`
`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 NUNIBER: 12/710,913
`
`FILING DATE: February 23, 2010
`
`PATENT NUMBER: 8,335,033
`
`iSSUE DATE: December 18, 2012
`
`By Authority of the
`
`Under Secretary of Commerce for Intellectual Property
`and Director of the United States Patent and Trademark Office
`
`Ro
`
`Certifying Officer
`
`FINISAR 1002
`TS0002021
`
`
`
`HAMILTON, BROOK, SMITH & REYNOLDS, P.C.
`Attorney Docket No.
`UTILITY
`3274.1003-004
`PATENT APPLICATION
`TRANSMITTAL
`
`Melanie Holmes
`
`First Named luventor
`
`(Only for new nonprovi’sional applications under
`37 CFR 1.53(b))
`
`Express Mail Label No.
`
`Title of
`Invention
`Name of Assignee for Thomas Swan & Co, Ltd,
`Publication Purposes
`
`OPTICAL PROCESSING
`
`City and State for
`Publication Purposes
`
`United Kingdom
`
`Commissioner %r Patents
`APPLICATION ELEMENTS
`P.O. Box I450
`ADDRESS TO:
`See MPEP chapter 600 co~merning utility patent application eontems, Alexandria, VA 22313-1450
`
`2. [] Specification Total Pages 104
`Both the claims and the abstract must start on a new page
`(F’ot’ m,ibrmatto~ m~ th~ pre/brred arral~geme,t~ see MPEP 608. O] (a))
`
`3. [] Drawing(s) (35 U.S,C. 113) Total Sheets 36
`[] Fig. of the Drawings for Pub{ication
`[] No Figure to be Published
`4. [] Oath or Declaration Total Pages [ ]
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`a. [] Newly executed (original or copy)
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`[] Copy from apriorapplication(37c.~a 1.63(d))
`
`Assignment Papers (Do not submit when e~filing application)
`
`37 CFR 3,73(b) Statement [] Power of Attorney
`(when ti~ere is ,’m assignee)
`English Translation Documer~t (ij’applicable)
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`Inibrmation Disclosure Statement
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`[] Copies of foreign patent does., publications, and other info.
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`Preliminary Amendment
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`Return Receipt Postcard (Check this box ~going by express mail)
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`~0. []
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`11. []
`[]
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`ffbr continuation/div~siona~ with Box 18 completed)
`[] A Foreign Priority Claim under 35 U.S.C. § 119 or 365
`i. [] DELETION OF INVENTOR. S(_~
`Signed statement attached deleting
`[] is made to [country], [app. #], filed 1[ ]
`i.
`inventor(s) named in the prior application,
`see 37 CFR t.63(d)(2) and 1.33(b).
`5. [] CD-ROM or CD-R in duplicate [] Text file attached herewith
`Large table or Computer Program (Appen&x)
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`ii, [] is presented in the attached
`[] Specification
`[] Preliminary Amendment
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`
`6,
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`[] Nucleotide andFor Amino Acid Sequence Submission
`(if applicable, items a.-c. are required)
`a. [] Computer Readable Form (CRF)
`i, [] Computer Readable Form (CRF)
`
`ii. [] Transfer Request (37 CFR 1.82l(e))
`b. [] Specification Sequence Listing on:
`[] CD-ROM or CD-R (2 copies); or
`i.
`ii. [] Text file attached herewith (elecwonicfiling)
`[ ] Pages
`iii~ [] Paper
`c. [] Statements verfl’ying identity of above copies
`
`[] Declaration
`13b. [] A Certified Copy of each Priority Document
`i.
`[] is enclosed
`[] was filed in U.S. Application No, [ ]
`ii.
`[] Nonpublication Request under 35 U SC. 122(bX2XB)(i).
`Applican! nmsl attach form PTO/SB!35 or equivalent
`[] Remarks
`[] Smalt Entity Statement(s)
`[] Other:
`
`14.
`
`15,
`16.
`17.
`
`18. If a CONTINUING APPLICATION, check appropriate box, and supply the requisite inl~rmation below and in the first sentence of the
`specification following the title:
`
`[] Continuation
`
`[] Divisional
`
`[] Continuation-in-part (C1P)
`
`of prior application No.: fl/978,258
`
`Group Art Unit: 2873
`Prior application information: Examiner: Loha Ben
`The entire disclosure of the prior application is considered a part of the disclosure of the accompanying application and is hereby
`incorporated b~ reference. (Add standard Related A~lications section with incorporation b~, re,[brence to s~eei~cation or u1~date same)
`19. CORRESPONDENCE ADDRESS
`
`Customer No. 02 [ 005
`HAMILTON, BROOK, SMITH & REYNOLDS, P.C,
`530 Virginia Road, P~O, Box 9133
`
`NAME
`
`ADDRESS
`CITY
`COUNTRY
`
`. Cow, cord
`i usa
`
`l STATE ~A ..............................
`! ziP COD~i";-10i74~L9lJ~ ............................................
`! ........ ~tqgiTii]~:i~i~g- ........
`, (978) 341-0036 ..... I .... ~.’.A.X ...... /(978) 341-0136 .......
`
`Signature
`
`:
`
`" ,! -
`
`-7//// 1/-~
`
`Date
`
`lypea or I tinted lxa~e
`
`961655_1
`
`~
`
`" ’
`
`"
`
`{
`
`-
`
`TS0002022
`
`
`
`961661~I
`TJM/jk
`February 23, 2010
`
`PATENT APPLICATION
`Attorney’s Docket No.: 3274.1003-004
`
`IN THE UNITED STATES PATENT AND TRADEMARK OFFICE
`
`Applicant:
`
`Melanie Hohnes
`
`Continuation Application of:
`
`Application No.:
`
`11/978,258
`
`Filed:
`
`October 29, 2007
`
`For:
`
`OPTICAL PROCESSING
`
`Date:
`
`EXPRESS MAIL LABEL NO.
`
`REMARKS
`
`Commissioner for Patents
`P.O. Box !450
`Alexandria, VA 223 t 3-1450
`
`Sir:
`
`The above-captioned application is a Continuation of application number 11/978,258
`
`filed on October 29, 2007 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.
`
`All of the claims from the parent application have been omitted. A new claim set is being
`
`presented herein for examination.
`
`Respectfully submitted,
`
`HAMILTON, BROOK, SMITH & REYNOLDS, P.C.
`
`By
`Ti~
`Registration No.: 39.
`Telephone: (978) 341-0036
`Facsimile: (978) 341-0136
`
`Concord, MA 01742-9133
`Date:
`
`TS0002023
`
`
`
`961516
`
`TJMijk
`February 23, 2010
`
`PATENT APPLICATION
`Docket No~ 3274.1003-004
`
`-1-
`
`Date:
`
`Express Mail Label No.
`
`Inv entor:
`
`Mel.anie Holmes
`
`Attorney’s Docket No.’
`
`3274.1003-004
`
`OPTICAL PROCESSING
`
`RELATED APPLICATIONS
`
`This application is a continuation of U.S. Application No. 11/978,258, filed
`
`October 29, 2007, which is a continuation of U.S. Application No. t 1/515,389, filed
`
`September 1, 2006, which is a divisional of U.S. Application No. 10/487,810, which is
`
`5
`
`the U.S. National Stage of International Application No. PCTiGB02/0401 I, filed
`
`September 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 September 3,
`
`2001. The entire teachings of the above application(s) are incorporated herein by
`
`reference.
`
`10
`
`FIELD OF THE INVENTION
`
`[0001 ] The present invention relates to an optical device and to a method of controlling
`
`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
`
`15
`
`field of application is mainly envisaged as being to fields in which reconfiguration
`
`between inputs mid outputs is likely, and stability of performance is a significant
`
`requirement.
`
`BACKGROUND OF THE INVENTION
`
`[0003] It has previously been proposed to use so-called spatial light modulators to
`
`20
`
`control the routing of light beams within an optical system, for instance from selected
`
`TS0002024
`
`
`
`3274.1003-004
`
`-2-
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`ones of a number of input optical fibres to selected ones of output fibres.
`
`[0004] 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
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`5
`
`system [:ailure or insertion toss due to the very tight alignment tolerances for optical
`
`fibres, especially for single-mode optical fibres. Every time a fibre connector is
`
`connected, it may provide a different alignment error. Another example is an optical
`
`switch in which aberrations, phase distortions and component misaligrm~ents result in
`
`poor optical coupling efficiency into the intended output optical fibres. This in turn may
`
`10
`
`lead to high insertion loss. The aberrated propagating waves may diffract into intensity
`
`fluctuations creating significant unwanted coupling of light into other output optical
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`tlbres, leading to levels of crosstalk that impede operation. In some cases, particularly
`
`where iong path lengths are involved, the component misalignment may occur due to
`
`ageing or temperature effects.
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`15
`
`[0005] 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 demuttiplexers use expensive thermally stable opto-mechanics to cope
`
`with the problems associated with long path lengths.
`
`[00061 Certain optical systems have a requirement for reconfigurability, Such
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`20
`
`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 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
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`25
`
`phase distortions may vary for each input beam or as a function of the required output
`
`port.
`
`[00071 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
`
`3O
`
`changes in the system behaviour due to temperature and ageing, create the desirability
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`TS0002025
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`
`
`3274.1003-004
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`-3-
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`for dynamic direction controt, aberration correction, phase distortion compensation or
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`misalignment compensation.
`
`[0009] It should be noted that the features of dynamic direction control, phase distortion
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`compensation and misalignment control are not restricted to systems using input bearns
`
`coming from optical fibres. Such features may also be advantageous in a reconl]gurable
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`optical system. Another static system in which dynamic control of phase distortion,
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`direction and (relative) misalignment would be advantageous is one in which the quality
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`and/or position of the input beams is time-varying.
`
`[0010] Often the input and output beams for optical systems contain a multiplex of
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`10
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`many optical signals at different wavelengths, and these signals may need to be
`
`separated and adaptively and individually processed inside the system. Sometimes,
`
`although the net aim of a systern 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
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`15
`
`device used to route each channel to have a low insertion loss and to operate quickly.
`
`[00 l 1] It is an aim of some aspects of the present invention at least partly to mitigate
`
`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.
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`20
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`[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
`
`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 m’e desirably inexpensive, and
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`25
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`desirably inhabit and successfully operate in environments thai 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
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`pertbrmance may be acceptable.
`
`TS0002026
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`
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`3274.t003-004
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`-4-
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`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
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`5
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`[0015] delineating groups of individual phase-modulating elements;
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`[00 ! 6] selecting, from stored control data, control data for each group of phase-
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`modulating elements;
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`[0017] generating from the respective selected control data a respective hologrmn at
`
`each group of phase-modulating elements; and
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`10
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`[00181 varying the delineation of the groups and/or the selection of control data
`
`whereby upon. illumination of said groups by respective light beams, respective
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`emergent light beams from the groups are controllable,,,~,~,~,.,~~"~ ..... ~’-~’~ of each other.
`
`[00191 In some embodiments, the variation of the delineation and/or control data
`
`selection is in response to a signal or signals indicming a non-optimal performance of
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`15
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`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
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`operating signal, for example a signal giving the result of sensing non-performance
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`system parameters such as temperature.
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`[0020] An advantage of the method of this aspect of the invention is that stable
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`20
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`operation can be achieved in the presence of effects such as ageing, temperature,
`
`component, change of path through the system and assembly tolerances.
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`[0021] Pre~i~rably, control of said light beams is selected from the group comprising:
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`control of direction, control of power, focussing, aberration compensation, sampling
`
`and bearn shaping.
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`25
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`[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 m’e likely to be needed to cope with changes of routing as
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`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
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`TS0002027
`
`
`
`3274.1003-004
`
`-5-
`
`power, and to allow sampling (both of which may in some cases be achieved by
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`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.
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`10
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`[0026] The preferred SLM uses a liquid crystal material to provide phase shift and the
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`liquid crystal material is not capable of large phase shifts beyond plus or minus 2m
`
`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
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`smaller.
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`15
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`[0027] Preferably the method comprises:
`
`[0028] providing a discrete number of voltages available for application to each phase
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`modulating element;
`
`[0029] on the basis of the respective generated holograms, determining the desired level
`
`of phase modulation at a predetermined point on each phase modulating element and
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`20
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`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 spectrum of available voltages. One way of coping with this is
`
`to determine the desired modulation for each pixel and to choose the individual voltage
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`25
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`which will provide the closest modulation to the desired level.
`
`[0031 ] In another embodimem, the method comprises:
`
`[0032] providing a discrete nmnber of voltages available for application to each phase
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`modulating element;
`
`[00331 determining a subset of the available voltages which provides the best fit to the
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`30
`
`generated hologram.
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`TS0002028
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`
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`3274.1003-004
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`[0034] Another technique is to look at the pixels of the group as a whole and to select
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`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
`
`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 fiarther comprise the step of providing sensors for detecting
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`10
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`temperature change, and performing said varying step in response to the outputs of
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`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
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`15
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`emergent beams are deflected from the specular reflection direction.
`
`[00391 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.
`
`[00401 According to a second aspect of the invention there is provided an optical device
`
`2O
`
`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, from stored control data, control data for each group of phase-modulating
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`25
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`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
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`TS0002029
`
`
`
`3274.1003-004
`
`[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 this aspect of the invention is that stable operation
`
`can be achieved in the presence of eft~cts such as ageing, temperature, component and
`
`assembly tolerances. Embodiments of the device can handle many light beams
`
`simultaneously. Embodiments can be wholly reconfigurable, for example compensating
`
`differently for a num.ber 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
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`10
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`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
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`15
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`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
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`20
`
`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
`
`hologram at each group of phase-modulating elements,
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`25
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`[0047J 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
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`30
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`beams in which the or each light beam is incident upon a respective group of pixels of a
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`TS0002030
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`
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`3274.1003-004
`
`-8-
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`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
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`5
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`constructed 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 diffi’action grating
`
`passes via the focussing device to form beams at tt~e array of phase modulating
`
`t0
`
`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.
`
`[005I] This device allows multiwavelength input light to be distributed in wavelength
`
`terms across different groups of phase-modulating elements. This allows different
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`15
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`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
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`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 array of
`
`controllable phase-modulating elements, selectively reflecting light ti’om dil~[’erent
`
`locations of said SLM and passing said reflected light to said focussing element and
`
`then to said grating.
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`25
`
`[0053] Preferably the method comprises delineating groups of individual phase-
`
`modulating elements to receive beams of light of differing wavelength;
`
`[0054] selecting, fi’om stored control data, control data tier 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
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`TS0002031
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`
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`3274.1003-004
`
`[00561 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 directio~ 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
`
`2O
`
`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 rome 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 of pixels, 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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`3O
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`value at said input to provide a phase modulation determined by said value, and a
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`TS0002032
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`3274.1003-004
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`-i0-
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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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`5
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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 tbr achieving the desired control of said beam;
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`2O
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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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`[00671 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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`[00691 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 light
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`modulator having plural pixels, of a type having an integrated wave plate and a
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`3O
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`reflective element, such that successive passes of a beam through the liquid crystal
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`TS0002033
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`3274.1003-004
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`-11 -
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`sub,~ect each orthogonally polarised component to a substantially similar electrically-set
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`phase chmage.
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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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`5
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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.
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`[0072] The use of the wave plate and the successive pass architecture allows the SLM
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`to be substantially polarisation independent.
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`[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
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`be used to route a beam of light, i.e. to select a new direction of propagation for the
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`bea~ 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-mm~y" (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 ofpixets 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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`30 essential.
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`TS0002034
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`3274.1003-004
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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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`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 pixeI.
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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.
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`[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.
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`[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 accomm