UNITED STATES DEPARTS/lENT OF CO~ERCE
`
`United States Patent and Trademark Office
`
`May 16, 2013
`
`THIS IS TO CERTIFY THAT ANNEXED IS A TRUE COPY FROM THE
`
`RECORDS OF THIS OFFICE OF THE FILE WRAPPER AND CONTENTS
`
`OF:
`
`APPLICATION NUMBER: 11/514,725
`FILING DATE: September 01, 2006
`
`PATENT NUMBER: 7,664,395
`
`ISSUE DATE: February 16, 2010
`
`By Authority of the
`
`Under Secretary of Commerce for Intellectual Property
`and Director of the United States Patent and Trademark Office
`
`R. PONDEXTER
`
`Certifying Officer
`
`FINISAR 1002
`TSO001167
`
`

`

`HAMILTON, BROOK, SMITH & REYNOLDS, P.C.
`UTILITY
`Attorney Docket No.
`3274.1003-002
`PATENT APPLICATION
`TRANSMITTAL
`~Ot~ for new nonprovisional applications under
`37 CFR 1.53(b))
`
`Express Mail Label No.
`
`Ev 214902601 us
`
`First Named Inventor
`
`Melanie Holmes
`
`Title of -
`Invention
`
`OPTICAL PROCESSING
`
`~ o~ APPLICATION ELEMENTS
`
`--~see MPEP chapter 600 concerning utility patent application contents.
`
`ADDRESS TO:
`
`Commissioner for Patents
`P.O. Box 1450
`Alexandria, VA 22313-1450
`
`1.
`
`[ ] Fee Transmittal Form
`(Submit an original and a duplicate for fee processing)
`
`ACCOMPANYING APPLICATION PARTS
`
`2. IX]
`
`Specification Total Pages ~. ’. [ 1 0 0 ]
`Both the claims and the abstract must start on a new page
`(For information on the preferred arrangement, see MPEP 608.01(a))
`
`3. ix]
`
`Drawing(s) (35 U.S.C. 113) Total Sheets [36 I
`[ X ] Fig. of the Drawings for Publication [ 13b ]
`
`[ ] No Figure to be Published
`
`7. []
`
`Assignment Papers (cover sheet & documents)
`
`Name of Assignee Thomas Swan & Co. Ltd.
`
`City & State:
`8. []
`
`Durham, United Kingdom
`
`37 CFR 3.73(b) Statement
`(when there is an assignee)
`
`[ ] Power of
`Attorney
`
`4.
`
`5.
`
`6.
`
`Total Pages [
`[ ] Oath or Declaration
`a. [ ] Newly executed (original or copy)
`Copy from a prior application (37 C.F.R. 1.63(d))
`(for continuation/divisional with Box 18 completed)
`
`b. [ ]
`
`l
`
`i.
`
`[ ] DELETION OF INVENTOR(S)
`Signed statement attached deleting
`inventor(s) named in the prior application,
`see 37 C.F.R. 1.63(d)(2) and 1.33(b).
`
`[ ] CD-ROM or CD-R in duplicate, large table or Computer
`Program (Appendix)
`
`[ ] Nucleotide and/or Amino Acid Sequence Submission
`(if applicable, items a.-c. are required)
`
`a. [ ] Computer Readable Form (CRF)
`
`i.
`ii.
`
`[ ] Computer Readable Form (CRF)
`[ ] Transfer Request (37 CFR 1.821(e))
`
`b.[]
`
`Specification Sequence Listing on:
`
`i.
`ii.
`
`[ ] CD-ROM or CD-R(2 copies); or
`[ ] Paper 11 Pages
`
`c.[]
`
`Statements verifying identity of above copies
`
`[ ] English Translation Document (if applicable)
`
`[X ] Information Disclosure Statement (PT0-1449)
`[ ] Copies of foreign patent documents, publications,
`and other information
`
`11.
`
`12.
`
`[ ] Preliminary Amendment
`
`[X] Return Receipt Postcard
`
`13a.
`
`[ ] Foreign Priority Claim under 35 U.S.C. § 119or365
`
`13b.
`
`[ ] Certified Copy of Priority Document(s)
`
`14.
`
`15.
`
`16.
`17.
`
`[ ] Nonpublication Request under 35 U.S.C. 122(b)(2)(B)(i).
`Applicant must attach form PTO/SB/35 or equivalent.
`
`[ X ] Remarks
`[ ] Small Entity Statement(s)
`[ ] Other
`
`18.
`
`If a CONTINUING APPLICATION, check appropriate box, and supply the requisite information below and in the first sentence of
`the specification following the title:
`
`[ ] Continuation [X ] Divisional [ ] Continuation-in-part (CIP) of prior application No.: 10/487,810
`
`Prior application information: Examiner: Loha Ben
`
`Group Art Unit:
`
`2873
`
`The entire disclosure of the prior application is considered a part of the disclosure of the accompanying application and is
`hereby incorporated by reference.
`(Add standard Related Applications section with incorporation by reference to specification or update same)
`
`CORRESPONDENCE ADDRESS
`
`19.
`Customer No. 021005
`HAMILTON, BROOK, SMITH & REYNOLDS, P.C.
`530 Virginia Road, P.O. Box 9133
`
`Concord
`USA
`
`STATE
`
`MA
`
`ZIP CODE 101742-9133
`
`I TELEPHONE
`
`(978) 341-0036
`
`FAX[ (978) 341-0136
`
`NAME
`
`ADDRESS
`CITY
`COUNTRY
`
`Signature
`
`Submitted by
`Typed or Printed Name
`(~oI:DcrJaop~::ODMA/MHODMA/HBSPJ)S;LMamg~7412; I
`
`, ¯
`.~._¢~ ("? ~ __
`~ "
`tj~e~
`~J/ Timothy~. eaghel(J
`"!
`
`Date
`
`Reg Number
`"
`
`39,302
`
`TS0001168
`
`

`

`@-’PFDesktop\::ODMA/MHODMA/HBSR05;iManage;644031 ; 1
`TJM/jk
`08/22/06
`
`PATENT APPLICATION
`Attorney’s Docket No.: 3274.1003-002
`
`IN THE UNITED STATES PATENT AND TRADEMARK OFFICE
`
`Applicant:
`
`Melanie Holmes
`
`Divisional Application of
`
`Application No.:
`
`10/487,810
`
`371C File Date:
`
`September 10, 2004
`
`For:
`
`OPTICAL PROCESSING
`
`REMARKS
`
`Commissioner for Patents
`P.O. Box 1450
`Alexandria, VA 22313-1450
`
`Sir:
`
`The above-captioned application is a divisional of application number 10/487,810 to
`
`which priority is claimed under 35 U.S.C. § 120.
`
`The specification of the present application is substantially the same as that of the parent
`
`application. The related applications paragraph has been revised to include a specific reference
`
`to the parent application.
`
`Claims 19-21 and 23-27 as presented in the parent application have been renumbered
`
`sequentially beginning with Claim 1. A newly executed declaration under 37 C.F.R. 1.63 is not
`
`believed to be necessary under 37 C.F.R. 1.63(d) or 1.67(b).
`
`Concord, MA 01742-9133
`
`Dated: ~ /,/.(~
`
`Respectfully submitted,
`
`HAMILTON, BROOK, SMITH & REYNOLDS, P.C.
`
`Timoth
`Registration No.~ 39,~02 ~
`Telephone: (978) 34’1-0036
`Facsimile: (978) 341-0136
`
`TSO001169
`
`

`

`C:hNrPon,bl~iManageklKERTY7.A\644025_ 1 .DOC
`TJM~jk
`08/22/06
`
`PATENT APPLICATION
`Docket No. 3274.1003-002
`
`-1-
`
`Date:
`
`Inventor:
`
`Melanie Holmes
`
`Attomey’s Docket No.:
`
`3274.1003-002
`
`OPTICAL PROCESSING
`
`RELATED APPLICATIONS
`
`This application is a divisional ofU.S. Appl. No. 10/487,810, which is the U.S.
`
`National Stage of International Appl. No. PCT/GB02/04011, filed September 2, 2002,
`
`and published in English. This application claims priority under 35 U.S.C. § 119 or 365
`
`to Great Britain Appl. No. 0121308.1, filed September 3,2001. The entire teachings of
`
`the above application(s) are incorporated herein by reference.
`
`FIELD OF THE INVENTION
`
`[0001 ] The present invention relates to an optical device and to a method of controlling
`
`10
`
`an optical device.
`
`[0002] 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 application is mainly envisaged as being to fields in which reconfiguration
`
`between inputs and outputs is likely, and stability of performance is a significant
`
`15
`
`requirement.
`
`BACKGROUND OF THE INVENTION
`
`[0003] 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.
`
`20
`
`[0004] Optical systems are subject to performance impairments resulting from
`
`TSO001170
`
`

`

`3274.1003-002
`
`-2-
`
`aberrations, phase distortions and component misalignment. An example is a multiway
`
`fibre connector, which although conceptually simple can o~en 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
`
`5
`
`connected, it may provide a different alignment error. Another example is an optical
`
`switch in which aberrations, phase distortions and component misalignments result in
`
`poor optical 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
`
`10
`
`fibres, leading to levels of crosstalk that impede operation. In some cases, particularly
`
`where long path lengths are involved, the component misalignment may occur due to
`
`ageing or temperature effects.
`
`[0005] Some prior systems seek to meet such problems by use of expensive
`
`components. For example in a communications context, known flee-space wavelength
`
`15 multiplexers and demultiplexers use expensive thermally stable opto-mechanics to cope
`
`with the problems associated with long path lengths.
`
`[0006] Certain optical systems have a requirement for reconfigurability. Such
`
`reconfigurable systems include optical switches, add/drop multiplexers and other optical
`
`routing systems where the mapping of signals fi’om input ports to output ports is
`
`20
`
`dynamic. In such systems the path-dependent losses, aberrations and phase distortions
`
`encountered by optical 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.
`
`25
`
`[0007] The prior art does not adequately address this situation.
`
`[0008] 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
`
`30 misalignment compensation.
`
`TSO001171
`
`

`

`3274.1Q03-002
`
`[0009] 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
`
`coming from optical fibres. Such features may also be advantageous in a reconfigurable
`
`optical system. Another static system in which dynamic control of phase distortion,
`
`5
`
`direction and (relative) misalignment would be advantageous is one in which the quality
`
`and/or position of the input beams is time-varying.
`
`[0010] Often the input and output beams for optical systems contain a multiplex of
`
`many optical signals at different wavelengths, and these signals may need to be
`
`separated and adaptively and individually processed inside the system. Sometimes,
`
`10
`
`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 often advantageous for the
`
`device used to route each channel to have a low insertion loss and to operate quickly.
`
`[0011] It is an aim of some aspects of the present invention at least partly to mitigate
`
`15
`
`difficulties of the prior art.
`
`[0012] It is desirable for certain applications that a method or device for addressing
`
`these issues should be polarisation-independent, or have low polarisation-dependence.
`
`[0013] SLMs have been proposed for use as adaptive optical components in the field of
`
`astronomical devices, for example as wavefront correctors. In this field of activity, the
`
`20
`
`constraints are different to the present field-for example in communication and like
`
`devices, the need for consistent performance is paramount if data is to be passed
`
`without errors. Communication and like devices are desirably inexpensive, and
`
`desirably inhabit and successfully operate in environments that are not closely
`
`controlled. By contrast, astronomical devices may be used in conditions more akin to
`
`25
`
`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.
`
`TSO001172
`
`

`

`3274.1Q03-002
`
`-4-
`
`SUMMARY OF THE INVENTION
`
`[0014] According to a first aspect of the invention, there is provided a method of
`
`operating an optical device comprising an SLM having a two-dimensional array of
`
`controllable phase-modulating elements, the method comprising
`
`5 .
`
`[0015] delineating groups of individual phase-modulating elements;
`
`[0016] selecting, from stored control data, control data for each group of phase-
`
`modulating elements;
`
`[0017] generating from the respective selected control data a respective hologram at
`
`each group of phase-modulating elements; and
`
`10
`
`[0018] 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 indeper~dently of each other.
`
`[0019] 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
`
`15
`
`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.
`
`[0020] An advantage of the method of this aspect of the invention is that stable
`
`20
`
`operation can be achieved in the presence of effects such as ageing, temperature,
`
`component, change of path through the system and assembly tolerances.
`
`[0021 ] 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.
`
`25
`
`[0022] 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
`
`TSO001173
`
`

`

`3274.1Q03-002
`
`-5-
`
`power, and to allow sampling (both of which may in some cases be achieved by
`
`direction changes).
`
`[0023] Advantageously, each phase modulating element is responsive to a respective
`
`applied voltage to provide a corresponding phase shift to emergent-light, and the
`
`method further comprises;
`
`[0024] 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;
`
`[0025] resolving the respective generated holograms modulo 2pi.
`
`10
`
`[0026] 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 27r.
`
`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.
`
`15
`
`[0027] Preferably the method comprises:
`
`[0028] providing a discrete number of voltages available for application to each phase
`
`modulating element;
`
`[00294] on the basis of the respective generated holograms, determining the desired
`
`level of phase modulation at a predetermined point on each phase modulating element
`
`20
`
`and choosing for each phase modulating element the available voltage which
`
`corresponds most closely to the desired level.
`
`[0030] Where a digital control device is used, the resolution of the digital signal does
`
`not provide a continuous spectnma of available voltages. One way of coping with this is
`
`to determine the desired modulation for each pixel and to choose the individual voltage
`
`25
`
`which will provide the closest modulation to the desired level.
`
`[0031] In another embodiment, the method comprises:
`
`[0032] providing a discrete number of voltages available for application to each phase
`
`modulating element;
`
`[0033] determining a subset of the available voltages which provides the best fit to the
`
`30
`
`generated hologram.
`
`TSO001174
`
`

`

`3274.1Q03-002
`
`-6-
`
`[0034] 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.
`
`[0035] Advantageously, the method further comprises the step of storing said control
`
`5
`
`data wherein the step of storing said control data comprises calculating an initial
`
`hologram using a desired direction change of a beam of light, applying said initial
`
`hologram to a group of phase modulating elements, and correcting the initial hologram
`
`to obtain an improved result.
`
`[0036] The method may further comprise the step of providing sensors for detecting
`
`10
`
`temperature change, and performing said varying step in response to the outputs of
`
`those sensors.
`
`[0037] The SLM may be integrated on a substrate and have an integral quarter-wave
`
`plate whereby it is substantially polarisation insensitive.
`
`[0038] Preferably the phase-modulating elements are substantially reflective, whereby
`
`15
`
`emergent beams are deflected from the specular reflection direction.
`
`[0039] In some aspects, for at least one said group ofpixels, 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.
`
`[0040] According to a second aspect of the invention there is provided an optical device
`
`20
`
`comprising an SLM and a control circuit, the SLM having a two-dimensional array of
`
`controllable phase-modulating elements and the control circuit having 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, fi’om stored control data, control data for each group of phase-modulating
`
`25
`
`elements, and to generate from the respective selected control data a respective
`
`hologram at each group of phase-modulating elements,
`
`[0041] wherein the control circuit is further constructed and arranged, to vary the
`
`delineation of the groups and/or the selection of control data
`
`TSO001175
`
`

`

`3274.1003-002
`
`-7-
`
`[0042] whereby upon illumination of said groups by respective light beams, respective
`
`emergent light beams from the groups are controllable independently of each other.
`
`[0043] An advantage of the device of ihis aspect of the invention is that stable operation
`
`can be achieved in the presence of effects such as ageing, temperature, component and
`
`5
`
`assembly tolerances. Embodiments of the device can handle many light beams
`
`simultaneously. Embodiments can be wholly reconfigurable, for example compensating
`
`differently for a number of routing configurations.
`
`[0044] 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
`
`10
`
`to vary said delineation and/or said selection.
`
`[0045] 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.
`
`[0046] In another, aspect, the invention provides an optical routing device having at least
`
`15
`
`.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 control circuit having a store
`
`20
`
`constructed and arranged to hold plural items of control data, the control circuit being
`
`constructed and an-anged 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
`
`hologram at each group of phase-modulating elements,
`
`25
`
`[0047] wherein the control circuit is further constructed and arranged, to vary the
`
`delineation of the groups and/or the selection of control data
`
`[0048] whereby upon illumination of said groups by respective light beams, respective
`
`emergent light beams from the groups are controllable independently of each other.
`
`[0049] In a further aspect, the invention provides a device for shaping one or more light
`
`30 beams in which the or each light beam is incident upon a respective group ofpixels of a
`
`TSO001176
`
`

`

`3274.1003-002
`
`-8-
`
`two-dimensional SLM, and the pixels of the or each respective group are controlled so
`
`that the corresponding beams emerging from the SLM are shaped as required.
`
`[0050] 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
`
`constructed and an’anged to receive light from the or each optical input, a focussing
`
`device and a continuous an’ay of phase modulating elements, the diffraction grating and
`
`the array of phase modulating elements being disposed in the focal plane of the
`
`focussing device whereby diverging light from a single point on the diffraction grating
`
`passes via the focussing device to form beams at the an’ay of phase modulating
`
`10
`
`elements, 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 constructed and arranged to output light to the or each optical output.
`
`[0051 ] This device allows multiwavelength input light to be distributed in wavelength
`
`terms across different groups of phase-modulating elements. This allows different
`
`15
`
`processing effects to be applied to any desired part or parts of the spectrum.
`
`[0052] 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 passing the emerging light to a focussing
`
`20
`
`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 an’ay of
`
`controllable phase-modulating elements, selectively reflecting light from different
`
`locations of said SLM and passing said reflected light to said focussing element and
`
`then to said grating.
`
`25
`
`[0053] Preferably the method comprises delineating groups of individual phase-
`
`modulating elements to receive beams of light of differing wavelength;
`
`[0054] selecting, from stored control data, control data for each group of phase-
`
`modulating elements;
`
`[0055] generating from the respective selected control data a respective hologram at
`
`30
`
`each group of phase-modulating elements; and
`
`TSO001177
`
`

`

`3274.1003-002
`
`-9-
`
`[0056] varying the delineation of the groups and!or the selection of control data.
`
`[0057] 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
`
`5 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
`
`holograms at locations of incidence of light to provide emergent beams whose direction
`
`deviates from the direction of specular reflection.
`
`[0058] In a yet further aspect, the invention provides a test or monitoring device
`
`10
`
`comprising an SLM having a two-dimensional array ofpixels, 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.
`
`[0059] The test or monitoring device may further comprise further sensors arranged to
`
`15
`
`provide signals indicative of light emerging in the specular directions.
`
`[0060] 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
`
`20
`
`beams.
`
`[0061 ] The invention further relates to an optical routing module having at least one
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`input and at least two outputs and operable to select between the outputs, the module
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`comprising a two dimensional SLM having an array ofpixels, with circuitry constructed
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`and arranged to display holograms on the pixels to route beams of different frequency to
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`respective outputs.
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`[0062] According to a later aspect of the invention there is provided an optoelectronic
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`device comprising an integrated multiple phase spatial light modulator (SLM) having a
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`plurality ofpixels, wherein each pixel can phase modulate light by a phase shift having
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`an upper and a lower limit, and wherein each pixel has an input and is responsive to a
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`30 value at said input to provide a phase modulation determined by said value, and a
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`controller for the SLM, wherein the controller has a control input receiving data
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`indicative of a desired phase modulation characteristic across an array of said pixels for
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`achieving a desired control of light incident on said array, the controller has outputs to
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`each pixel, each output being capable of assuming only a discrete number of possible
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`values, and the controller comprises a processor constructed and arranged to derive,
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`from said desired phase modulation characteristic, a non-monotonic phase modulation
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`not extending outside said upper and lower limits, and a switch constructed and
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`arranged to select between the possible values to provide a respective one value at each
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`output whereby the SLM provides said non-monotonic phase modulation.
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`10
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`[0063] Some or all of the circuitry may be on-chip leading to built-in intelligence. This
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`leads to more compact and ultimately low-cost devices. In some embodiments, some or
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`all on-chip circuitry may operate in parallel for each pixel which may provide huge time
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`advantages; in any event the avoidance of the need to transfer data off chip and
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`thereafter to read in to a computer allows configuration and reconfiguration to be faster.
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`15
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`[0064] According to another aspect of the invention there is provided a method of
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`controlling a light beam using a spatial light modulator (SLM) having an array of
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`pixels, the method comprising:
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`[0065] determining a desired phase modulation characteristic across a sub-array of said
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`pixels for achieving the desired control of said beam;
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`20
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`[0066] controlling said pixels to provide a phase modulation derived from the desired
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`phase modulation, wherein the controlling step comprises
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`[0067] providing a population of available phase modulation levels for each pixel, said
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`population comprising a discrete number of said phase modulation levels;
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`[0068] on the basis of the desired phase modulation, a level selecting step of selecting
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`25
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`for each pixel a respective one of said phase modulation levels; and
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`[0069] causing each said pixel to provide the respective one of said phase modulation
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`levels.
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`[0070] The SLM may be a multiple phase liquid crystal over silicon spatial ligh~
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`modulator having plural pixels, of a type having an integrated wave plate and a
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`reflective element, such that successive passes of a beam through the liquid crystal
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`subject each orthogonally polarised component to a substantially similar electrically-set
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`phase change.
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`[0071 ] If a non-integrated wave plate is used instead, a beam after reflection and
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`passage through the external wave plate will not pass through the same zone of the
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`SLM, unless it is following the input path, in which case the zero order" component of
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`said beam will re-enter the input fibre.
`
`[0072] The use of the wave plate and the successive pass architecture allows the SLM
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`to be substantially polarisation independent.
`
`[0073] In one embodiment the desired phase modulation at least includes a linear
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`10
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`component.
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`[0074] 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 "
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`beam. In many routing applications, two SLMs are used in series, and the displayed
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`information on the one has the inverse effect to the information displayed on the other.
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`15
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`Since the information represents phase change data, it may be regarded as a hologram.
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`Hence an output SLM may display a hologram that is the inverse of that displayed on
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`the input SLM. Routing may also be "one-to-many" (i.e. multicasting) or "one-to-all"
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`(i.e. broadcasting) rather than the more usual one-to-one in many routing devices. This
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`may be achieved by correct selection of the relevant holograms.
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`20
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`[0075] Preferably the linear modulation is resolved modulo 2pi to provide a periodic
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`ramp.
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`[0076] In another embodiment the desired phase modulation includes a non-linear
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`component.
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`[0077] Preferably the method further comprises selecting, from said array ofpixels, a
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`sub-array ofpixels for incidence by said light beam.
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`[0078] The size of a selected sub-array may vary from switch to switch according to the
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`physical size of the switch and of the pixels. However, a typical routing device may
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`have pixel arrays of between 100" 100 and 200*200, and other devices such as add/drop
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`multiplexers may have arrays of between 10"10 and 50*50. Square arrays are not
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`essential.
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`[0079] In one embodiment the level-selecting step comprises determining the desired
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`level of phase modulation at a predetermined point on each pixel and choosing for each
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`pixel, the available level which corresponds most closely to the desired level.
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`[0080] In another embodiment, the level-selecting step comprises determining a subset
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`5
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`of the available levels, which provides the best fit to the desired characteristic.
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`[0081] The subset may comprise a subset of possible levels for each pixel.
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`[0082] Alternatively the subset may comprise a set of level distributions, each having a
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`particular level for each pixel.
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`[0083] In one embodiment, the causing step includes providing a respective voltage to
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`10
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`an electrode of each pixel, wherein said electrode extends across substantially the whole
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`of the pixel.
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`[0084] Preferably again the level selecting step comprises selecting the level by a
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`modulo 2pi comparison with the desired phase modulation. The actual phase excursion
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`may be from A to A+27r where A is an arbitrary angle.
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`15
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`[0085] Preferably the step of determining the desired phase modulation comprises
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`calculating a direction change of a beam of light.
`
`[0086] Conveniently, after the step of calculating a direction change, the step of
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`determining the desired phase modulation further comprises correcting the phase
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`modulation obtained from the calculating step to obtain an improved result.
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`20
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`[0087] Advantageously, the correction step is retroactive.
`
`[0088] In another embodiment the step of determining the desired phase modulation is
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`retroactive, whereby parameters of the phase modulation are varied in response to a
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`sensed error to reduce the error.
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`[0089] A first class of embodiments relates to the simulation/synthesis of generally
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`25
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`corrective elements. In some members of the first class, the method of the invention is
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`performed to provide a device, referred to hereinafter as an accommodation element for
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`altering the focus of the light beam.
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`[0090] An example of an accommodation element is a lens. An accommodation element
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`may also be an anti-astigmatic device, for instance comprising the superposition of two
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`30 cylindrical lenses at arbitrary orientations.
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`[0091 ] In other members of the first class, the method of the invention is performed to
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`provide an aberration correction device for correcting great