Abstract:
A multi-unit wavelength dispersive optical device includes a plurality of independent planar lightwave circuit (PLC) wavelength dispersive optical devices in a single device in which a plurality of independent front and backend units can utilize the same dispersion platform and share the same opto-mechanics and packaging.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority of U.S. Provisional Patent Application No. 60/789,564 file Apr. 6, 2006, entitled “Wavelength Switch With Multiple Units” which is incorporated herein by reference for all purposes. 
     
    
     TECHNICAL FIELD  
       [0002]     The present invention relates to a multi-unit wavelength dispersive optical device, and in particular to the integration of a plurality of independent planar lightwave circuit (PLC) wavelength dispersive optical devices into a single device.  
       BACKGROUND OF THE INVENTION  
       [0003]     Conventional optical wavelength dispersive devices, such as those disclosed in U.S. Pat. No. 6,097,859 issued Aug. 1, 2000 to Solgaard et al; U.S. Pat. No. 6,498,872 issued Dec. 24, 2002 to Bouevitch et al; U.S. Pat. No. 6,707,959 issued Mar. 16, 2004 to Ducellier et al; U.S. Pat. No. 6,810,169 issued Oct. 26, 2004 to Bouevitch; and U.S. Pat. No. 7,014,326 issued Mar. 21, 2006 to Danagher et al, separate a multiplexed optical beam into constituent wavelengths, and then direct individual wavelengths or groups of wavelengths, which may or may not have been modified, back through the device to a desired output port. Typically the back end of the device includes individually controllable devices, such as a micro-mirror array, which are used to redirect selected wavelengths back to one of several output ports, or an array of liquid crystal cells, which are used to block or attenuate selected wavelengths.  
         [0004]     In the case of a wavelength blocker (WB), or a dynamic gain equalizer (DGE) the front end unit can include a single input/output port with a circulator or one input port and one output port. Typically the front end unit will include a polarization diversity unit for ensuring the beam of light has a single state of polarization. The backend unit for a WB or a DGE can be an array of liquid crystal cells, which independently rotate the state of polarization of the wavelength channels to either partially attenuate or completely block selected channels from passing back through the polarization diversity unit in the front end. Examples of WB and DGE backend units are disclosed in U.S. Pat. No. 7,014,326 issued Mar. 21, 2006 to Danagher et al; U.S. Pat. No. 6,498,872 issued Dec. 24, 2002 to Bouevitch et al; and U.S. Pat. No. 6,810,169 issued Oct. 26, 2004 to Bouevitch, which are incorporated herein by reference.  
         [0005]     The arrayed waveguide diffraction grating (AWG) was invented by Dragone (C. Dragone, IEEE Photonics Technology Letters, Vol. 3, No. 9, pp. 812-815, September 1991) by combining a dispersive array of waveguides (M. K. Smit, Electronics Letters, Vol. 24, pp. 385-386, 1988) with input and output “star couplers” on a planar lightwave circuit chip. (C. Dragone, IEEE Photonics Technology Letters, Vol. 1, No. 8, pp. 241-243, August 1989). The AWG can work both as a DWDM demultiplexer and as a DWDM multiplexer, as taught by Dragone in U.S. Pat. No. 5,002,350 (March 1991), which is incorporated herein by reference.  
         [0006]     U.S. Pat. No. 7,027,684 issued Apr. 11, 2006 to Ducellier et al, and United States Patent Publication No. 2004/0252938 published Dec. 16, 2004 to Ducellier et al relate to single and mulit-layer planar lightwave circuit (PLC) wavelength selective switches (WSS), respectively, which are illustrated in  FIGS. 1 and 2 . A single level device  75 , illustrated in  FIG. 1 , includes a PLC  74  with an input diffraction grating in the middle, and a plurality of output diffraction gratings on either side of the input diffraction grating. An input optical signal launched into the input diffraction grating is dispersed into constituent wavelengths, which are directed at different angles through lensing  78  to an array of tiltable mirrors  76 . The light is collimated in one direction, e.g. vertically, by a first cylindrical lens  77  adjacent to the PLC  74 , while a cylindrical switching lens  79  focuses the output light in the horizontal direction onto the tiltable mirrors  76 . Each wavelength channels falls onto a different one of the tiltable mirrors  76 , which redirect the individual wavelength channels back through the lensing  78  to whichever output diffraction grating is desired for recombination and output an output port. For the single level device the tiltable mirrors  76  rotate about a single axis to redirect the wavelength channels within the dispersion plane, i.e. the plane of the PLC  74 .  
         [0007]     A two level device  75 ′, illustrated in  FIG. 2 , includes a second PLC  74 ′, similar to the PLC  74 , superposed above the PLC  74  with a plurality of input or output diffraction gratings and ports. A second cylindrical lens  77 ′ is superposed above the first cylindrical lens  77  for focusing the beams of light onto the output diffraction gratings provided on the second PLC  74 ′. For the two-level device, tiltable mirrors  76 ′ rotate about two perpendicular axes to redirect the wavelength channels within the dispersion plane (as above) and at an acute angle to the dispersion plane into a plane parallel to the dispersion plane, i.e. the plane of the PLC  74 ′.  
         [0008]     Unfortunately, each time a customer wishes to purchase a WB, a DGE, a WSS or any form of monitor therefor, they must purchase a separate dispersion platform, i.e. spherical lens and tiltable mirror MEMS chip, along with associated opto-mechanics and packaging. An object of the present invention is to overcome the shortcomings of the prior art by providing a multi-unit wavelength dispersive device, in which a plurality of independent front and backend units can utilize the same dispersion platform and share the same opto-mechanics and packaging.  
       SUMMARY OF THE INVENTION  
       [0009]     Accordingly, the present invention relates to a multi-unit planar lightwave circuit device comprising:  
         [0010]     a first planar lightwave circuit chip including a first input port, a first input arrayed waveguide grating, a first plurality of output arrayed waveguide gratings, and a first plurality of output ports, wherein a first input optical signal launched into the first input arrayed waveguide grating via the first input port is dispersed into wavelength channels in a first dispersion plane upon exiting the first input arrayed waveguide grating;  
         [0011]     a first cylindrical lens for collimating the first input optical signal in a first direction after exiting the first planar lightwave circuit;  
         [0012]     a first array of switching elements for independently redirecting each of the wavelength channels from the first input optical signal to selected first output arrayed waveguide gratings forming a plurality of first output optical signal for output respective first output ports;  
         [0013]     a second planar lightwave circuit chip including a second input port, a second input arrayed waveguide grating, at least one second output arrayed waveguide gratings, and at least one second output ports, wherein a second input optical signal launched into the second input arrayed waveguide grating via the second input port disperses according to wavelength into a second dispersion plane upon exiting the second input arrayed waveguide grating;  
         [0014]     a second cylindrical lens for collimating the second input optical signal in the first direction after exiting the second planar lightwave circuit;  
         [0015]     a second array of switching elements for independently redirecting each of the wavelength channels from the second input optical signal to selected second output arrayed waveguide gratings for output respective second output ports; and  
         [0016]     a switching lens for focusing the wavelength channels of the first input optical signal onto respective switching elements from the first array of switching elements, and for focusing the wavelength channels of the second optical signal onto respective switching elements from the second array of switching elements. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The invention will be described in greater detail with reference to the accompanying drawings which represent preferred embodiments thereof, wherein:  
         [0018]      FIG. 1  is a plan view of a conventional PLC WSS;  
         [0019]      FIG. 2  is a side view of a conventional multi-layer PLC WSS;  
         [0020]      FIG. 3  is a side view of a multi-unit PLC wavelength dispersive device according to the present invention; and  
         [0021]      FIG. 4  is a top view of a first level of the device of  FIG. 3 ;  
         [0022]      FIG. 5  is a cross-sectional view of a second level of the device of  FIG. 3 ;  
         [0023]      FIG. 6  is a side view of another embodiment of a multi-unit PLC wavelength dispersive device according to the present invention;  
         [0024]      FIG. 7  is a cross-sectional view of a third level of the device of  FIG. 6 ;  
         [0025]      FIG. 8  is a cross-sectional view of a second level of the device of  FIG. 6 ;  
         [0026]      FIG. 9  is a cross-sectional view of a fourth level of the device of  FIG. 6 ; and  
         [0027]      FIG. 10  is a top view of a first level of the device of  FIG. 6 ; 
     
    
     DETAILED DESCRIPTION  
       [0028]     With reference to FIGS.  3  to  5 , a multiple independent unit, planar lightwave circuit, (PLC) free-space, hybrid wavelength selective switch (WSS)  11  operates on the same principle shown in  FIG. 1  above. A first wavelength multiplexed signal, including a plurality of wavelength channels, enters a first input port  12 , e.g. the middle port, of a first PLC chip  13 . The light exiting the first PLC  13  angularly disperses, i.e. fans out, according to wavelength in a first dispersion plane, as a result of an arrayed waveguide grating (AWG)  14  on the PLC  13 . The light is collimated in one direction or plane, e.g. vertically or in the first dispersion plane, by a first cylindrical lens  16  adjacent to the PLC  13 . The collimated wavelength channels pass through a cylindrical switching lens  17  on one side of a central OA thereof, which focuses the output light in the other direction or plane, e.g. a horizontal direction perpendicular to the dispersion plane, onto a first array or switching elements  18 , e.g. a MEMS array of tiltable mirrors or an array of liquid crystal cells for redirecting, attenuating or blocking all or a portion of selected wavelength channels. Each wavelength channel falls onto a different switching element  19   a  to  19   f  in the switching element array  18 , which independently redirect each of the individual wavelength channels back through the switching lens  17  and the first cylindrical lens  16  to whichever output diffraction grating  21   a  to  21   d  is desired or back to the input diffraction grating  14 . The first array of switching elements  18  may also perform partial attenuation or full wavelength channel blocking, as is well known in the art. The output diffraction gratings  21   a  to  21   d  recombine the wavelength channels directed thereto and output the recombined output signals to respective output ports  22   a  to  22   d.  Preferably, the input port  12  and the output ports  22   a  to  22   d  are optically coupled to waveguides, e.g. optical fibers, for transmission to and from an optical network. In a one dimensional system with MEMS mirrors, each MEMS mirror  19   a  to  19   f  can rotate about a single axis to redirect the wavelength channels within the first dispersion plane, i.e. the plane of the PLC  13 , and do not redirect any of the channels to other PLCs.  
         [0029]     The illustrated embodiment of  FIG. 4  provides a 1×4 switch, but any number of output diffraction gratings and output ports within suitable optical and mechanical parameters is within the scope of the present invention. Furthermore, converting some of the output ports to input ports or input/output ports is also possible to provide additional functionality, e.g. add/drop multiplexer, cross-connect multiplexer.  
         [0030]     With reference to  FIG. 5 , a second PLC chip  23  is positioned parallel to, i.e. superposed under or on top of, the first PLC chip  13  with a second cylindrical lens  26  adjacent thereto. The second PLC chip  23  can be identical to the first PLC chip  13  or can include more or less diffraction gratings, input ports and output ports, as desired. As above, a second input optical signal, including a plurality of constituent wavelength channels, is launched via a second input port  22  into a second input diffraction grating  24 , which disperses the wavelength channels at an angle according to wavelength. The second cylindrical lens  26  collimates the dispersed light in one direction or plane, e.g. vertically or in the second dispersion plane.  
         [0031]     The wavelength channels from the second input beam pass through the same cylindrical switching lens  17 , on an opposite side of the central axis to the wavelength channels from the first input optical signal. The cylindrical switching lens  17  focuses the output light in the other direction or plane, e.g. horizontal direction and perpendicular to the second dispersion plane, onto a second array of switching elements  28 , e.g. a MEMS array of tiltable mirrors  29   a  to  29   f  or an array of liquid crystal cells for redirecting, attenuating or blocking all or a portion of selected wavelength channels, which are parallel to the first array of switching elements  18 , but independently controlled. Each wavelength channel falls onto a different switching element  29   a  to  29   f  (only one of which is shown) in the second switching element array  28 , which independently redirect each of the individual wavelength channels back through the switching lens  17  and the second cylindrical lens  26  to whichever output diffraction grating  31   a  to  31   d  is desired or back to the input diffraction grating  24 . The second array of switching elements  28  may also perform partial attenuation or full wavelength channel blocking, as is well known in the art. The output diffraction gratings  31   a  to  31   d  recombine the wavelength channels directed thereto and output the recombined output signals to respective output ports. As above, in a one dimensional system with MEMS mirrors, each MEMS mirror  29   a  to  29   d  is the second array of switching elements  28  can rotate about a single axis to redirect the wavelength channels within the second dispersion plane, i.e. the plane of the PLC  23 , and do not redirect any channels to other PLCs.  
         [0032]     Accordingly, the device  11  of the present invention provides two fully functioning and independent 1×4 switching (or attenuating or blocking) devices within a single package  35 , with virtually the same optics size as a single 1×4 device, by adding a second row of switching elements  28  and by adjusting the alignment of the cylinder collimating lenses  16  and  26  in front of the PLC&#39;s  13  and  23 , respectively, as shown in  FIG. 3 . Ideally, the independent rows of switching elements  18  and  28 , e.g. MEMS mirrors, are fabricated on the same substrate  30  to reduce size and cost, but are independent of each other, i.e. the first row of switching elements  19   a  to  19   f  only directs light to the first plurality of output waveguide gratings  21   a  to  21   d  and  14 , while the second row of switching elements  29   a  to  19   f  only directs light to the second plurality of output waveguides  31   a  to  31   d  and  24 .  
         [0033]     In an exemplary embodiment, the first array of switching elements  18  comprises MEMS mirror  19   a  to  19   f,  while the second array of switching elements  28  comprises a different wavelength channel adjusting means, e.g. an attenuator or a blocker, whereby at least one of output signals from output ports  22   a  to  22   d  is input the input port  22  of the second PLC  23  and undergoes wavelength selective attenuation, equalization or blocking in accordance with desired power levels or wavelength selections.  
         [0034]     For channel monitoring, a plurality of wavelength channels, e.g. λ 1m  to λ 11m , are launched via the second input port  22 , and one wavelength channel, λ nm , at a time is redirected by the array of MEMs mirrors  28  to the output port  32   a,  which is optically coupled to a photodetector for measuring the output optical power of the selected wavelength channel as each wavelength channel is selected sequentially. The remaining wavelength channels are redirected back to the second input port  22  or another one of the output ports  32   b  to  32   d.    
         [0035]     FIGS.  6  to  10  illustrates a multiple independent unit, planar lightwave circuit (PLC), free-space, hybrid wavelength selective switch (WSS)  41  with a more complex combination of devices within a single package  42 . The second and third levels comprise a 1×9 wavelength switch, the fourth or bottom layer comprises a 1×3 DGE or WB, and the first or top layer comprise a 1×1 wavelength switch, which could be operated as a wavelength monitor. Accordingly, multiple PLC, free-space, hybrid wavelength switch devices incorporated into a single free-space optics block, by adding additional PLCs, cylindrical collimating lens, and rows of switching elements, whereby the independent devices share the same cylinder focusing lens  47 , MEMS substrate  50 , and package  42 .  
         [0036]     With reference to  FIGS. 7 and 8 , the double layer 1×9 WSS includes a first PLC  43  and an second PLC  63 . In use, a first wavelength multiplexed signal, including a plurality of wavelength channels, enters a first input port  42 , e.g. the middle port, of the first PLC chip  43 . The light exiting the first PLC  43  angularly disperses, i.e. fans out, according to wavelength in a first dispersion plane, as a result of an arrayed waveguide grating (AWG)  44  on the first PLC  43 . The light is collimated in one direction or plane, e.g. vertically or in the first dispersion plane, by a first cylindrical lens  46  adjacent to the PLC  43 . The collimated wavelength channels pass through a cylindrical switching lens  47  on one side of an optical axis OA thereof, which focuses the output light in the other direction or plane, e.g. horizontal direction perpendicular to the first dispersion plane, onto a first array or switching elements  48 , e.g. a MEMS array of tiltable mirrors  49   a  to  49   f  or an array of liquid crystal cells for redirecting, attenuating or blocking all or a portion of selected wavelength channels. The tiltable mirrors  49   a  to  49   f  rotate about two perpendicular axes to redirect the wavelength channels within the first dispersion plane, i.e. the plane of the PLC  43 , and at an acute angle to the first dispersion plane into a plane parallel to the first dispersion plane, i.e. the plane of the PLC  63 . Each wavelength channel falls onto a different switching element  49   a  to  49   f,  which independently redirect each of the individual wavelength channels back through the switching lens  47  and either the first cylindrical lens  46  or a second cylindrical lens  66  to whichever output diffraction grating  51   a  to  51   d  and  71   a  to  71   e  is desired or back to the input diffraction grating  44 . In the illustrated embodiment, mirrors  49   c,    49   d  and  49   e  rotate about both axes for directing their respective wavelength channels out of the first dispersion plane to the second cylindrical lens  66  for output the output gratings  71   b  and  71   c,  but not to any other PLC, i.e. PLC  83  or  103 . Simultaneously, the mirrors  49   b  and  49   f  rotate about a single axis, which is perpendicular to the first dispersion plane, to switch their respective wavelength channels within the first dispersion plane to output gratings  51   a  and  51   d,  i.e. not to any other output gratings on other PLCs. The array of first switching elements  48  may also perform partial attenuation or full wavelength channel blocking, as is well known in the art. The first output diffraction gratings  51   a  to  51   d  and  71   a  to  71   e  recombine the wavelength channels directed thereto and output the recombined output signals to respective output ports  52   a  to  52   d  and  72   a  to  72   e.  Preferably, the input port  42  and the output ports  52   a  to  52   d  and  72   a  to  72   e  are optically coupled to waveguides, e.g. optical fibers, for transmission to and from an optical network.  
         [0037]     With reference to  FIG. 9 , the bottom level of the device  41  includes a third PLC  83  with an input port  82  and a plurality of output ports  92   a  to  92   c.  In use, a second wavelength multiplexed signal, including a plurality of wavelength channels, enters the second input port  82 , e.g. the middle port, of the third PLC chip  83 . The light exiting the third PLC  83  angularly disperses, i.e. fans out, according to wavelength in a second dispersion plane parallel to the first dispersion plane, as a result of an arrayed waveguide grating (AWG)  84  on the third PLC  83 . The light is collimated in one direction or plane, e.g. vertically or in the second dispersion plane, by a third cylindrical lens  86  adjacent to the third PLC  83 . The collimated wavelength channels pass through the cylindrical switching lens  47  on the other side of an optical axis OA thereof, which focuses the output light in the other direction or plane, e.g. horizontal direction perpendicular to the third dispersion plane, onto a third array of switching elements  88 , e.g. an array of liquid crystal cells  89   a  to  89   f  for redirecting, attenuating or blocking all or a portion of selected wavelength channels. An example of a suitable liquid crystal device is a liquid crystal on silicon (LCoS) phased array, such as those disclosed in United States Patent Publication No. 2006/0067611 published Mar. 30, 2006 to Frisken et al, which is incorporated herein by reference.  
         [0038]     Each wavelength channel falls onto a different switching element  89   a  to  89   f,  which independently attenuates, either partially or entirely, and redirects each of the individual wavelength channels back through the switching lens  47  and the third cylindrical lens  86  to whichever output diffraction grating  91   a  to  91   c  is desired or back to the input diffraction grating  84 , i.e. not to any other output gratings on other PLCs. The output diffraction gratings  91   a  to  91   c  recombine the wavelength channels directed thereto and output the recombined output signals to respective output ports  92   a  to  92   c.  Preferably, the input port  92  and the output ports  92   a  to  92   c  are optically coupled to waveguides, e.g. optical fibers, for transmission to and from an optical network.  
         [0039]     For channel monitoring, a plurality of wavelength channels, e.g. λ 1m  to λ 11m , are launched via a third input port  102  into a fourth PLC  103 , superposed on the second PLC  63 . The light exiting the fourth PLC  103  angularly disperses, i.e. fans out, according to wavelength in a third dispersion plane parallel to the first dispersion plane, as a result of an arrayed waveguide grating (AWG)  104  on the fourth PLC  103 . The light is collimated in one direction or plane, e.g. vertically or in the third dispersion plane, by a fourth cylindrical lens  106  adjacent to the fourth PLC  103 . The collimated wavelength channels pass through a cylindrical switching lens  47  on the one side of an optical axis OA thereof, which focuses the output light in the other direction or plane, e.g. horizontal direction perpendicular to the third dispersion plane, onto a third array of switching elements  108 , e.g. an MEMS mirrors  109   a  to  109   f  for redirecting, attenuating or blocking all or a portion of selected wavelength channels. One wavelength channel, λ nm , at a time is redirected by the third array of MEMs mirrors  108  through the switching lens  47  and the fourth cylindrical lens  106  to an output port  112  via an output grating  111  i.e. not to any other output gratings on other PLCs. The output port  106  is optically coupled to a photodetector  115  for measuring the output optical power of the selected wavelength channel as each wavelength channel is selected sequentially. The remaining wavelength channels are redirected by the array of switching elements  108  back to the third input port  102  via the input grating  104  or to a different output port via an additional grating (not shown). Accordingly, the third input port  102  may include a circulator for directing the output wavelength channels to a separate output port.  
         [0040]     In use the output ports of one of the PLC&#39;s may be optically coupled to the input ports of the other PLC&#39;s to provide cascaded functionality, e.g. one of the signals output the WWS formed by PLC&#39;s  43  and  63  can be output to the channel monitor formed by PLC  103  and/or the signal output the channel monitor (PLC  103 ) can be then output to an attenuator/WB formed by PLC  83 . Alternatively, all of the channels can be sent to the channel monitor (PLC  103 ) initially and then passed to the WSS (PLC  43  and  63 ) and/or to the attenuator/WB (PLC  83 ).