`
`500% Favalora et' a1‘
`6’570’68l B1
`6/2003 Khoury
`6,577,417 B1
`6/2003 Hung
`6,583,901 B1
`7/2003 Li et a1,
`6,594,082 B1
`8/2003 Pu
`6,603,894 B1
`6,654,516 B2 11/2003 So
`6,657,770 B2 12/2003 M?f0m_ et 31
`21111553111115“ ft
`uc _1 e 3'
`’
`’
`3/2004 Ducelher
`6’7ll’316 B2
`3/2004 May
`6,714,309 B2
`5/2004 Marom
`6 738 540 B2
`6/2004 Kellyet a1‘
`637473774 B2
`7/2004 Garrett et al.
`6,760,511 B2
`8/2004 MacKinnOn et a1‘ ““““ “ 356/326
`6,781,691 132*
`9/2004 Rakuljic et a1,
`6,795,182 B2
`10/2004 Garrett et al.
`6,804,428 B1
`6,813,408 B2 11/2004 Bortolini
`6,842,549 B2
`l/2005 So
`
`’
`’
`E
`12/2005 Warr et al.
`6,975,786 B1
`V2006 weverka
`6’990’268 B2
`7/2006 Bortol1n1et a1.
`7,079,723 B2
`900% Yam-‘Ida et 31'
`7413702 B2
`7,127,168 B2 10/2006 Kanlet al.
`7,151,601 B2* 12/2006 MacKinnon etal. ....... .. 356/326
`7’l77’496 Bl, 2/2007 Polynkm m1‘
`7,230,746 B2
`6/2007 Cameron et al. ................ .. 359/9
`7’436’588 B2 10/2008 Rl’thenberg et a1‘
`7,536,108 B2
`5/2009 H1rano et al.
`7,796,319 B2* 9/2010 MacKinnon etal. ....... .. 359/239
`8’089’683 B2
`V2012 Holmes
`2001/0050787 A1 12/2001 Crossland et al.
`2002/0060760 A1
`5/2002 Weiner
`2003/0142378 A1
`7/2003 Mears et al.
`2004/0126120 A1
`7/2004 Cohen etal.
`2005/0270616 A1 12/2005 Weiner
`2007/0035803 A1
`2/2007 Holmes
`2007/0268537 A1 11/2007 Holmes
`
`FOREIGN PATENT DOCUMENTS
`
`EP
`EP
`W0
`W0
`W0
`W0
`W0
`
`5/2002
`1207 418 A1
`7/2003
`1053 501 B1
`4/2001
`WO0125840 A1
`4/2001
`WO0125848 A2
`WO0190823 A1 11/2001
`W0 02 079870 A2 10/2002
`WO02101451 A1
`12/2002
`
`.
`oTlilER PUBLICATIONS .
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`roelectric Liquid-Crystal Smart Pixels,” IEEE Journal of Selected
`Topics in uantum Electronics, vol. 2, No. 1, Apr. 1996, pp. 35-46.
`_
`Mears, R. J., et al., “WDM Channel Management Us1ng Program
`mable Holographic Elements,” IEE Colloquim on Multiwavelength
`Optical Networks: Devices, Systems and Network Implementations,
`IEE, London, GB, Jun. 18, 1998, pp. 11-1-11-6.
`Pan, Ci-Ling, et al., “Tunable Semiconductor Laser with Liquid
`Crystal Pixel Mirror in Grating-Loaded External Cavity,” Electronics
`Letters, IEE Stevenage, GB, V01. 35, N0. 17, Aug. 19, 1999, pp.
`
`Marom, D.M., et al., “Wavelength-Selective 1><4 Switch for 128
`WDM Channels at 50 GhZ Spacing,” OFC Postdeadline Paper, pp.
`13137-143373 (2002)
`_
`_
`_
`Y 919 H CW
`11 M “4 4F 5
`O I 13 {11
`><
`.,
`amaz ,
`.,an amaguc 1,
`ree- pace p 1ca w1 c -
`ing Using Real-Time Binary Phase-Only Holograms Generated by a
`Liquid-Crystal Display,” Optics Letters, vol. 16, No. 18, pp. 1415
`1417, Sep. 15, 1991.
`Holmes, M.J. et al., “Low Crosstalk Devices for Wavelength-Routed
`Networks,” IEEE Colloquium on Guided Wave Optical Signal Pro
`cessing, pp. 1-10 (Jun. 8, 1995).
`Rhee, J .-K. etal, “Variable Passband Optical Add-Drop Multiplexer
`Usin W 1
`th s 1
`t'
`s 't h”P 27”‘E c
`0 t
`g ave eng
`e ec1ve w1 c ,
`roc.
`un onf on p.
`Comm. (ECOC’0liAmersterdam), pp. 550-551 (Sep. 30, 2001
`through Oct 4, 2001) “
`_
`_
`Marom, D.M., et al., Wavelength-Select1ve 1><4 Sw1tch for 128
`WDM Channels at 50 GhZ Spacing,” OFC Postdeadline Paper, pp.
`FB7-1-FB7-3 (Mar. 2002).
`
`* cited by examiner
`
`

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`US. Patent
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`Dec. 18, 2012
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`Sheet 1 0f 36
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`US 8,335,033 B2
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`20111 I
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`26A
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`290 /
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`FIG. 1
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`

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`Dec. 18, 2012
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`Sheet 2 0f 36
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`US 8,335,033 B2
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`6
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`US. Patent
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`Dec. 18, 2012
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`Sheet 3 0f 36
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`US 8,335,033 B2
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`FIG. 3
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`

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`Dec. 18, 2012
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`Sheet 4 0f 36
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`US 8,335,033 B2
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`US. Patent
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`Dec. 18, 2012
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`Sheet 5 0f 36
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`US 8,335,033 B2
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`FIG. 5
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`

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`US. Patent
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`Dec. 18, 2012
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`Sheet 6 0f 36
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`US 8,335,033 B2
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`US. Patent
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`Dec. 18, 2012
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`Sheet 8 0f 36
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`US 8,335,033 B2
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`

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`US. Patent
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`Dec. 18, 2012
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`Sheet 9 0f 36
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`US 8,335,033 B2
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`FIG. 9
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`

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`Dec. 18, 2012
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`Sheet 10 0f 36
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`US 8,335,033 B2
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`Dec. 18, 2012
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`Sheet 12 0f 36
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`US 8,335,033 B2
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`US. Patent
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`Dec. 18, 2012
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`Sheet 16 0f 36
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`US 8,335,033 B2
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`Dec. 18,2012
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`U.S. Patent
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`Dec. 18,2012
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`Sheet 29 of 36
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`Dec. 18, 2012
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`Sheet 33 of 36
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`Sheet 34 of 36
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`Sheet 35 of 36
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`Sheet 36 of 36
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`FIG. 35
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`

`
`1
`OPTICAL PROCESSING
`
`RELATED APPLICATIONS
`
`US 8,335,033 B2
`
`2
`
`This application is a continuation of U.S. application Ser.
`No. 11/978,258, filed Oct. 29, 2007, which is a continuation
`ofU.S. application Ser. No. 11/515,389, filed Sep. 1, 2006,
`now issued U.S. Pat. No. 7,612,930, which is a divisional of
`U.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 of International 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 incorpo-
`rated 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 ofappli-
`cation is mainly envisaged as being to fields in which recon-
`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 of light 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
`misalignment. 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
`alignment tolerances for optical fibres, especially for single-
`mode optical fibres. Every time a fibre connector is con-
`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-
`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 ofcrosstalk 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-
`urability. Such reconfigurable systems
`include optical
`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-
`cal beams may vary from beam to beam according to the route
`taken by the beam through the system. Therefore the path-
`
`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.
`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-
`alignment compensation.
`It should be noted that the features of dynamic direction
`control, phase distortion compensation and misalignment
`control are not restricted to systems using input beams com-
`ing from optical fibres. Such features may also be advanta-
`geous in a reconfigurable optical system. Another static sys-
`tem in which dynamic control of phase distortion, direction
`and (relative) misalignment would be advantageous is one in
`which the quality and/or position of the input beams is time-
`varying.
`Often the input and output beams for optical systems con-
`tain a multiplex of many optical signals at different wave-
`lengths, and these signals may need to be separated and
`adaptively and individually processed inside the system.
`Sometimes, although the net aim ofa 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
`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-
`independent, or have low polarisation-dependence.
`SLMs have been proposed for use as adaptive optical com-
`ponents in the field of astronomical devices, for example as
`wavefront correctors. In this field of activity, the constraints
`are different to the present field—for example in communi-
`cation and like devices, the need for consistent performance is
`paramount if data is to be passed without errors. Communi-
`cation and like devices are desirably inexpensive, and desir-
`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 of light within a
`system, and variations in performance may be acceptable.
`
`SUMMARY OF THE INVENTION
`
`According to a first aspect of the invention, there is pro-
`vided a method of operating an optical device comprising an
`SLM having a two-dimensional array of controllable phase-
`modulating elements, the method comprising
`delineating groups of individual phase-modulating ele-
`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-
`ments; and
`varying the delineation ofthe 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.
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`In some embodiments, the variation ofthe 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
`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-perforrnance 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
`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
`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).
`is
`Advantageously, each phase modulating element
`responsive to a respective applied voltage to provide a corre-
`sponding phase shift to emergent light, and the method fur-
`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.
`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 275. 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 ofvoltages available for appli-
`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-
`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-
`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 ofvoltages available for appli-
`cation to each phase modulating element;
`determining a subset of the available voltages which pro-
`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
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`initial hologram to a group ofphase modulating elements, and
`correcting the initial hologram to obtain an improved result.
`The method may further comprise the step of providing
`sensors for detecting temperature change, and performing
`said varying step in response to the outputs of those sensors.
`The SLM may be integrated on a substrate and have an
`integral quarter-wave plate whereby it is substantially polari-
`sation insensitive.
`
`Preferably the phase-modulating elements are substan-
`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-
`lable phase-modulating elements and the control circuit hav-
`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-
`gram at each group of phase-modulating elements,
`wherein the control circuit
`is further constructed and
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`arranged, to vary the delineation of the groups and/or the
`selection of control data
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`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 ofthe device ofthis aspect ofthe invention is
`that stable operation canbe achieved in the presence ofeffects
`such as ageing, temperature, component and assembly toler-
`ances. Embodiments of the device can handle many light
`beams simultaneously. Embodiments can be wholly recon-
`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
`array of controllable phase-modulating elements and the con-
`trol circuit having a store constructed and arranged to hold
`plural items of control data, the control circuit being con-
`structed and arranged to delineate groups of individual phase-
`modulating elements, to select, from stored control data, con-
`trol data for each group ofphase-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
`selection of control data
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`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-
`dimensional SLM, and the pixels of the or each respective
`group are controlled so that the corresponding beams emerg-
`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-
`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
`ofthe 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-
`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-
`structed and arranged to output light to the or each optical
`output.
`This device allows multiwavelength input light to be dis-
`tributed in wavelength terms across different groups ofphase-
`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-
`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 SUM having a
`two-dimensional array of controllable phase-modulating ele-
`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 45
`group of phase-modulating elements;
`generating from the respective selected control data a
`respective hologram at each group of phase-modulating ele-
`ments; and
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`control data.
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`According to a still further aspect of the invention there is
`provided an optical add/drop multiplexer having a reflective
`SLM having a two-dimensional array of controllable phase-
`modulating elements, a diffraction device and a focussing 55
`device wherein light beams from a common point on the
`diffraction device are mutually parallel when incident upon
`the SLM, and wherein the SLM displays respective holo-
`grams at locations of incidence of light to provide emergent
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`reflection.
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`In a yet further aspect, the invention provides a test or
`monitoring device comprising an SLM having a two-dimen-
`sional array of pixels, and operable to cause incident light to
`emerge in a direction deviating from the specular direction,
`the device having light sensors at predetermined locations
`arranged to provide signals indicative of said emerging light.
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`The test or monitoring device may further comprise further
`sensors arranged to provide signals indicative of light emerg-
`ing in the specular directions.
`Yet a further aspect of the invention relates to a power
`control device for one or more beams of lights in which the
`said beams are incident on respective groups of pixels of a
`two-dimensional SLM, and holograms are applied to the
`respective group so that the emergent beams have power
`reduced by comparison to the respective incident beams.
`The invention further relates to an optical routing module
`having at least one input and at least two outputs and operable
`to select between the outputs, the module comprising a two
`dimensional SLM having an array of pixels, with circuitry
`constructed and arranged to display holograms on the pixels
`to route beams of different frequency to respective outputs.
`According to a later aspect of the invention there is pro-
`vided an optoelectronic device comprising an integrated mul-
`tiple phase spatial light modulator (SLM) having a plurality
`of pixels, wherein each pixel can phase modulate light by a
`phase shift having an upper and a lower limit, and wherein
`each pixel has an input and is responsive to a value at said
`input to provide a phase modulation determined by said value,
`and a controller for the SLM, wherein the controller has a
`control input receiving data indicative of a desired phase
`modulation characteristic across an array of said pixels for
`achieving a desired control of light incident on said array, the
`controller has outputs to each pixel, each output being
`capable of assuming only a discrete number of possible val-
`ues, and the controller comprises a processor constructed and
`arranged to derive, from said desired phase modulation char-
`acteristic, a non-monotonic phase modulation not extending
`outside said upper and lower limits, and a switch constructed
`and arranged to select between the possible values to provide
`a respective one value at each output whereby the SLM pro-
`vides said non-monotonic phase modulation.
`Some or all of the circuitry may be on-chip leading to
`built-in intelligence. This leads to more compact and ulti-
`mately low-cost devices. In some embodiments, some or all
`on-chip circuitry may operate in parallel for each pixel which
`may provide huge time advantages; in any event the avoid-
`ance ofthe need to transfer data off chip and thereafter to read
`in to a computer allows configuration and reconfiguration to
`be faster.
`
`According to another aspect of the invention there is pro-
`vided a method of controlling a light beam using a spatial
`light modulator (SLM) having an array of pixels, the method
`comprising:
`determining a desired phase modulation characteristic
`across a sub-array of said pixels for achieving the desired
`control of said beam;
`controlling said pixels to provide a phase modulation
`derived from the desired phase modulation, wherein the con-
`trolling step comprises
`providing a population of available phase modulation lev-
`els for each pixel, said population comprising a discrete num-
`ber of said phase mo