WO2016148717A1

WO2016148717A1 - Transceiver nodes coupled to arrayed waveguide gratings

Info

Publication number: WO2016148717A1
Application number: PCT/US2015/021412
Authority: WO
Inventors: Joaquin MATRES; Wayne Victor Sorin; Mike Schlansker; Jean Tourrilhes; Lars Helge Thylen; Michael Renne Ty Tan
Original assignee: Hewlett Packard Enterprise Development Lp
Priority date: 2015-03-19
Filing date: 2015-03-19
Publication date: 2016-09-22

Abstract

In the examples provided herein, an apparatus includes an arrayed waveguide grating (AWG) with input and output ports, where a signal at one of the input ports is routed to one of the output ports based on a signal wavelength. The apparatus also includes transceiver nodes, each node comprising optical transmitters, where each transmitter is tunable over multiple wavelength channels within a different wavelength band; receivers to receive light within the different wavelength bands; a multiplexer and demultiplexer to multiplex and demultiplex, respectively, the multiple wavelength channels within each different wavelength band; a first fiber to couple an output of the multiplexer to one of the input ports; and a second fiber to couple one of the output ports to an input of the demultiplexer. Each of the first fibers couples to a different input port, and each of the second fibers couples to a different output port.

Description

TRANSCEIVER NODES COUPLED TO ARRAYED WAVEGUIDE

GRATINGS

BACKGROUND

[0001] A data center is a facility that stores, manages, and disseminates data using bandwidth-intensive devices, such as servers, storage devices, and backup devices. Traffic demands in data centers is ever increasing, leading to upgrading of switches inside the data center to higher speeds to serve the growing demand. However, the bandwidth-intensive devices in data centers are interconnected with optical cables, and physically changing the connections between devices can be slow, costly, and error-prone.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] The accompanying drawings illustrate various examples of the principles described below. The examples and drawings are illustrative rather than limiting.

[0003] FIG. 1A depicts an example reconfigurable photonic switch.

[0004] FIG. 1 B depicts example wavelength channels and wavelength bands that a transceiver node may transmit and receive.

[0005] FIG. 1 C depicts tables showing example wavelength bands that may be transmitted and received by each of the transceiver nodes.

[0006] FIG. 1 D depicts example filter profiles used in a band multiplexer and band demultiplexer.

[0007] FIG. 1 E depicts example components of a transceiver node.

[0008] FIG. 1 F depicts an example system including a reconfigurable photonic switch and a controller.

[0009] FIG. 2A depicts an example reconfigurable photonic switch. [0010] FIG. 2B depicts an example system including a reconfigurable photonic switch and a controller.

[0011] FIG. 3 depicts a flow diagram illustrating an example process of calibrating a reconfigurable photonic switch by using an arrayed waveguide grating in the reconfigurable photonic switch as a reference.

[0012] FIGS. 4A-4B depict a flow diagram illustrating an example process of calibrating a reconfigurable photonic switch by using an arrayed waveguide grating in the reconfigurable photonic switch as a reference.

DETAILED DESCRIPTION

[0013] Reconfigurable photonic switch systems based upon an arrayed waveguide grating (AWG) device are presented below that allow connections between nodes of the system to be reestablished dynamically without physically changing connections in the system. The input ports and output ports of the AWG are coupled to specific transceiver nodes. Tunable transmitters are used in the transceiver nodes to change the emitted wavelength of a signal, and the AWG automatically routes the signal to a particular output port of the AWG based on the wavelength of the signal. A controller may be used to configure the connections dynamically via software commands sent to the tunable transmitters to change the emitted wavelength.

[0014] An AWG may be an MxN port device, where M is the number of input ports and N is the number of output ports. Light at different wavelengths entering each of the input ports may be demultiplexed into different output ports. When the AWG is operated in the reverse direction, light entering the output ports may be multiplexed and exit through the input ports.

[0015] An AWG operates based upon constructive and destructive interference. Light entering one of the input ports is coupled into a first cavity, and then the light from the first cavity is coupled to one end of an array of waveguides. The length of each waveguide in the array increases across the array, such that the optical path length difference between neighboring waveguides introduces wavelength- dependent phase delays. The other end of the array of waveguides is coupled to a second cavity, and light from the second cavity is coupled to the output ports of the AWG via a series of waveguides. Constructive interference occurs when the optical path length difference of the array of waveguides is equal to an integer number of wavelengths. As a result, different wavelengths of light are focused by the AWG into different ones of the output ports. The AWG has a free spectral range (FSR) that characterizes the periodicity of the demultiplexer. The periodic property arises because constructive interference at the output ports can arise for wavelengths that are spaced by a free spectral range.

[0016] FIG. 1A depicts an example reconfigurable photonic switch having multiple transceiver nodes 121 -124 coupled to the input ports 1 1 1 -1 14 and output ports 1 15-1 18 of an AWG 1 10. In the example of FIG. 1A, the AWG 1 10 has four input ports 1 1 1 -1 14 and four output ports 1 15-1 18, however, an AWG in a reconfigurable photonic switch may have any number of input ports and any number of output ports. For convenience, the input ports 1 1 1 -1 14 of the AWG 1 10 are labeled A 1 1 1 , B 1 12, C 1 13, and D 1 14, while the output ports 1 15-1 18 are labeled W 1 15, X 1 16, Y 1 17, and Z 1 18.

[0017] Four transceiver nodes 121 -124 are shown in the example of FIG. 1A, however, any number of transceiver nodes may be used in the reconfigurable photonic switch. As shown in the inset of FIG. 1A, a transceiver node may include tunable optical transmitters 131 -134, receivers 141 -144, a band multiplexer 130, and a band demultiplexer 140. While four tunable transmitters 131 -134 and four receivers 141 -144 are shown in the inset, any number of tunable transmitters and receivers may be used. An electrical input may enter each transmitter 131 -134, the optical outputs of the transmitters 131 -134 may be multiplexed by the band multiplexer 130, and an output waveguide 135, such as an optical fiber, may exit the band multiplexer 130 carrying the multiplexed signals. An input waveguide 145, such as an optical fiber, may enter the band demultiplexer 140 carrying multiplexed signals in different wavelength bands, the demultiplexed wavelength bands may be sent to different receivers 141 -144, and an electrical output may exit each of the receivers 141 -144.

[0018] The tunable transmitters 131 -134 are optical transmitters that emit light at a central wavelength over a narrow band of wavelengths, referred to as a wavelength channel, and the wavelength of the emitted light should be tunable over a range of wavelengths across multiple wavelength channels. In some implementations, the tunable transmitter 131 -134 may be a tunable laser, such as a vertical cavity surface emitting laser (VCSEL) or distributed feedback semiconductor laser (DFB), that may be tuned, for example, through the use of a heating element. In some implementations, each tunable transmitter 131 -134 located within a single transceiver node 121 -124 may emit light in a different wavelength band. In some implementations, each tunable transmitter 131 -134 located within a single transceiver node 121 -124 may emit light in the same wavelength band. In some implementations, some tunable transmitters 131 -134 located within a single transceiver node 121 -124 may emit light in overlapping wavelength bands.

[0019] FIG. 1 B depicts example wavelength channels and wavelength bands that a transceiver node 121 -124 may transmit and receive. Sixteen evenly spaced wavelength channels, labeled 1 through 16 are shown in the graph, however, in some implementations, some wavelength channels may be skipped. In some implementations, the wavelength channels may coincide with some of the wavelength channels on the wavelength grid specified by the ITU (International Telecommunication Union), where the wavelength channels are spaced by 100 GHz. In FIG. 1 B, the first four wavelength channels, labeled 1 -4, fall within band 1 ; the second four wavelength channels, labeled 5-8, fall within band 2; the third four wavelength channels, labeled 9-12, fall within band 3; and the fourth four wavelength channels, labeled 13-16, fall within band 4. In some implementations, the wavelength range spanned by one of the bands may be a FSR of the AWG. In some implementations, the wavelength range spanned by one of the bands may include portions of one or multiple FSRs of the AWG.

[0020] FIG. 1 C depicts tables showing example wavelength bands that may be transmitted and received by each of the transceiver nodes 121 -124. In the transmitter tables, transmitters are labeled as Txn, where n is the number of the transmitter, and following each Txn transmitter label is a row of four possible wavelength channels to which the transmitter may be tuned. Each indicated wavelength channel in FIG. 1 C is part of an indicator in the format K-MN, where K is the emission wavelength channel (1 -16 in this example), M is the input port (A-D in this example) of the AWG to which the transmitter output is coupled, and N is the output port (W-Z in this example) of the AWG to which the transmitter output is routed.

[0021] In some examples, for node 1 121 , the emission wavelength of transmitter 1 (Tx1 ) may be tuned to one of the four wavelength channels 1 , 2, 3, 4 in band 1 , and the output of the transmitter may be coupled to port A 1 1 1 of the AWG 1 10. If the wavelength is tuned to wavelength channel 1 , the light may be routed to output port W 1 15 of the AWG 1 10, as indicated by Ί -AW; if the wavelength is tuned to wavelength channel 2, the light may be routed to output port X 1 16 of the AWG 1 10, as indicated by '2-AX'; if the wavelength is tuned to wavelength channel 3, the light may be routed to output port Y 1 17 of the AWG 1 10, as indicated by '3- AY'; and if the wavelength is tuned to wavelength channel 4, the light may be routed to output port A 1 18 of the AWG 1 10, as indicated by '4-AZ'. Similarly, in some examples, transmitter 2 (Tx2) may be tuned to one of four wavelength channels 5, 6, 7, 8 in band 2; transmitter 3 (Tx3) may be tuned to one of four wavelength channels 9, 10, 1 1 , 12 in band 3; and transmitter 4 (Tx4) may be tuned to one of four wavelength channels 13, 14, 15, 16 in band 4. The outputs of the four transmitters may be multiplexed by multiplexer (mux) 130 and sent to input port A 1 1 1 of the AWG 1 10. [0022] The transmitters in the other nodes, node 2 122, node 3 123, and node 4 124, may operate similarly, where each of the transmitters may be tuned to one of four wavelength channels. The light emitted by the four transmitters in each node may be multiplexed together using a band multiplexer 130 and sent to a different input node of the AWG. The band multiplexer 130 may multiplex or couple each of the optical outputs from the tunable transmitters 131 -134 onto a single output fiber 135. The band multiplexer 130 may be implemented with different technologies, such as thin film filters, fused fibers, and microring resonators. The multiplexed output from node 2 122 may be coupled to input node B 1 12 of the AWG; the multiplexed output from node 3 123 may be coupled to input node C 1 13 of the AWG; and the multiplexed output from node 4 124 may be coupled to input node D 1 14 of the AWG.

[0023] If the wavelength range spanned by each of the bands 1 , 2, 3, 4 coincides with the FSR of the AWG, wavelength channels 1 , 5, 9, 13 are each separated by a FSR, and thus, are routed to the same output port of the AWG when entering the AWG at the same input port. Similarly, if wavelength channels 2, 6, 10, 14 are each separated by a FSR, they are routed to the same output port of the AWG when entering the AWG at the same input port; if wavelength channels 3, 7, 1 1 , 15 are each separated by a FSR, they are routed to the same output port of the AWG when entering the AWG at the same input port; and if wavelength channels 4, 8, 12, 16 are each separated by a FSR, they are routed to the same output port of the AWG when entering the AWG at the same input port.

[0024] Returning to node 1 121 , a waveguide, such as an optical fiber, couples the output port W 1 15 of the AWG 1 10 to a demultiplexer 140 via optical waveguide 145. Demultiplexer 140 separates the light exiting output node W 1 15 into four bands: light from band 1 may be directed to receiver Rx1 , light from band 2 may be directed to receiver Rx2, light from band 3 may be directed to receiver Rx3, and light from band 4 may be directed to receiver Rx4. Similar to multiplexer 130, the demultiplexer 140 may be implemented with different technologies, such as thin film filters, fused fibers, and microring resonators.

[0025] FIG. 1 C also depicts example receiver tables for each of the transceiver nodes 121 -124 in a similar format as for the transmitter tables. In the receiver tables, receivers are labeled as Rxn, where n is the number of the receiver, and following each Rxn receiver label is a row of four possible wavelength channels that the receiver may receive from the demultiplexer. Each wavelength is part of an indicator in the format K-MN, where K is the received wavelength channel (1 -16 in this example), M is the input port (A-D in this example) of the AWG from which the light was routed, and N is the output port (W-Z in this example) of the AWG to which the receiver's demultiplexer is coupled.

[0026] As indicated in the example receiver table for node 1 121 in FIG. 1 C, receiver Rx1 may receive wavelengths in band 1 : wavelength channel 1 from input node A 1 1 1 of the AWG; wavelength channel 2 from input node D 1 14 of the AWG; wavelength channel 3 from input node C 1 13 of the AWG; and wavelength channel 4 from input node B 1 12 of the AWG. Receiver Rx2 may receive wavelengths in band 2: wavelength channel 5 from input node A 1 1 1 of the AWG; wavelength channel 6 from input node D 1 14 of the AWG; wavelength channel 7 from input node C 1 13 of the AWG; and wavelength channel 8 from input node B 1 12 of the AWG. Receiver Rx3 may receive wavelengths in band 3: wavelength channel 9 from input node A 1 1 1 of the AWG; wavelength channel 10 from input node D 1 14 of the AWG; wavelength channel 1 1 from input node C 1 13 of the AWG; and wavelength channel 12 from input node B 1 12 of the AWG. Receiver Rx4 may receive wavelengths in band 4: wavelength channel 13 from input node A 1 1 1 of the AWG; wavelength channel 14 from input node D 1 14 of the AWG; wavelength channel 15 from input node C 1 13 of the AWG; and wavelength channel 16 from input node B 1 12 of the AWG.

[0027] Similarly, in node 2 122, receivers Rx5, Rx6, Rx7, Rx8 may be coupled via a demultiplexer to output port X 1 16 of the AWG 1 10; in node 3 123, receivers Rx9, Rx10, Rx1 1 , Rx12 may be coupled via a demultiplexer to output port Y 1 17 of the AWG 1 10; and in node 4 124, receivers Rx13, Rx14, Rx15, Rx16 may be coupled via a demultiplexer to output port Z 1 18 of the AWG 1 10. Also, receivers Rx5 in node 2 122, Rx9 in node 3 123, and Rx13 in node 4 124 may receive wavelengths in band 1 ; receivers Rx6 in node 2 122, Rx10 in node 3 123, and Rx14 in node 4 124 may receive wavelengths in band 2; receivers Rx7 in node 2 122, Rx1 1 in node 3 123, and Rx15 in node 4 124 may receive wavelengths in band 3; and receivers Rx8 in node 2 122, Rx12 in node 3 123, and Rx16 in node 4 124 may receive wavelengths in band 4.

[0028] In some implementations, each of receivers Rx1 , Rx2, Rx3, Rx4 may be identical and capable of detecting light in any of the wavelength bands 1 , 2, 3, 4, for example, a photodetector or a charge-coupled device (CCD).

[0029] Rather than using consecutive wavelength channels in each of the different wavelength bands over which the tunable transmitters 131 -134 may be tuned, selective wavelength channels may be skipped so that specifications on the filters used in the band multiplexer 130 and the band demultiplexer 140 may be relaxed. In the example of FIG. 1 D, the top and bottom graphs show close up views of the wavelength channels 1 -10 in band 1 , band 2, and part of band 3 along with example spectral profiles of filters 180, 181 , 182 that may be used in multiplexer 130 and demultiplexer 140. In the top graph of FIG. 1 D, if every consecutive wavelength channel from 1 through 10 are used, to prevent crosstalk between edge channels 4 and 5 and edge channels 8 and 9 of neighboring bands, filters 180, 181 , 182 would need sharper edges, and thus, have tighter specifications.

[0030] However, for the example where the AWG has a FSR that is four wavelength channels wide, and the system uses four channels per band, if one channel is skipped for every four consecutive wavelength channels that are used, for example, channel 5 and channel 9, as shown in the bottom graph of FIG. 1 D, the filter specifications may be relaxed because the filter edges of filters 185, 186 do not need to be as sharp to prevent crosstalk between edge channels 4 and 6. Thus new band 1 ' covering four consecutive wavelength channels 1 -4 and new band 2' covering four consecutive wavelength channels 6-9 may be used with the filters 185, 186 which would have relaxed specifications and would also be less expensive. The wavelength channel configuration where four consecutive channels are used and one wavelength channel is skipped is referred to as 4 skip 1 . More than one channel may also be skipped. For example, consecutive channels 1 -4 may be used, channels 5 and 6 may be skipped, and consecutive channels 7-10 may be used, and channels 1 1 and 12 may be skipped. This wavelength channel configuration is referred to as 4 skip 2, which further relaxes the specifications on the filter designs for the multiplexer 130 and the demultiplexer 140. Any number of channels may be skipped, for example, 4 skip 3 and 4 skip 4. Thus, in some implementations, each optical transmitter in a transceiver node is tunable over multiple wavelength channels within a different wavelength band, where the multiple wavelength channels are evenly spaced by a channel spacing. Also, one or more wavelength channels may be skipped between the different wavelength bands such that specifications on the band multiplexer and band demultiplexer are relaxed compared to when no wavelength channels are skipped.

[0031] In some implementations, the reconfigurable photonic switch may include an arrayed waveguide grating (AWG) having a plurality of input ports and a plurality of output ports, where a signal within a given wavelength channel transmitted to one of the input ports is routed to one of the output ports based on a signal wavelength and a plurality of transceiver nodes. Each transceiver node may include a plurality of optical transmitters, where each optical transmitter is tunable over multiple wavelength channels within a different wavelength band; a plurality of receivers to receive wavelengths of light within the different wavelength bands; a band multiplexer to multiplex the multiple wavelength channels within each different wavelength band; a band demultiplexer to demultiplex the multiple wavelength channels within each different wavelength band; a first fiber to couple an output of the band multiplexer to one of the input ports of the AWG; and a second fiber to couple one of the output ports of the AWG to an input of the band demultiplexer. Each of the first fibers couples to a different one of the input ports of the AWG, and each of the second fibers couples to a different one of the output ports of the AWG.

[0032] In some implementations, each of the optical transmitters of the plurality of transceiver nodes may be tunable over the different wavelength bands, and the band multiplexer and band demultiplexer may also be tunable. By not restricting each of the optical transmitters to emitting wavelengths within a single band, the reconfigurable optical switch may be more flexible with more functionality. Further, if the emission wavelength ranges of the optical transmitters are not restricted to a single band, the band multiplexer and the band demultiplexer should also be tunable to match the tuning of the optical transmitters.

[0033] In some implementations, to reduce the costs of the reconfigurable photonic switch, each transceiver node may include an integrated transceiver, such that the plurality of optical transmitters, the plurality of receivers, the band multiplexer, and the band demultiplexer are integrated on a single die or chip. Examples of suitable die materials include silicon and indium phosphide.

[0034] FIG. 1 E depicts example components of a transceiver node. In addition to the tunable transmitters 131 -134, receivers 141 -144, band multiplexer 130, and band demultiplexer 140 described above, a transceiver node may also include modulators 151 -154, one modulator for each tunable transmitter. The modulators 151 -154 may modulate the emitted light of each of the tunable transmitters 131 -134, where the modulation of the output of the transmitters is the data to be transmitted from the transceiver node to a different transceiver node. Examples of modulators 151 -154 may include a direct modulator that modulates the current driving the tunable transmitter 131 -134 or an external optical modulator, such as a Mach- Zehnder modulator, an electro-absorption modulator that modifies the absorption of a semiconductor material when an external electric field is applied, or an electro- optic modulator that modifies the refractive index of a material under the application of an external electric field and is used in conjunction with an interferometric structure. [0035] FIG. 1 F depicts an example system including reconfigurable photonic switch 100 and a controller 190. The reconfigurable photonic switch 100 may be similar to the example switch described above with respect to FIG. 1A. Note that the number of transceiver nodes may be greater than or less than four, and the number of input ports and output ports of the AWG may also be greater than or less than four.

[0036] The controller 190 may be a single or distributed controller used to tune the emission wavelength of the tunable transmitters 131 -134 in the nodes 121 -124. The tunable transmitters 131 -134 may be tuned by the controller to the particular emission wavelength that will cause the AWG 1 10 to route the signal to the appropriate output port to be addressed. In some implementations, the controller 190 may use a look-up table that provides a corresponding output port for each emission wavelength, and each transmitter has its own look-up table. Further, by controlling the emission wavelength of each of the optical transmitters in the transceiver nodes, the controller 190 may prevent collisions from occurring within the reconfigurable photonic switch by ensuring that emission wavelengths of two different optical transmitters are not transmitted simultaneously to a same receiver via the AWG.

[0037] In some cases, the AWG may be designed to be athermal with internal passive temperature compensation. For example, a thermally expanding piece of material may be used to align waveguide coupling positions so that the channels routed by the AWG do not drift away from predetermined channels, such as the ITU grid, due to changes in refractive index with temperature. By using an athermally designed AWG in the reconfigurable photonic switch, no active temperature compensation is used for the AWG. Moreover, with the athermal AWG, the controller 190 may calibrate the optical transmitters relative to the AWG's routing of wavelengths between the input ports and the output ports of the AWG. The controller 190 may perform a coarse calibration of the tunable transmitters that may involve sweeping the emission wavelength of the tunable transmitters over several wavelength channels to identify and lock in the wavelength channels of the AWG reference. A coarse calibration may occur when the reconfigurable photonic switch system is initially installed, prior to transmission of data by the tunable transmitters.

[0038] Additionally, because the emission wavelength of the tunable transmitters may drift with temperature changes, or the reference wavelength channels of the athermal AWG may also drift slightly, periodic calibration of the optical transmitters relative to the AWG may be performed. The periodic calibration performed after the initial coarse calibration may be a fine calibration where the emission wavelength of the tunable transmitters is swept over the local wavelength channel identified during the coarse calibration. The fine calibration may be performed prior to transmitting data by the tunable transmitters. The fine calibration may also be performed while data is being transmitted by the tunable transmitters, such that real-time tracking of the emitted wavelengths of the tunable transmitters is performed during data transmission. In some implementations, the controller 190 may direct the transceiver nodes 121 -124 to perform the fine calibration to self- calibrate the tunable optical transmitters 131 -134 relative to the AWG's routing of wavelengths between the input ports and the output ports. In these cases, the tunable transmitters 131 -134 have already been locked to the AWG reference channels during the coarse calibration, and the receivers 141 -144 within each transceiver node 121 -124 may be used by a processor in the transceiver nodes to self-calibrate the tunable transmitters 131 -134.

[0039] FIG. 2A depicts an example reconfigurable photonic switch having a first AWG 210 that has a plurality of first input ports and a plurality of first output ports, where light entering each of the first input ports is routed to one of the plurality of first output ports based on a wavelength of the light. The example reconfigurable photonic switch also has a second AWG 220 that has a plurality of second input ports and a plurality of second output ports, where light entering each of the second input ports is routed to one of the plurality of second output ports based on a wavelength of the light. In the example of FIG. 2A, two AWGs 210, 220 are used, but more AWG's may be used in the reconfigurable photonic switch. Also, each of the AWGs has four input ports 21 1 -214, 221 -224, and each of the AWGs has four output ports 215-218, 225-228, however, each AWG may have any number of input ports and any number of output ports in the reconfigurable photonic switch.

[0040] Further, the example reconfigurable photonic switch in FIG. 2A may have a plurality of transceiver nodes 201 -204. Each transceiver node may include a plurality of optical transmitters, where each optical transmitter is tunable over multiple wavelength channels within a different wavelength band; a plurality of receivers to receive wavelengths of light within the different wavelength bands; a band multiplexer to multiplex the multiple wavelength channels within each different wavelength band; a band demultiplexer to demultiplex the multiple wavelength channels within each different wavelength band; a first fiber to couple an output from the band multiplexer to one of the first input ports of the first AWG; and a second fiber to couple an output from one of the second output ports of the second AWG to an input of the band demultiplexer. Each of the first fibers may couple to a different one of the first input ports of the first AWG, and each of the second fibers may couple to a different one of the second output ports of the second AWG.

[0041] Four transceiver nodes 201 -204 are shown in the example of FIG. 2A, however, any number of transceiver nodes may be used in the reconfigurable photonic switch. As shown in the inset of FIG. 2A, a transceiver node may include tunable transmitters 231 -234, receivers 241 -244, a band multiplexer 230, and a band demultiplexer 240. While four tunable transmitters 231 -234 and four receivers 241 -244 are shown in the inset, any number of tunable transmitters and receivers may be used. An electrical input may enter each transmitter 231 -234, the optical outputs of the transmitters 231 -234 may be multiplexed by the band multiplexer 230, and an output waveguide 235, such as an optical fiber, may exit the band multiplexer 230 carrying the multiplexed signals. An input waveguide 245, such as an optical fiber, may enter the band demultiplexer 240 carrying multiplexed signals in different wavelength bands, the demultiplexed wavelength bands may be sent to different receivers 241 -244, and an electrical output may exit each of the receivers 241 -244. In some implementations, each tunable transmitter 231 -234 may have a modulator to apply a signal to the light emitted by the tunable transmitter.

[0042] Additionally, the example reconfigurable photonic switch in FIG. 2A may have a plurality of packet switch nodes 205-208. Each packet switch node may have an input switch port; an output switch port; a third fiber to couple one of the first output ports from the first AWG to the input switch port; and a fourth fiber to couple an output from the output switch port to one of the second input ports of the second AWG. Each of the third fibers may couple to a different one of the first output ports of the first AWG, and each of the fourth fibers may couple to a different one of the second input ports of the second AWG.

[0043] Four packet switch nodes 205-208 are shown in the example of FIG. 2A, however, any number of packet switch nodes may be used in the reconfigurable photonic switch. Packet switch nodes may receive packets via the third fiber at the input switch port, identify a destination address in a header of the packet, and send the packet through the output switch port to the appropriate destination via the fourth fiber.

[0044] In the example reconfigurable photonic switch shown in FIG. 2A, data transmitted by a transceiver node 201 -204 may be transmitted to one of the packet switch nodes 205-208 via the AWG 210, and the packet switch nodes 205-208 may transmit packet data via AWG 220 to a receiver at one of the transceiver nodes 201 - 204. In some implementations, the wavelength switching performed by controlling the emission wavelength of the tunable lasers in the transceiver nodes 201 -204 may be considered a slower type of circuit switching for the routing of data between the input and output ports of the AWGs 210, 220, while the packet switch nodes 205- 208 may perform faster packet switching. The transceiver nodes 201 -204 do not communicate directly with each other in this example configuration, rather, optical data transmitted by a transceiver node 201 -204 may be converted to electrical data by one of the packet switching nodes 205-208 to determine a packet address in a header converted back to optical data for optically re-transmission back to a receiver at one of the transceiver nodes 201 -204. In contrast, in the example reconfigurable photonic switch shown in the example of FIG. 1A above, the transceiver nodes 121 - 124 are able to communicate directly with each other, as would be the case in a peer-to-peer network configuration. Thus, the example configurations shown in FIGS. 1A and 2A serve different purposes.

[0045] FIG. 2B depicts an example system including a reconfigurable photonic switch 200 and a controller 290. The reconfigurable photonic switch 200 may be similar to the switch described above with respect to FIG. 2A. Note that the number of nodes may be greater than or less than four, and the number of input ports and output ports of the AWG may also be greater than or less than four.

[0046] As with the controller 190 described above with respect to FIG. 1 F, the controller 290 may be a single or distributed controller used to tune the emission wavelength of the tunable transmitters in the transceiver nodes 201 -204. The tunable transmitters may be tuned to the particular emission wavelength that will cause the AWGs 210, 220 to route the signal to the appropriate output port to be addressed. In some implementations, the controller 290 may use a look-up table that provides a corresponding output port for each emission wavelength, and each transmitter has its own look-up table.

[0047] As with the controller 190 used with the reconfigurable photonic switch 100 shown in the example of FIG. 1 F, the controller 290 may control an emission wavelength of each of the optical transmitters in the plurality of transceiver nodes201 -204 such that emission wavelengths from two different optical transmitters are not transmitted simultaneously to a same input switch port of one of the packet node switches via the AWG.

[0048] FIG. 3 depicts a flow diagram illustrating an example process 300 of calibrating a reconfigurable photonic switch by using an arrayed waveguide grating in the reconfigurable photonic switch as a reference. The process 300 begins at block 305 where a first light output from a first tunable transmitter may be tuned over a first wavelength range near a first channel. During an initial coarse calibration, the first light output may be tuned over several wavelength channels, while in a subsequent fine calibration, the first light output may be tuned over a single wavelength channel. The first light output may be coupled to a first input port of an AWG, and the AWG routes a given input over the first wavelength range at the first input port to a first output port of the AWG. The routing of the first light output by the AWG is dependent upon the wavelength.

[0049] At block 310, a first output power may be monitored from the first output port. For example, the first output port may be coupled to a receiver at one of the transceiver nodes via an optical fiber and a demultiplexer, and the first output power may be an average power measured by the receiver and monitored by a processor, such as the controller, or by a local processor within the transceiver node.

[0050] At block 315, a first wavelength at which the first output power is a maximum may be determined. For example, the controller may store monitored average powers and determine the maximum average power after the first tunable transmitter has been tuned over the first wavelength range.

[0051] At block 320, the first tunable transmitter may be operated such that the first light output is at the first wavelength determined at block 315. In some implementations, data carried by the light emitted by the first tunable transmitter may be sent to a particular packet address to communicate to the controller during the process 300.

[0052] FIGS. 4A-4B depict a flow diagram illustrating an example process 400 of calibrating a reconfigurable photonic switch by using an arrayed waveguide grating in the reconfigurable photonic switch as a reference. The process begins at block 405, which may be similar to block 305 described with respect to the process 300 of FIG. 3. Blocks 410, 415, and 420 may also be similar to blocks 310, 315, and 320, respectively, of FIG. 3. [0053] At block 425, each additional light output from each additional tunable transmitter of the reconfigurable photonic switch may be tuned over an additional wavelength range near an additional channel, where each additional light output is coupled to one of the input ports of the AWG. Thus, the other tunable transmitters in the reconfigurable photonic switch may also be calibrated by using the AWG as a reference.

[0054] At block 430, each additional output power from the output ports of the AWG may be monitored. For example, the output ports of the AWG may be coupled to a receiver at one of the transceiver nodes via an optical fiber and a demultiplexer, and the additional output power may be an average power measured by the receiver and monitored by a controller or local processor.

[0055] At block 435, each additional wavelength at which each additional output power is a maximum may be monitored. For example, the controller or local processor may store monitored average powers for each additional tunable transmitter and determine the maximum after the each additional tunable transmitter has been tuned over the additional wavelength range.

[0056] At block 440, each additional tunable transmitter may be operated such that each additional light output from the additional tunable transmitters is at each additional wavelength determined at block 435.

[0057] At block 445, the calibration of the first tunable transmitter and each tunable transmitter may be periodically repeated. For example, the calibration processes 300 and 400 may be repeated every minute, to ensure that the reconfigurable photonic switch does not drift too far with changes in temperature. Further, because the tunable transmitters are tuned relative to the AWG, the AWG may not need active temperature compensation so that any minor drift of the channel wavelengths of the AWG is tracked by the calibration of the tunable transmitters. [0058] In some implementations, the first light output and each additional light output may be modulated with data during the repeating of the calibration. For example, a coarse calibration of the first tunable transmitter and the additional tunable transmitters may be initially performed prior to using the reconfigurable photonic switch for switching data. Subsequently, fine calibration of the first tunable transmitter and the additional tunable transmitters may be performed to ensure that the tunable transmitters do not drift too far from the AWG reference. During the fine calibration, data may or may not be transmitted by the transceivers.

[0059] Not all of the steps, or features presented above are used in each implementation of the presented techniques.

[0060] As used in the specification and claims herein, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

Claims

CLAIMS What is claimed is:

1 . An apparatus comprising:

an arrayed waveguide grating (AWG) having a plurality of input ports and a plurality of output ports, wherein a signal within a given wavelength channel transmitted to one of the input ports is routed to one of the output ports based on a signal wavelength; and a plurality of transceiver nodes, each transceiver node comprising:

a plurality of optical transmitters, wherein each optical transmitter is tunable over multiple wavelength channels within a different wavelength band;

a plurality of receivers to receive wavelengths of light within the different wavelength bands;

a band multiplexer to multiplex the multiple wavelength channels within each different wavelength band;

a band demultiplexer to demultiplex the multiple wavelength channels within each different wavelength band;

a first fiber to couple an output of the band multiplexer to one of the input ports of the AWG; and

a second fiber to couple one of the output ports of the AWG to an input of the band demultiplexer,

wherein each of the first fibers couples to a different one of the input ports of the AWG, and each of the second fibers couples to a different one of the output ports of the AWG.

2. The apparatus of claim 1 , wherein each transceiver node further comprises a modulator for each of the plurality of optical transmitters to modulate the emitted light.

3. The apparatus of claim 1 , further comprising a controller to control an emission wavelength of each of the optical transmitters in the plurality of transceiver nodes such that emission wavelengths of two different optical transmitters are not transmitted simultaneously to a same receiver via the AWG.

4. The apparatus of claim 1 , wherein the controller further directs the transceiver nodes to self-calibrate the optical transmitters relative to the AWG's routing of wavelengths between the input ports and the output ports.

5. The apparatus of claim 1 , wherein each transceiver node comprises an integrated transceiver, such that the plurality of optical transmitters, the plurality of receivers, the band multiplexer, and the band demultiplexer are integrated on a single die.

6. The apparatus of claim 1 , wherein the AWG is not actively temperature compensated.

7. The apparatus of claim 1 ,

wherein each of the optical transmitters of the plurality of transceiver nodes is further tunable over the different wavelength bands, and further wherein the band multiplexer and band demultiplexer are tunable.

8. The apparatus of claim 1 ,

wherein the multiple wavelength channels are evenly spaced by a channel spacing, and further wherein one or more wavelength channels is skipped between the different wavelength bands,

such that specifications on the band multiplexer and band demultiplexer are relaxed compared to when no wavelength channels are skipped.

9. An apparatus comprising:

a first arrayed waveguide grating (AWG) having a plurality of first input ports and a plurality of first output ports, wherein light entering each of the first input ports is routed to one of the plurality of first output ports based on a wavelength of the light;

a second AWG having a plurality of second input ports and a plurality of second output ports, wherein light entering each of the second input ports is routed to one of the plurality of second output ports based on a wavelength of the light;

a plurality of transceiver nodes, each transceiver node comprising:

a first fiber to couple an output from the band multiplexer to one of the first input ports of the first AWG; and

a second fiber to couple an output from one of the second output ports of the second AWG to an input of the band demultiplexer, wherein each of the first fibers couples to a different one of the first input ports of the first AWG, and each of the second fibers couples to a different one of the second output ports of the second AWG; and

a plurality of packet switch nodes, each packet switch node comprising: an input switch port;

an output switch port;

a third fiber to couple one of the first output ports from the first

AWG to the input switch port; and

a fourth fiber to couple an output from the output switch port to one of the second input ports of the second AWG, wherein each of the third fibers couples to a different one of the first output ports of the first AWG, and each of the fourth fibers couples to a different one of the second input ports of the second AWG.

10. The apparatus of claim 9, further comprising a controller to control an emission wavelength of each of the optical transmitters in the plurality of transceiver nodes such that emission wavelengths from two different optical transmitters are not transmitted simultaneously to a same input switch port of one of the packet node switches via the AWG.

1 1 . A method of calibrating a reconfigurable photonic switch, the method comprising:

tuning a first light output from a first tunable transmitter over a first wavelength range near a first channel, wherein the first light output is coupled to a first input port of an arrayed waveguide grating (AWG), and further wherein the AWG routes a given input over the first wavelength range at the first input port to a first output port of the AWG; monitoring a first output power from the first output port;

determining a first wavelength at which the first output power is a maximum; and

operating the first tunable transmitter such that the first light output is at the first wavelength.

12. The method of claim 1 1 , further comprising

tuning each additional light output from each additional tunable transmitter of the reconfigurable photonic switch over an additional wavelength range near an additional channel, wherein each additional light output is coupled to one of the input ports of the AWG;

monitoring each additional output power from the output ports of the AWG;

determining each additional wavelength at which each additional output power is a maximum; and

operating each additional tunable transmitter such that each additional light output is at each additional wavelength.

13. The method of claim 12, further comprising periodically repeating the calibration of the first tunable transmitter and each tunable transmitter.

14. The method of claim 13, wherein the first light output and each additional light output is modulated with data during the repeating of the calibration.

15. The method of claim 1 1 , wherein the AWG is not temperature compensated.