MULTI-UNIT PLANAR LIGHTWAVE CIRCUIT WAVELENGTH DISPERSIVE DEVICE

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

TECHNICAL FIELD

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

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.

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.

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.

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.

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′.

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

Accordingly, the present invention relates to a multi-unit planar lightwave circuit device comprising:

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;

a first cylindrical lens for collimating the first input optical signal in a first direction after exiting the first planar lightwave circuit;

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;

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;

a second cylindrical lens for collimating the second input optical signal in the first direction after exiting the second planar lightwave circuit;

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

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

The invention will be described in greater detail with reference to the accompanying drawings which represent preferred embodiments thereof, wherein:

FIG. 1 is a plan view of a conventional PLC WSS;

FIG. 2 is a side view of a conventional multi-layer PLC WSS;

FIG. 3 is a side view of a multi-unit PLC wavelength dispersive device according to the present invention; and

FIG. 4 is a top view of a first level of the device of FIG. 3;

FIG. 5 is a cross-sectional view of a second level of the device of FIG. 3;

FIG. 6 is a side view of another embodiment of a multi-unit PLC wavelength dispersive device according to the present invention;

FIG. 7 is a cross-sectional view of a third level of the device of FIG. 6;

FIG. 8 is a cross-sectional view of a second level of the device of FIG. 6;

FIG. 9 is a cross-sectional view of a fourth level of the device of FIG. 6; and

FIG. 10 is a top view of a first level of the device of FIG. 6;

DETAILED DESCRIPTION

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 19a to 19f 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 21a to 21d 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 21a to 21d recombine the wavelength channels directed thereto and output the recombined output signals to respective output ports 22a to 22d. Preferably, the input port 12 and the output ports 22a to 22d 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 19a to 19f 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.

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.

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.

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 29a to 29f 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 29a to 29f (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 31a to 31d 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 31a to 31d 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 29a to 29d 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.

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'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 19a to 19f only directs light to the first plurality of output waveguide gratings 21a to 21d and 14, while the second row of switching elements 29a to 19f only directs light to the second plurality of output waveguides 31a to 31d and 24.

In an exemplary embodiment, the first array of switching elements 18 comprises MEMS mirror 19a to 19f, 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 22a to 22d 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.

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 32a, 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 32b to 32d.

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.

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 49a to 49f or an array of liquid crystal cells for redirecting, attenuating or blocking all or a portion of selected wavelength channels. The tiltable mirrors 49a to 49f 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 49a to 49f, 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 51a to 51d and 71a to 71e is desired or back to the input diffraction grating 44. In the illustrated embodiment, mirrors 49c, 49d and 49e 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 71b and 71c, but not to any other PLC, i.e. PLC 83 or 103. Simultaneously, the mirrors 49b and 49f 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 51a and 51d, 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 51a to 51d and 71a to 71e recombine the wavelength channels directed thereto and output the recombined output signals to respective output ports 52a to 52d and 72a to 72e. Preferably, the input port 42 and the output ports 52a to 52d and 72a to 72e are optically coupled to waveguides, e.g. optical fibers, for transmission to and from an optical network.

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 92a to 92c. 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 89a to 89f 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.

Each wavelength channel falls onto a different switching element 89a to 89f, 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 91a to 91c 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 91a to 91c recombine the wavelength channels directed thereto and output the recombined output signals to respective output ports 92a to 92c. Preferably, the input port 92 and the output ports 92a to 92c are optically coupled to waveguides, e.g. optical fibers, for transmission to and from an optical network.

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 109a to 109f 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.

In use the output ports of one of the PLC's may be optically coupled to the input ports of the other PLC's to provide cascaded functionality, e.g. one of the signals output the WWS formed by PLC'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).

Claims

1. A multi-unit planar lightwave circuit device comprising: 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; a first cylindrical lens for collimating the first input optical signal in a first direction after exiting the first planar lightwave circuit; 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; 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 parallel to the first dispersion plane upon exiting the second input arrayed waveguide grating; a second cylindrical lens for collimating the second input optical signal in the first direction after exiting the second planar lightwave circuit; a second array of switching elements, parallel to the first 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 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.

2. The device according to claim 1, wherein the first and second array of switching elements comprise two parallel rows of MEMs mirrors on a same substrate.

3. The device according to claim 1, further comprising a photo-detector optically coupled to one of the second output waveguide gratings; wherein the second array of switching elements consecutively redirects each wavelength channel in the second input optical signal to the one output waveguide grating, while directing remaining wavelength channels to the second input waveguide for output the second output port.

4. The device according to claim 3, wherein the second output port is optically coupled to the first input port.

5. The device according to claim 3, further comprising: a third planar lightwave circuit chip including a third input port, a third input arrayed waveguide grating, a third plurality of output arrayed waveguide gratings, and a third plurality of output ports, wherein a third input optical signal launched into the third input arrayed waveguide grating via the third input port disperses according to wavelength into a third dispersion plane upon exiting the third input arrayed waveguide grating; a third cylindrical lens for collimating the third input optical signal in the first direction after exiting the third planar lightwave circuit; and a third array of switching elements for independently attenuating and redirecting each of the wavelength channels from the third input optical signal to selected third output arrayed waveguide gratings for output respective third output ports; wherein the switching lens focuses the wavelength channels of the third input optical signal onto respective switching elements from the third array of switching elements.

6. The device according to claim 5, wherein the first, second and third array of switching elements comprise three parallel rows of MEMs mirrors on a same substrate.

7. The device according to claim 5, wherein at least one of the first output ports is optically coupled to the second input port.

8. The device according to claim 7, wherein at least one of the second output ports is optically coupled to the third input port.

9. The device according to claim 5, wherein at least one of the second output ports is optically coupled to the third input port.

10. The device according to claim 5, wherein the second array of switching elements independently attenuates and redirects each of the wavelength channels from the second input optical signal to selected second output arrayed waveguide gratings for output respective second output ports.

11. The device according to claim 10, wherein at least one of the first output ports is optically coupled to the second input port.

12. The device according to claim 1, wherein the second array of switching elements independently attenuates and redirects each of the wavelength channels from the second input optical signal to selected second output arrayed waveguide gratings for output respective second output ports.

13. The device according to claim 1, further comprising: a third planar lightwave circuit chip including a third input port, a third input arrayed waveguide grating, a third plurality of output arrayed waveguide gratings, and a third plurality of output ports, wherein a third input optical signal launched into the third input arrayed waveguide grating via the third input port disperses according to wavelength into a third dispersion plane upon exiting the third input arrayed waveguide grating; a third cylindrical lens for collimating the third input optical signal in the first direction after exiting the third planar lightwave circuit; and a third array of switching elements for independently attenuating and redirecting each of the wavelength channels from the third input optical signal to selected third output arrayed waveguide gratings for output respective third output ports; wherein the switching lens focuses the wavelength channels of the third input optical signal onto respective switching elements from the third array of switching elements.

14. The device according to claim 13, wherein the first, second and third array of switching elements comprise three parallel rows of MEMs mirrors on a same substrate.

15. The device according to claim 1, further comprising: a fourth planar lightwave circuit chip positioned adjacent and parallel to the first planar lightwave circuit including a fourth plurality of output arrayed waveguide gratings, and a fourth plurality of output ports, wherein each of the switching elements in the first array of switching elements pivots about a first axes for directing wavelength channels back in the first dispersion plane to the first plurality of output diffraction gratings, and about a second axis perpendicular to the first axis for directing wavelength channels at an acute angle to the first dispersion plane; and a fourth cylindrical lens for receiving and focusing the wavelength channels from the first input optical signal redirected out of the first dispersion plane onto the fourth plurality of output arrayed waveguides.