WO2004005993A1 - Dynamic multifunction, multichannel optical device - Google Patents

Dynamic multifunction, multichannel optical device Download PDF

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Publication number
WO2004005993A1
WO2004005993A1 PCT/AU2003/000870 AU0300870W WO2004005993A1 WO 2004005993 A1 WO2004005993 A1 WO 2004005993A1 AU 0300870 W AU0300870 W AU 0300870W WO 2004005993 A1 WO2004005993 A1 WO 2004005993A1
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WO
WIPO (PCT)
Prior art keywords
optical
elements
optical device
diffracted
channels
Prior art date
Application number
PCT/AU2003/000870
Other languages
French (fr)
Inventor
Kamran Eshraghian
Kamal Alameh
Original Assignee
Edith Cowan University
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Publication date
Application filed by Edith Cowan University filed Critical Edith Cowan University
Priority to AU2003281376A priority Critical patent/AU2003281376A1/en
Publication of WO2004005993A1 publication Critical patent/WO2004005993A1/en

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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
    • G02B6/24—Coupling light guides
    • G02B6/42—Coupling light guides with opto-electronic elements
    • G02B6/4201—Packages, e.g. shape, construction, internal or external details
    • G02B6/4246—Bidirectionally operating package structures
    • 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
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29304—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating
    • G02B6/29305—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating as bulk element, i.e. free space arrangement external to a light guide
    • G02B6/29307—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating as bulk element, i.e. free space arrangement external to a light guide components assembled in or forming a solid transparent unitary block, e.g. for facilitating component alignment
    • 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
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29304—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating
    • G02B6/29305—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating as bulk element, i.e. free space arrangement external to a light guide
    • G02B6/29308—Diffractive element having focusing properties, e.g. curved gratings
    • 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
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29304—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating
    • G02B6/29305—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating as bulk element, i.e. free space arrangement external to a light guide
    • G02B6/2931—Diffractive element operating in reflection
    • 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
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29304—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating
    • G02B6/29305—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating as bulk element, i.e. free space arrangement external to a light guide
    • G02B6/29311—Diffractive element operating in transmission
    • 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
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29379—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device
    • G02B6/2938—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device for multiplexing or demultiplexing, i.e. combining or separating wavelengths, e.g. 1xN, NxM
    • G02B6/29382—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device for multiplexing or demultiplexing, i.e. combining or separating wavelengths, e.g. 1xN, NxM including at least adding or dropping a signal, i.e. passing the majority of signals
    • G02B6/29383—Adding and dropping
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/25—Arrangements specific to fibre transmission
    • H04B10/2507—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion
    • H04B10/25073—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion using spectral equalisation, e.g. spectral filtering
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0201—Add-and-drop multiplexing
    • H04J14/0202—Arrangements therefor
    • H04J14/021—Reconfigurable arrangements, e.g. reconfigurable optical add/drop multiplexers [ROADM] or tunable optical add/drop multiplexers [TOADM]
    • 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
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29379—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device
    • G02B6/29395—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device configurable, e.g. tunable or reconfigurable
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B2210/00—Indexing scheme relating to optical transmission systems
    • H04B2210/25—Distortion or dispersion compensation
    • H04B2210/258—Distortion or dispersion compensation treating each wavelength or wavelength band separately
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0201—Add-and-drop multiplexing
    • H04J14/0202—Arrangements therefor
    • H04J14/021—Reconfigurable arrangements, e.g. reconfigurable optical add/drop multiplexers [ROADM] or tunable optical add/drop multiplexers [TOADM]
    • H04J14/0212—Reconfigurable arrangements, e.g. reconfigurable optical add/drop multiplexers [ROADM] or tunable optical add/drop multiplexers [TOADM] using optical switches or wavelength selective switches [WSS]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0201—Add-and-drop multiplexing
    • H04J14/0202—Arrangements therefor
    • H04J14/0213—Groups of channels or wave bands arrangements
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0221—Power control, e.g. to keep the total optical power constant

Definitions

  • This invention relates to multifunction optical devices for actively managing multichannel optical data transmission systems, and more particularly to dynamic optical devices to selectively or simultaneously add/drop, multiplex/demultiplex, filter, attenuate and/or equalise individual wavelengths (or optical channels).
  • WDM wavelength division multiplexing
  • DWDM dense wavelength division multiplexing
  • an optical device comprising:
  • two or more diffraction elements to diffract individual optical channels propagating from the waveguides; and one or more reconfigurable holographic elements to reflect the diffracted optical channels back to the diffraction elements so that the reflected diffracted optical channels are diffracted again toward the waveguides;
  • reconfigurable holographic elements are configurable to selectively vary the reflection angle of the reflected diffracted optical channels to thereby individually and continuously control the optical power level of the twice-diffracted optical channels received by the waveguides.
  • the optical device is selectively or simultaneously operable to add/drop, multiplex/demultiplex, filter, attenuate and/or equalise individual optical channels propagating from/to the waveguides.
  • the diffraction elements comprise passive diffraction gratings. More preferably, the passive diffraction gratings comprise two-dimensional holographic diffraction gratings.
  • the reconfigurable holographic elements comprise phase holograms.
  • the phase holograms are generated by an optoelectronic very large scale integrated (VLSI) circuit chip.
  • the optoelectronic VLSI circuit chip comprises detectors to monitor the optical power level of the diffracted optical channels, and a processor and an associated memory storing programs to operate the processor to control the generation of the phase holograms in response to the monitored optical power levels of the diffracted optical channels to thereby individually and continuously control the optical power level of the twice-diffracted optical channels received by the waveguides.
  • the optical device further comprises two or more collimator elements between the waveguides and the diffraction elements to collimate the diffracted optical channels and the twice-diffracted optical channels.
  • the collimator elements comprise a collimator array.
  • the optical device further comprises one or more relay elements between the diffraction elements and the reconfigurable holographic elements to route the diffracted optical channels to the reconfigurable holographic elements, and to route the reflected diffracted optical channels back to the diffraction elements.
  • the relay elements comprise one or more macrolens.
  • the macrolens are fixedly positioned in optical alignment by a rigid telescopic support.
  • the relay elements comprise one or more diffractive optical elements.
  • the optical device further comprises two or more optical circulators to route input/output optical signals to/from the two or more waveguides.
  • the optical device further comprises an optical substrate.
  • the optical substrate comprises first and second spaced apart parallel planar surfaces, wherein the two or more diffraction elements and the optoelectronic VLSI circuit chip are provided on the first planar surface and a diffractive optical element is provided on the second planar surface so that the optical channels propagate in the optical substrate by internal reflection between the diffraction elements, the diffractive optical element and the optoelectronic VLSI circuit chip.
  • the optoelectronic VLSI circuit chip is flip-chip bonded to the optical substrate. More advantageously, the collimator array comprises microlens etched in the optical substrate.
  • the optical substrate comprises glass or sapphire.
  • a method of selectively or simultaneously adding/dropping, multiplexing/demultiplexing, filtering, attenuating and/or equalising individual optical channels in a multichannel optical data transmission system comprising the steps of: diffracting individual optical channels propagating from two or more waveguides using two or more diffraction elements;
  • the reconfigurable holographic elements dynamically and continuously configuring the reconfigurable holographic elements to selectively vary the reflection angle of the diffracted optical channels to thereby individually and continuously control the optical power level of the twice-diffracted optical channels received by the waveguides.
  • Figure 1 is a schematic representation of an optical device in accordance with a first embodiment of the present invention.
  • Figure 2 is a schematic representation of a lens relay and optoelectronic VLSI circuit chip in the optical device of Figure 1.
  • Figure 3 is a schematic perspective view of an optical device in accordance with the present invention.
  • Figure 4 is a schematic representation of the operation of the optical device of Figure 1 as an attenuator.
  • Figure 5 is a schematic representation of the operation of the optical device of Figure 1 as an equaliser.
  • Figure 6 is a schematic representation of the operation of the optical device of Figure 1 as a tunable filter.
  • Figure 7 is a schematic representation of the operation of the optical device of Figure 1 as an add/drop multiplexer.
  • Figure 8 is a schematic representation of an optical circulator used in the optical device of Figure 1.
  • Figure 9 is a schematic perspective view of an optical device in accordance with a second embodiment of the present invention.
  • Figure 10 is a schematic representation of a fibre collimator array used in the optical device of Figure 9.
  • Figure 11 is a schematic side view of an optical device in accordance with a preferred embodiment of the present invention.
  • the optical device 100 generally comprises optical circulator 20, fibre collimators 40, diffractive gratings 60, a lens relay 70, and an optoelectronic (or opto-VLSI) chip 90.
  • the optical device 100 comprises two input fibre ports comprising an input port 10 and an add port 12, and two output fibre ports comprising an output port 11 and a drop port 13. These are provided to the circulator 20 as illustrated in Figure 1.
  • the input fibre port 10 introduces an input signal 15 to be processed.
  • the add port 12 introduces a to-be added channel 17 when the optical device 100 is used as an add/drop multiplexer as described in further detail below.
  • the output port 11 delivers a processed output signal 16 and the drop output port 13 delivers a dropped channel 18 when the optical device 100 is used as an add/drop multiplexer.
  • the circulator 20 comprises first and second circulators 21 , 22.
  • the optical device 100 uses the first optical circulator 21 to route the input signal 15 to first port 24 of the circulator 20, and a reflected signal 31 to the output port 11.
  • the second optical circulator 22 routes the added channel 17 to second port 25 of the circulator 20, and the dropped channel 18 to the drop port 13.
  • the fibre collimators 40 comprise first and second fibre collimators 41 , 42.
  • the first and second fibre collimators 41 , 42 are used to convert the input-fibre signals 15, 17 to collimated optical beams 51 , 52.
  • the diffractive gratings 60 comprise first and second diffractive gratings 61 , 62.
  • the first and second diffractive gratings 61 , 62 are two-dimensional holographic grating plates.
  • the diffractive gratings 61 , 62 have large chromatic dispersion so that the wavelength components of the collimated beams 51 , 52 are steered and dispersed along different angles with respect to the incident beam axis as shown in Figure 1.
  • An antireflection coating is provided on the grating to minimise loss.
  • the lens relay 70 comprises three lenses 72, 74, 76 whose focal lengths and separations are optimised to adequately separate the wavelengths of the resultant emergent beams indicated by reference numerals 82, 84 and 86 in Figure 1 , and to also maintain an adequate beam diameter for all beams 82, 84, 86 when they arrive at the opto-VLSI chip 90.
  • Figure 2 shows the layout of the lens relay 70 and also the propagation of three different beams.
  • the emergent beams 82, 84, 86 are routed to and incident upon different pixel blocks 92, 94, 96 of the opto-VLSI chip 90 with adequate isolation.
  • the role of the opto-VLSI chip 90 is to sense the positions and diameters of the incident beams 82, 84, 86 using integrated photodetectors (not shown) and assign pixel blocks of 64x64 pixels that appropriately process the incident beams 82, 84, 86 to achieve the required processing function as discussed further below.
  • the photodetectors are coupled to a processor, which processes the signals from the photodetectors to generate control signals to appropriately process the incident beams and to generate phase holograms as discussed further below.
  • the processing functions can be: (i) reflecting the beams back along the input optical path to realise minimum attenuation,
  • Figure 3 shows a three-dimensional representation of an embodiment of the multifunction optical device 100 of the present invention.
  • Figure 4 illustrates how the optical device 100 can be used to provide variable optical attenuation.
  • An input optical signal 15 is routed via first circulator 21 to the first port 24 and is converted to a free-space collimated beam 51 using the first fibre collimator 41.
  • the collimated beam 51 is then incident upon the two- dimensional holographic grating plate 61.
  • the beam 51 is transformed to a beam 86, which is incident upon and illuminates a small area on the opto-VLSI chip 90.
  • the position and intensity of the incident beam 86 are evaluated by the photodetectors (not shown) integrated on the opto-VLSI chip 90, and a pixel block (64x64 pixels) is assigned to the incident beam 86, and an appropriate phase hologram is generated, which transforms (reflects) the incident beam into reflected beam 85.
  • the processor (not shown) on the opto- VLSI chip 90 determining the power of incident beam 86 at any particular pixel block and deriving a signal representative thereof.
  • the processor processes the signals representative of the determined power, and controls the generation of the phase hologram to achieve the desired output power by the processing.
  • a storage medium (not shown) containing computer executable instructions for processing the measured input signal powers.
  • the storage medium stores a computer algorithm that allows the opto-VLSI chip 90 to generate the optimum phase holograms required for best performance.
  • the processing in other operation of the optical device 100 is carried out in a similar manner.
  • the reflected beam 85 is then routed back through the lens relay 70 to the first two-dimensional holographic grating plate 61.
  • the beam 53 that emerges from the holographic grating plate 61 is coupled into the fibre port 24 via the first fibre collimator 41 and then routed to the output port 11 via the optical circulator 21.
  • the graph inset 200 of Figure 4 shows a typical response of the optical attenuation (i.e. Pou t /Pin, where, P ou t and P
  • FIG. 5 schematically illustrates how the optical device 100 can be used for dynamic spectral equalisation.
  • an input optical signal 15 is a WDM signal.
  • an input optical signal 15 is routed via first circulator 21 to the first port 24 and is then converted to a free-space collimated beam 51 using the first fibre collimator 41.
  • the collimated beam 51 is then incident upon the first two-dimensional holographic grating 61 , and, after processing through the first holographic grating plate 61 and the lens relay 70, the collimated beam 51 is transformed into a multiplicity of optical beams 82, 84 and 86 of different wavelengths, each of which illuminate different areas on the opto- VLSI chip 90.
  • the positions and intensities of the incident beams 82, 84, and 86 are evaluated by the photodetectors (not shown) integrated on the chip, and a pixel block (64x64 pixels) is assigned to each beam 82, 84, 86, and appropriate phase holograms are generated, which transform (reflect) the incident beams 82, 84, 86 into reflected beams 81, 83, and 85.
  • the required beam diffraction angles ( ⁇ r , ⁇ g , and ⁇ b ) of the various pixel blocks can be estimated to equalise the WDM power profile.
  • the reflected beams 81 , 83, 85 are then routed back through the lens relay 70, and are incident upon the first two-dimensional holographic grating 61.
  • the beam that emerges from the holographic grating 61 is coupled into the first fibre port 24 via the first fibre collimator 41 and then routed to the output port 11 via the optical circulator 21 as output signal 16.
  • Figure 6 illustrates schematically how the optical device 100 can be used for tunable optical filtering.
  • the spectrum of the input optical signal P in 15 is assumed to be uniform.
  • an input optical signal 15 is routed via the first circulator 21 to the first port 24 and is then converted to a free-space collimated beam 51 using the first fibre collimator 41.
  • the collimated beam 51 is incident on the two-dimensional holographic grating 61 , and, after processing through the holographic grating plate 61 , and the lens relay 70, the beam 51 is transformed into a multiplicity of optical beams 82, 84, 86 of equally spaced spectral windows, which are incident upon and illuminate the whole area of the opto-VLSI chip 90.
  • the selected window can be reflected back with minimum attenuation while significantly attenuating the remaining spectral windows.
  • This is shown in Figure 6 where the incident beam 86 is reflected back on itself, whereas the other two incident beams 82, 84 are reflected at angles ⁇ g , ⁇ b .
  • the reflected beams 86, 81 , 83 are routed back through the lens relay 70 and are incident upon the first 2D diffractive holographic grating 61.
  • the reflected beam 86 that emerges from the first two-dimensional holographic grating 61 is coupled into the first fibre port 24 via the first fibre collimator 41 and then routed to the output port 11 via the optical circulator 21 as output signal 16.
  • the reflected beams 81 , 83 emerge as beams 54, 55, and are not coupled to the optical circulator 21 as illustrated in Figure 6.
  • the inset 110 of Figure 6 shows a typical response of the tunable optical filter. To tune the filter's centre wavelength to ⁇ j , all holograms on the pixel blocks can be adjusted to attenuate the beams incident on them, and alter the hologram on the jth pixel block (where the wavelength ⁇ j is incident) to reflect back the beam incident on it.
  • Figure 7 illustrates schematically how the optical device 100 can be used for dynamic add/drop multiplexing.
  • an input optical signal 15 is routed via the first circulator 21 to the first port 24 and is then converted to a free-space collimated beam 51 using the first fibre collimator 41.
  • the collimated beam 51 is incident upon the two-dimensional holographic diffractive grating plate 61 , and after processing through the holographic grating plate 61 and the lens relay 70, the beam 51 is transformed into a multiplicity of optical beams 82, 84 and 86 of different wavelengths, each illuminating different areas on the opto-VLSI chip 90.
  • the reflected beam of wavelength ⁇ dro p that emerges from the second two- dimensional holographic diffractive grating plate 62 is coupled into the second fibre port 25 via the second fibre collimator 42 and then routed to the output port 13 via the second optical circulator 22 and output as signal 18.
  • the additional channel 17 of added wavelength, ⁇ add (thick line), input at add port 12 is routed to the second port 25 via the second circulator 22, and it is then converted, via the second fibre collimator 42, to a second collimated beam 52.
  • the added wavelength beam follows the same optical path as that of the dropped wavelength but in the opposite direction - that is, along beam 83 and 84. Therefore, the added channel 17 is combined with the WDM channels and routed back to the output port 11 in the same way.
  • the optical device 100 is also capable of simultaneously adding/dropping many channels by appropriately routing the WDM channels either to output port 11 or to drop port 13.
  • the photodetector sensors integrated on the opto-VLSI chip 90 allow accurate measurements of the power levels of the WDM channels to be performed, and hence the required variable attenuation for each channel can be estimated.
  • a single 6-port optical circulator can replace two 3-port optical circulators 21 and 22 used in the embodiments described above.
  • Figure 8 shows a 6-port optical circulator which routes a forward signal launched into port 1 to port 3 and a backward signal launched into port 3 to port 2. In addition, it routes a forward signal launched into port 4 to port 6 and a backward signal launched into port 6 to port 5.
  • a single 6-port circulator 120 has replaced two 3-port circulators 21 and 22 above.
  • the first and second collimators 40 and 42 have been replaced by a linear collimator array 140.
  • the macrolens are advantageously aligned, appropriately spaced, and centered at a 90-degree angle to the optical axis.
  • Figures 3 and 9 illustrate a possible implementation of the lens relay 70, whereby a telescope-like assembly is used to ensure the lens alignment and positions are highly accurate.
  • the input fibre and collimation lens may be integrated in a single steel barrel. Fibre collimators featuring very low insertion and return losses are now commercially available.
  • the collimating lens may be a macrolens or a microlens depending on the required collimated beam diameter. In another embodiment, the collimating lens is an 8-16 level diffractive element on glass, so as to minimize aberration.
  • a general structure of the fibre collimator array is shown in Figure 10.
  • a thick epoxy may be deposited between the microlens array 147 and the fibre array 137 so as to achieve refractive index matching.
  • Typical characteristics of commercially available fibre collimator arrays are as follows:
  • Lenslet type Epoxy on glass or fused silica Lens diameter/pitch: 0.1-2.0 mm Pitch accuracy: 0.5 micron Working distance: 10-500 mm Insertion loss: 0.5 dB Return loss: -50 dB Operating temperature: -40-85 °C
  • a preferred alternative embodiment of the optical device 100 shown in Figure 11 utilises the same general concepts used in Figures 4 to 7, except that a transparent optical substrate 201 replaces free space for beam propagation.
  • This elimination of free space in the design has the advantage of allowing the device to be more robust.
  • An input light beam 202 enters the device through the optical fibre 203 and is routed via the circulator 204 to the WDM port of the fibre collimator array 205, which collimates the input beam 206 via microlens etched directly into the optical substrate.
  • the collimated beam 206 is demultiplexed by the diffraction grating 207 and the diffracted beams 208 are reflected by a diffractive optical element 209 and incident upon and illuminate an area of the opto-VLSI processor 210.
  • the diffractive optical element 209 is employed to equalise the beam diameters, and being reflective it reduces the length of the optical device 100.
  • the opto-VLSI processor 210 is flip-chip bonded to the optical substrate 201. To minimise the size of the optical substrate, the maximum incidence angles between the processed beams 211 and the normal axis of the opto-VLSI processor equal to the maximum steering angle of the opto-VLSI processor.
  • the diffracted beams 208 are now guided inside the substrate 201 by total internal reflections from the diffractive optical element 209 mounted on the surface of the optical substrate 201.
  • the general principle of operation of the embodiment shown in Figure 11 is similar to that of the embodiment in Figure 1 as illustrated in Figures 4 to 7.
  • preferred embodiments of the invention provide multifunction all-optical devices that employ the steering capability of opto-VLSI chips and use diffraction grating plates to achieve variable optical attenuation, dynamic spectral equalisation, tunable optical filtering and reconfigurable optical add/drop multiplexing.
  • diffraction grating plates By optimising the holographic diffraction grating on the opto-VLSI chip, an incident WDM beam can be decomposed into many output beams that can be arbitrarily controlled.
  • This feature of the opto-VLSI technology is used to provide dynamic control, and hence flexible service management in intelligent optical networks.
  • each hologram on a pixel block set is optimised to work as an independent multifunction all-optical processor, allowing dense and cost- effective all-optical processing to be realised.
  • preferred embodiments of the present invention allow a significantly low cost and improved performance to be attained, in comparison to similar systems implemented using conventional discrete components.
  • a single opto-VLSI chip can integrate with up to 16 multi- function processors in a compact device.
  • Preferred embodiments of the present invention therefore provide a multifunction optical apparatus comprising an opto-VLSI chip that can dynamically be configured to perform high-resolution variable optical attenuation, dynamic spectral equalisation of multichannel signals, precise multiband tunable optical filtering, and dynamic add/drop multiplexing of optical signals.
  • Preferred embodiments have particular, although not exclusive, utility in intelligent optical networks, optical measuring instruments, fibre-array-based systems, photonic signal processors, reconfigurable focal plane arrays, spectroscopy, optical sensing and dense optical computers.
  • Optical communications systems are a key and fast-growing element of communications networks.
  • Such optical systems include, but are not restricted to, telecommunications systems, cable television systems and local area networks (LANs).
  • Most existing optical networks are point-to-point links with most of the intelligence performed by electronics on both sides of the optical link.
  • Recently emerged optical communication networks have comprised many nodes linked by a number of different fibre-optic links for the transport of WDM signals. Although this approach has significantly increased the network capacity and flexibility, service providers will not be able to offer more reliable and cost-effective network usage before dynamically configurable all-optical telecommunication networks (AONs) are deployed.
  • AONs all-optical telecommunication networks
  • Dynamic WDM optical components that perform variable optical attenuation, spectral equalisation, tunable optical filtering, and optical add/drop multiplexing will allow AONs to operate with fewer components, more speed and even larger cost savings. Future AONs will require a variety of functional components to route and control light throughout the network. Signals must be optically attenuated, dynamically spectrally equalised, optically added and dropped, and optically cross-connected and switched within the network. Precise variable optical attenuation enables dynamic attenuation change, which is crucial for the metro optical network market. In an exceptional case, where a WDM signal propagates through an optical amplifier, it is important to maintain the WDM power profile approximately uniform in order to ensure an adequate SNR or BER performance.
  • Dynamic gain equalisation is an effective means that controls and adjusts optical power in different spectral bands arriving at a node in a network.
  • spectral equalisation has been performed by demultiplexing the WDM channels, then using discrete attenuators to independently attenuate each WDM channel, and after that multiplexing all WDM channels into a single optical fibre.
  • This method has the disadvantages that (i) it requires many discrete optical components, (ii) it introduces significant insertion loss in the optical path because of the increased number of components required, and (iii) it results in a high cost and complexity that increase with the number of WDM channels.
  • Tunable optical filters are key components for WDM networks, reconfigurable focal plane arrays, spectroscopy, and optical sensing. Tunable optical filters also play a critical role in wavelength division multiplexed (WDM) optical telecommunication networks, by enabling selective removal of WDM channels. Compared to fixed optical band-pass filters, tunable optical band-pass filters provide better flexibility in fibre optic capacity management.
  • the essential characteristics of next-generation tunable optical filters include low insertion loss, wide tuning range, the capability of providing variable bandwidths, the ability to arbitrarily change the transfer function, high stopband rejection, fast tuning speed, software-driven control, small size, and low cost.
  • ROADMs reconfigurable optical add/drop multiplexers
  • the essential characteristics of next-generation ROADMs include low insertion loss, large number of channels, low crosstalk, fast add/drop speed, software-driven control, small size, and low cost.
  • An all-optical processor that simultaneously offers variable optical attenuation, dynamic WDM equalisation, tunable optical filtering, and reconfigurable optical add/drop multiplexing, will enable a cost-effective and flexible control of future optical networks.
  • Preferred embodiments of the present invention used liquid crystal over silicon (LCOS) technology, which allows the generation of reconfigurable holographic diffraction gratings to process multiple optical beams simultaneously.
  • Preferred embodiments of opto-VLSI chips have low pixel size, low loss, low polarisation dependence, adequate switching speed, and low switching voltage.

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Abstract

An optical device (100) comprising two or more waveguides, two or more diffraction elements (207) to diffract individual optical channels (208) propagating from the waveguides, and one or more reconfigurable holographic elements (210) to reflect the diffracted optical channels (211) back to the diffraction elements (207) so that the reflected diffracted optical channels are diffracted again toward the waveguides. The reconfigurable holographic elements (210) are configurable to selectively vary the reflection angle of the reflected diffracted optical channels to thereby individually and continuously control the optical power level of the twice-diffracted optical channels received by the waveguides.

Description

DYNAMIC MULTIFUNCTION, MULTICHANNEL OPTICAL DEVICE
Field of the Invention
This invention relates to multifunction optical devices for actively managing multichannel optical data transmission systems, and more particularly to dynamic optical devices to selectively or simultaneously add/drop, multiplex/demultiplex, filter, attenuate and/or equalise individual wavelengths (or optical channels).
Background Art
The management of individual optical channels in conventional multichannel optical data transmission systems, for example wavelength division multiplexing (WDM) or dense wavelength division multiplexing (DWDM) communication systems, typically involves using multiplexers/demultiplexers, add/drop multiplexers, tunable filters, gain equalisers and optical switches in parallel or serial architectures. This use of many discrete optical devices is inefficient and disadvantageous because of high cost, multiple insertion loss, low flexibility and poor scalability.
It would be advantageous to provide multifunction optical devices to dynamically manage multichannel optical data transmission systems on a channel-by-channel basis.
Disclosure of the Invention
According to a first aspect of the invention, there is provided an optical device comprising:
two or more waveguides;
two or more diffraction elements to diffract individual optical channels propagating from the waveguides; and one or more reconfigurable holographic elements to reflect the diffracted optical channels back to the diffraction elements so that the reflected diffracted optical channels are diffracted again toward the waveguides;
wherein the reconfigurable holographic elements are configurable to selectively vary the reflection angle of the reflected diffracted optical channels to thereby individually and continuously control the optical power level of the twice-diffracted optical channels received by the waveguides.
Advantageously, the optical device is selectively or simultaneously operable to add/drop, multiplex/demultiplex, filter, attenuate and/or equalise individual optical channels propagating from/to the waveguides.
Preferably, the diffraction elements comprise passive diffraction gratings. More preferably, the passive diffraction gratings comprise two-dimensional holographic diffraction gratings.
Advantageously, the reconfigurable holographic elements comprise phase holograms. More advantageously, the phase holograms are generated by an optoelectronic very large scale integrated (VLSI) circuit chip. Preferably, the optoelectronic VLSI circuit chip comprises detectors to monitor the optical power level of the diffracted optical channels, and a processor and an associated memory storing programs to operate the processor to control the generation of the phase holograms in response to the monitored optical power levels of the diffracted optical channels to thereby individually and continuously control the optical power level of the twice-diffracted optical channels received by the waveguides.
Preferably, the optical device further comprises two or more collimator elements between the waveguides and the diffraction elements to collimate the diffracted optical channels and the twice-diffracted optical channels. More preferably, the collimator elements comprise a collimator array. Advantageously, the optical device further comprises one or more relay elements between the diffraction elements and the reconfigurable holographic elements to route the diffracted optical channels to the reconfigurable holographic elements, and to route the reflected diffracted optical channels back to the diffraction elements. More advantageously, the relay elements comprise one or more macrolens. Preferably, the macrolens are fixedly positioned in optical alignment by a rigid telescopic support. Alternatively, the relay elements comprise one or more diffractive optical elements.
Preferably, the optical device further comprises two or more optical circulators to route input/output optical signals to/from the two or more waveguides.
Advantageously, the optical device further comprises an optical substrate.
In a preferred embodiment, the optical substrate comprises first and second spaced apart parallel planar surfaces, wherein the two or more diffraction elements and the optoelectronic VLSI circuit chip are provided on the first planar surface and a diffractive optical element is provided on the second planar surface so that the optical channels propagate in the optical substrate by internal reflection between the diffraction elements, the diffractive optical element and the optoelectronic VLSI circuit chip.
Advantageously, the optoelectronic VLSI circuit chip is flip-chip bonded to the optical substrate. More advantageously, the collimator array comprises microlens etched in the optical substrate.
Preferably, the optical substrate comprises glass or sapphire.
According to a second aspect of the invention, there is provided a method of selectively or simultaneously adding/dropping, multiplexing/demultiplexing, filtering, attenuating and/or equalising individual optical channels in a multichannel optical data transmission system, the method comprising the steps of: diffracting individual optical channels propagating from two or more waveguides using two or more diffraction elements;
reflecting the diffracted optical channels back to the diffraction elements using one or more reconfigurable holographic elements;
diffracting the reflected diffracted optical channels again toward the waveguides using the diffraction elements; and
dynamically and continuously configuring the reconfigurable holographic elements to selectively vary the reflection angle of the diffracted optical channels to thereby individually and continuously control the optical power level of the twice-diffracted optical channels received by the waveguides.
Brief Description of the Drawings
Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:
Figure 1 is a schematic representation of an optical device in accordance with a first embodiment of the present invention.
Figure 2 is a schematic representation of a lens relay and optoelectronic VLSI circuit chip in the optical device of Figure 1.
Figure 3 is a schematic perspective view of an optical device in accordance with the present invention.
Figure 4 is a schematic representation of the operation of the optical device of Figure 1 as an attenuator.
Figure 5 is a schematic representation of the operation of the optical device of Figure 1 as an equaliser. Figure 6 is a schematic representation of the operation of the optical device of Figure 1 as a tunable filter.
Figure 7 is a schematic representation of the operation of the optical device of Figure 1 as an add/drop multiplexer.
Figure 8 is a schematic representation of an optical circulator used in the optical device of Figure 1.
Figure 9 is a schematic perspective view of an optical device in accordance with a second embodiment of the present invention.
Figure 10 is a schematic representation of a fibre collimator array used in the optical device of Figure 9.
Figure 11 is a schematic side view of an optical device in accordance with a preferred embodiment of the present invention.
Best Mode(s) for Carrying Out the Invention
An embodiment of an optical device 100 in accordance with the present invention is shown in Figure 1. The optical device 100 generally comprises optical circulator 20, fibre collimators 40, diffractive gratings 60, a lens relay 70, and an optoelectronic (or opto-VLSI) chip 90. The optical device 100 comprises two input fibre ports comprising an input port 10 and an add port 12, and two output fibre ports comprising an output port 11 and a drop port 13. These are provided to the circulator 20 as illustrated in Figure 1.
The input fibre port 10 introduces an input signal 15 to be processed. The add port 12 introduces a to-be added channel 17 when the optical device 100 is used as an add/drop multiplexer as described in further detail below. The output port 11 delivers a processed output signal 16 and the drop output port 13 delivers a dropped channel 18 when the optical device 100 is used as an add/drop multiplexer. The circulator 20 comprises first and second circulators 21 , 22. The optical device 100 uses the first optical circulator 21 to route the input signal 15 to first port 24 of the circulator 20, and a reflected signal 31 to the output port 11. Similarly, the second optical circulator 22 routes the added channel 17 to second port 25 of the circulator 20, and the dropped channel 18 to the drop port 13.
The fibre collimators 40 comprise first and second fibre collimators 41 , 42. The first and second fibre collimators 41 , 42 are used to convert the input-fibre signals 15, 17 to collimated optical beams 51 , 52.
The diffractive gratings 60 comprise first and second diffractive gratings 61 , 62. In the embodiment described herein, the first and second diffractive gratings 61 , 62 are two-dimensional holographic grating plates. The diffractive gratings 61 , 62 have large chromatic dispersion so that the wavelength components of the collimated beams 51 , 52 are steered and dispersed along different angles with respect to the incident beam axis as shown in Figure 1. An antireflection coating is provided on the grating to minimise loss.
The lens relay 70 comprises three lenses 72, 74, 76 whose focal lengths and separations are optimised to adequately separate the wavelengths of the resultant emergent beams indicated by reference numerals 82, 84 and 86 in Figure 1 , and to also maintain an adequate beam diameter for all beams 82, 84, 86 when they arrive at the opto-VLSI chip 90.
Figure 2 shows the layout of the lens relay 70 and also the propagation of three different beams. By adjusting the distances between the lenses 72, 74, 76 and their focal lengths the emergent beams 82, 84, 86 are routed to and incident upon different pixel blocks 92, 94, 96 of the opto-VLSI chip 90 with adequate isolation. The role of the opto-VLSI chip 90 is to sense the positions and diameters of the incident beams 82, 84, 86 using integrated photodetectors (not shown) and assign pixel blocks of 64x64 pixels that appropriately process the incident beams 82, 84, 86 to achieve the required processing function as discussed further below. The photodetectors are coupled to a processor, which processes the signals from the photodetectors to generate control signals to appropriately process the incident beams and to generate phase holograms as discussed further below.
The processing functions can be: (i) reflecting the beams back along the input optical path to realise minimum attenuation,
(ii) reflecting the beams back slightly along the input optical path to realise variable optical attenuation, or
(iii) steering the beams away from the input optical path to drop them to another port.
Figure 3 shows a three-dimensional representation of an embodiment of the multifunction optical device 100 of the present invention.
Figure 4 illustrates how the optical device 100 can be used to provide variable optical attenuation. An input optical signal 15 is routed via first circulator 21 to the first port 24 and is converted to a free-space collimated beam 51 using the first fibre collimator 41. The collimated beam 51 is then incident upon the two- dimensional holographic grating plate 61. After processing through the two- dimensional holographic grating plate 61 and the lens relay 70, the beam 51 is transformed to a beam 86, which is incident upon and illuminates a small area on the opto-VLSI chip 90.
The position and intensity of the incident beam 86 are evaluated by the photodetectors (not shown) integrated on the opto-VLSI chip 90, and a pixel block (64x64 pixels) is assigned to the incident beam 86, and an appropriate phase hologram is generated, which transforms (reflects) the incident beam into reflected beam 85. This is achieved by the processor (not shown) on the opto- VLSI chip 90 determining the power of incident beam 86 at any particular pixel block and deriving a signal representative thereof. The processor processes the signals representative of the determined power, and controls the generation of the phase hologram to achieve the desired output power by the processing. ln addition, there is provided a storage medium (not shown) containing computer executable instructions for processing the measured input signal powers. The storage medium stores a computer algorithm that allows the opto-VLSI chip 90 to generate the optimum phase holograms required for best performance. The processing in other operation of the optical device 100 is carried out in a similar manner.
By reflecting the reflected beam 85 back along the direction of incident beam 86, a minimum attenuation is achieved, whereas steering the reflected beam 85 arbitrarily with respect to the position of incident beam 86 can realise variable optical attenuation. The reflected beam 85 is then routed back through the lens relay 70 to the first two-dimensional holographic grating plate 61. The beam 53 that emerges from the holographic grating plate 61 is coupled into the fibre port 24 via the first fibre collimator 41 and then routed to the output port 11 via the optical circulator 21.
The graph inset 200 of Figure 4 shows a typical response of the optical attenuation (i.e. Pout/Pin, where, Pout and P|n are the signal strengths of the output and input signals respectively) versus the hologram diffraction angle θ. It can be seen that linear variable attenuation may be provided.
Figure 5 schematically illustrates how the optical device 100 can be used for dynamic spectral equalisation. In this mode of operation, an input optical signal 15 is a WDM signal. As before, an input optical signal 15 is routed via first circulator 21 to the first port 24 and is then converted to a free-space collimated beam 51 using the first fibre collimator 41. The collimated beam 51 is then incident upon the first two-dimensional holographic grating 61 , and, after processing through the first holographic grating plate 61 and the lens relay 70, the collimated beam 51 is transformed into a multiplicity of optical beams 82, 84 and 86 of different wavelengths, each of which illuminate different areas on the opto- VLSI chip 90. The positions and intensities of the incident beams 82, 84, and 86 are evaluated by the photodetectors (not shown) integrated on the chip, and a pixel block (64x64 pixels) is assigned to each beam 82, 84, 86, and appropriate phase holograms are generated, which transform (reflect) the incident beams 82, 84, 86 into reflected beams 81, 83, and 85. By measuring the intensities of the various, incident beams 82, 84, 86, the required beam diffraction angles (θr, θg, and θb) of the various pixel blocks can be estimated to equalise the WDM power profile. The reflected beams 81 , 83, 85 are then routed back through the lens relay 70, and are incident upon the first two-dimensional holographic grating 61. The beam that emerges from the holographic grating 61 is coupled into the first fibre port 24 via the first fibre collimator 41 and then routed to the output port 11 via the optical circulator 21 as output signal 16.
Figure 6 illustrates schematically how the optical device 100 can be used for tunable optical filtering. To illustrate the principle of operation of this mode, the spectrum of the input optical signal Pin 15 is assumed to be uniform. As before, an input optical signal 15 is routed via the first circulator 21 to the first port 24 and is then converted to a free-space collimated beam 51 using the first fibre collimator 41. The collimated beam 51 is incident on the two-dimensional holographic grating 61 , and, after processing through the holographic grating plate 61 , and the lens relay 70, the beam 51 is transformed into a multiplicity of optical beams 82, 84, 86 of equally spaced spectral windows, which are incident upon and illuminate the whole area of the opto-VLSI chip 90.
By selecting a specific spectral window and assigning to it a pixel block, the selected window can be reflected back with minimum attenuation while significantly attenuating the remaining spectral windows. This is shown in Figure 6 where the incident beam 86 is reflected back on itself, whereas the other two incident beams 82, 84 are reflected at angles θg, θb. The reflected beams 86, 81 , 83 are routed back through the lens relay 70 and are incident upon the first 2D diffractive holographic grating 61. The reflected beam 86 that emerges from the first two-dimensional holographic grating 61 is coupled into the first fibre port 24 via the first fibre collimator 41 and then routed to the output port 11 via the optical circulator 21 as output signal 16. However, the reflected beams 81 , 83 emerge as beams 54, 55, and are not coupled to the optical circulator 21 as illustrated in Figure 6. The inset 110 of Figure 6 shows a typical response of the tunable optical filter. To tune the filter's centre wavelength to λj, all holograms on the pixel blocks can be adjusted to attenuate the beams incident on them, and alter the hologram on the jth pixel block (where the wavelength λj is incident) to reflect back the beam incident on it.
Figure 7 illustrates schematically how the optical device 100 can be used for dynamic add/drop multiplexing. In this mode of operation, the input optical signal 15 is assumed to be a uniform WDM. It is required to drop the channel 18 of wavelength λdr0p (represented by the dotted arrow in Figure 7) from drop port 13, and add a new channel 17 of wavelength λacid, (where λadd = λ rop) through add port 12.
As in the previous descriptions, an input optical signal 15 is routed via the first circulator 21 to the first port 24 and is then converted to a free-space collimated beam 51 using the first fibre collimator 41. The collimated beam 51 is incident upon the two-dimensional holographic diffractive grating plate 61 , and after processing through the holographic grating plate 61 and the lens relay 70, the beam 51 is transformed into a multiplicity of optical beams 82, 84 and 86 of different wavelengths, each illuminating different areas on the opto-VLSI chip 90. By assigning a pixel block to each of the beam areas, all wavelengths can be reflected back with minimum attenuation (in the same way as is done in the previous operations), except the beam 84 having wavelength λdrθp, which is steered and routed onto the second 2D holographic diffractive grating plate 62 as reflected beam 83. This is illustrated in Figure 7.
The reflected beam of wavelength λdrop that emerges from the second two- dimensional holographic diffractive grating plate 62 is coupled into the second fibre port 25 via the second fibre collimator 42 and then routed to the output port 13 via the second optical circulator 22 and output as signal 18. The additional channel 17 of added wavelength, λadd (thick line), input at add port 12 is routed to the second port 25 via the second circulator 22, and it is then converted, via the second fibre collimator 42, to a second collimated beam 52. Being at the same wavelength as the dropped wavelength λdr0p, the added wavelength beam follows the same optical path as that of the dropped wavelength but in the opposite direction - that is, along beam 83 and 84. Therefore, the added channel 17 is combined with the WDM channels and routed back to the output port 11 in the same way. The optical device 100 is also capable of simultaneously adding/dropping many channels by appropriately routing the WDM channels either to output port 11 or to drop port 13.
By slightly steering the reflected beam around the minimum attenuation position spectral equalisation as well as add/drop multiplexing can simultaneously be performed. The photodetector sensors integrated on the opto-VLSI chip 90 allow accurate measurements of the power levels of the WDM channels to be performed, and hence the required variable attenuation for each channel can be estimated.
A single 6-port optical circulator can replace two 3-port optical circulators 21 and 22 used in the embodiments described above. Figure 8 shows a 6-port optical circulator which routes a forward signal launched into port 1 to port 3 and a backward signal launched into port 3 to port 2. In addition, it routes a forward signal launched into port 4 to port 6 and a backward signal launched into port 6 to port 5. By using a two-dimentional fibre collimator array instead of a one- dimensional fibre collimator array, several independent multifunction, multichannel optical devices can simultaneously be realised with a single opto- VLSI processor, as shown in Figure 9. A single 6-port circulator 120 has replaced two 3-port circulators 21 and 22 above. The first and second collimators 40 and 42 have been replaced by a linear collimator array 140.
To ensure a robust lens relay 70, wherein all elements 72, 74, 76 remain stable and well aligned and removal, replacement and repositioning is possible, the macrolens are advantageously aligned, appropriately spaced, and centered at a 90-degree angle to the optical axis. Figures 3 and 9 illustrate a possible implementation of the lens relay 70, whereby a telescope-like assembly is used to ensure the lens alignment and positions are highly accurate.
To ensure that the mounting of the fibre and collimating lens in the optical device 100 is correct, the input fibre and collimation lens may be integrated in a single steel barrel. Fibre collimators featuring very low insertion and return losses are now commercially available. The collimating lens may be a macrolens or a microlens depending on the required collimated beam diameter. In another embodiment, the collimating lens is an 8-16 level diffractive element on glass, so as to minimize aberration.
A general structure of the fibre collimator array is shown in Figure 10. A thick epoxy may be deposited between the microlens array 147 and the fibre array 137 so as to achieve refractive index matching. Typical characteristics of commercially available fibre collimator arrays are as follows:
Lenslet type: Epoxy on glass or fused silica Lens diameter/pitch: 0.1-2.0 mm Pitch accuracy: 0.5 micron Working distance: 10-500 mm Insertion loss: 0.5 dB Return loss: -50 dB Operating temperature: -40-85 °C
Minor changes in the characteristics of the fibre collimator array or misalignment of the components of the lens relay will route the various beams to positions. However, the capability of the opto-VLSI chip to dynamically partition its active area into pixel blocks that effectively surround the various beams, can compensate for such minor misalignment and tolerance.
A preferred alternative embodiment of the optical device 100 shown in Figure 11 utilises the same general concepts used in Figures 4 to 7, except that a transparent optical substrate 201 replaces free space for beam propagation. This elimination of free space in the design has the advantage of allowing the device to be more robust. An input light beam 202 enters the device through the optical fibre 203 and is routed via the circulator 204 to the WDM port of the fibre collimator array 205, which collimates the input beam 206 via microlens etched directly into the optical substrate. The collimated beam 206 is demultiplexed by the diffraction grating 207 and the diffracted beams 208 are reflected by a diffractive optical element 209 and incident upon and illuminate an area of the opto-VLSI processor 210. The diffractive optical element 209 is employed to equalise the beam diameters, and being reflective it reduces the length of the optical device 100. The opto-VLSI processor 210 is flip-chip bonded to the optical substrate 201. To minimise the size of the optical substrate, the maximum incidence angles between the processed beams 211 and the normal axis of the opto-VLSI processor equal to the maximum steering angle of the opto-VLSI processor. Unlike the previous embodiments, however, the diffracted beams 208 are now guided inside the substrate 201 by total internal reflections from the diffractive optical element 209 mounted on the surface of the optical substrate 201. Otherwise, the general principle of operation of the embodiment shown in Figure 11 is similar to that of the embodiment in Figure 1 as illustrated in Figures 4 to 7.
It will be apparent from the above description that preferred embodiments of the invention provide multifunction all-optical devices that employ the steering capability of opto-VLSI chips and use diffraction grating plates to achieve variable optical attenuation, dynamic spectral equalisation, tunable optical filtering and reconfigurable optical add/drop multiplexing. By optimising the holographic diffraction grating on the opto-VLSI chip, an incident WDM beam can be decomposed into many output beams that can be arbitrarily controlled. This feature of the opto-VLSI technology is used to provide dynamic control, and hence flexible service management in intelligent optical networks. In addition, by partitioning the opto-VLSI chip into several pixel-block sets (for example, 4) in preferred embodiments, each hologram on a pixel block set is optimised to work as an independent multifunction all-optical processor, allowing dense and cost- effective all-optical processing to be realised. Thus, it will be apparent that preferred embodiments of the present invention allow a significantly low cost and improved performance to be attained, in comparison to similar systems implemented using conventional discrete components. By using fibre collimator arrays, a single opto-VLSI chip can integrate with up to 16 multi- function processors in a compact device.
Preferred embodiments of the present invention therefore provide a multifunction optical apparatus comprising an opto-VLSI chip that can dynamically be configured to perform high-resolution variable optical attenuation, dynamic spectral equalisation of multichannel signals, precise multiband tunable optical filtering, and dynamic add/drop multiplexing of optical signals. Preferred embodiments have particular, although not exclusive, utility in intelligent optical networks, optical measuring instruments, fibre-array-based systems, photonic signal processors, reconfigurable focal plane arrays, spectroscopy, optical sensing and dense optical computers.
Optical communications systems are a key and fast-growing element of communications networks. Such optical systems include, but are not restricted to, telecommunications systems, cable television systems and local area networks (LANs). Most existing optical networks are point-to-point links with most of the intelligence performed by electronics on both sides of the optical link. Recently emerged optical communication networks have comprised many nodes linked by a number of different fibre-optic links for the transport of WDM signals. Although this approach has significantly increased the network capacity and flexibility, service providers will not be able to offer more reliable and cost-effective network usage before dynamically configurable all-optical telecommunication networks (AONs) are deployed. Dynamic WDM optical components that perform variable optical attenuation, spectral equalisation, tunable optical filtering, and optical add/drop multiplexing will allow AONs to operate with fewer components, more speed and even larger cost savings. Future AONs will require a variety of functional components to route and control light throughout the network. Signals must be optically attenuated, dynamically spectrally equalised, optically added and dropped, and optically cross-connected and switched within the network. Precise variable optical attenuation enables dynamic attenuation change, which is crucial for the metro optical network market. In an exceptional case, where a WDM signal propagates through an optical amplifier, it is important to maintain the WDM power profile approximately uniform in order to ensure an adequate SNR or BER performance. Dynamic gain equalisation (DGE) is an effective means that controls and adjusts optical power in different spectral bands arriving at a node in a network. The ability to cost-effectively integrate wideband dynamic WDM equalisation capability (over -100 nm wavelength span), is a critical requirement for next generation optical networks. Conventionally, spectral equalisation has been performed by demultiplexing the WDM channels, then using discrete attenuators to independently attenuate each WDM channel, and after that multiplexing all WDM channels into a single optical fibre. This method has the disadvantages that (i) it requires many discrete optical components, (ii) it introduces significant insertion loss in the optical path because of the increased number of components required, and (iii) it results in a high cost and complexity that increase with the number of WDM channels.
Tunable optical filters are key components for WDM networks, reconfigurable focal plane arrays, spectroscopy, and optical sensing. Tunable optical filters also play a critical role in wavelength division multiplexed (WDM) optical telecommunication networks, by enabling selective removal of WDM channels. Compared to fixed optical band-pass filters, tunable optical band-pass filters provide better flexibility in fibre optic capacity management. The essential characteristics of next-generation tunable optical filters include low insertion loss, wide tuning range, the capability of providing variable bandwidths, the ability to arbitrarily change the transfer function, high stopband rejection, fast tuning speed, software-driven control, small size, and low cost.
Future intelligent WDM systems also require reconfigurable optical add/drop multiplexers (ROADMs) to dynamically add or drop one or more wavelength channels. The essential characteristics of next-generation ROADMs include low insertion loss, large number of channels, low crosstalk, fast add/drop speed, software-driven control, small size, and low cost. An all-optical processor that simultaneously offers variable optical attenuation, dynamic WDM equalisation, tunable optical filtering, and reconfigurable optical add/drop multiplexing, will enable a cost-effective and flexible control of future optical networks.
Preferred embodiments of the present invention used liquid crystal over silicon (LCOS) technology, which allows the generation of reconfigurable holographic diffraction gratings to process multiple optical beams simultaneously. Preferred embodiments of opto-VLSI chips have low pixel size, low loss, low polarisation dependence, adequate switching speed, and low switching voltage.
It will be further apparent that the advantages of preferred embodiments of the multifunction optical processor include:
(1 ) multichannel variable optical attenuation, for future optical networks, (2) dynamic spectral equalisation, which improves quality of service,
(3) multi-band tunable optical filtering, which is critical for many future applications,
(4) reconfigurable optical add/drop multiplexing, which is crucial for future intelligent optical networks, (5) formulated as a static device, therefore, it is reliable, and
(6) cost-effective since all wavelength channels share a single opto-VLSI chip.
With mass production a substantial reduction in multifunction optical processor cost is achieved by preferred embodiments.
The embodiments have been described by way of example only and modifications are possible within the scope of the invention.
Throughout the specification, unless the context requires otherwise, the word "comprise" and variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Claims

The Claims Defining the Invention are as Follows
1. An optical device comprising:
two or more waveguides;
two or more diffraction elements to diffract individual optical channels propagating from the waveguides; and
one or more reconfigurable holographic elements to reflect the diffracted optical channels back to the diffraction elements so that the reflected diffracted optical channels are diffracted again toward the waveguides;
wherein the reconfigurable holographic elements are configurable to selectively vary the reflection angle of the reflected diffracted optical channels to thereby individually and continuously control the optical power level of the twice-diffracted optical channels received by the waveguides.
2. An optical device as claimed in claim 1 , wherein the optical device is selectively or simultaneously operable to add/drop, multiplex/demultiplex, filter, attenuate and/or equalise individual optical channels propagating from/to the waveguides.
3. An optical device as claimed in claim 1 or 2, wherein the diffraction elements comprise passive diffraction gratings.
4. An optical device as claimed in claim 3, wherein the passive diffraction gratings comprise two-dimensional holographic diffraction gratings.
5. An optical device as claimed in any one of the preceding claims, wherein the reconfigurable holographic elements comprise phase holograms.
6. An optical device as claimed in claim 5, wherein the phase holograms are generated by an optoelectronic very large scale integrated (VLSI) circuit chip.
7. An optical device as claimed in claim 6, wherein the optoelectronic VLSI circuit chip comprises detectors to monitor the optical power level of the diffracted optical channels, and a processor and an associated memory storing programs to operate the processor to control the generation of the phase holograms in response to the monitored optical power levels of the diffracted optical channels to thereby individually and continuously control the optical power level of the twice-diffracted optical channels received by the waveguides.
8. An optical device as claimed in any one of the preceding claims, further comprising two or more collimator elements between the waveguides and the diffraction elements to collimate the diffracted optical channels and the twice-diffracted optical channels.
9. An optical device as claimed in claim 8, wherein the collimator elements comprise a collimator array.
10. An optical device as claimed in any one of the preceding claims, further comprising one or more relay elements between the diffraction elements and the reconfigurable holographic elements to route the diffracted optical channels to the reconfigurable holographic elements, and to route the reflected diffracted optical channels back to the diffraction elements.
11. An optical device as claimed in claim 10, wherein the relay elements comprise one or more macrolens.
12. An optical device as claimed in claim 11 , wherein the macrolens are fixedly positioned in optical alignment by a rigid telescopic support.
13. An optical device as claimed in claim 10, wherein the relay elements comprise one or more diffractive optical elements.
14. An optical device as claimed in any one of the preceding claims, further comprising two or more optical circulators to route input/output optical signals to/from the waveguides.
15. An optical device as claimed in any one of the preceding claims, further comprising an optical substrate.
16. An optical device as claimed in claim 15 as dependent on claim 13, wherein the optical substrate comprises first and second spaced apart parallel planar surfaces, wherein the two or more diffraction elements and the reconfigurable holographic elements are provided on the first planar surface and a diffractive optical element is provided on the second planar surface so that the optical channels propagate in the optical substrate by internal reflection between the diffraction elements, the diffractive optical element and the reconfigurable holographic elements.
17. An optical device as claimed in claim 16 as dependent on claim 6, wherein the optoelectronic VLSI circuit chip is flip-chip bonded to the optical substrate.
18. An optical device as claimed in claim 16 or 17 as dependent on claim 9, wherein the collimator array comprises microlens etched in the optical substrate.
19. An optical device as claimed in any one of claims 15 to 18, wherein the optical substrate comprises glass or sapphire.
20. A method of selectively or simultaneously adding/dropping, multiplexing/demultiplexing, filtering, attenuating and/or equalising individual optical channels in a multichannel optical data transmission system, the method comprising the steps of: diffracting individual optical channels propagating from two or more waveguides using two or more diffraction elements;
reflecting the diffracted optical channels back to the diffraction elements using one or more reconfigurable holographic elements;
diffracting the reflected diffracted optical channels again toward the waveguides using the diffraction elements; and
dynamically and continuously configuring the reconfigurable holographic elements to selectively vary the reflection angle of the reflected diffracted optical channels to thereby individually and continuously control the optical power level of the twice-diffracted optical channels received by the waveguides.
21. An optical device substantially as hereinbefore described with reference to the accompanying drawings.
22. A method of selectively or simultaneously adding/dropping, multiplexing/demultiplexing, filtering, attenuating and/or equalising individual optical channels in a multichannel optical data transmission system substantially as hereinbefore described with reference to the accompanying drawings.
PCT/AU2003/000870 2002-07-05 2003-07-04 Dynamic multifunction, multichannel optical device WO2004005993A1 (en)

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AU2002950003A AU2002950003A0 (en) 2002-07-05 2002-07-05 A multi-function opto-vlsi processor for intelligent optial networks

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