EP0257059A1 - Dispositif de commutation de faisceaux optiques ajustable par tension - Google Patents

Dispositif de commutation de faisceaux optiques ajustable par tension

Info

Publication number
EP0257059A1
EP0257059A1 EP87901187A EP87901187A EP0257059A1 EP 0257059 A1 EP0257059 A1 EP 0257059A1 EP 87901187 A EP87901187 A EP 87901187A EP 87901187 A EP87901187 A EP 87901187A EP 0257059 A1 EP0257059 A1 EP 0257059A1
Authority
EP
European Patent Office
Prior art keywords
liquid crystal
voltage
crystal cell
grating
optical
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP87901187A
Other languages
German (de)
English (en)
Inventor
Gregory L. Tangonan
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Raytheon Co
Original Assignee
Hughes Aircraft Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Hughes Aircraft Co filed Critical Hughes Aircraft Co
Publication of EP0257059A1 publication Critical patent/EP0257059A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1343—Electrodes
    • G02F1/134309—Electrodes characterised by their geometrical arrangement
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/29—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the position or the direction of light beams, i.e. deflection
    • G02F1/292—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the position or the direction of light beams, i.e. deflection by controlled diffraction or phased-array beam steering

Definitions

  • This invention relates generally to optical information transmission systems and, more particularly, to optical phase gratings and arrangements for optically switching and splitting information utilizing liquid crystal cells.
  • Liquid crystal (LC) cells have been typically used in a wide range of image display applications and more recently have been increasingly used in real-time optical signal processing applications.
  • one of the electrodes on one of the substrates is constructed to have a stripe-type electrode structure at a predeter ⁇ mined spatial period.
  • An alternative construction wherein an electric field is applied to the liquid crystal layer through a high resistance layer of periodical shape on the electrode attached over the whole surface of the substrate is also disclosed.
  • a two-dimensional embodiment uses a light mask and three gratings arranged in different directions as means for forming plural types of diffraction gratings in the liquid crystal layer, on the writing light side of the photoconductive layer.
  • optical switch applications require high efficiency beam control to ensure that the controllable diffracted orders contain most of the incident power.
  • the transmitted power intensity in the different diffracted orders must be very nearly equal, with variation being less than _+ 10%.
  • variation of the diffracted intensity of the different orders as a function of the voltage or wavelength is an important consideration for optical switch applications, a consideration not typically present in the case of image display applications.
  • U.S. Patent No. 4,351,589 discloses an implementation utilizing an LC light valve operating in a mode in which a locally variable phase grating is produced.
  • the variable grating mode (VGM) operation of a liquid crystal device useful for optical processing is discussed by B.H. Soffer et al. in "Variable Grating Mode Liquid Crystal Device for Optical Processing," SPIE, Vol. 218, Devices and Systems for Optical Signal Processing, pp.
  • VGM operation a variable phase grating is formed in the liquid crystal cell.
  • the grating period depends upon the applied voltage and therefore can be changed by varying the voltage applied to the LC cell, or in response to an optical signal by adding a photoconductive layer to the cell. In the latter case, each input signal component will generate a local grating structure with a particular spatial frequency which depends on the intensity level of that component. Thus, in VGM operation, the resultant grating period is neither fixed nor uniform throughout the cell.
  • VGM operation of nematic liquid crystals has been utilized to achieve 1 * 3 or active splitting devices as reported by G. L. Tangonan in "Variable-Grating-Mode Liquid Crystals for Fiber-Optic Applications,” Electronics Letters, Vol. 21, No. 16, pp. 701-2, August 1985.
  • G. L. Tangonan in "Variable-Grating-Mode Liquid Crystals for Fiber-Optic Applications," Electronics Letters, Vol. 21, No. 16, pp. 701-2, August 1985.
  • an "Electro-optical Switch for Unpolarized Optical Signals" which uses a polarizing beam splitter cube and a reflector to separate an arbitrarily polarized incident light beam into polarized components which propagate along parallel paths.
  • a polarization rotator is positioned in the path of the reflected component to rotate the plane of polarization of the light beam component to be coplanar with that of the undeviated light beam in the parallel path.
  • the two beams are simultaneously or individually deflected by selectively activating the electrodes of a liquid crystal nematic reflector/transmitter array confined between prismatic bodies to emerge at one or more of a plurality of desired outputs.
  • the "individual segmented optically transparent electrodes” are preferably disposed in two parallel rows, with one optically transparent electrode in opposition to the individual segmented electrodes, and a single, uniform liquid crystal film confined between the electrode layers.
  • This embodiment provides an array of four parallel LC cells for independent switching of either beam,,.making possible eight outputs.
  • Star couplers and bidirectional couplers utilizing binary phase transmission gratings are discussed by U. Killat et al. in "Binary Phase Gratings for Couplers Used in Fiber-Optic Communications," Fiber and Integrated Optics, Vol. 3, Nos. 2-3, pp. 221-235, 1980. The concepts presented in this article are extended further by Killat et al.
  • a holographic optical switch which deflects light beams using a diffraction grating recorded by holographic means in a light-sensitive crystal, preferably bismuth silicon oxide, to connect two N x N matrices of optical fibers, is disclosed in U.S. Patent No. 4,543,662, entitled "Optical Beam Switching Device and Telephone Exchange Comprising a Device of This Kind.” Although this optical switch overcomes the bandwidth limitations of the electrical switches because it is holographic rather than electrical, once the grating is holographi- cally recorded in the crystal, the device acts as a passive optical switch.
  • the orientation and spatial frequency of the grating can thereafter be changed only be erasing and rewriting the grating. Therefore, erasure of the existing grating and recording of a new grating will have to be done each time a change in- the switching pattern is desired. This would necessitate using several lasers for hologram formation, if a plurality of beams are controlled.
  • the holographic switch performs only N x N switching and, in a variety of telecommunications, signal processing and data communications areas, 1 * N switching is necessary.
  • the present invention provides an LC optical switch which utilizes an LC cell in which a layer of liquid crystal material is sandwiched between two plates of transpar nt material such as glass.
  • the plates are coated with a transparent conductive electrode layer, and a grating pattern is formed on one of the plates of the LC cell.
  • the device acts as a voltage tunable phase grating, whose grating strength is controlled by an externally applied field.
  • An advantage of the present invention is the provision of an optical switch for 1 * N splitting with even outputs.
  • Another advantage of the present invention is the utilization of liquid crystal cells to provide one- dimensional and two-dimensional switching for 1 * N coupling of light to fibers.
  • a further advantage of the present invention is that it achieves the splitting in a single stage.
  • Yet another advantage of the present invention is the potential for use in active star networks and power manifolding.
  • FIG. la is a sectional view of the LC cell of the present invention
  • FIG. lb is an exploded perspective view of component parts of the cell shown in FIG. la;
  • FIG. lc is a schematic diagram of the switching arrangement of the present invention.
  • FIGS. 2-5 show the various diffraction orders resulting when different operating voltages are applied to the device of the present invention
  • FIG. 6a is a schematic diagram of the arrangement for two-dimensional switching utilizing the present invention.
  • FIG. 6b is a display resulting from the two- dimensional switching achieved using the arrangement shown in FIG. 6a. DESCRIPTION OF THE PREFERRED EMBODIMENTS
  • FIG. la is a sectional view showing the basic structure of the LC cell 10 of the present invention.
  • Two transparent, smooth plates 1 and 3 of a material such a ⁇ glass, preferably with a thickness of the order of 1 mm, are coated with a transparent, conductive material such as indium tin oxide (ITO) to provide conductive electrode surfaces 5 and 7.
  • ITO indium tin oxide
  • Homogeneous alignment ot the liquid crystal molecules in the quiescent state is induced by conventional methods such as rubbing or ion bombardment etch-alignment. In a homogeneously aligned LC, the quiescent state alignment is parallel to the boundary surface.
  • the LC material 9 is sandwiched in a thin layer, as is typically done, between plates 1 and 3. Liquid crystal layers of thickness-on the order of 6 ⁇ m are used in conventional cells to provide efficient electro-optic modulation and reasonably lov drive voltages ( ⁇ 10 V).
  • a grating pattern is then formed in ITO layer 5 by photolithographically forming a mask thereon and then removing the unmasked ITO portions using conventional ion beam sputtering.
  • Other suitable conventional techniques can be used to form the grating pattern.
  • the electrode 5 of the present invention is thus arranged in a typical grating pattern 11, as a series of parallel lines of uniform and identical widths with uniform spacing or gaps between them.
  • the width of the grating lines and the grating period selected will depend on individual system require- ments and the following generally applicable design consideration. The thicker the LC layer, the lower is the operating voltage required.
  • the lines 11 are made extremely narrow (for example, 5 ⁇ m) and the gaps between them of .equal width or greater, the effect of the electrical field they exert may result only in insufficient local rearrangement of the molecular alignment in an LC layer 9 on the order of 6-12 ⁇ thick.
  • the lines are, for example, 25 ⁇ m wide and the gaps between them are of equal or greater width, the effect of the electric fields exerted by the relatively wider electrode lines will be more efficiently localized, resulting in rearrangement of molecular alignment over a larger area.
  • the LC cell 10 of the present invention can be made by any of the techniques commonly used in the liquid crystal electro-optic device art.
  • the primary difference between the LC cell 10 of the present invention and the prior electro-optic liquid crystalline devices is the patterning of the electrode structure to provide a voltage-tunable phase grating suitable for electro- optic switching.
  • the LC cell described above is driven by conventional external circuitry in a known manner.
  • Patterning of ITO layer 5 was then accomplished by photolithographically forming a mask thereon, and removing the ITO left exposed by the mask using ion beam sputtering.
  • a grating pattern 11 with lines 25 ⁇ wide with 25 ⁇ m spacing between them was formed.
  • the oscilloscope display of the transmitted light output for an operating voltage of 3.5 V shows that the maximum intensity transmitted corresponds to the zero order and a weak tap state on the order of 0.9 dB exists at the two first orders on either side of the zero order.
  • the loss figures given above include the loss to th ⁇ unwanted orders.
  • the experimental observations indicate that the splitting efficiency is high since the overall loss figure is only on the order of 1 dB and the LC grating generates diffraction orders of equal intensity. The latter is visually evident in FIGS. 3 and 4.
  • the spread in output intensities was observed to be on the order of 1/50. Cell transmission is typically > 95%, neglecting reflections.
  • FIG. 6a The two-dimensional switching embodiment for the present invention is illustrated in FIG. 6a.

Landscapes

  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Geometry (AREA)
  • Mathematical Physics (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Liquid Crystal (AREA)

Abstract

La présente invention se rapporte à un dispositif de commutation électro-optique à cristaux liquides utilisant une cellule de cristaux liquides (10), dans laquelle une électrode (5) présente une structure à quadrillage (11) et l'autre électrode est une couche plane. Ledit dispositif sert au quadrillage de phase par tension, la force du quadrillage étant régulée par un champ externe appliqué aux électrodes. Le commutateur permet d'obtenir une division unidimensionnelle 1 * N avec des sorties égales et une commutation bidimensionnelle 1 * N dans une configuration à quadrillage transversal.
EP87901187A 1986-02-18 1987-01-15 Dispositif de commutation de faisceaux optiques ajustable par tension Withdrawn EP0257059A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US83004586A 1986-02-18 1986-02-18
US830045 1986-02-18

Publications (1)

Publication Number Publication Date
EP0257059A1 true EP0257059A1 (fr) 1988-03-02

Family

ID=25256184

Family Applications (1)

Application Number Title Priority Date Filing Date
EP87901187A Withdrawn EP0257059A1 (fr) 1986-02-18 1987-01-15 Dispositif de commutation de faisceaux optiques ajustable par tension

Country Status (4)

Country Link
EP (1) EP0257059A1 (fr)
JP (1) JPS63502533A (fr)
IL (1) IL81259A0 (fr)
WO (1) WO1987005125A1 (fr)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5650835A (en) * 1993-09-03 1997-07-22 Hughes Electronics Reconfigurable optical beam splitter and method
FI114945B (fi) 2002-09-19 2005-01-31 Nokia Corp Sähköisesti säädettävä diffraktiivinen hilaelementti

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2254057A1 (en) * 1973-11-27 1975-07-04 Thomson Csf Deflector for coherent polarised light - has transparent electrodes on liquid crystalline bed forming diffraction grating
NL8104122A (nl) * 1981-09-07 1983-04-05 Philips Nv Optische schakelaar.

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO8705125A1 *

Also Published As

Publication number Publication date
IL81259A0 (en) 1987-08-31
JPS63502533A (ja) 1988-09-22
WO1987005125A1 (fr) 1987-08-27

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Inventor name: TANGONAN, GREGORY, L.