UNITED STATES DEPARTMENT OF COMMERCE
`
`United States Patent and Trademark Office
`
`May 16, 2013
`
`THIS ISTO CERTIFY THAT 3ANNEXED IS A TRUE COPY FROM THE
`
`RECORDS OF THIS OFFICE OF THE FILE WRAPPER AND CONTENTS
`
`OF:
`
`APPLICATION NUMBER: 10/487,810
`FILING DATE: September 10, 2004
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`PATENT NUMBER: 7,145,710
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`ISSUE DATE: December 05, 2006
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`By Authority of the
`
`Under Secretary of Commerce for Intellectual Property
`and Director of the United States Patent and Trademark Office
`
`R. PONDEXTER
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`Certifying Officer
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`FNC 1013
`TS0000290
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`(.12) INTERNATIONAL APPLICATION PUBLISHED UN-DER THE PATENT COOPERATION TREATY (PC’T)
`
`(19) World Intellectual Pr.opertY Organization
`International Bureau
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`I!11111 111111111111111111111111111111111111111111111111111111111 111111111111
`
`(4 International Publication Date
`29 November 2001 (29.11.2001)
`
`PCT
`
`(10) International Publication Number
`WO 01/90823 A1
`
`(51) International Patent ClassificationT:
`1/12, 1/08
`
`G03H 1/26, (74)
`
`Agent: RUGGIERO, Charles, N., J.; Ohlandt, Gree-
`ley, Ruggiero & Perle, L.L.E, 10th floor, One Landmark
`Sqlaare, Stamford, CT 06901-2682 (US)..
`
`International Application Number: ’ PCT/US01/16174
`
`International Filing Date:
`
`18 May 2001 (18.05.2001)
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`Filing Language:
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`Publication Language:
`
`English
`
`English
`
`(81) Designated States (national.): AE, AG, AL, AM, AT, AU,
`AZ, BA, BB, BG, BR, BY, BZ, CA, CH, CN, CO, CR, CU,
`CZ~, DE, DK, DM, DZ, EE, ES, FI, GB, GD, GE, GH, GM,
`HR, HU, ID, IL, IN, IS, JP, KE, KG, KP, KR, KZ, LC, LK,
`LR, LS, LT, LU, LV, MA, MD, MG, MK, MN, MW, MX,
`MZ, NO, NZ; PL, 1717, RO, RU, SD, SE, SG, SI, SK, SL,
`TJ, TN[, TR, T[’, TZ, UA, UG, UZ, VN, YIJ, ZA,
`
`Priority Data: ,
`60/206,074:
`
`I
`22 May 200!~ (22.05.2000) US
`
`(71)
`
`Applicant: INTELLIGENT PIXELS, INC. [-LIS/US];
`100 Mill Plain Road, Danbury, CT 06811 (US).
`
`Designated States (regional): AR_IPO patent (GH, GM,
`KE, IS, MW, MZ, SD, SL, SZ, TZ, UG, ZW), Era’asian
`patent (AM, AZ,.BY, KG, KZ, MD, RU, TJ, TIM), European
`patent (AT,. BE, CH; CY" DE, DK~
`IT, LU, MC, NL; PT, SE, TR), OAPI patent 03F, B J, CF,
`CG, CI, CM, GA, GN, GW, ML, M-R, NE, SN, TD, TG).
`
`(21)
`
`(22)
`
`(26)
`
`0o)
`
`(72)
`
`Inventorsi CROSSLAND, William, Alden; 15 School
`Lane, Marlow, Essex CM20 2QD (GB).-WILKINSON,
`Timothy, David; Jesus College, Jesus Lane, Cambridge
`CB5 8BL (GB). ESHRAGHIAN, Kamran; 23 Caldera
`Close, Mindarie,_W.A. 6030 (ALl).
`
`Published:
`-- with international searcti report
`before the expiration of the time limit for amending the
`claims and to be republished in the event of receipt of
`amendments
`
`[Continued on next page]
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`(54) Title: ELECTRO-OPTICAL COMPONENT HAVING A RECON-FIGURABLE PHASE STATE
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`¯ ~ (57) Abstract: There is provided.an electro-optical component comprising: a substrate (130); a phase,variable element carried on
`the substrate (135); a memory carried on the substrate for storing data representative of a phase state for the phase-v_affable element;
`~and a controller (140) carried on the substrate, for utilizing [he data and setting the phase statefor the element. There also provided
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`~ an electro-optical componenVcomprising: substrate (730); a phase-variable element carded on the substrate (735); and a circuit (740)
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`carried on the substrate for computing and applying a phase state for the phase-variable element. -
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`I IIIIIIIIIIIIIIII111111111111111111111i1111111111111111111111111t1 111111i111!1
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`For two-letter codes and other abbreviations, refer to the "Guid-
`ance Notes on Codes andAbbreviations" appearing at the begin-
`ning of each regular issue of the PCT Gazette.
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`ELECTRO-OPTICAL COMPONENT
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`HAV’E~G A RECONFIGURABLE ~PHASE STATE
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`¯ BACKGROUND.. OF TI--IE ~0N
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`~5
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`1. Field of the Invention
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`The present invention relates to an electro-optical component having.a
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`reconfigurable phase state. The component is particularly suitable for steering an
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`10
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`optical beam. Such a component can be used in applications such as metropolitan
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`area network (MAN)optical terabit switching/routing, all-optical cross-connect
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`systems for dense wave dlvision.multipiexing (DWDM) networks, photonies signal
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`processing, and free space laser eommunleation.
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`21 . .-Descriptionofthe l~rior Art
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`One of the most critical elements within the framework of optical transport
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`networks based on wavelength-division multiplexing is an optical cross-connect
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`(OXC). This optical routing device provides network management in the optical
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`layer, with potential throughputs ofterabits per second. An optical cross connection
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`may be acc6mplishedby either a hybrid approach or by an all-optical approach.
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`The hybrid approach converts an optical data stream into an electronic data
`stream: It USes an electronic cross connection, and then performs an electrical-optical
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`25
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`conversion. There is an inherent problem with the hybrid approach when used in a
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`networked environment. Historically, microprocessor speed has doubled almost
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`every 18 months, but demand for network capacity has increased at a much faster rate,
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`thus eansing a widening gap between the microprocessor speed and the volume of
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`network traffic.. The effect of this gap places a great burden on the electronic cross
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`30
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`connections for optical links that are implemented in metropolitan and long-haul
`
`networks. Optic...a! (cid:128) .a~rier 48 (OC-48) is one of the layers of hierarchy in a..
`conventional:Synehronous optical.network (SONET). The procedure of optical-
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`electrical-optical (OEO) conversion becomes more difficult as the.speed ofthe link
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`reaches 0C-48 (2.5 Gbps), and is even more difficult at higher speeds. At such
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`speeds, the electronic circuitry of the OEO causes a network bottleneck.
`
`The all optical approach performs the cross connection entirely in the.opti~al
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`domain. The all optical approach does not have the same speed limitations as the
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`hybrid approach. It is normally used for fiber channel, high bandwidth cross
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`¯
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`connections. Taking ~x.bl to represent the dimension of the OXC, Le. the number of ’
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`input and output ports, then 1V is typically between 2 and 32 for an all optical OXC. ...
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`10
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`However,. larger dimension OXCs, with Nup to several hundreds.or even a thousand
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`are contemplated, h4any proposed optical cross-connectarchitectures include a set 0f..
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`optical space switches capable of switching a.large number of input and output fibers.
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`However, despite a significant investment for development of an all photonics OXC,
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`it is presently a major challenge to design a reliable all photonics, non-blocking, low -
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`loss, scalable and ~econfigurable optical switch, even for :N in the order o£32-40.
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`Several different technologies have been tried for Optical interconnects, but
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`none is yet regarded as a technology .or market place leader. This is due, in part, to an
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`impracticality of the switching media or to a lack of scalability in cross-connecting a
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`2O
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`suitable number ofinpurt and output ports. .-
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`For example, guided wave systems use nonlinear electro-0ptic components,
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`sometimes with diffraction effects, to couple Optical signals from one fiber ~wave- ~.
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`guide to another. Prominent attention in this class of devices has been given to fiber
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`25
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`Bragg switches and other fiber pro~mity coupling schemes such as. devices.using "
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`electro-optic effects in lithium niobite, silica or polymerbased materials. Alimitation
`
`o£these switch meehanismsis scalability. It is_difficult to construct guided,wave
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`switches greater than an 8x8 size because they use substrates of limited size,. The
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`interconnection o£ several small switches to construct a largo switch is also.
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`3O
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`impractical because of the bulkiness of optical fiber harnesses.
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`¯ An advantage of a f~ee-space optical switching system is that it can exploit the
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`non-interfer’enceproperty of optiCal’signals to switch a large number of optical ports.
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`¯ The two most c~mmon mechanisms for bea__m steeringin this c.lassof devices are
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`diffraction and mechanical steer!~g... ~.
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`For mechanical beam steering devices, a good deal of development effort
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`appears to be concentrated on mirrors using micro, electro mechanical systems
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`0ViF.~). Several devices being manufactured, commercially, such as.the Lambda
`RouterTM fromLucent Technologies, Inc.
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`10
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`Another mechanical approach that has received considerable attention is the
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`use of micro-"bubbles", such as in the 1~13565A "32 x 32 Photonic Switch", 9ffered by
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`Agilent Technologies. !n a micro-bubble system,~ the index of refraction of a ..
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`transmission media is modified by mechanically moving a microsoopi~ bubble in the
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`15
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`medial
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`" :" Disadvantages of a MP_NIS-based switch include limitations relating to
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`mechanical, thermal and electrostatic stability. A MEMS-based.switeh typically
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`requires continiaous adaptive alignment tO maintain a connection and its reliability is a
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`20
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`function of that adaptive alignment. Another disadvantage of’the MEMS-based
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`switch is its optics, which typically require highly collimated optical paths, usually
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`employing microlenses that eannof significantly dit~act the light bean~
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`In diffractivesteering,, an optical signal is redirected using a phase hologram,
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`25
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`also known as a grating or a diffraction pattern, recorded on a spatial light modulator.
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`Several materials have been proposed for use in such systems, including HI-V
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`semiconductors such as InCmAs/InP, and liquid crystal on silicon systems (LCOS).
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`One advantage of using direct-gap semiconductors is.the ease with which active
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`optical components, such as lasers and Optical amplifiers, can be incorporated into a
`circuit, thus allowing the possibility of signal boosting at the switching stage~ A
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`30
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`disadvantage of such materials is the cost and difficulty of large-scale manufacturing.
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`s~Y OF THE INVENTION
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`It is an obj ect Of the present invention to provide an improved optical
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`component having a variable phase state.
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`It is another object of the present invention to employ such .a component in an
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`optical switch in which a plurality of’the, components are configured in an array ffor
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`’ phase modulating light in order to steer the fight, from an input port to an output port
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`-by diffraction.
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`I0
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`It is yet another object of the present invention to provide such a switch in
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`which the arrayoff phase modulating components and the parallel processing
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`capability are both carried on the same substrate.
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`15
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`It is a further object of the present invention to.provide such a switch in vc~ch
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`the circuit computes a reconfigurable phase pattern or.hologram to optimize the
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`performance of the switch by reducing optical, losses, and to minimize the quanta of
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`optical signal falling into adjacent channels, i.e. crosstalk.
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`20
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`It is yet a further object ofthepresent invention to provide such a switch in
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`which a hologram routes light from a single input port to a single output port, or from
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`a single input port to multiple output ports, i.e., multicasting, or from multiple input
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`ports to a single output port, i.e., inverse-multieasting.
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`25
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`These and other objects of the present invention are provided by an electro-
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`optical component in accordance With the present invention. One embodiment
`
`provides an electro-optical component comprising (a) a substrate, (b) a phase-variable
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`element carried on the substrate, (e) a memory carried on the substrate for.storing data
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`¯ representativeoff a phase state for the. phase-variable element; andi(d) a controller
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`30
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`carried on the substrate, for utilizing the data and settingthe phase state for the
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`element. Another embodiment provides an eleetro-o ~tical component comprising (a)
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`4
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`a substrate, (b) a phase-variable element carried on the subStrate’ and (e) a circuit ,
`carried on the substrate for computing a phase state for the phase-variable element.
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`DESCRIPTION OF THE DRAWING.S
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`Fig. 1 is a schematic representation of an optioal switch in accordance with the
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`present invention.
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`Figs. 2A and 2B are schematic representations of alternate embodiments of
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`10
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`optical switches in accordance with the present invention
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`Fig. 3 is an illustration showing a relationship between a hologram and its
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`replay field.
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`15
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`Fig. 4 is a side-section view of a spatial light modulator, as used in an optical
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`switch in accordance with the present invention.
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`Figs. 5A- 5C are illustrations of various arrangements ofone or more phase~
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`variable elements and circuitry on a substrate.
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`20
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`Fig. 6 is a flowchart of an algorithm for generating a hologram by projection
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`of oonstraints.
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`Fig. 7 is a schematic representation of an optical switch in accordance with the
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`25
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`present -invention.
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`DESCRIPTION OF ~ INVENTION
`
`An embodiment of the Present invention provides for. an electro-optical
`component comprising (a) a substrate, (b) a phase-variable element carded on the
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`30
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`substrate, (b)a memory Carried onthe substrate for storing data representative of a
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`phase state for the phase-variable element; and (d) a"c0ntroller carded on the
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`Substrate, for utilizing the data and setting the phase state for the phase-variable
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`element. The component can be employed in an optical switch to direct light from a
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`first port to a second port.
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`5
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`Another embodiment of the present invention provides for an electro-optical
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`component comprising(a) a substrate, (b) a phase-variable element carried on the
`
`substrate, and (e) a circuit carried on the substrate for computing a phase state.for the
`phase-variable element. This component can also be employed in an optical wc~i_’teh to
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`direct light f~om a first port to a second port.
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`10
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`15
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`In another embodiment, the optical switch includes (a) a substrate, (b)a. liquid
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`crystal carried on the substrate; and (c) a circuit carried on the substrate for computing
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`a hologram and controlling the liquid crystal to produce the hologram to direct fight
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`from a first port to a second port.. "
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`. The optical switch uses a dynamic beam steering phase hologram written onto
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`a liquid crystal over silicon (LeO.S) spatial light modulator (SLM). A phase
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`hologram is a transmissive or reflective element that changes the phase of fight
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`transmitted through, or reflected by, the element.~ A replay field is the result of the
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`20
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`phase hologram. The LCOS SLM produces a hologram, i.e., a pattern of phases, that.
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`steers light by diffraction in order to route the light from One or mo{e input fibers to ..
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`one or more output fibers.
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`The holograms produced on the SLM may appear as a one-dimensional or
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`25 _ ¯ two-dimensional image. Accordingly, the image elements, whether transmissive or
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`~eflective, are sometimes referred,to as "pixels", i.e., picture elements.
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`Fig. 7 is a schematic representation of an optical switch 700 in accordance
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`with the present invention. The principal elements of switch 700 include an input port
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`30.
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`705, a spatial light modulator (SLM) 715, and a plurality of output ports 725A, 725B.
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`and 725C~ A first lens 710 is interposed between input port 705 and SLM 715, and a
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`second lens 720 is interposed between SLM 715 and output ports 725A, 72513 and
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`72512.
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`Light from input port 705 is cast upon lens 710, which collimates the fight and
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`projects it onto SLM 715. The light travels through SLM 715 and onto lens 720,
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`- which focuses the light onto one or more of output ports 725A, 72533 and725C. A
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`hologr_a.m produced on SLM 715 directs the lightto one or more of output ports 725A,
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`725B and 725C. In Fig. 7, the light is shown as being directed to output port 725A..
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`10
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`sLM 715 is an electro-optical component that includes a substrate 730 upon
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`which is carried (a) an element, shown in 17ig. 7 as one of an array of elements 735
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`and (b) a circuit 740. Elements 735 have a variable phase. That is, the phase, i.e.,
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`time delay, of light propagating through elements 735 can be varied. When the phase
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`of light propagating through an element 735 is varied relative to the phase of another
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`15
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`element 735, the light forms an interference pattern that influences.the direction in
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`which the light travels, as is well known in the field of optics. Thus, by controlling
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`the rdative phasing, the light can be directed to a desired target. Liquid crystal is a
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`suitable material for elements 735. Liquid crystal is conventionally provided in a thin
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`film sheet, and as such, individuals of elements 735 would-correspond to regions of
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`the liquid crystal rather than being discrete, separate, Squid crystal elements.
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`Circuit 740 sets the phase states for elements 735 for directing the light’from
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`input port 705 to output port 725A. That is, a hologram is produced b~ elements 735.
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`Optionally, circuit 740 also computes the hologram. In Fig. 7, the result of the
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`25
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`hologram, causes a point of light intensity at output port 725,6,.
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`Fig. 1 is a schematic representation of an optical switch.100 in accordance
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`with the present invention. The principal components of switch 100 include a fiber
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`array 115, an SLM 105, and a lens 110 interposed between fiber array 115 "and SLNI
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`¯ Fiber array 115 has afirst port 120 and a second port 125. Light entezs switch
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`100 via first port 120 and proceeds to lens 1i0, which is, for example, a Fourier lens.
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`having a positive focal length. Lens 110 collimates the light. From lens 110, the light
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`is projected onto SLM105. The light is reflected by SLM !05(and travels via lens
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`5
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`110 to second port 125. As explained below, a hologram produced on SLM 105
`
`steers the lightfrom first port 120 to second port 125.
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`SLM 105 is an electro-optical compon?nt that includes a substrate 130 upon
`which is disPosed (a) areflective element, shown in Fig~ 1 as one of an array of
`
`10
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`reflective elements 135, and (b) a circuit 140 underneath and around reflective "
`elements 135. Reflective elements 135. have a variable phase state That is, the phase, "
`
`i.e., time delay, of.light reflected by reflective elements 135 can be varied. When the
`light is reflected by two or more of reflective elements 135, the iight forms an
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`interference pattern that influences the direction in which the light is reflected. As the
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`15
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`phase state of an individual reflective element 135 is .variable, it can be altered
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`relative to the phase state of other reflective elements 135 to control the direction in
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`which the fight is reflected.. A practical embodiment of array reflective elements 135
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`can be realized by employing a liquid crystal over an array of mirrors.
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`20
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`Circuit 140 controls the phase state, i.e., hologram, for reflective elements 135
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`to control the direction in which the light is reflected. Optionally, circuit 140also
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`computes the hologram. The result of the.hologram is projected on fiber array 115,
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`with points of intensity at one ormore ports in fiber array 115. In Fig.. 1 the light is
`¯ Shown as being directed from first port 120 to second port 125, however, in terms of
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`25
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`functionality, first port 120 and second port 125 are preferably ~acha hi-directional
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`input/output port.
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`Fig. 2A is a schematic representation of an optical switch 200 configuredwith
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`two SLMs 210 and 215, to provide a greater number 0f ports than that of the
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`30
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`configuration in Fig. 1. Switch 200 also includes a first fiber array 205, a second fiber
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`First fiber array 205 arid second fiber array 220 are each an array ofbi-
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`directioriM fiber ports. Lens array 225 is a series of refractive optical elements that
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`transfer one or more optical beams through switch 200.
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`5
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`Input signals inthe form of light beams or pulses are projected from one or
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`more ports in first fiber array 205, through one or more lenses of lens array 225 onto
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`SLM 210. SLM 210 produces a first routing hologram that directs the light through
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`one or more lenses of lens array 225 onto SLM 215. SLM 215 produces a second.
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`routing hologram that directs the light through-one or more lenses Of lens array 225
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`10
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`onto one or more ports in second fiber array 220.
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`. SLMs 210 and 215 each havo an array ofphase-variablo reflective elements on
`
`its Surface to produce reconfigurable phase holograms that control the deflection
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`angle of a beam of light. Thus, fight from any port of first fiber array 205 can be
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`15
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`selectively routed to any port of second fiber array 220, and vice versa.
`
`Switch 200 accommodates fiber arrays of a substantially greater dimension
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`than that of typical prior art swi~tches. For example, first fiber array 205 and second
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`fiber array 220 may each have 1000 poRs. " ~
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`The optical configuration of switch 200 influences the distribution of the
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`pixels on each of SL1VIs 21Oand 215, and the manner in which a hologram is
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`generated thereon. For example, the optical configuration influences the size of the
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`region on each of SLIVIs 210 and 2!5 onto which the light is projected~
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`20
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`25
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`Fig. 2B is a schematic representation of an optical switch 250 in another
`
`embodiment 0£the present invention. Switch 250 includes an input/output fiber array
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`230, a lens 235, e.g~, a l~ourier transform lens, an SLM 240 and a reflector 245. ,
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`30
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`Light from a first port 232 of input/output fiber array 230 is projected through
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`lens 235 onto a first region 242 of SLM-240. SLM 240 produces a first hologram.in
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`first region 242 that. directs .th~ light to reflector 245, which, in turn, directs ttie light
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`to a second region 247 of SLM 240. SLM 240 produces a second hologr_am’in second
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`region 247 to direct the light through lens 235 and.onto a selected second polt234 of
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`i.nput/output fiber¯ array 230. . .
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`5
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`Referring again to Fig. 2A, the architecture in Fig. 2A can be made tomimic
`
`that of Fig. 2B by "folding" switch 200 about a central point.. That is, the architecture
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`of Fig. 2A approaches that of Fig. 2B by placing a mirror at the central point so that
`first fiber array 205 and second fiber array 220 are s~de by side, and SLM 210and
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`SLM 215 are side by side. .-
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`10
`
`Fig. 3 is an illustration showing a relationship between.a hologram and its
`
`replay field as can be-provided by the optical switch of the present invention....
`
`Referring again to Fig. 2A for example, a reconfigurable phase hologram 305 .is
`
`situated at a Fourier plane, e.g., on the array of phase-variable reflective elements at
`
`the surface of SLMs 210 and 215. In the preferred embodiment,, phase hologram 305
`
`is written into, that is, programmed in_to, the reflective elements to provide phase-only
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`modulation of’the incident fight. The reflective elements diffi, aet the light from first
`
`fiber array 205 to produce phase hologram 305. Ai%er a Fourier tran.~form of the
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`hologram, a resulting diffi’acted.pattern, also known as a replay field 310, is produced
`
`20
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`at second fiber array 220.
`
`Note that.replay field 310 shows 16 points ofhght. Fig: 3 illustrates a.feature
`
`of the present invention called multieasting. In a multioast, one input port is coupled
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`to two or more output ports, i.e., simultaneous routing of light from one. input port to a
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`25
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`plurality of output ports. This can be done with a hologram that generates multiple
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`peaks, as shown in replay field 310, rather than a single peak. Fig. 3 shows an
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`example era 1 to 16 multicast hologram In a similar fashion, the same set of
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`holograms can also be used to route ¯multiple input ports to a single output po~
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`referred to as multiplexing, provided that the inputs have different wavelengths~ This
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`30. can be used for wavelength division multiplexing (WDM).
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`Fig. 4 shows a cross section of an exemplary, sLM 400 in accordance with the
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`present inveiafion. The principal features, of SLM 400 are a substrate ¯410 that carries
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`(a) a silicon die 405 containing a circuit 406, (b) an array of mirrors 407, and (c) a
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`liquid crystal element415, which has a variable phase state. In Fig. 4, SL1V1400 is ¯
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`configured to show liquid crystal element 415 positioned upon array of mirrors 407,
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`which ispositioned upon circuit 406.. ¯However, .any convenient arrangement of these
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`components is contemplated as being within the scope of the Present invention. ’
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`The phase shift of light through liquid crystal elemen~ 415 is varied, or set for
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`a specificvalue, by applying an electric field across liquid crystal dement 415.
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`Circuit 406 controls the phase state of liquidcrystal element 415 by applying voltages
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`to the array of mirrors 407 and thus developingthe elech-ic field across liquid crystal
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`dement 415. In practiceeach mirror 407 influences the phase state era region of - ¯
`liquid crystal element 415 to which themirror is adjacent. Thus, circuit 406,controls
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`.the phase state era plurality ofr’egions of liquid crystal dement 415 by controlling
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`the individual voltages applied to each of mirrors 407.
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`¯ Circuit 406 executes the processes described herein, and it may include one or
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`more subordinate circuits for executing portions of the processes or ancillary
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`20
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`funeti0ns. In one embodiment of the present invention, circuit 406 includes a
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`memory for storing data representative of a plurality of configurations of phase state
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`for liquid crystal dement 415, and a controller for utilizing the dataand setting the
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`phase states by applying signals to mirrors 407. Such data can be determined by an
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`external system in a calibration procedure during manufacturing of SLM 400,or
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`25
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`during manufacturing of an assembly in which SLM 400 is a component. The
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`external system computes.the phase states, and thereafter, the data is written into the
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`memory of circuit 406. In another embodiment, circuit 406 includes a processor and
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`associated memory for storing data in order to.compute the phase states locally, and a
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`controller to Set the ~hases states by applying signals to mirrors 407.
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`SLM 400 also includes, on top of liquid crystal elements 415, a glass co~rer
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`420.
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`Glass cover 420 has a layer 435 o£Indium TinOxide (ITO) to provide a.return
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`path conductor for signals from circuit 406 via bond-wires 425.
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`5
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`On the optical side of SLM 400, the_array of mirrors 407 allows for steering of"
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`a light beam by producing a hologram using v .m-iable phase liquid ~rystal elements
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`415. In cirbuit 406, the.following functionalities can be implemented:
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`¯ DC balance schemes inciuding shifting and scrolling;
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`10
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`¯ Algorithms for reconfigurable beam steering and hologrern generation;
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`¯ Generation ofmulticast hologram patterns;
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`¯ Hologram t~ming for crosstalk optimization;
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`¯ Hologram tuning for adaptive port alignment;
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`¯ Phase aberration correction; and
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`15
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`- ~ Additio..nal processing of various.network traffic parameters.
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`Figs. 5A - 5C illustrate several viable arrangements of phase-variable elements
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`and circuitry on the SLM of the p.resent invention. Fig. 5A illustrates a die-based
`arrangement with a substrate 505 carrying circuitry 510 around and/or underneath an
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`20
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`array of phase-variable elements 515. The array of phase-variable elements 515 is
`partitioned into several subsets of phase-variable elements (515A, 515B~ 515C and
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`515D), each operating as an independent SLNL Fig. 5B shows a substrate 519
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`carrying several groups of components, Damely, circuitry 520A, 520B, 520C and
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`520D, and an array of phase-variable elements 525A, 525B, 525C and 525D,
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`25
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`respectively. Fig. 5C shows an individual phase-variable element 535 and circuitry
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`530 for controlling phase-variable element 535.
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`In Fig. 5A, circuit 510 controls the operation of the full array of phase-variable.
`elements, that is,~ each 0£515A, 515B, 515C and 515D. Fig. 5A illustrates an "
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`30
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`arrangement in which t’our holograms can be simultaneously produced, i.e., one for
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`each o£subsets 515A, 515B, 515C and 515D. Circuit 510.computes"a first phasestate
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`for subset 515A to direct a first light beam from a first port to a second port, and ¯
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`’ computes a second phase state for subset 515B to direct a second light be_am from a
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`third port tea fourth port. Similarly for subsets 515C and 515D, circuit computes
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`respective phase states for routing of a third light beam and a fourth light beam.
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`Because the phase states of the individuals in the arrayphase-variable elements 515
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`are individually reeonfigurable, circuit 510 can determine which of phase-variable
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`dements 515 are members of the first subset 515A, which of phase-variable dements
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`515 are members of the second subset 515B, and likewise, which of phase-variable.
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`dements 515 are members of the subsets 515C and 515D. In Fig. 5A, subsets 515A,
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`515B, 515C a~d 515D cab be located adjacent to one another, or alternatively they
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`10
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`can be spaced apart from one another by a region of substrate 505 that does not
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`include any ph. ase-variable dements.
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`An appropriate dimension for an array of phase-variable elements, i.e., pixds,.
`per hologram, is about 100 x 100 pixels for good Gausstan beam perforrnanee. "
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`15
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`Accordingly, an array of 600 x 600 pixels provides for 36 holograms. However, the.
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`present invention is not limited to any particular dimension for the array, nor is it
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`limited to any particular number of phase-variable elements or any arrangement of
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`phase-variable elements. Theoretically, some beam steering functionality can be
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`achieved with as few as two phase-~tering elements, only one of which needs to have
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`20
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`a variable phase. Furthermore, the phase-variable elements do not need to be
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`arranged in an array, per se, as any suitable arrangement is contemplated as being
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`within the scope of the present invention.
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`Referring again to Fig. 5B, a gap 526 is a legion.of substrate 519 that does not
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`25
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`¯ include any phase-variable elements. Gap 526 is located between phase,variable
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`elements 525B and 525D, and thus prevents crosstalk between the holograms of
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`phase-variableelements 525B and 525D.
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`The arrangement shown in Fig. 5A can deal with crosstalk in a manner
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`different from that of Fig. 5B. In Fig. 5A, pixel subset 515A includes a region of
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`pixels 516A upon which a hologram is produced. Pixel subset 515A also includes a
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`~ubset of pixels 517A positioned along a peripheral edge of subset 516A_ Subset
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`517A is thus a.buffer region for p~eventing erosstalkbetween the hologram of subset
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`515A, and the holograms of subsets 515B and 515C. .
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`Also; as those skilled in the art will appreciate, a hologram is shiR invariant,
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`that is the same.replay field is generated for any shifted position of the hologram.
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`Thus, as a fm-ther improvement, the phases of the pixels in subset 517Aare set by
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`cir~axit 510 to take advantage of the shiR invariant property of the hologram such that
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`a misali~t~nment of the light beam incident on subset 515A will nevertheless produce
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`the desired hologran~ Therefore, provided that the misalignment is within a
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`10
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`predetermined tolerance, i.e., such that the incident light falls within the bounds of
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`subset 515A, the hologram is produced notwithstanding a misalignment.of the light ¯
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`from an input port.
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`To take further advantage of the reconfigurable capability of-the optical
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`15
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`switch, circuit 510 receives a signal that represents whether light is bein~ directed to
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`particular port. This feature enables circuit 510.to perform an adaptive optical
`alignment, where circuit 510 receives an input signal indicating that the iigfi