111111
`
`1111111111111111111111111111111111111111111111111111111111111
`US008335033B2
`
`c12) United States Patent
`Holmes
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 8,335,033 B2
`Dec. 18, 2012
`
`(54) OPTICAL PROCESSING
`
`(56)
`
`References Cited
`
`(75)
`
`Inventor: Melanie Holmes, Woodbridge (GB)
`
`(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
`
`(65)
`
`Prior Publication Data
`
`US 2010/0209109 Al
`
`Aug. 19, 2010
`
`Related U.S. Application Data
`
`(60)
`
`Continuation of application No. 11/978,258, filed on
`Oct. 29, 2007, which is a continuation of application
`No. 11/515,389, filed on Sep. 1, 2006, now Pat. No.
`7,612,930, which is a division of application No.
`10/487,810, filed as application No. PCT /GB02/04011
`on Sep. 2, 2002, now Pat. No. 7,145,710.
`
`(30)
`
`Foreign Application Priority Data
`
`Sep. 3, 2001
`
`(GB) ................................... 0121308.1
`
`(51)
`
`Int. Cl.
`G02F 1101
`(2006.01)
`G03H 1108
`(2006.01)
`(52) U.S. Cl. .............. 359/279; 359/9; 359/11; 359/238;
`359/615; 369/103; 356/326
`(58) Field of Classification Search .................. 359/3, 9,
`359/11,237-239,279,556,558,559,566,
`359/24, 29; 385/15-18, 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 file for complete search history.
`
`U.S. PATENT DOCUMENTS
`3,773,401 A
`1111973 Douklias et al.
`3,917,380 A * 1111975 Kato eta!. ...................... 359/35
`4,317,610 A * 3/1982 Breglia eta!. ................... 359/24
`4,952,010 A
`8/1990 Healey eta!.
`(Continued)
`
`EP
`
`FOREIGN PATENT DOCUMENTS
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`1112000
`(Continued)
`
`OTHER PUBLICATIONS
`
`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).
`
`(Continued)
`
`Primary Examiner- Loha Ben
`(74) Attorney, Agent, or Firm- Hamilton, Brook, Smith &
`Reynolds, P.C.
`
`(57)
`
`ABSTRACT
`
`A modular routing node includes a single input port and a
`plurality of output ports. The modular routing node is
`arranged to produce a plurality of different deflections and
`uses small adjustments to compensate for wavelength differ(cid:173)
`ences and alignment tolerances in an optical system. An opti(cid:173)
`cal device is arranged to receive a multiplex of many optical
`signals at different wavelengths, to separate the optical sig(cid:173)
`nals into at least two groups, and to process at least one of the
`groups adaptively.
`
`91 Claims, 36 Drawing Sheets
`
`1700
`
`/
`
`1721
`
`1711
`,G----"'-----
`1701
`1712
`j)----"'-----
`1702
`
`1713
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`1703
`1714
`17040----"'-----
`
`FINISAR 1001
`
`

`

`US 8,335,033 B2
`Page 2
`
`U.S. PATENT DOCUMENTS
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`
`4/2005 Weiner
`6,879,426 B1
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`1112007 Holmes
`
`FOREIGN PATENT DOCUMENTS
`1 207 418 A1
`5/2002
`1 053 501 B1
`7/2003
`WO 01 25840 A1
`4/2001
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`4/2001
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`1112001
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`10/2002
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`
`EP
`EP
`wo
`wo
`wo
`wo
`wo
`
`OTHER PUBLICATIONS
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`mable Holographic Elements," lEE Colloquim on Multiwavelength
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`1472-1473.
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`Yamazaki, H., and Yamaguchi, M., "4x4 Free-Space Optical Switch(cid:173)
`ing Using Real-Time Binary Phase-Only Holograms Generated by a
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`1417, Sep. 15, 1991.
`Holmes, M.J. eta!., "Low Crosstalk Devices for Wavelength-Routed
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`
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`through Oct. 4, 2001).
`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 (Mar. 2002).
`* cited by examiner
`
`

`

`U.S. Patent
`
`Dec. 18, 2012
`
`Sheet 1 of 36
`
`US 8,335,033 B2
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`U.S. Patent
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`Dec. 18, 2012
`Dec. 18, 2012
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`US 8,335,033 B2
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`

`U.S. Patent
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`Dec. 18, 2012
`Dec. 18, 2012
`
`Sheet 3 of 36
`Sheet 3 of 36
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`US 8,335,033 B2
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`

`U.S. Patent
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`
`Dec. 18, 2012
`Dec. 18, 2012
`
`Sheet 4 of 36
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`US 8,335,033 B2
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`

`U.S. Patent
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`
`Dec. 18, 2012
`Dec. 18, 2012
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`

`U.S. Patent
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`Dec. 18, 2012
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`Sheet 6 of 36
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`US 8,335,033 B2
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`U.S. Patent
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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 8 of 36
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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 10 of 36
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`US 8,335,033 B2
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`Dec. 18, 2012
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`

`

`U.S. Patent
`
`Dec. 18, 2012
`
`Sheet 21 of 36
`
`US 8,335,033 B2
`
`0~--------------------------------~
`
`-10
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`-30
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`Thi (u, 2)
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`FIG. 20
`
`

`

`U.S. Patent
`
`Dec. 18, 2012
`
`Sheet 22 of 36
`
`US 8,335,033 B2
`
`{A. 1, A.2, /t3 ....... ... AN} ... ..
`
`{1<.2, A.5, lv13, lv20}
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`{A-7, A, 19, A-37}
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`,
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`. . . . . . . . . . ,. ...
`
`FIG. 21
`
`

`

`U.S. Patent
`US. Patent
`
`Dec. 18, 2012
`Dec. 18, 2012
`
`Sheet 23 of 36
`Sheet 23 of 36
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`US 8,335,033 B2
`US 8,335,033 B2
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`2
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`FIG. 22
`FTICS. 2222
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`

`

`U.S. Patent
`US. Patent
`
`Dec. 18, 2012
`Dec. 18, 2012
`
`Sheet 24 of 36
`Sheet 24 of 36
`
`US 8,335,033 B2
`US 8,335,033 B2
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`720 722
`720
`722
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`733 734
`733 734
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`730
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`FIG. 23
`
`

`

`U.S. Patent
`US. Patent
`
`Dec. 18, 2012
`Dec. 18, 2012
`
`Sheet 25 of 36
`Sheet 25 of 36
`
`US 8,335,033 B2
`US 8,335,033 B2
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`761
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`762
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`771
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`760
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`766 765
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`765
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`FIG. 24
`FIG. 24
`
`

`

`U.S. Patent
`
`Dec. 18, 2012
`
`Sheet 26 of 36
`
`US 8,335,033 B2
`
`794
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`794o
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`7950
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`791iy+
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`792
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`792i~
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`793
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`793iy+
`
`FIG. 25
`
`

`

`U.S. Patent
`
`Dec. 18, 2012
`
`Sheet 27 of 36
`
`US 8,335,033 B2
`
`r--------. 862
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`861
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`863
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`880
`)
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`881
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`883
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`866
`
`884
`
`FIG. 26
`
`

`

`U.S. Patent
`
`Dec. 18, 2012
`
`Sheet 28 of 36
`
`US 8,335,033 B2
`
`Cr.WHcL
`
`510
`
`511
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`501
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`500
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`FIG. 27
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`

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`_..,..-600
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`QPIIQ$~ -'~
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`ROUTING OPTICS
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`FIG. 28
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`FIG. 29
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`u. = w
`w = N
`
`

`

`U.S. Patent
`
`Dec. 18, 2012
`
`Sheet 31 of 36
`
`US 8,335,033 B2
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`900~
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`FIG. 30
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`

`

`U.S. Patent
`US. Patent
`
`Dec. 18, 2012
`Dec. 18, 2012
`
`Sheet 32 of 36
`Sheet 32 of 36
`
`US 8,335,033 B2
`US 8,335,033 B2
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`: :
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`942 945
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`FIG. 31
`FIG. 31
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`

`

`U.S. Patent
`
`Dec. 18, 2012
`
`Sheet 33 of 36
`
`US 8,335,033 B2
`
`960
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`FIG. 32
`
`

`

`U.S. Patent
`US. Patent
`
`Dec. 18, 2012
`Dec. 18, 2012
`
`Sheet 34 of 36
`Sheet 34 of 36
`
`US 8,335,033 B2
`US 8,335,033 B2
`
`
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`
`975
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`FIG. 33
`FIG. 33
`
`

`

`U.S. Patent
`US. Patent
`
`Dec. 18, 2012
`Dec. 18, 2012
`
`Sheet 35 of 36
`Sheet 35 of 36
`
`US 8,335,033 B2
`US 8,335,033 B2
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`980
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`FIG. 34
`FIG. 34
`
`

`

`U.S. Patent
`US. Patent
`
`Dec. 18, 2012
`Dec. 18, 2012
`
`Sheet 36 of 36
`Sheet 36 of 36
`
`US 8,335,033 B2
`US 8,335,033 B2
`
`990
`990
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`
`FIG. 35
`FIG. 35
`
`

`

`US 8,335,033 B2
`
`1
`OPTICAL PROCESSING
`
`RELATED APPLICATIONS
`
`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(cid:173)
`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 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 50
`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 55
`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- 60
`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- 65
`cal beams may vary from beam to beam according to the route
`taken by the beam through the system. Therefore the path-
`
`2
`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,
`10 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
`15 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
`20 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
`25 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
`30 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
`35 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
`40 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
`45 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.
`
`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
`SLM having a two-dimensional array of controllable phase(cid:173)
`modulating elements, the method comprising
`delineating groups of individual phase-modulating ele(cid:173)
`ments;
`selecting, from stored control data, control data for each
`group of phase-modulating elements;
`generating from the respective selected control data a
`respective hologram at each group of phase-modulating ele(cid:173)
`ments; and
`varying the delineation of the groups and/or the selection of
`control data whereby upon illumination of said groups by
`respective light beams, respective emergent light beams from
`the groups are controllable independently of each other.
`
`

`

`US 8,335,033 B2
`
`3
`In some embodiments, the variation of the delineation and/
`or control data selection is in response to a signal or signals
`indicating a non-optimal performance of the device. In other
`embodiments, the variation is performed during a set up or
`training phase of the device. In yet other embodiments, the
`variation is in response to an operating signal, for example a
`signal giving the result of sensing non-performance system
`parameters such as temperature.
`An advantage of the method of this aspect of the invention
`is that stable operation can be achieved in the presence of 10
`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, 15
`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 20
`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 25
`cases be achieved by direction changes).
`Advantageously, each phase modulating element is
`responsive to a respective applied voltage to provide a corre(cid:173)
`sponding phase shift to emergent light, and the method fur(cid:173)
`ther comprises;
`controlling said phase-modulating elements of the spatial
`light modulator to provide respective actual holograms
`derived from the respective generated holograms, wherein the
`controlling step comprises;
`resolving the respective generated holograms modulo 2 pi. 35
`The preferred SLM uses a liquid crystal material to provide
`phase shift and the liquid crystal material is not capable of
`large phase shifts beyond plus or minus 2Jt. Some liquid
`crystal materials can only provide a smaller range of phase
`shifts, and if such materials are used, the resolution of the 40
`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- 45
`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 50
`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 65
`control data comprises calculating an initial hologram using a
`desired direction change of a beam of light, applying said
`
`4
`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
`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(cid:173)
`sation insensitive.
`Preferably the phase-modulating elements are substan(cid:173)
`tially reflective, whereby emergent beams are deflected from
`the specular reflection direction.
`In some aspects, for at least one said group of pixels, the
`method comprises providing control data indicative of two
`holograms to be displayed by said group and generating a
`combined hologram before said resolving step.
`According to a second aspect of the invention there is
`provided an optical device comprising an SLM and a control
`circuit, the SLM having a two-dimensional array of control(cid:173)
`lable phase-modulating elements and the control circuit hav(cid:173)
`ing a store constructed and arranged to hold plural items of
`control data, the control circuit being constructed and
`arranged to delineate groups of individual phase-modulating
`elements, to select, from stored control data, control data for
`each group of phase-modulating elements, and to generate
`from the respective selected control data a respective holo(cid:173)
`gram at each group of phase-modulating elements,
`wherein the control circuit is further constructed and
`arranged, to vary the delineation of the groups and/or the
`30 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
`55 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(cid:173)
`trol circuit having a store constructed and arranged to hold
`plural items of control data, the control circuit being con-
`60 structed and arranged to delineate groups of individual phase(cid:173)
`modulating elements, to select, from stored control data, con(cid:173)
`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
`selection of control data
`
`

`

`US 8,335,033 B2
`
`5
`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
`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 10
`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