`Holmes
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`US 7,664,395 B2
`Feb. 16, 2010
`
`US007664395B2
`
`(54) OPTICAL PROCESSING
`
`_
`.
`-
`Inventor. Melanie Holmes, lpsW1ch (GB)
`.
`(73) Ass1gnee: Thomas Swan & Co. Ltd., Durham
`(GB)
`_
`
`_
`
`_
`
`75
`(
`)
`
`( * ) Not1ce:
`
`_
`
`(21) App1.N0.: 11/514,725
`
`(22) F1led:
`
`Sep. 1, 2006
`
`Subject to any d1scla1mer, the term of th1s
`patent is extended or adjusted under 35
`U.S.C. 154(1)) by 3 days.
`
`_
`
`8/1990 Healey et al.
`4,952,010 A
`4/1992 Ohuchida
`5,107,359 A
`5/1994 Hong ........................ .. 398/79
`5,315,423 A *
`@1995 Rejman_Greene et a1‘
`5,428,466 A
`6/1996 Warren
`5,526,171 A
`7/l996 Liu et a1‘
`5,539,543 A
`5,589,955 A 12/1996 Amako et al.
`5,629,802 A
`5/1997 Clark
`
`5,938,309 A
`
`8/1999 Taylor
`_
`(Commued)
`FOREIGN PATENT DOCUMENTS
`
`EP
`
`1 050 775 A1 11/2000
`(Continued)
`
`(65)
`
`Prior Publication Data
`
`OTHER PUBLICATIONS
`
`Us 2007/0035803 A1
`
`Feb- 15, 2007
`
`Related U-s- APPIiC?tiOIl Data
`(62) Division of application No. 10/487,810, ?led as appli-
`cation No. PCT/GB02/04011 on Sep. 2, 2002, noW
`Pat NO 7 145 710
`’
`’
`Foreign Application Priority Data
`
`(30)
`
`Mears, R. J., et al., “Telecommunications Applications of Fer
`roelectric Liquid-Crystal Smart Pixels,” IEEE Journal of Selected
`Topics in Quantum Electronics, vol. 2, No. 1, Apr. 1996, pp. 35-46.
`(Continued)
`
`_
`_
`_
`Primary ExammeriAlessandro Amar1
`(74) Attorney, Agent, or FirmiHamilton, Brook, Smith &
`Reynolds’ P~C~
`
`Sep. 3, 2001
`
`(GB) ............................... .. 01213081
`
`(57)
`
`ABSTRACT
`
`51
`
`Int. Cl.
`(2006.01)
`H04J 14/00
`(52) US. Cl. ...................................................... .. 398/49
`(58) Field of Classi?cation 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 ?le for Complete Search history
`_
`References Clted
`U S PATENT DOCUMENTS
`
`(56)
`
`To 0 erate an o tical device com risin an SLM With a tWo
`P
`P
`P
`g
`dimensional array of controllable phase-modulating ele
`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 11/1973 Douklias et a1.
`
`27 Claims, 36 Drawing Sheets
`
`350
`
`300
`
`310
`
`13-22)
`
`304
`301
`i 1’
`
`301a
`
`301C301b
`
`a] i T 303D 303a
`305
`302
`306
`
`7 ~320a
`7 ~320b
`7 V3200
`
`302a
`3012b
`
`3020
`
` 1
`
`THOMAS SWAN 2003
`Finisar v. Thomas Swan
`IPR2014-00465
`
`
`
`US 7,664,395 B2
`Page 2
`
`US. PATENT DOCUMENTS
`
`9/1999 Psaltis et a1.
`5,959,747 A
`9/1999 Tomlinson
`5,960,133 A
`5,995,251 A 11/1999 Hesselink et al.
`6,072,608 A
`6/2000 Psaltis 6t
`6,115,123 A
`9/2000 Stappaerts et al.
`6,243,176 B1
`6/2001 Ishikawa et al.
`6,529,307 B1
`3/2003 Peng et al.
`
`115111213111} et a1
`30004 May
`'
`6’7 l4’309 B2
`60004 Kelly et a1
`6’747’774 B 2
`7/2004 Garrett et 2'11
`6’760’5ll B2
`6,954,252 B1 * 10/2005 Crossland @1111
`6’975’786 B l
`l 2/2005 Wan et a1
`' """"" "
`’
`’
`'
`2001/0050787 A1: 12/2001 Crossland et al. ........... .. 359/15
`\cxflllgiret' """"""""" " 349/96
`Zoos/0270616 A1 12/2005 Weiner
`
`349/196
`
`3212::
`
`FOREIGN PATENT DOCUMENTS
`
`EP
`W0
`W0
`W0
`W0
`W0
`
`7/2003
`1 053 501 B1
`4/2001
`W0 01 25840 A1
`4/2001
`W0 01 25848 A2
`W0 01 90823 A1 11/2001
`W0 02 079870 A2 10/2002
`W0 02 101451 A1 12/2002
`
`OTHER PUBLICATIONS
`
`Mears, R. J ., et al., “WDM Channel Management Using Program
`mable Holographlc Elements,” IEE Colloqu1m on Multiwavelength
`Opt1cal Networks: Devices, Systems and Network Implementat1ons,
`IEE, London, GB, Jun. 18, 1998, pp. 11-1-11-6.
`Pan’ Ci'Ling’ 8t ‘11'.’ “Tullable Semiconductor Lag.“ with Liq‘lid
`Crystal Pixel M1rror1n Grating-Loaded External Cav1ty,” Electronics
`Letters, IEE Stevenage, GB, vol. 35, No. 17, Aug. 19, 1999, pp.
`1472447}
`Marom, D.M., et al., “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
`Time Binary Phase-Only Holograms Generated by a Liquid-Crystal
`Display,” Optical Society ofAmerica, 16(18): 1415-1417(1991).
`
`EP
`
`1207 418 A1
`
`5/2002
`
`* cited by examiner
`
` 2
`
`
`
`US. Patent
`
`Feb. 16, 2010
`
`Sheet 1 6136
`
`US 7,664,395 B2
`
`4-221
`23OW///|[///// V////
`
`2612
`
`200 /
`
`FIG. 1
`
` 3
`
`
`
`US. Patent
`
`Feb. 16, 2010
`
`Sheet 2 6136
`
`US 7,664,395 B2
`
`6
`
`5
`
`3
`
`4
`
`1
`
`2
`
`13
`
`10
`
`11
`15/
`
`14
`
`12$|
`
`16
`
` 4
`
`
`
`US. Patent
`
`Feb. 16, 2010
`
`Sheet 3 6f 36
`
`US 7,664,395 B2
`
`FIG. 3
`
` 5
`
`
`
`US. Patent
`
`Feb. 16, 2010
`
`Sheet 4 6f 36
`
`US 7,664,395 B2
`
`123
`/\
`
`125»
`
`122»
`
`124~—
`
`A
`
`A A
`
`FIG. 4
`
` 6
`
`
`
`US. Patent
`
`Feb. 16, 2010
`
`Sheet 5 6136
`
`US 7,664,395 B2
`
`4
`
`33
`
`5
`
`3
`
`2
`
`1
`
`2 1
`
`1
`
`30\
`
`1
`
`2
`
`6
`
`2
`
`31-|__|
`32 ‘:1:
`
`34 15
`
`16
`
`~36
`1/37
`
`I,
`
`\35
`
`FIG. 5
`
` 7
`
`
`
`US. Patent
`
`Feb. 16, 2010
`
`Sheet 6 6f 36
`
`US 7,664,395 B2
`
`48
`)
`
`2 1
`
`2 1
`
`4)?
`
`41»-
`
`l
`
`V
`
`FIG. 6
`
`44
`f
`
`_ \40
`
`45
`\
`\
`42
`
`~43
`
` 8
`
`
`
`US. Patent
`
`Feb. 16, 2010
`
`Sheet 7 6f 36
`
`US 7,664,395 B2
`
`FIG. 7
`
` 9
`
`
`
`US. Patent
`
`Feb. 16, 2010
`
`Sheet 8 6f 36
`
`US 7,664,395 B2
`
`216- ----------- — -
`
`0
`
`Q/m
`
`FIG. 8A
`
`211;
`
`0
`
`Q/m
`
`FIG. 8B
`
`
`
`10
`
`
`
`U.S. Patent
`
`Feb. 16, 2010
`
`Sheet 9 of 36
`
`US 7,664,395 B2
`
`96
`
`2a
`
`97
`
`2a7
`
`»—1b
`
`2b/
`
`1a
`
`A4
`
`91jj93
`
`95
`
`90
`
`9294
`
`FIG.9
`
`
`
`11
`
`
`
`US. Patent
`
`Feb. 16, 2010
`
`Sheet 10 6f 36
`
`US 7,664,395 B2
`
`IMAGINARY
`
`READ
`C036
`
`FIG. 10
`
`
`
`12
`
`
`
`US. Patent
`
`Feb. 16, 2010
`
`Sheet 11 6136
`
`US 7,664,395 B2
`
`FIG. 11
`
`/104a
`
`
`
`100\ 1036;\
`
`
`
`13
`
`
`
`US. Patent
`
`Feb. 16, 2010
`
`Sheet 12 6136
`
`US 7,664,395 B2
`
`350
`\
`
`300
`.L
`
`310
`
`304% 391
`—'
`
`3013
`
`301C 3016
`
`91 Q J 3036 303a
`305
`302
`306
`
`302a
`3026
`
`3020
`
`320
`i
`
`7 ~320a
`7 ~320b
`7 ~320C
`
`FIG. 1 2
`
`
`
`14
`
`
`
`US. Patent
`
`Feb. 16, 2010
`
`Sheet 13 6f 36
`
`US 7,664,395 B2
`
`S 141
`
`140
`/
`
`a1 ‘
`
`m1
`
`\ 92
`
`
`
`v 92
`
`131
`
`130
`
`1
`13a
`
`130a
`
`133
`
`FIG. 13A
`
`
`
`15
`
`
`
`US. Patent
`
`Feb. 16, 2010
`
`Sheet 14 6f 36
`
`US 7,664,395 B2
`
`138a
`
`136a
`
`1388b
`
`136b
`
`139
`
`135
`
`137
`
`134
`
`FIG. 13B
`
`
`
`16
`
`
`
`US. Patent
`
`Feb. 16, 2010
`
`Sheet 15 6f 36
`
`US 7,664,395 B2
`
`O
`o .......................................................... -.
`<r
`\
`
`A
`
`A
`
`<r
`
`T
`
`9
`Li.
`
`S v
`
`“(L6 *\ \
`
`\
`
`=1
`
`v
`A
`a
`
`v
`
`_A
`a
`v
`
`0")
`CD
`<1‘
`
`/
`/
`/
`
`v
`
`S} /
`
`(D
`
`g
`5
`C2)
`; g
`E
`Z
`0
`<(
`E
`Q
`
`v
`
`
`
`17
`
`
`
`US. Patent
`
`Feb. 16, 2010
`
`Sheet 16 6136
`
`US 7,664,395 B2
`
`154
`
`153
`
`"GROUND"
`
`151
`
`152
`
`FIG. 15
`
`
`
`18
`
`
`
`US. Patent
`
`Feb. 16, 2010
`
`Sheet 17 6136
`
`US 7,664,395 B2
`
`168 \
`
`169 f
`
`7.»
`163a
`
`K
`165a
`
`164D
`
`l 162b
`
`
`
`.llllllllllllllllllIl-IIIIIII-lllll IIllll-ll
`
`163b
`
`FIG. 16
`
`
`
`19
`
`
`
`US. Patent
`
`Feb. 16, 2010
`
`Sheet 18 6f 36
`
`US 7,664,395 B2
`
`176
`
`"GROUND"
`
`
`
`20
`
`
`
`U.S. Patent
`
`Feb. 16, 2010
`
`Sheet 19 of 36
`
`US 7,664,395 B2
`
`C’)
`‘C
`
`9!
`
`%
`
`°;|
`
`ml
`
`>
`
`I-
`
`O0
`1""
`
`9
`U-
`
`(V
`‘°
`
`1-
`
`El
`
`Z 2
`
`0.2
`
`0
`
`<r
`(6
`
`“I
`>
`
`‘SI
`
`Tu
`
`
`
`21
`
`
`
`U.S. Patent
`
`Feb. 16, 2010
`
`Sheet 20 of 36
`
`US 7,664,395 B2
`
`-0.5
`
`-0.4
`
`-0.3
`
`-0.2
`
`-0.1
`
`0.1
`
`0.2
`
`0.3
`
`0.4
`
`0.5
`
`O
`
`u
`
`FIG. 19
`
`22
`
`
`
`22
`
`
`
`U.S. Patent
`
`Feb. 16,2010
`
`Sheet 21 of 36
`
`US 7,664,395 B2
`
`FIG. 20
`
`23
`
`
`
`23
`
`
`
`U.S. Patent
`
`Feb. 16,2010
`
`Sheet 22 of 36
`
`US 7,664,395 B2
`
`0.1, 7.3, 7.17}
`
`
`0.2, 15,113,120}
`
`{7.7, 7.19, 7.37}
`
`0.1, 712,13 ........ ..7.N}
`
`FIG. 21
`
`24
`
`
`
`24
`
`
`
`U.S. Patent
`
`Feb. 16, 2010
`
`Sheet 23 of 36
`
`US 7,664,395 B2
`
`
`
`663 664 665 672 673 674
`
`FIG. 22
`
`25
`
`
`
`25
`
`
`
`U.S. Patent
`
`Feb. 16,2010
`
`Sheet 24 of 36
`
`US 7,664,395 B2
`
`720
`
`722
`
`733 734
`
`730
`
`
`
`FIG. 23
`
`26
`
`
`
`26
`
`
`
`U.S. Patent
`
`Feb. 16, 2010
`
`Sheet 25 of 36
`
`US 7,664,395 B2
`
`
`
`766
`
`765
`
`771
`
`FIG. 24
`
`27
`
`
`
`27
`
`
`
`U.S. Patent
`
`Feb. 16, 2010
`
`Sheet 26 of 36
`
`US 7,664,395 B2
`
`==,w—I
`I MI"
`::=-.Mw.-:-
`W‘ N If‘
`5;;-J E::='
`
`FIG. 25
`
`28
`
`
`
`28
`
`
`
`U.S. Patent
`
`Feb. 16, 2010
`
`Sheet 27 of 36
`
`US 7,664,395 B2
`
`
`
`FIG. 26
`
`29
`
`
`
`29
`
`
`
`U.S. Patent
`
`Feb. 16, 2010
`
`Sheet 28 of 36
`
`US 7,664,395 B2
`
`FIG. 27
`
`30
`
`
`
`30
`
`
`
`U.S. Patent
`
`Feb. 16, 2010
`
`Sheet 29 of 36
`
`US 7,664,395 B2
`
`FIG.28
`
`co
`
`2:
`
`-
`D_
`
`O 0 Zr
`
`-—
`:3
`
`OI
`
`
`
`31
`
`
`
`U.S. Patent
`
`Feb. 16, 2010
`
`Sheet 30 of 36
`
`US 7,664,395 B2
`
`FIG.29
`
`32
`
`
`
`32
`
`
`
`U.S. Patent
`
`Feb. 16, 2010
`
`Sheet 31 of 36
`
`US 7,664,395 B2
`
`900 \
`
`928
`
`
`
`
`
`901
`
`902
`
`919 920
`
`915
`
`916
`
`917
`
`918
`
`903
`
`904
`
`921
`
`922
`
`910
`
`924
`
`
`
`WHMJH W
`
`905
`
`906
`
`925
`
`926
`
`929
`
`FIG. 30
`
`33
`
`
`
`33
`
`
`
`U.S. Patent
`
`Feb. 16, 2010
`
`Sheet 32 of 36
`
`US 7,664,395 B2
`
`
`
`FIG. 31
`
`34
`
`
`
`34
`
`
`
`U.S. Patent
`
`Feb. 16, 2010
`
`Sheet 33 of 36
`
`US 7,664,395 B2
`
`FIG. 32
`
`35
`
`
`
`35
`
`
`
`U.S. Patent
`
`Feb. 16, 2010
`
`Sheet 34 of 36
`
`US 7,664,395 B2
`
`975
`
`970
`
`972
`
`971
`
`973
`
`974:
`
`FIG. 33
`
`36
`
`
`
`36
`
`
`
`U.S. Patent
`
`Feb. 16, 2010
`
`Sheet 35 of 36
`
`US 7,664,395 B2
`
`980
`
`985
`
`986
`
`987
`
`932
`
`984
`
`988
`
`981
`
`983
`
`FIG. 34
`
`37
`
`
`
`37
`
`
`
`U.S. Patent
`
`Feb. 16, 2010
`
`Sheet 36 of 36
`
`US 7,664,395 B2
`
`FIG. 35
`
`38
`
`
`
`38
`
`
`
`1
`OPTICAL PROCESSING
`
`RELATED APPLICATIONS
`
`US 7,664,395 B2
`
`2
`
`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 or 365 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 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 efiiciency into the intended output optical fibres.
`This in mm 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 difiiculties 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.
`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
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`39
`
`
`
`39
`
`
`
`US 7,664,395 B2
`
`3
`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 2pi.
`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
`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.
`
`4
`
`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
`
`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 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
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`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.
`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
`
`65
`
`40
`
`
`
`40
`
`
`
`US 7,664,395 B2
`
`5
`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 SLM 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
`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.
`
`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
`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
`beams whose direction deviates from the direction of specular
`reflection.
`
`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.
`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
`
`6
`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 modulation levels;
`on the basis ofthe desired phase modulation, a level select-
`ing step of selecting for each pixel a respective one of said
`phase modulation levels; and
`causing each saidpixel to provide the respective one of said
`phase modulation levels.
`The SLM may be a multiple phase liquid crystal over
`silicon spatial light modulator having plural pixels, of a type
`having an integrated wave plate and a reflective element, such
`that successive passes of a beam through the liquid crystal
`subject each orthogonally polarised component to a substan-
`tially similar electrically-set phase change.
`If a non-integrated wave plate is used instead, a beam after
`reflection and passage through the external wave plate will
`not pass through the same zone of the SLM, unless it is
`following the input path, in which case the zero order com-
`ponent of said beam will re-enter the input fibre.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`60
`
`65
`
`41
`
`
`
`41
`
`
`
`US 7,664,395 B2
`
`7
`The use of the wave plate and the successive pass architec-
`ture allows the SLM to be substantially polarisation indepen-
`dent.
`
`In one embodiment the desired phase modulation at least
`includes a linear component.
`Linear phase modulation, or an approximation to linear
`phase modulation may be used to route a beam of light, i.e. to
`select a new direction of propagation for the beam. In many
`routing applications, two SLMs are used in series, and the
`displayed information on the one has the inverse effect to the
`information displayed on the other. Since the information
`represents phase change data, it may be regarded as a holo-
`gram. Hence an output SLM may display a hologram that is
`the inverse of that displayed on the input SLM. Routing may
`also be “one-to-many” (i.e. multicasting) or “one-to-all” (i.e.
`broadcasting) rather than the more usual one-to-one in many
`routing devices. This may be achieved by correct selection of
`the relevant holograms.
`Preferably the linear modulation is resolved modulo 2pi to
`provide a periodic ramp.
`In another embodiment the desired phase modulation
`includes a non-linear component.
`Preferably the method further comprises selecting, from
`said array ofpixels, a sub-array ofpixels for incidence by said
`light beam.
`The size of a selected sub-array may vary from switch to
`switch according to the physical size of the switch and of the
`pixels. However, a typical routing device may have pixel
`arrays of between l00*l00 and 200*200, and other devices
`such as add/drop multiplexers may have arrays of between
`l0*l0 and 50*50. Square arrays are not essential.
`In one embodiment the level-selecting step comprises
`determining the desired level of phase modulation at a pre-
`determined point on each pixel and choosing for each pixel,
`the available level which correspo