WO1991015790A1 - Dispositif d'interconnexion optique - Google Patents

Dispositif d'interconnexion optique Download PDF

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Publication number
WO1991015790A1
WO1991015790A1 PCT/CA1991/000113 CA9100113W WO9115790A1 WO 1991015790 A1 WO1991015790 A1 WO 1991015790A1 CA 9100113 W CA9100113 W CA 9100113W WO 9115790 A1 WO9115790 A1 WO 9115790A1
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WO
WIPO (PCT)
Prior art keywords
optical
light
refractive index
faces
optical device
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Application number
PCT/CA1991/000113
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English (en)
Inventor
Mohsen Kavehrad
Mahmoud Tabiani
Original Assignee
University Of Ottawa
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Publication date
Priority claimed from US07/594,137 external-priority patent/US5179605A/en
Application filed by University Of Ottawa filed Critical University Of Ottawa
Priority to JP91506715A priority Critical patent/JPH05508718A/ja
Priority to AU75762/91A priority patent/AU7576291A/en
Publication of WO1991015790A1 publication Critical patent/WO1991015790A1/fr

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B6/12007—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind forming wavelength selective elements, e.g. multiplexer, demultiplexer
    • G02B6/12009—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind forming wavelength selective elements, e.g. multiplexer, demultiplexer comprising arrayed waveguide grating [AWG] devices, i.e. with a phased array of waveguides
    • G02B6/12011—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind forming wavelength selective elements, e.g. multiplexer, demultiplexer comprising arrayed waveguide grating [AWG] devices, i.e. with a phased array of waveguides characterised by the arrayed waveguides, e.g. comprising a filled groove in the array section
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B6/12007—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind forming wavelength selective elements, e.g. multiplexer, demultiplexer
    • G02B6/12009—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind forming wavelength selective elements, e.g. multiplexer, demultiplexer comprising arrayed waveguide grating [AWG] devices, i.e. with a phased array of waveguides
    • G02B6/12016—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind forming wavelength selective elements, e.g. multiplexer, demultiplexer comprising arrayed waveguide grating [AWG] devices, i.e. with a phased array of waveguides characterised by the input or output waveguides, e.g. tapered waveguide ends, coupled together pairs of output waveguides
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/14—Mode converters
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/2804—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/2804—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers
    • G02B6/2848—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers having refractive means, e.g. imaging elements between light guides as splitting, branching and/or combining devices, e.g. lenses, holograms
    • 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 
    • G02F1/03—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 ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
    • G02F1/0338—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 ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect structurally associated with a photoconductive layer or having photo-refractive properties
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B2006/12083—Constructional arrangements
    • G02B2006/12107—Grating
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B2006/12133—Functions
    • G02B2006/1215—Splitter

Definitions

  • This invention relates to optical devices, ana is especially, but not exclusively, applicable to N x N' interconnectors or couplers such as are used in local area networks and backplanes of telecommunications and computer equipment.
  • Embodiments of the invention may also be used to interconnect components in integrated circuits, to interconnect integrated circuits on a circuit board, and in analogous situations in the field of optical communications, especially where single mode optical fibres are to be interconnected.
  • the invention also relates to optical interconnects or couplers having limited or selective coupling capability in that each input port is coupled to preselected ones of a plurality of output ports.
  • the invention also encompasses lightwave communications systems incorporating such couplers and. for example, the so-called "multihop" networks including the afore-mentioned couplers having limited or selective coupling capability.
  • N x N' star coupler is one of the key elements in Local Area Network (LAN) applications of optical fibre.
  • the simplest single-mode 2 x 2 star coupler can be manufactured by bringing the cores of two single-mode fibres sufficiently close together over an appropriate coupling length.
  • Various such structures have been built by using etching, grinding and polishing, or fusion.
  • a 2 x 2 star coupler can be used as a basic building block to construct larger N x N' couplers where N is equal to an arbitrary power of two. However, this involves interconnecting a large number of 2 x 2 couplers, increasing the excess loss for larger values of N.
  • N x N' star optical coupler comprising a dielectric slab and two arrays of strip waveguide formed on a glass substrate. Opposite surfaces of the dielectric slab. to which the strip waveguides are attached, are curved. The radius of curvature and the distance between the surfaces are such that the optical axis of each waveguide at one surface extends radially across the slab to the centre of the other curved surface.
  • the configuration is said to provide even distribution of light from each waveguide to the waveguide at the opposite side of the dielectric slab.
  • the optimized efficiency of such a coupler varies between 0.34 at the edge and 0.55 at the middle of the array, which is not entirely satisfactory. This gives better coupling efficiency compared with a slab having parallel sides, in which light from a particular input waveguide will cover more than the entire area of the opposite face, so it is relatively inefficient since much of the light is diffused before it reaches the output side of the coupler.
  • US patent number 4,057,319 discloses a coupler connecting one fibre in a bundle to the fibre in another bundle.
  • a phase hologram plate is interposed between an input bundle of fibres and the output bundle of fibres.
  • the phase hologram effectively focuses the light onto the output optical fibre and so improves coupling efficiency.
  • a disadvantage of this device is that it is suitable only for individual connections and hence not suitable for applications requiring N x N' coupling.
  • US patent number 4,838,630 issued June 13, 1989 [and incorporated herein by reference] discloses a planar optical interconnector for 1 x N or N x 1 coupling in interconnecting integrated circuits.
  • the interconnector comprises a Bragg planar volume hologram which distributes optical signals, but is not capable of N x N' coupiing.
  • the interconnection device for optically interconnecting a plurality of optical devices.
  • the interconnection device comprises an optically transparent spacer with photosensitive material on its opposite sides. Fringes are formed, fixedly positioned, on one of the surfaces.
  • the fringes comprise a plurality of "sub-holograms".
  • the other surface has positions for the optical devices.
  • the fringe pattern is formed by directing a coherent light beam through the spacer and photosensitive material to one position and directing a second coherent light beam from a second position to interfere with the first beam.
  • Each source device emits a light beam which traverses the transparent spacer, is reflected by the holograph on the opposite face, and returns to a different position.
  • the hologram is, in effect a plurality of discrete holograms each one dedicated to one pair of positions. This kind of interconnection device provides logic functions for optical computing but is limited to 1 x N coupling.
  • an optical device comprising a stratified volume Bragg diffraction means, for example a hologram, having its refractive index varying spatially according to the expression: ;
  • m is an input position or mode, corresponding to one optical axis
  • m' is an output position or mode, corresponding to one optical axis
  • ⁇ m,m' is the coefficient of coupling between m and m'
  • r is the space vector.
  • the device comprises a body having cylindrical opposed faces, said stratified volume Bragg diffraction means being provided in said body such that its refractive index varies spatially and periodically in one plane of the body, the arrangement being such that a planar light wave incident upon one of said faces of the body in said plane, at a predetermined angle, with the electric field of such light wave extending in the same direction as the axes of said cylindrical opposed faces, will be refracted to emerge at one or more discrete angles determined by the spatially varying refractive index, such incident light being distributed substantially equally among the plurality of output refracted beams.
  • Such a diffraction means may be arranged to couple substantially all of the input light to the predetermined refracted beams, i.e. with minimal loss.
  • an N x N' optical interconnector comprises a planar body having cylindrical opposed faces and two arrays of optical emitters and/or receivers, said arrays being disposed one at each of said faces, respectively, said body having a refractive index which varies spatially and periodically with the electric field of such light wave extending in the same direction as the axes of said cylindrical opposed faces, such that light emanating from each of said emitters is distributed equally among the receivers at the opposite face.
  • the refractive index n(x,z) of the stratified volume Bragg diffraction means varies spatially in accordance with the expression:-
  • d is the radius of curvature of the curved faces
  • m is an input position or mode, corresponding to one optical axis
  • m' is an output position or mode, corresponding to one optical axis
  • ⁇ m,m' is the coefficient of coupling between m and m'; r is the space vector;
  • N is the total number of modes and is equal to 2M + 1.
  • the optical emitters/receivers may comprise waveguides, for example optical fibres, or electro-optic devices for directing or receiving light.
  • Each optical emitter is positioned so as to direct light along an optical axis extending radially of one face to the middle of the opposite face.
  • each optical receiver is positioned to receive light along an optical axis extending radially of the face with which the receiver is associated from the middle of the opposite face.
  • the arrangement is such that substantially all of the light from each emitter is received by the optical receivers.
  • a method of making a diffraction means for an optical interconnector by irradiating a body of photorefractive material having cylindrical opposed faces using a two wave mixing process employing two light beams comprising substantially planar waves, the method comprising the steps of:-
  • a method of making a diffraction means for an optical interconnector comprises the steps of :-
  • apparatus for producing a diffraction means for an optical interconnection device comprises first and second sources of substantially planar light wave, means for supporting a body of photorefractive material, said body having cylindrical opposed faces, so as to be irradiated by light from both said sources, the electric fields of the planar light waves extending in the same direction as the cylindrical axes of said opposed faces, means for rotating one of said sources stepwise relative to the other source and about an axis extending through said body, means for rotating the other source stepwise about the same point as the rotation of the first source, the resulting interference pattern being recorded in said body such that a light beam incident upon one of said opposed faces will be refracted and distributed equally among a plurality of output beams emerging from the other of said opposed faces.
  • apparatus for providing a diffraction means for an optical interconnector comprises:
  • a plurality of optical devices in two planar arrays, one each side of the support, the devices being positioned with their optical axes extending radially from a common point and mutually spaced by a predetermined angle, said devices comprising plane wave light sources for providing planar light waves with their electric fields extending in the same direction as the cylindrical axes of said cylindrical opposed faces;
  • One embodiment of the present invention comprises an optical interconnection device which has its spatially-varying refractive index configured so that each individual input light wave is coupled to selected ones of a plurality of outputs.
  • Such a coupler finds application in so-called multihop lightwave communication networks.
  • the superimposed light signals are made available to all the receivers, with each receiver tuning to one wavelength.
  • a disadvantage of this approach is that pretransmission coordination is required so that each receiver knows to which channel it must tune for each time interval. Also, users need to rapidly and accurately tune the receivers (or transmitter) over the available band to allow any user to communicate with any other user.
  • An object of the present invention is to mitigate this problem.
  • an optical device comprising a stratified volume Bragg diffraction means, for example a hologram, having its refractive index varying spatially according to the expression:
  • m is an input position or mode, corresponding to one optical axis
  • m' is an output position or mode, corresponding to one optical axis
  • ⁇ m,m' is the coefficient of coupling between m and m'; and r is the space vector.
  • optical interconnection device may be similar to that described above with reference to the first aspect of the invention. It may also be made using much the same method of maufacture as described above.
  • a limited-broadcast coupler comprising such a body can be designed for virtually any arbitrary shuffle network with the following parameters:
  • N Ip I : Total number of interface nodes.
  • a communication network comprising a plurality of nodes interconnected by such a limited or selective coupler.
  • the limited-broadcast coupler effects the necessary physical connections of two successive columns of the shuffle network. Having access to such a limited-broadcast coupler as a central piece of the network will make many desired architectures feasible for future optical networks.
  • a space- varying refractive index slab is introduced as a key design element for such a coupler.
  • the network may comprise a plurality of said optical devices connected in tandem, each device having a passband overlapping the passband of the device to which it is coupled, whereby signals having wavelengths within the overlapping regions of the band will be relayed through said interconnecting devices.
  • the network may be arranged such that the wavelengths of light beams transmitted through the network are selected to correspond substantially with peaks of the period of the periodic refractive index.
  • Figure 1 is plan view, partially cut away, of an optical interconnector
  • Figure 2 is a schematic representation of the optical interconnector.
  • Figure 3(a), 3(b) and 3(c) depict refraction of an input light beam into three specified modes
  • Figure 4(a), 4(b) and 4(c) illustrate coupling modes individually and collectively
  • Figure 5 is a schematic diagram of apparatus for preparing a body having a spatially varying refractive index for use in the optical interconnector of Figure 1;
  • Figure 7 represents regions of different refractive index in the body
  • Figures 8(a), 8(b) 9(a), 9(b) 10(a) and 10(b) illustrate vectors for star couplers having 2 and 4 output modes
  • Figure 11 is a block schematic diagram of an alternative apparatus for making a diffraction means having a spatially varying refractive index
  • Figure 12 is a simplified schematic diagram of a "shuffle net" lightwave communication system incorporating a limited- broadcast coupler and a plurality of user interfaces;
  • Figure 13 is a connectivity graph for the shuffle net of Figure 12.
  • Figure 14 is a block diagram of one of the user interfaces of Figure 12.
  • Figure 1 shows an optical interconnector comprising a glass substrate formed by two plates 102 and 104, respectively.
  • a diffraction means in the form of body 106 of dielectric material, such as lithium niobate (LiNbO 3 ) formed as a Bragg volume hologram, is sandwiched between the two plates 102 and 104.
  • dielectric material such as lithium niobate (LiNbO 3 ) formed as a Bragg volume hologram
  • the opposite faces 112 and 114 are cylindrical sections and symmetrical. The distance between the faces 112 and 114, at their midpoints, is equal to the radius of curvature, d , of the surfaces 112 and 114.
  • the end portions 116 of the optical fibres 108, 110. where they abut the block 106, are enlarged to about 100 microns diameter which is about ten times the diameter of the typical single mode optical fibre.
  • the transition between each single mode fibre and its enlarged end portion is gradual i.e. tapered.
  • the thickness of the dielectric body 106 is equal to the width of each of the enlarged portions 116, i.e. about 100 microns for a 9 x 9 coupler, so that substantially all of the light incident upon its end faces 112, 114 is channelled into the attached optical fibres.
  • the optical fibres 108 and 110 serve as emitters or receivers, the emitters being arranged to transmit "nearly plane wave" light beams.
  • the optical interconnector is represented schematically in Figure 2.
  • the transit distance i.e. the distance between the arcuate surfaces 112 and 114 at their mid-points is d and the are length of each arcuate surface is D.
  • Each enlarged end portion 116 on the input array has a width a such that
  • the width a should be large enough compared to the spatial wavelength of n(x,z), i.e.,
  • the width of the body 106 i.e. the distance d between the arcuate surfaces 112, 114 at their midpoints, is defined as:
  • the width should be large enough to satisfy the thick grating condition given later by Equation (3); while the geometry should also meet the condition defined later by Equation (28).
  • a beam of light emanating from any one of the array of optical fibres 108 will be diffracted by the thin film body 106 into a plurality of modes, one for each of the array of optical fibres 110 at the opposite side of the body
  • the z ordinate extends in the direction of the axis joining the middles of the arcuate faces
  • the arcuate faces 112, 114 are actually cylindrical segments.
  • the refractive index of the block 106 is n(x,z).
  • the number of optical fibres in each array, N, is 2M+1 and the angle between the optical axes of adjacent optical fibres is ⁇ 0 degrees.
  • optical fibre whose optical axis coincides with the middle of the two arcuate surfaces 112 and 114, respectively, is deemed to be the 0th mode and the modes on either side of that axis are numbered 1 to +M and 1 to -M.
  • Figure 3 illustrates refraction for a single perturbation term, the 0th mode in the array of optical fibres 108.
  • the angle of refraction is M ⁇ 0 degrees, resulting in the Mth mode being transmitted to the endmost optical fibre in the array 110.
  • Figure 3(b) shows that the 0th mode is refracted at an angle (M-1) ⁇ 0 degrees and
  • Figure 3(c) shows that the 0th mode is refracted at an angle ⁇ 0 degrees.
  • the same refractive index grating pattern will couple the 0 to Mth modes of the array of optical fibres 110 to the 0th mode of the array of optical fibres 108.
  • the block 106 can thus be considered to be a plurality of sub-holograms, each providing a different output mode for a given input mode.
  • Each sub-hologram which, in effect, can be considered to be a 1 x (2M+1), or (2M+1) x 1 coupler, is formed by two-wave mixing on a holographic film.
  • Figure 4(a) and Figure 4(b) illustrate how the coupler embodying the invention would couple the Mth mode and (M-2)th mode, respectively, to all output modes.
  • the refractive index n(x,z) is given as:
  • Figure 4(c) illustrates how all of the modes are provided to achieve N x N' coupling, the refractive index n(x,z) varying in accordance with the expression:
  • the block 106 comprises a holographic pattern characterized by a spatial variation of this refractive index n(x,z).
  • Such a pattern can be implemented using known techniques, see for example a Ph.D. thesis by M. Tabiani entitled “Spatial Temporal Optical Signal Processing", M.I.T., August 1979, a paper entitled “Bragg Gratings on InGaAsP/InP Waveguides as Polarization Independent Optical Filters", by C.Cremer et al, IEEE Journal of Lightwave Technology, Vol. 7, No. 11, November 1989, and also the disclosures of European patent application number 0,339,657, US Patent number 4,705,344 and US. patent number 4,838,630. All of these disclosures are incorporated herein by reference.
  • the pattern may be provided on a single film of photorefracti ve material (thick grating or volume holography on a single crystal or film).
  • Figure 5 illustrates manufacture of the body 106 with its spatially varying refractive index for an N x N' coupler.
  • the implementation is based on two wave mixing employing a rotating mechanism, to mix E m and E m' by varying m and m' in successive steps.
  • FIG. 5 is a block schematic diagram of the apparatus for implementing such two-wave mixing, comprising two coherent light sources 502 and 504, respectively, mounted for rotation by two motors 506 and 508, respectively.
  • the light sources 502 and 504 generate nearly plane waves E m and E m , respectfully.
  • the centre of rotation for both of the motors 506 and 508, is the middle of the arcuate surface 112 which is furthest away as indicated at 510.
  • the relative positions of the drive motors 506 and 508 are controlled by drive control means 512 which rotates the motors about point 510.
  • the first motor, 506, rotates the first nearly plane wave source 502 (Em) such that its propagation vector makes an
  • Second motor 508 aligns
  • the second nearly plane wave source 504 (E m' ) such that its propagation vector makes an angle [m/ - (M+1) ] with the -z
  • second motor 508 varies the direction incrementally such that m' varies between m + 1 to N - (m -1).
  • the first motor 506 will bring the first source 502 to the new position and the process continues.
  • the beams E m and E m' from the two sources, 502 and 504 are mixed to form (print) a desired term of Equation (8) on the photorefractive material.
  • the body After printing all the terms of Equation (8), the body will have a refractive index varying in accordance with the equation (8).
  • the body 106 When placed between the two circular arrays 108 and 110 of the coupler shown in Figure 1, the body 106 will form an N x N' optical interconnection.
  • the coupling pattern can be modified by varying the intensities of the beams E m and E m 'at any particular step to provide other then N x N' coupling.
  • the intensity is controlled by means of attenuation filters 514 and 516 in the optical paths of light sources 502 and 504, respectively.
  • the attenuation filters 514 and 516 are controlled by means of an intensity control means 518 which operates in conjunction with the drive means 512.
  • Figure 12 illustrates a mu l t i hop perfect shuff l e network compr i s i ng a pass i ve opti ca l star coupler 120 and a set of eight user interfaces 121 - 128, respectively.
  • Eight input ports 1 - 8 are distributed along one curved face 129 of the coupler 120 and eight output ports 1' - 8' are distributed along opposed curved face 130.
  • the interfaces 121 - 128 comprise laser transmitters 131 - 138 and photodiode receivers 141 - 148, respectively.
  • the input ports 1 - 8 are connected to respective outputs of laser transmitters 121 - 128 and output ports 1' - 8' are connected to respective ones of the inputs of photodiode receivers 141 - 148.
  • the star coupler 120 comprises a stratified volume holographic medium having a spatially-varying refractive index. As in the case of the coupler of Figure 1, the refractive index varies according to the general expression
  • the transmitters 121 - 128 are each capable of transmitting signals with either of two wavelengths, by selecting either of two lasers. Of course, a single laser which can be switched between two wavelengths might be substituted.
  • the receivers 141 - 148 each have a photodiode receiver stage for detecting two wavelengths. These are not the same as the transmitter wavelengths but correspond to wavelengths of two other user interfaces to which the receiver is connected.
  • a signal from an individual transmitter arrives at the corresponding input port, and is launched into the coupler 120, it will be directed to one or the other of two output ports depending upon its wavelength. For example, a signal with wavelength ⁇ 1 transmitted from laser transmitter 121 to input port 1 will be coupled to output port 5', whereas a signal at wavelength ⁇ 2 transmitted by way of the same input port 1 will be directed to output port 6'.
  • the stratified volume hologram has a refractive index varying according to the expression
  • the coupler 120 functions to couple 2 out of 8, i.e. each input port 1 - 8 can couple to a predetermined two of the output ports 1' - 8'.
  • the connectivity of the shuffle network of Figure 12 is illustrated in Figure 13.
  • the network is a "perfect" shuffle network in that each user can communicate with every other user, even though each individual user interface has only two direct linkages to other user interfaces.
  • some signals will be relayed. For example, if user 1 wishes to transmit a packet of data to user 6, user interface 121 will append user 6's address onto the packet, select wavelength ⁇ 2 , and launch the signal into input port 1. The signal will go directly to output port 6' and thence to receiver interface 146 where it will be demodulated, the address detected, and the packet delivered to user 6.
  • user interface 121 will address the packet, select a wavelength ⁇ 2 to direct the signal to receiver interface 146 of user 6.
  • the address information will be detected and indicate that the packet is to be relayed to receiver interface 144 of user 4 on ⁇ 12.
  • receiver interface 144 the address will be detected and again indicate that the packet is to be relayed. Consequently, user interface 124 selects a wavelength of ⁇ 8 and transmits the packet by way of input port 4 and output port 8' to receiver interface 148.
  • receiver interface 148 the signal will be detected and the packet delivered to user 8.
  • FIG 14 illustrates, as an example, receiver i nte rface 141, which comprises a photodetector receiver stage 150 connected to output port 1'.
  • the photodetector receiver stage 150 includes two photodiode detectors (not shown) for detecting signals having wavelengths ⁇ 9 and ⁇ 13 , respectively.
  • Detecting circuitry 151 decodes the address information prefixed to the incoming signal. If the address is its own, it directs the incoming signal to a hardware interface 152 for user 1. If, on the other hand, the address indicates that the message is to be relayed, in which case it will also contain information as to which user interfaces are in the relay chain.
  • Laser transmitter stage 131 includes a selector 153 and lasers 154 and 155 having operating wavelengths ⁇ 1 and ⁇ 2 , respectively. Detecting means 151 will control selector 153 to direct the outgoing signal to the appropriate one of transmitters 154 and 155.
  • the limited or selective star coupler 120 can be fabricated using similar techniques and apparatus as that illustrated in Figures 5 and 11 and described with respect to the manufacture of the full broadcast star coupler.
  • the input array width is chosen such that
  • each single- mode input/output fiber It is preferable to expand the diameter of each single- mode input/output fiber. This expansion can be done by using appropriate tapers. Beam expansion ratios in the range of 5- 10 are feasible with a corresponding insertion loss per taper of less than 0.01 - 0.025 dB. By using these numerical values, the thick grating condition holds.
  • the specified routing matrix ⁇ can be constructed by the wave-mixing method as discussed earlier.
  • m-th mode as a plane wave travelling in the direction that makes an angle m ⁇ 0 with the z axis; independent of y as:
  • c.c. means complex conjugate of the first term.
  • x,y and z are spatial coordinates, and h and k refer to optical frequency and wave vector, respectively.
  • n ⁇ x, z) 1 + ⁇ m,m / sin (2)
  • ⁇ m,m' is the coupling coefficient between input m-th and output m'-th modes and represents dimensions of the space, whe re and i is the unity vector
  • n' -4, -3, -2, -1, 0, 1, 2, 3, 4.
  • Equations (4) to (6) for such an input.
  • the reader is directed to the paper by M. Tabiani referred to hereinbefore.
  • Equations (3) to (6) for all m,m' -M, ... ,0, ... , +M.
  • the implementation is still based on two- wave mixing with a rotating mechanism and with an intensity control apparatus comprising the intensity control means 518 and attenuation filters 514, 516 described earlier with reference to Figure 5.
  • ⁇ m,m' is an element of the ⁇ routing matrix and must satisfy the conditions defined in equations 3 to 6
  • Equation (14) Defining E II (x,z,t) by the summation term on the right in Equation (14), we can accommodate n(x,z) by using the wave equation:
  • Equation (16) is the coupled-mode equation for the system shown in Figure 7 with n(x,z) given by Equation (12).
  • Equation (16) shows that the refractive index n(x,z; given by Equation (12) serves the purpose, as stated earlier.
  • Equation (16) shows that the refractive index n(x,z; given by Equation (12) serves the purpose, as stated earlier.
  • transition matrix (z) can be found by a Fourier Transform method such as is disclosed by R. W. Brackett in Chapter 11 of the book entitled “Finite Dimensional Linear Systems", J. Wiley, New York, 1970. The result is as follows:
  • Equation (21) in the specific case of the full broadcast NxN coupler, where
  • the N input elements are equally spaced on the surface of the outer circle, while each input is aligned with the centre of the circle. Also, the distance between the m-th input mode and the m'-th output mode, d m,m' , again depends on m,m' and ⁇ 0 parameters, such that for small angles:
  • Equation (8) To realize the refractive index given by Equation (8), let us consider as a vector whose amplitude and
  • R - (29) where represents the optical wave vector.
  • the refractive index perturbation will be a periodic function in space with a spatial frequency when E n and E' n are mixed.
  • N 5 waves E 1 , E 2 , E 3 , E 4 and E 5 as shown in Figure 10A to create all corresponding .
  • N 9 waves (E 1 ??.........E 9 ) to create all corresponding .
  • E 1 has an angle — with -z direction and E i has an angle ⁇ 0 with E i-1 , and so on. Therefore, we have to have only two waves at the same frequency.
  • the first field is placed in the E M direction and the second wave on the E M+ . and the E M+2 direction while mixing the pairs in each position. Therefore, with this method, by two wave mixing we can create all vectors corresponding to n(x,z) given by Equation
  • the width a should be large enough compared to the spatial wavelength of n(x,z), i.e., (33)
  • the width of the slab is d and is defined as
  • the slab width should be large enough to satisfy the thick grating condition given by Equation (3); while the geometry should also meet the condition defined by Equation (28).
  • Equation (28) The same arguments apply to the output surface of the coupler.
  • D increases as M 2 while d increases as M.
  • the medium with space-varying refractive index n(x,z) given by Equation (8) may be created by the two wave mixing methods mentioned herein for a given N.
  • Equations (4), (6), (10) and (27b) are satisfied.
  • ⁇ m,m' is determined by the routing matrix
  • ⁇ can vary between ⁇ - ⁇ to ⁇ + ⁇ .
  • the coupler will still operate if we keep the perturbation on term of Equation (10) to be much smaller than ⁇ . This can be done by limiting ⁇ such that:
  • Equation (33) is satisfied as where MAX stands for maximum. Also, the condition given by Equation (26) is satisfied by choosing
  • Equation (37) points to expanding the diameter for each single-mode input/output fibre. This expansion can be done by using appropriate tapers. Beam expansion ratios in the range of 5-10 are feasible with a corresponding insertion loss per taper of less than 0.01 - .025dB. By using these numerical values, the thick grating condition governed by Equation (3) holds.
  • the refractive index n(x,z) in Equation (8) for a given M will be created as described hereinbefore with two wave mixing and rotation operation. Parameter ⁇ m,m' should be chosen such that the conditions in Equation (9), (10) and (26) are satisfied.
  • N was defined as 2M + 1
  • the number of ports is an odd number.
  • the ninth port is simply not used. In essence, a row of zeros will appear in the connectivity matrix.
  • equation 11a To calculate the 3 - dB bandwidth, instead of equation 11a, we must have: ( 39 )
  • the bandwidth presented in equation 43 is the available band around the nominal central wavelength ⁇ .
  • Such a coupler can be designed around the central wavelength ⁇ 0 for dense wavelength division multiplexing applications. All wavelengths used around ⁇ 0 that fall within the 3 - dB band of the coupler will get through the coupler. Going back to Figure 12, we can choose 16 wavelengths around ⁇ 0 such that they fall within the 3 - dB band of the coupler. By forming the proper holographic patterns on the photosensitive slab, the perfect shuffle connectivity can be establ ished.
  • one way is to cascade several couplers with mutually overlapping passbands and use wavelengths within the overlapped regions of the band as a means of connecting couplers.
  • Another alternative is to select the wavelengths used in a WDM network such that their values match those at the peaks of the sine function in equation 11a. Using the latter methoc, the coupling efficiency remains at its peak.
  • Figure 11 illustrates an alternative apparatus for preparing a diffraction means with a spatially varying refractive index as described hereinbefore.
  • the block of photorefractive material 106' is positioned in a recess 1102 in a jig 1104.
  • the jig 1104 has a plurality of optical fibres in two arrays 1108 and 1110, respectively. These arrays of optical fibres correspond to the arrays of optical fibres 108 and 110, respectively, in the optical interconnector shown in Figure 1.
  • Each of the optical fibres in array 108 is connected to a respective one of a plurality of light sources 1112.
  • the light sources may be any commercial single mode source.
  • each of the optical fibres in array 110 is connected to a respective one of an array of light sources 1114.
  • Light sources 1112 are connected to drive means 1116 and light sources 1114 are connected to drive means 1118.
  • the drive means are controlled by control means 1120 which selectively and sequentially energizes the light sources in pairs to irradiate the block 106' in order to "write" the spatially varying refractive index described with respect to Figure 1.
  • selective coupling i.e. N is not the same as N', may be achieved simply by varying the intensity of the light sources so as to omit to write the photorefracti ve material at any position where no coupling is required.
  • the embodiment of Figure 11 can be modified to achieved this quite easily by controlling the individual light sources by way of their respective drive means 1116 and 1118.
  • intensity control means 1122 operates in conjunction with drive indexing means to vary the intensity at the appropriate positions.
  • the coupler described as a specified embodiment has an odd number of inputs and outputs if could be modified quite readily to provide an even number of inputs and outputs, for example by omitting the 0-th mode.
  • the number of inputs is the same as the number of outputs, they could be different if so desired. This could be achieved quite readily by omitting to "write" the specific part of the diffraction pattern as described with reference to Figures 5 and 11.

Abstract

Un dispositif d'interconnexion optique adapté à un coupleur N x N' utilisé, par exemple, dans un réseau local, comprend un moyen de diffraction se présentant sous la forme d'un corps (106) ayant un indice de réfraction variant dans l'espace et périodiquement dans un plan du corps. L'agencement est tel que la lumière incidente sur le corps dans le plan et à un angle prédéterminé est réfracté pour émerger à une pluralité d'angles discrets déterminés par l'indice de réfraction variant dans l'espace. La lumière incidente est répartie de manière égale dans la pluralité de faisceaux réfractés de sortie et sensiblement toute ladite lumière incidente est couplée à la pluralité de faisceaux réfractés. Le moyen de diffraction comprend un corps cylindrique (106) et le dispositif comprend également deux réseaux (108, 110) d'émetteurs et/ou récepteurs optiques. Les réseaux sont disposés sur des faces respectivement opposées (112, 114) du corps, chacun des récepteurs optiques ayant un axe optique aligné avec un des angles discrets. Un réseau de mélange parfait peut comprendre une pluralité de n÷uds (121, 128) interconnectés par ledit coupleur, chaque n÷ud comprenant un émetteur (131, 138) pouvant fonctionner à plusieurs longueurs d'onde, un récepteur (141 à 148), ainsi qu'un moyen destiné à déterminer si un signal reçu doit être relayé et, si tel est le cas, la longueur d'onde de transmission appropriée.
PCT/CA1991/000113 1990-04-11 1991-04-10 Dispositif d'interconnexion optique WO1991015790A1 (fr)

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JP91506715A JPH05508718A (ja) 1990-04-11 1991-04-10 光相互接続装置
AU75762/91A AU7576291A (en) 1990-04-11 1991-04-10 Optical interconnection device

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USPCT/CA90/00119 1990-04-11
US07/594,137 US5179605A (en) 1990-10-10 1990-10-10 Optical interconnection device
US594,137 1990-10-10

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1993016405A1 (fr) * 1992-02-07 1993-08-19 University Of Ottawa Dispositif optique d'interconnexion
FR2742882A1 (fr) * 1995-12-22 1997-06-27 Corning Inc Demultiplexeur de longueurs d'onde, realise en optique integree
US6141152A (en) * 1996-07-01 2000-10-31 Corning Incorporated Multiplexer/demutiplexer with flattened spectral response

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0284293A2 (fr) * 1987-03-26 1988-09-28 AT&T Corp. Réseau de communication par ondes optiques à canaux multiples et à bonds multiples
EP0340987A2 (fr) * 1988-05-03 1989-11-08 AT&T Corp. N x N coupleur optique en étoile

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0284293A2 (fr) * 1987-03-26 1988-09-28 AT&T Corp. Réseau de communication par ondes optiques à canaux multiples et à bonds multiples
EP0340987A2 (fr) * 1988-05-03 1989-11-08 AT&T Corp. N x N coupleur optique en étoile

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
Applied Optics, volume 27, no. 11, 1 June 1988, Optical Society of America, Pochi Yeh et al.: "Optical interconnection using photorefractive dynamic holograms", pages 2093-2096 *

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1993016405A1 (fr) * 1992-02-07 1993-08-19 University Of Ottawa Dispositif optique d'interconnexion
FR2742882A1 (fr) * 1995-12-22 1997-06-27 Corning Inc Demultiplexeur de longueurs d'onde, realise en optique integree
EP0811281A1 (fr) * 1995-12-22 1997-12-10 Corning Incorporated Demultiplexeur de longueurs d'ondes a optique integree
EP0811281A4 (fr) * 1995-12-22 1999-03-10 Corning Inc Demultiplexeur de longueurs d'ondes a optique integree
US6141152A (en) * 1996-07-01 2000-10-31 Corning Incorporated Multiplexer/demutiplexer with flattened spectral response

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