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
  • G02B6/26—Optical coupling means
  • G02B6/35—Optical coupling means having switching means
  • G02B6/354—Switching arrangements, i.e. number of input/output ports and interconnection types
  • G02B6/356—Switching arrangements, i.e. number of input/output ports and interconnection types in an optical cross-connect device, e.g. routing and switching aspects of interconnecting different paths propagating different wavelengths to (re)configure the various input and output links
• • 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
  • G02B6/35—Optical coupling means having switching means
  • G02B6/351—Optical coupling means having switching means involving stationary waveguides with moving interposed optical elements
  • G02B6/3512—Optical coupling means having switching means involving stationary waveguides with moving interposed optical elements the optical element being reflective, e.g. mirror
• • 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
  • G02B6/35—Optical coupling means having switching means
  • G02B6/354—Switching arrangements, i.e. number of input/output ports and interconnection types
  • G02B6/3544—2D constellations, i.e. with switching elements and switched beams located in a plane
  • G02B6/3548—1xN switch, i.e. one input and a selectable single output of N possible outputs
• • 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
  • G02B6/35—Optical coupling means having switching means
  • G02B6/354—Switching arrangements, i.e. number of input/output ports and interconnection types
  • G02B6/3554—3D constellations, i.e. with switching elements and switched beams located in a volume
  • G02B6/3556—NxM switch, i.e. regular arrays of switches elements of matrix type constellation
• • 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
  • G02B6/35—Optical coupling means having switching means
  • G02B6/354—Switching arrangements, i.e. number of input/output ports and interconnection types
  • G02B6/3554—3D constellations, i.e. with switching elements and switched beams located in a volume
  • G02B6/3558—1xN switch, i.e. one input and a selectable single output of N possible outputs
• • 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
  • G02B6/35—Optical coupling means having switching means
  • G02B6/3594—Characterised by additional functional means, e.g. means for variably attenuating or branching or means for switching differently polarized beams

Definitions

• the present invention relates to the field of fast optical switches, whose operation is wavelength dependent, especially those having a large number of switchable ports.
• optical wavelengths are used as optical carriers for carrying digital or analog information. Also, the different wavelengths may be used to discriminate one set or channel of information from another. When a plurality of wavelengths are coupled or multiplexed onto a single fiber, this is called wavelength division multiplexing (WDM). Use of such WDM increases the overall bandwidth of the system.
• WDM wavelength division multiplexing
• the wavelength dispersion may preferably be performed by a diffraction grating, and the polarization-splitting by a polarized beam splitter.
• a polarization rotation device such as a liquid crystal polarization modulator, pixelated along the wavelength dispersive direction such that each pixel operates on a separate wavelength channel, is operative to rotate the polarization of the light signal passing through each pixel, according to the control voltage applied to the pixel.
• the polarization modulated signals are then wavelength-recombined and polarization-recombined by means of similar or the same dispersion and polarization combining components as were used to respectively disperse and split the input signals.
• the direction in which the resulting output signal is directed is determined by whether the polarization of the particular wavelength channel was rotated by the polarization modulator pixel, or not.
• a multi-port switchable router using beam steering elements which can be either an array of Micro-Electro- Mechanical System (MEMS) components, such as micro-mirrors, or a set of serially disposed liquid crystal arrays and wedge shaped birefringent crystals, which generate different angles of propagation to the beam passing therethrough according to the different polarizations of the beams produced by the setting of the liquid crystal array pixels, or a liquid crystal-on-silicon (LCQS) spatial light modulator acting as a phased array.
• MEMS Micro-Electro- Mechanical System
• LCDQS liquid crystal-on-silicon
• the present invention seeks to provide a new fiber-optical, wavelength selective switch structure (WSS), such as is used for channel routing applications in optical communication and information transmission systems.
• WSS wavelength selective switch structure
• the number of switchable ports is generally limited.
• One limitation is that an increase in the number of ports would result in an increase in the height of the component, which would not be practical for integration into an optical communication system.
• Another limitation is the difficulty in providing suitable optical components, especially the focusing optics, for such a large multi-beam cross section.
• Exemplary devices described in the present disclosure to overcome this limitation may comprise a multi-port WSS, typically of up to 1 x 12 way (this being a typical practical limit to the height of currently designed WSS structures for use in deployed commercial systems), with this switch functionality doubled by using a polarization switching architecture which can deflect any of the switched beams in a plane perpendicular to the beam steering plane used by the WSS array.
• a polarization switching architecture which can deflect any of the switched beams in a plane perpendicular to the beam steering plane used by the WSS array.
• a total of 24 ports is made available, in two stacks of 12 ports, the stacks being positioned side by side.
• the beams are deflected to the desired port level in either of the stacks by means of the beam steering assembly, such as any of those described in the above mentioned WO2007/029260.
• a particularly convenient method of beam steering may use a MEMS array.
• any beam deflected to any of the port levels can be directed to either of the stacks by means of polarization switching components operative to divert the beams laterally between the two stacks.
• the direction of beam steering deflection for channel selection is performed in what is called the height of the switch, with the ports arranged vertically, while the beam deflection to select to which stack the steered beam is directed is performed in the direction of what is called the width the switch, with the two stacks arranged side-by-side.
• This polarization switching assembly may advantageously be constructed of a liquid crystal (LC) cell with a birefringent crystal wedge, as described in co-pending US Provisional Patent Application No. 61/213,544 to some inventors of the present application, entitled “Liquid Crystal Wavelength Selectable Router”. In this manner, the port count is doubled up without the need for a wide angular swing of the beam steering arrangement, and without excessive height of the switch assembly.
• LC liquid crystal
• a sequence of more than one polarization switching mechanism can be used in series, as shown in WO2007/029260, to enable switching of the steered output beams in more than two alternative lateral directions, such that the beam steering stack can be tripled-up or even more, thus generating an even larger WSS array.
• a wavelength dispersive element receiving an input optical beam from one of the ports, and dispersing wavelength components thereof in a dispersion plane
• a pixelated beam steering array disposed such that a wavelength components is steered in a plane generally perpendicular to the dispersion plane according to the settings of the pixel of the beam steering array associated with the wavelength component
• a polarization dependent deflection array comprising:
• a pixilated polarization rotation element adapted to rotate the polarization of light passing through pixels thereof according to control signals applied to the pixels
• the pixelated beam steering array may advantageously be a reflective MEMS array
• the pixelated polarization rotation component may be a pixelated liquid crystal cell.
• the polarization of a wavelength component passing through a pixel of the liquid crystal cell may be rotated in accordance with the voltage applied across the liquid crystal pixel.
• the birefringent element may be a birefringent wedge with its taper aligned such that it deflects light of different polarizations in different angular directions generally perpendicular to the beam steering direction. If so, then the angular direction in which the wavelength component is deflected by the birefringent wedge should be dependent on the voltage applied across the pixel of the liquid crystal cell through which the wavelength component passed before impingement on the wedge.
• the two dimensional array of ports may advantageously be arranged in two adjacent stacks, such that the switch provides twice the port capacity to that of a switch of similar height in which the ports are arranged in a one-dimensional array.
• the ports may be arranged such that light can be switched between one port and any of the other ports.
• Such switches may further comprise a pixelated liquid crystal attenuator array, such that any wavelength component can be attenuated in passage through the switch.
• Fig.1 illustrates schematically a prior art wavelength selective switch structure (WSS);
• Fig. 2 illustrates schematically a wavelength selective switch structure (WSS), constructed and operative according to a preferred embodiment of the present invention
• Figs. 3 and 4 illustrate schematically alternative methods of generating input beam polarization diversity using a polarization beam splitter or a polarization beam combiner respectively.
• Fig. 1 illustrates schematically a top view of a prior art wavelength selective switch structure (WSS), such as is described in International Patent Application, Publication No. WO2007/029260, and as used for channel routing applications in optical communication and information transmission systems.
• the WSS includes a stack 10 of fiber collimators for inputting and outputting the optical signals. Only one collimator is visible in the drawing since the stack is being viewed from the top.
• the dispersion plane of the switch is generally called the lateral plane, such that the view in the dispersion plane is called the side view, while the view perpendicular to the dispersion plane is called the plan view, or the view from the top.
• the drawing insert shows a side view of the stack 10 of fiber collimators.
• the beam issuing from each fiber collimator is then converted into a pair of closely disposed beams having the same predefined polarization direction for transmission through the WSS.
• This may be achieved by the use of a birefringent walk-off crystal 19, such as a YVO 4 crystal, having a half wave plate over part of its output face.
• the output of each input collimator channel is thus converted into a pair of beams having the same polarization direction, disposed in a predetermined plane.
• these beams can then advantageously be laterally expanded in that same predetermined plane, such as by an anamorphic prism pair.
• These optional beam expansion components being well known in the art, are not shown in Fig. 1.
• These input beams are wavelength dispersed in the plane of the drawing, conveniently by means of a diffraction grating 11.
• the wavelength dispersed beams are focused by a lens 12 onto a one-dimensional beam steering and switching array 13.
• a MEMS array 14 is used for the beam steering, and a pixilated liquid crystal cell 15 for attenuation of the switched beams.
• 3 separate wavelength channels and three pixels are shown in Fig. 1 , though it is to be understood that using a channel spacing of 100GHz or even 50 GHz, the number of channels that will fit into the bandwidth of the device will be much larger than that.
• the MEMS array steers the signals destined for different output ports in a direction out of the plane of the drawing, i.e. in the direction of the height of the switch, such that output signals are differently directed to enter different fiber optical collimators 10 shown in the side view of the collimator stack.
• Fig. 2 illustrates schematically a wavelength selective switch structure (WSS), according to one exemplary implementation of the switches of the present disclosure.
• the WSS of Fig. 2 differs from that of Fig. 1 in that the beam steering and switching array 20 now includes two switching arrays.
• the first is the reflective MEMS array 14 used for the beam steering, in the same way as in the embodiment of Fig. 1. This steers the beams in the direction of the height of the switch, i.e. in the direction out of the plane of the drawing, to output the WSS at any of the different output port levels of the output port collimator array 10.
• the second switching array is positioned in front of the MEMS array 14, and it is operative to switch the beams in a direction generally perpendicular to the beam steering direction. It is shown in Fig. 2 operating as an LC polarization mode switching array, comprising a birefringent crystal wedge 21 and associated pixilated LC cell 22. The operation of such an LC polarization mode switching array is described more fully in co-pending US Provisional Patent Application No. 61/213,544 for "Liquid Crystal Wavelength Selectable Router", herewith incorporated by reference in its entirety.
• the LC cell 22 changes the polarization direction of light passing through, in accordance with the voltage applied to the LC cell electrodes, and the birefringent crystal wedge 22 laterally deflects the beam in accordance with the polarization of the incident light.
• the taper of the wedge has to be aligned laterally so that its deflection plane is also lateral, i.e. in the dispersion plane, and perpendicular to the beam steering plane.
• the beam can thus be deflected according to the voltage applied to the LC pixel 22 through which it is passing. For instance, .
• the LC voltage is applied to fully activate a cell ON, no change in the polarization direction of the traversing light occurs, and the beam passes through the wedge undeviated. If the LC is turned OFF, the polarization of the traversing light is rotated 90 degrees, and is then deflected by the wedge.
• the wedge orientation is such as to deflect the beam when switched, in the plane of the drawing, i.e. in the dispersion plane.
• the deflected beam angle as determined by the birefractivity of the crystal material, is such that the deviation diverts the beam such that it now enters a second collimator array 25, disposed next to the first collimator array 10.
• the output beam can be switched between corresponding output port levels in collimator array 10 or 25.
• the output beam can be switched to any of the output ports in the two side-by-side collimator arrays, 10, 25.
• one is situated behind the other, both occupying the same height of the WSS.
• the beam steering and switching array 20 may also include an LC attenuation array 15, generally comprising a linear polarizer and a pixilated LC cell, as is known in the art.
• this particular embodiment of the WSS of the present invention is a 1 x 23 way WSS.
• the height of the WSS need be no more than a 12-port WSS, and the increased footprint engendered by the second collimator stack is minimal.
• Fig. 3 illustrates an alternative method of generating the polarization diversity required at the input to the switch, using a polarization beam splitter (PBS) assembly 32.
• the input beams 30 from the input collimators shown as being 9 beams in the example of Fig. 3, are passed into the PBS, in which the p-component of any beam is transmitted undiverted, while the s-component is reflected such that it emerges parallel to the p- component.
• a half wave plate 33 disposed over the region of the PBS where the diverted beam emerge, changes the s-polarization to p-, such that both beams now have the same p-polarization for transmission through the switch. Any of the 9 beams are then beam steered and laterally deflected as described in the previous examples of Fig. 2.
• Fig. 4 illustrates an alternative method of generating the polarization diversity required at the input to the switch, using a polarization beam combiner assembly 42. Only a single input beam is shown in Fig. 4, though it is to be understood that multiple beams can be used as in Fig. 3.
• the input beams 40 from the input collimators are passed into the PBC, usually made of a birefringent block, such that the s- and p-components of the input beam are diverted into different angular directions.
• the diverging beams enter a prism 44, where they are refracted to a parallel configuration again, and a half wave plate 43 disposed over the region where the s-component beam emerges, changes the s-polarization to p-, such that both beams now have the same p-polarization for transmission through the switch. Any of the 9 beams are then beam steered and laterally deflected as described in the previous examples of Fig. 2.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
• Liquid Crystal (AREA)

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• 2010
  • 2010-06-17 CN CN2010800372682A patent/CN102498427A/zh active Pending
  • 2010-06-17 WO PCT/IL2010/000479 patent/WO2010146589A1/en active Application Filing

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