Optical receiving device and optical transmitting / receiving device

Abstract

To provide an optical reception device that uniquely determines a relationship between an output port and a wavelength of a signal light.SOLUTION: An optical transmission and reception device TR1 comprises an input port Pin; and a plurality of output ports P#1 to P#4, and comprises: a first optical demultiplexer 1 that divides a wavelength multiplex signal light Sz input from the input port into a signal light in each wavelength and outputs it from each of the plurality of output ports; a multiwavelength light output part L1 that outputs a wavelength light in each wavelength contained in the wavelength multiplex signal light Sz to the input port of the first optical demultiplexer; and a control part 108 that controls the first optical demultiplexer and the multiwavelength light output part. A first splitter includes: a plurality of asymmetrical Mach-Zehnder interferometers (AMZ); and a plurality of adjusters that adjusts each of optical phases in the inner part. The control part allows the sequential output of the wavelength light in each wavelength to the multiwavelength light output part, and controls an adjustment amount of each optical phase to each adjuster of each AMZ on a path connecting the input port into which the wavelength light is input from the multiwavelength light output part and the output port in accordance with the wavelength of the wavelength light of the plurality of output ports.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical receiving device and an optical transmitting / receiving device. [Background technology]

[0002] An optical repeater that repeats an optical signal in which a service wavelength and an OSC (Optical Supervisory Channel) light are wavelength-multiplexed is known. This optical repeater includes a demultiplexer that demultiplexes the optical signal into the service wavelength and the OSC light, and a demultiplexer that demultiplexes the service wavelength into those whose output ports have the same wavelength. This optical repeater also includes a multiplexer that multiplexes the service wavelength and outputs the multiplexed service wavelength and a multiplexer that multiplexes the service wavelength and the OSC light and outputs the multiplexed service wavelength (see Patent Document 1 for the above). In addition, optical demultiplexers that demultiplex wavelength-multiplexed signal light by wavelength and optical multiplexers that multiplex signal light of different wavelengths are also known (see Patent Document 2, for example).

[0003] There are various types of optical demultiplexers known, including an optical demultiplexer in which asymmetric Mach-Zehnder interferometers (AMZs), each having a pair of arms with different lengths, are connected in multiple stages in a tree shape (hereinafter referred to as an AMZ-type optical demultiplexer) (see, for example, Patent Document 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2017 / 109830 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-254018 [Patent Document 3] Japanese Patent Application Publication No. 2019-135524 Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, the signal light for each wavelength demultiplexed by the above-mentioned AMZ-type optical demultiplexer is output from the rearmost AMZ, but the output port is determined randomly by the initial optical phase within the pair of arms of each AMZ. In other words, it is not possible to uniquely determine which output port of the AMZ-type optical demultiplexer will output which wavelength of the signal light. This poses a problem that each signal light cannot be output from the desired output port. Note that this problem is not limited to the above-mentioned AMZ-type optical demultiplexer, but also exists in other optical demultiplexers using AMZ in which the output port of the signal light is determined randomly.

[0006] Therefore, in one aspect, an object is to provide an optical receiving device and an optical transmitting / receiving device that uniquely determine the relationship between an output port and the wavelength of signal light. [Means for solving the problem]

[0007] In one embodiment, an optical receiving device includes an input port and a plurality of output ports, an optical demultiplexer that demultiplexes wavelength-multiplexed signal light input from the input port into signal light for each wavelength and outputs the demultiplexed signal light from each of the plurality of output ports, a multi-wavelength optical output unit that outputs wavelength light for each wavelength included in the wavelength-multiplexed signal light to the input port of the optical demultiplexer, and a control unit that controls the optical demultiplexer and the multi-wavelength optical output unit, and the optical demultiplexer includes a plurality of asymmetric Mach-Zehnder interferometers each having arm pairs with different lengths, and and a plurality of adjusters that adjust the optical phase within each of the asymmetric Mach-Zehnder interferometers, the plurality of asymmetric Mach-Zehnder interferometers being connected to one another in a tree configuration so as to connect the input port and the plurality of output ports, and the control unit causing the multi-wavelength optical output unit to output the wavelength light sequentially for each wavelength, and controlling the amount of adjustment of the optical phase for the adjusters of the asymmetric Mach-Zehnder interferometers on a path connecting the input port to which the wavelength light from the multi-wavelength optical output unit is input and one of the plurality of output ports corresponding to the wavelength of the wavelength light.

[0008] In one embodiment, an optical transceiver includes an input port and a plurality of output ports, an optical demultiplexer that demultiplexes wavelength-multiplexed signal light input from the input port into signal light for each wavelength and outputs the demultiplexed signal light from each of the plurality of output ports, a multi-wavelength optical output unit that outputs wavelength light for each wavelength included in the wavelength-multiplexed signal light to the input port of the optical demultiplexer, and a control unit that controls the optical demultiplexer and the multi-wavelength optical output unit, wherein the optical demultiplexer has a plurality of asymmetric Mach-Zehnder interferometers each having an arm pair with a different length, and a plurality of adjusters that adjust optical phases in the plurality of asymmetric Mach-Zehnder interferometers, and the plurality of asymmetric Mach-Zehnder interferometers are connected to each other in a tree shape so as to connect the input port and the plurality of output ports, and the control unit controls the multi-wavelength optical output unit to output the wavelength light for each wavelength. and controls an adjustment amount of an optical phase for the adjuster of the asymmetric Mach-Zehnder interferometer on a path connecting the input port to which the wavelength light from the multi-wavelength light output unit is input and an output port among the plurality of output ports according to the wavelength of the wavelength light, the number of the input port being one, the wavelength multiplexed signal light and the wavelength light being selectively input to the input port, the multi-wavelength light output unit comprising a plurality of single-wavelength light sources, switches the output destination of the wavelength light output from each of the plurality of single-wavelength light sources to either a first waveguide or a second waveguide, the number of the switches being the same as the number of the single-wavelength light sources, and an optical coupler coupling each of the first waveguides to one third waveguide, and each of the second waveguides comprises a plurality of detection circuits for each wavelength that detect the signal light using the wavelength light as local light and a detection circuit for detecting the signal light using the wavelength light as transmission light. 、 an electrical signal corresponding to the signal light The transmitted light based on The optical fiber is connected to a plurality of modulation circuits for each wavelength. [Effects of the Invention]

[0009] The relationship between the output port and the wavelength of the signal light can be uniquely determined. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is an example of an optical transmitting and receiving device according to a first embodiment. [Figure 2] 1 is an example of a first optical demultiplexer. [Figure 3] 4A and 4B are diagrams illustrating an example of the operation of the first optical demultiplexer. [Figure 4] 5 is a flowchart showing an example of the operation of a control unit according to the first embodiment. [Figure 5] 10 is an example of an optical transmitting and receiving device according to a second embodiment. [Figure 6] 1 is an example of a second optical demultiplexer. [Figure 7] 10A and 10B are diagrams illustrating an example of the operation of the second optical demultiplexer. [Figure 8] 10 is a flowchart showing an example of the operation of a control unit according to the second embodiment. [Figure 9] 10 is an example of an optical transmitting and receiving device according to a third embodiment. [Figure 10] 10 is an example of an optical transmitting and receiving device according to a fourth embodiment. [Figure 11] 1 is an example of a monitor. [Figure 12] FIG. 1 is a diagram illustrating an example of adjacent channels and non-adjacent channels. [Figure 13] 10 is a flowchart showing an example of the operation of a control unit according to the fourth embodiment. [Figure 14] 10 is a flowchart illustrating an example of a correspondence relationship identification process. [Figure 15] FIG. 10 is a diagram illustrating an example of a correspondence relationship specifying process. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0012] (First embodiment) As shown in Fig. 1, the optical transceiver TR1 includes a first LD (Laser Diode) 101, a second LD 102, a third LD 103, and a fourth LD 104. The first LD 101, the second LD 102, the third LD 103, and the fourth LD 104 are all examples of single-wavelength light sources. The first LD 101 to the fourth LD 104 output wavelength light Wa, Wb, Wc, and Wd having center wavelengths λa to λd at regular wavelength intervals, respectively. In the first embodiment, four single-wavelength light sources are used for description, but the number is not particularly limited, and for example, eight single-wavelength light sources may be used.

[0013] The optical transceiver TR1 also includes a PIC (Photonics Integrated Circuit) 105, optical amplifiers 106 and 107, and a control unit 108. The optical amplifiers 106 and 107 include, for example, EDFAs (Erbium Doped Fiber Amplifiers). The optical amplifiers 106 and 107 each amplify a wavelength-multiplexed signal light Sz, which is a wavelength-multiplexed signal light.

[0014] The PIC 105 includes a first SW (switch) 151, a second SW 152, a third SW 153, a fourth SW 154, an optical coupler 155, input optical SWs 156 and 157, and transceivers 158 and 159. The first SW 151, the second SW 152, the third SW 153, and the fourth SW 154 each have one input terminal and two output terminals. The optical coupler 155 has four input terminals and one output terminal. The input optical SWs 156 and 157 each have two input terminals and one output terminal. The transceivers 158 and 159 each have four first input terminals, one second input terminal, and one output terminal. In the first embodiment, four SWs, the first SW 151, the second SW 152, the third SW 153, and the fourth SW 154, are used for explanation, but the number is not particularly limited as long as it is the same as the number of single-wavelength light sources.

[0015] The first LD 101, the second LD 102, the third LD 103, the fourth LD 104, the first SW 151, the second SW 152, the third SW 153, the fourth SW 154, and the optical coupler 155 are included in the multi-wavelength optical output unit L1.

[0016] The input end of the first SW 151 is connected to the first LD 101. The input end of the second SW 152 is connected to the second LD 102. The input end of the third SW 153 is connected to the third LD 103. The input end of the fourth SW 154 is connected to the fourth LD 104. Therefore, the wavelength light Wa output from the first LD 101 is input to the input end of the first SW 151. The second SW 152 to the fourth SW 154 are similar to the first SW 151, so their explanation will be omitted.

[0017] One of the output terminals of each of the first SW 151, the second SW 152, the third SW 153, and the fourth SW 154 is connected to each of the four input terminals of the optical coupler 155 via a first waveguide 161. The other of the output terminals of each of the first SW 151, the second SW 152, the third SW 153, and the fourth SW 154 is connected to each of the four first input terminals of the transmitter / receiver units 158 and 159 via a second waveguide 162. In other words, the first SW 151, the second SW 152, the third SW 153, and the fourth SW 154 are optical switches that switch the waveguide direction of the wavelength light Wa, Wb, Wc, and Wd between the first waveguide 161 and the second waveguide 162.

[0018] One output end of the optical coupler 155 is connected to one of the input ends of the input optical SWs 156 and 157 via the third waveguide 163. That is, the waveguide connecting the optical coupler 155 and the input optical SWs 156 and 157 branches along the way. The other of the input ends of the input optical SWs 156 and 157 is both connected to the optical amplifier 106. The output end of the input optical SW 156 is connected to a second input end of the transceiver 158. The output end of the input optical SW 157 is connected to a second input end of the transceiver 159. That is, the input optical SW 156 is an optical switch that switches the wavelength-multiplexed signal light Sz input to the second input end of each of the transceivers 158 and 159 to any of the wavelength lights Wa, Wb, Wc, and Wd.

[0019] The transmitter / receivers 158 and 159 receive the wavelength-multiplexed signal light Sz and transmit the wavelength-multiplexed signal light Sz. More specifically, when the transmitter / receivers 158 and 159 receive the wavelength-multiplexed signal light Sz from the optical amplifier 106, they convert the received wavelength-multiplexed signal light Sz into an electrical signal corresponding to the wavelength-multiplexed signal light Sz. When the transmitter / receivers 158 and 159 convert the wavelength-multiplexed signal light Sz into an electrical signal, they perform various signal processing on the electrical signal to regenerate the electrical signal and convert the processed electrical signal into the wavelength-multiplexed signal light Sz. The transmitter / receivers 158 and 159 transmit the wavelength-multiplexed signal light Sz converted from the electrical signal to the optical amplifier 107. Note that the transmitter / receiver 158 corresponds to the X-polarized component of the wavelength-multiplexed signal light Sz, and the transmitter / receiver 159 corresponds to the Y-polarized component of the wavelength-multiplexed signal light Sz.

[0020] The transceiver 158 includes a first optical demultiplexer 1, 90-degree hybrid circuits 7a-7d, BPD (Balanced Photodiodes) 6ai-6di, 6aq-6dq, IQ Modulators 8a-8d, and an optical multiplexer 9. The 90-degree hybrid circuits 7a-7d are an example of a detection circuit. The IQ Modulators 8a-8d are an example of a modulation circuit. In addition, although not shown, the transceiver 158 includes a DSP (Digital Signal Processor), an ADC (Analogue Digital Converter), a DAC (Digital Analogue Converter), and the like that perform the above-mentioned signal processing. The 90-degree hybrid circuits 7a-7d and the IQ Modulators 8a-8d are respectively connected to four first input terminals of the transceiver 158. Note that the configuration of the transceiver 159 is basically the same as that of the transceiver 158, and therefore detailed description is omitted in FIG. 1.

[0021] Incidentally, the optical transceiver TR1 can also be configured as an optical receiving device by excluding the above-mentioned IQ Modulators 8a to 8d, the optical multiplexer 9, and the DAC from the transceiver unit 158. In this case, the transceiver unit 158 ​​may simply be configured as a receiving unit. That is, when the optical transceiver TR1 is configured as an optical receiving device, it is sufficient that the receiving unit includes the first optical demultiplexer 1, the 90-degree hybrid circuits 7a to 7d, the BPDs 6ai to 6di, 6aq to 6dq, the DSP, and the ADC.

[0022] The first optical demultiplexer 1 has one input port and four output ports. The input port of the first optical demultiplexer 1 is connected to the second input terminal of the transceiver 158. The first optical demultiplexer 1 demultiplexes the X-polarized component of the wavelength-multiplexed signal light Sz into signal light Sa with wavelength λa, signal light Sb with wavelength λb, signal light Sc with wavelength λc, and signal light Sd with wavelength λd.

[0023] The 90-degree hybrid circuit 7a uses wavelength light Wa with a center wavelength λa as a local light with a center wavelength λa, and causes interference between the signal light Sa and the local light to detect the I channel (in-phase component) and Q channel (quadrature component) of the X polarization component. That is, the 90-degree hybrid circuit 7a causes interference between the signal light Sa and the local light to detect the interference signal, and performs coherent detection to detect the amplitude and phase of the signal light Sa. The 90-degree hybrid circuit 7a outputs optical field components corresponding to the amplitude and phase of the signal light Sa to the downstream BPDs 6ai and 6aq. The BPDs 6ai and 6aq convert the optical field components into electrical analog signals. The 90-degree hybrid circuits 7b to 7d and BPDs 6bi to di and 6bq to dq are basically the same as the 90-degree hybrid circuit 7a and BPDs 6ai and 6aq, and therefore detailed description thereof will be omitted.

[0024] IQ Modulator 8a uses wavelength light Wa with center wavelength λa as transmission light with center wavelength λa, and optically modulates the X-polarized component of the transmission light based on the electrical signal after signal processing. The optically modulated X-polarized component of the transmission light with center wavelength λa is input to optical multiplexer 9. Note that IQ Modulators 8b to 8d are basically the same as IQ Modulator 8a, so detailed description will be omitted.

[0025] The optical multiplexer 9 has four input ports and one output port. The output port of the optical multiplexer 9 is connected to the output end of the transmitter / receiver 158. Transmission light with a central wavelength λa, transmission light with a central wavelength λb, transmission light with a central wavelength λc, and transmission light with a central wavelength λd are input to the four input ports of the optical multiplexer 9, respectively. The optical multiplexer 9 multiplexes these four transmission lights to generate the X polarization component of the wavelength-multiplexed signal light Sz. The optical multiplexer 9 outputs the X polarization component of the wavelength-multiplexed signal light Sz from the output port. The X polarization component of the wavelength-multiplexed signal light Sz is polarization-multiplexed with the Y polarization component of the wavelength-multiplexed signal light Sz and transmitted to the optical amplifier 107 as the wavelength-multiplexed signal light Sz.

[0026] The control unit 108 controls the operations of the first LD 101, the second LD 102, the third LD 103, the fourth LD 104, the first SW 151, the second SW 152, the third SW 153, the fourth SW 154, the input optical SWs 156 and 157, and the first optical demultiplexer 1. The control unit 108 includes hardware circuits such as an FPGA (Field Programmable Gate Array) and a memory. Instead of an FPGA, the control unit 108 may be a hardware circuit such as an ASIC (Application Specific Integrated Circuit) or a CPU (Central Processing Unit).

[0027] For example, the control unit 108 outputs on / off signals to the first LD 101, the second LD 102, the third LD 103, the fourth LD 104, and the first optical demultiplexer 1 to control the operations of the first LD 101, the second LD 102, the third LD 103, the fourth LD 104, and the first optical demultiplexer 1. For example, in the case of the first LD 101, the on / off signal is a signal that switches between outputting and stopping output of the wavelength light Wa. The second LD 102, the third LD 103, and the fourth LD 104 are similar to the case of the first LD 101, so their explanation will be omitted. In the case of the first optical demultiplexer 1, the on / off signal is a signal that switches between on and off of the output port. Note that the on / off of the output port will be explained in detail later.

[0028] On the other hand, the control unit 108 outputs switching signals to the first SW 151, the second SW 152, the third SW 153, the fourth SW 154, and the input optical SWs 156 and 157 to control the operations of the first SW 151, the second SW 152, the third SW 153, the fourth SW 154, and the input optical SWs 156 and 157. For example, the control unit 108 outputs a switching signal to the first SW 151 to switch the first SW 151 to the first waveguide 161 side. The control unit 108 also outputs a switching signal to the input optical SW 156 to input wavelength light. As a result, if wavelength light Wa with center wavelength λa is output from the first LD 101, this wavelength light Wa is input to the input port of the first optical demultiplexer 1.

[0029] The first optical demultiplexer 1 will be described in detail with reference to Figures 2 and 3. In Figure 3, the same components as those in Figure 2 are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0030] The first optical demultiplexer 1 has a front-stage demultiplexing circuit 11 and back-stage demultiplexing circuits 12 and 13 optically connected to the rear of the front-stage demultiplexing circuit 11. For example, the first optical demultiplexer 1 demultiplexes wavelength-multiplexed signal light Sz having four wavelengths λa to λd into signal lights Sa, Sb, Sc, and Sd having center wavelengths λa to λd spaced at regular wavelength intervals. The first optical demultiplexer 1 performs demultiplexing processing using each of the front-stage demultiplexing circuit 11 and the back-stage demultiplexing circuits 12 and 13 as a unit.

[0031] The first optical demultiplexer 1 has AMZs 1a to 1i connected in multiple stages in a tree configuration. The pre-demultiplexing circuit 11 has AMZs 1a to 1c, the post-demultiplexing circuit 12 has AMZs 1d to 1f, and the post-demultiplexing circuit 13 has AMZs 1g to 1i. In other words, the first optical demultiplexer 1 corresponds to an AMZ-type optical demultiplexer. The AMZs 1a to 1i each have a pair of arms Au and Ad with different lengths (waveguide lengths), an input coupler Ca, and an output coupler Cb. The AMZs 1a to 1i may each have multiple arm pairs. For example, the AMZ 1a may have a pair of arms Au and Ad as an arm pair, or may have two or more pairs of arms as an arm pair. The input coupler Ca and output coupler Cb are each 2x2 couplers with two input ports and two output ports.

[0032] The input ends of the pair of arms Au, Ad are optically connected to two output ports of an input coupler Ca. The output ends of the pair of arms Au, Ad are optically connected to two input ports of an output coupler Cb. The wavelength-multiplexed signal light Sz input to the input coupler Ca is input to the pair of arms Au, Ad.

[0033] A phase shifter Hu is provided in the upper arm Au, and a phase shifter Hd is provided in the lower arm Ad. The phase shifters Hu and Hd adjust the optical phases in the pairs of arms Au and Ad of the AMZs 1a to 1i, respectively. This compensates for optical phase shifts due to manufacturing variations and the like. The phase shifters Hu and Hd are heaters formed from a thin metal (resistive) film such as tungsten, titanium, or platinum, and change the temperature of the waveguides in the arms Au and Ad. This changes the refractive index in the arms Au and Ad, thereby adjusting the optical phases in the arms Au and Ad. Note that the configuration of the phase shifters Hu and Hd is not limited to this, and may be a means for electrically changing the carrier density in the waveguides of each arm Au and Ad using the carrier plasma effect.

[0034] Furthermore, the first optical demultiplexer 1 includes monitor circuits Mon#1-#12 that monitor the power of the output light from the AMZs 1a-1i to control the phase shifters Hu and Hd of the AMZs 1a-1i, compensation circuits Dec#1-#6 that decrease the power in accordance with the monitoring results of the output light power, and compensation circuits Inc#1-#3 that increase the power in accordance with the monitoring results of the output light power. The compensation circuits Dec#1-#6 and Inc#1-#3 are examples of adjusters. The monitor circuits Mon#1-#12 are realized, for example, by PDs, and the compensation circuits Dec#1-#3 and Inc#1-#3 are realized, for example, by FPGAs or ASICs.

[0035] The monitor circuits Mon#1 to Mon#12 monitor the power of the output light from the AMZs 1b, 1c, 1e, 1f, 1h, and 1i, respectively. The compensation circuits Dec#1 to Dec#6 and Inc#1 to Dec#3 compensate for the optical phase shift by controlling the amount of optical phase adjustment in the pair of arms Au and Ad for the phase shifters Hu and Hd according to the power of the output light. For example, the compensation circuits Dec#1 to Dec#6 and Inc#1 to Dec#3 control the heater power supplied to the phase shifters Hu and Hd.

[0036] The front-stage demultiplexing circuit 11 is provided with AMZs 1a-1c, compensation circuits Inc#1, Dec#2, #3, and monitor circuits Mon#1-#4. AMZs 1b and 1c are optically connected downstream of AMZ 1a. AMZs 1d and 1g are optically connected downstream of AMZs 1b and 1c. The input end of AMZ 1a is provided with an input port Pin to which one of wavelength light Wa-Wd or wavelength-multiplexed signal light Sz is input.

[0037] Monitor circuits Mon#1 and #3 are optically connected to one output port of output coupler Cb of AMZ1b and AMZ1c, respectively, via branch couplers CP. Monitor circuit Mon#1 monitors the power of the output light output from AMZ1b to AMZ1d. Monitor circuit Mon#1 notifies compensation circuit Inc#1 of the monitored power. Monitor circuit Mon#3 monitors the power of the output light output from AMZ1c to AMZ1g. Monitor circuit Mon#3 notifies compensation circuit Inc#1 of the monitored power.

[0038] The monitor circuits Mon#2 and #4 are optically connected to the other output ports of the output couplers Cb of the AMZs 1b and 1c, respectively. The monitor circuits Mon#2 and #4 monitor the power of the output light output from the other output ports of the output couplers Cb. The monitor circuit Mon#2 notifies the compensation circuit Dec#1 of the power of the monitoring result. The monitor circuit Mon#4 notifies the compensation circuit Dec#2 of the power of the monitoring result.

[0039] Compensation circuit Inc#1 controls the amount of optical phase adjustment for phase shifters Hu and Hd of AMZ1a in accordance with the results of monitoring the output light by monitor circuits Mon#1 and Mon#3. Compensation circuit Dec#1 controls the amount of optical phase adjustment for phase shifters Hu and Hd of AMZ1b in accordance with the results of monitoring the output light by monitor circuit Mon#2. Compensation circuit Dec#2 controls the amount of optical phase adjustment for phase shifters Hu and Hd of AMZ1c in accordance with the results of monitoring the output light by monitor circuit Mon#4.

[0040] With the above configuration, the power of the output light output from one output port of the output coupler Cb of AMZ1b and 1c to the subsequent AMZ1d and 1g increases, and the power of the output light output from the other output port of the output coupler Cb of AMZ1b and 1c to the monitor circuits Mon#2 and #4 decreases.

[0041] The post-stage demultiplexing circuit 12 includes AMZs 1d-1f, compensation circuits Inc#2, Dec#3, #4, and monitor circuits Mon#5-#8. AMZs 1e and 1f are optically connected to the rear of AMZ 1d. One output port of the output coupler Cb of AMZs 1e and 1f is provided with output ports P#1 and P#2, respectively, from which the branched light is output. Output port P#1 is connected to a 90-degree hybrid circuit 7a. Output port P#2 is connected to a 90-degree hybrid circuit 7b.

[0042] Monitor circuits Mon#5 and #7 are optically connected to one output port of output coupler Cb of AMZ1e and AMZ1f, respectively, via branch coupler CP. Monitor circuit Mon#5 monitors the power of the output light output from AMZ1e to output port P#1. Monitor circuit Mon#5 notifies compensation circuit Inc#2 of the monitored power. Monitor circuit Mon#7 monitors the power of the output light output from AMZ1f to output port P#2. Monitor circuit Mon#7 notifies compensation circuit Inc#2 of the monitored power.

[0043] The monitor circuits Mon#6 and #8 are optically connected to the other output ports of the output couplers Cb of the AMZ1e and 1f, respectively. The monitor circuits Mon#6 and #8 monitor the power of the output light output from the other output ports of the output couplers Cb. The monitor circuit Mon#6 notifies the compensation circuit Dec#3 of the power of the monitoring result. The monitor circuit Mon#8 notifies the compensation circuit Dec#4 of the power of the monitoring result.

[0044] Compensation circuit Inc#2 controls the amount of optical phase adjustment for phase shifters Hu and Hd of AMZ1d in response to the results of monitoring the output light by monitor circuits Mon#5 and Mon#7. Compensation circuit Dec#3 controls the amount of optical phase adjustment for phase shifters Hu and Hd of AMZ1e in response to the results of monitoring the output light by monitor circuit Mon#6. Compensation circuit Dec#4 controls the amount of optical phase adjustment for phase shifters Hu and Hd of AMZ1f in response to the results of monitoring the output light by monitor circuit Mon#8.

[0045] With the above configuration, the power of the output light output from one output port of the output coupler Cb of AMZ1e, 1f to the subsequent output ports P#1, #2 increases, and the power of the output light output from the other output port of the output coupler Cb of AMZ1e, 1f to the monitor circuits Mon#6, #8 decreases.

[0046] The post-stage demultiplexing circuit 13 includes AMZs 1g-1i, compensation circuits Inc#3, Dec#5, #6, and monitor circuits Mon#9-#12. AMZs 1h and 1i are optically connected to the rear of AMZ 1g. One output port of the output coupler Cb of AMZs 1h and 1i is provided with output ports P#3 and P#4, respectively, from which the branched light is output. Output port P#3 is connected to a 90-degree hybrid circuit 7c. Output port P#4 is connected to a 90-degree hybrid circuit 7d.

[0047] Monitor circuits Mon#9 and #11 are optically connected to one output port of output coupler Cb of AMZ1h and AMZ1i via branch coupler CP, respectively. Monitor circuit Mon#9 monitors the power of the output light output from AMZ1h to output port P#3. Monitor circuit Mon#9 notifies compensation circuit Inc#3 of the monitored power. Monitor circuit Mon#12 monitors the power of the output light output from AMZ1i to output port P#4. Monitor circuit Mon#11 notifies compensation circuit Inc#3 of the monitored power.

[0048] The monitor circuits Mon#10 and #12 are optically connected to the other output ports of the output couplers Cb of the AMZ1h and 1i, respectively. The monitor circuits Mon#10 and #12 monitor the power of the output light output from the other output ports of the output couplers Cb. The monitor circuit Mon#10 notifies the compensation circuit Dec#5 of the power of the monitoring result. The monitor circuit Mon#12 notifies the compensation circuit Dec#6 of the power of the monitoring result.

[0049] Compensation circuit Inc#3 controls the amount of optical phase adjustment for phase shifters Hu and Hd of AMZ1g in accordance with the results of monitoring the output light by monitor circuits Mon#9 and #11. Compensation circuit Dec#5 controls the amount of optical phase adjustment for phase shifters Hu and Hd of AMZ1h in accordance with the results of monitoring the output light by monitor circuit Mon#10. Compensation circuit Dec#6 controls the amount of optical phase adjustment for phase shifters Hu and Hd of AMZ1i in accordance with the results of monitoring the output light by monitor circuit Mon#12.

[0050] With the above configuration, the power of the output light output from one output port of the output coupler Cb of AMZ1h, 1i to the subsequent output ports P#3, #4 increases, and the power of the output light output from the other output port of the output coupler Cb of AMZ1h, 1i to the monitor circuits Mon#10, #12 decreases.

[0051] In this way, the front-stage demultiplexing circuit 11 and the rear-stage demultiplexing circuits 12, 13 are connected in multiple stages in a tree configuration so that the wavelength-multiplexed signal light Sz with center wavelengths λa to λd is input from AMZ 1a to AMZs 1b and 1c, respectively, and then input from AMZs 1b and 1c to the subsequent separate AMZs 1d and 1g, respectively. The wavelength spacing of the transmission bands of AMZs 1a to 1i is determined according to their arm length differences. More specifically, the wavelength spacing of the transmission bands of AMZs 1a to 1i is substantially inversely proportional to their arm length differences.

[0052] The arm length difference between AMZs 1a to 1c is set so that the wavelength interval of the transmission band is the wavelength interval Δλ between the center wavelengths λa to λd. The arm length difference between AMZs 1d to 1f and AMZs 1g to 1i is set to 1 / 2 the arm length difference between AMZs 1a to 1c so that the wavelength interval of the transmission band is twice the interval Δλ of the center wavelengths (2×Δλ).

[0053] As a result, the front-stage demultiplexing circuit 11 demultiplexes the wavelength-multiplexed signal light Sz into wavelength-multiplexed signal light Sac with center wavelengths λa and λc and wavelength-multiplexed signal light Sbd with center wavelengths λb and λd. The rear-stage demultiplexing circuit 12 demultiplexes the wavelength-multiplexed signal light Sac into signal lights Sa and Sc with center wavelengths λa and λc. The rear-stage demultiplexing circuit 13 demultiplexes the wavelength-multiplexed signal light Sbd into signal lights Sb and Sd with center wavelengths λb and λd.

[0054] At this time, the output ports P#1 to P#4 for the signal light Sa to Sd with center wavelengths λa to λd are randomly determined by the initial optical phase in a pair of arms Au, Ad of each of the AMZs 1a to 1i. Therefore, the signal light Sa with center wavelength λa may be output from output port P#1, or, as shown in parentheses, the signal light Sd with center wavelength λd may be output from output port P#1. Similarly, the signal light Sc with center wavelength λc may be output from output port P#2, or the signal light Sb with center wavelength λb may be output. The signal light Sb may be output from output port P#3, or the signal light Sc may be output. The signal light Sd may be output from output port P#4, or the signal light Sa may be output. Thus, the combinations of the signal light Sa, Sb, Sc, and Sd with center wavelengths λa to λd and the output ports P#1 to P#4 are not constant.

[0055] For this reason, the signal lights Sa, Sb, Sc, and Sd cannot be output to any desired output destination, and it is difficult to perform appropriate signal processing for each of the signal lights Sa, Sb, Sc, and Sd.

[0056] For example, a method is conceivable in which the signal lights Sa, Sb, Sc, and Sd output from each output port P#1 to P#4 are detected, and an electrical cross-connect switch that selects the output destination of the signal lights Sa, Sb, Sc, and Sd is switched based on the detection result. The detection of the signal lights Sa, Sb, Sc, and Sd can be realized by, for example, a PD. If a PD and a cross-connect switch are provided between the first optical demultiplexer 1 and the 90-degree hybrid circuits 7a to 7d, appropriate signal processing can be performed on each of the signal lights Sa, Sb, Sc, and Sd according to the center wavelengths λa to λd.

[0057] However, as the number of wavelengths increases, the size of the electronic circuitry, including the cross-connect switch, increases, and it may become impossible to accommodate it on a single chip. In this case, additional wiring may be required to span between chips. In other words, if this method is adopted, a new problem may arise in that the size of the electronic circuitry and power consumption increase as the number of wavelengths increases.

[0058] Here, as shown in Figure 3, it is also possible to input wavelength light of a specific center wavelength from the center wavelengths λa to λd into the first optical demultiplexer 1 and assign the light of the specific center wavelength to any of the output ports P#1 to #4 by operating only the compensation circuits Inc#1 to #3 and Dec#1 to #6 on the path from the input port Pin to any of the output ports P#1 to #4.

[0059] As an example, consider a technique in which output port P#1 is assigned to wavelength light Wa with a center wavelength λa. Of the wavelengths λa to λd, only wavelength light Wa with a center wavelength λa is input to input port Pin. To ensure that wavelength light Wa with a center wavelength λa is output from output port P#1, compensation circuits Inc#1, Dec#1, and #3 on path K connecting input port Pin and output port P#1 are operated under the control of the control unit 108, while the other compensation circuits Inc#3, Dec#2, and #4 to #6 are stopped under the control of the control unit 108. Furthermore, to prevent the monitoring results of monitor circuits Mon#3 and #7 on portions other than path K from affecting the control of compensation circuits Inc#1 and #2, the connection between them is cut off under the control of the control unit 108. In the first embodiment, such operation, stop of operation, and disconnection controlled by the control unit 108 are defined as turning on output port P#1 and turning off output ports P#2 to P#4.

[0060] By controlling the optical phase along path K in this way, it is possible to intentionally guide wavelength light Wa with center wavelength λa to output port P#1. Furthermore, by controlling the optical phase of each of the other wavelength lights Wb, Wc, and Wd with center wavelengths λb to λd in the same manner as above, it is possible to assign them to any of output ports P#2 to P#4. That is, by turning on output port P#2 and turning off output ports P#1, P#3 to P#4, wavelength light Wb with center wavelength λb can be guided to output port P#2. By turning on output port P#3 and turning off output ports P#1 to P#2 and P#4, wavelength light Wc with center wavelength λc can be guided to output port P#3. By turning on output port P#4 and turning off output ports P#1 to P#3, wavelength light Wd with center wavelength λd can be guided to output port P#4.

[0061] Therefore, in the first embodiment, by utilizing the above-described method of assigning light of a specific center wavelength to any output port P#1 to #4, the control unit 108 realizes control that uniquely determines the relationship between the output port and the wavelength of the signal light without employing an electronic circuit including a cross-connect switch.

[0062] The operation of the control unit 108 according to the first embodiment will be described with reference to FIG.

[0063] First, the control unit 108 instructs the first LD 101, the second LD 102, the third LD 103, the fourth LD 104, the first SW 151, the second SW 152, the third SW 153, the fourth SW 154, the input optical SWs 156 and 157, and the first optical demultiplexer 1 to enter an initial state (step S1). More specifically, the control unit 108 outputs on / off signals to the first LD 101, the second LD 102, the third LD 103, and the fourth LD 104 to stop outputting the wavelength light Wa, Wb, Wc, and Wd. The control unit 108 outputs switching signals to the first SW 151, the second SW 152, the third SW 153, and the fourth SW 154 to switch them to the second waveguide 162 side. The control unit 108 outputs switching signals to the input optical SWs 156 and 157 to input the wavelength-multiplexed signal light Sz. The control unit 108 outputs an ON / OFF signal that instructs the first optical demultiplexer 1 to turn off the output ports P#1 to #4, thereby maintaining the initial state before the start of the receiving operation of the wavelength-multiplexed signal light Sz.

[0064] Next, the control unit 108 outputs a switching signal to the input optical SWs 156 and 157 to input the wavelength light Wa, Wb, Wc, and Wd. The control unit 108 outputs an ON / OFF signal to instruct the output port P#1 to be ON. The control unit 108 outputs a switching signal to the first SW 151 to switch to the first waveguide 161. The control unit 108 outputs an ON / OFF signal to the first LD 101 to output the wavelength light Wa (step S2). As a result, the wavelength light Wa is input to the first optical demultiplexer 1. The wavelength light Wa is also input to the first optical demultiplexer (not shown) of the transceiver 159. Furthermore, since the output port P#1 of the first optical demultiplexer 1 is switched ON, the wavelength light Wa is guided to the output port P#1 (see FIG. 3). In this way, the optical signal with the center wavelength λa can be determined as the initial optical phase to be guided to the output port P#1.

[0065] Next, the control unit 108 outputs an ON / OFF signal instructing to turn off the output port P#1 and turn on the output port P#2. The control unit 108 outputs a switching signal to the first SW 151 to switch to the second waveguide 162 side. The control unit 108 outputs a switching signal to the second SW 152 to switch to the first waveguide 161 side. The control unit 108 outputs an ON / OFF signal to the first LD 101 to stop outputting the wavelength light Wa. The control unit 108 outputs an ON / OFF signal to the second LD 102 to output the wavelength light Wb (step S3). As a result, the input of the wavelength light Wa to the first optical demultiplexer 1 is stopped, and the wavelength light Wb is input to the first optical demultiplexer 1. The wavelength light Wb is also input to the first optical demultiplexer (not shown) of the transceiver unit 159 in the same way. Furthermore, since the output port P#2 of the first optical demultiplexer 1 is switched on, the wavelength light Wb is guided to the output port P#2. In this way, the optical signal with the center wavelength λb can be determined as the initial optical phase to be guided to the output port P#2.

[0066] Next, the control unit 108 outputs an ON / OFF signal instructing the output port P#2 to be turned off and the output port P#3 to be turned on. The control unit 108 outputs a switching signal to the second SW 152 to switch to the second waveguide 162 side. The control unit 108 outputs a switching signal to the third SW 153 to switch to the first waveguide 161 side. The control unit 108 outputs an ON / OFF signal to the second LD 102 to stop outputting the wavelength light Wb. The control unit 108 outputs an ON / OFF signal to the third LD 103 to output the wavelength light Wc (step S4). As a result, the input of the wavelength light Wb to the first optical demultiplexer 1 is stopped, and the wavelength light Wc is input to the first optical demultiplexer 1. The wavelength light Wc is also input to the first optical demultiplexer (not shown) of the transceiver unit 159 in the same way. Furthermore, since the output port P#3 of the first optical demultiplexer 1 is switched on, the wavelength light Wc is guided to the output port P#3. In this way, the optical signal with the center wavelength λc can be determined to have an initial optical phase that is guided to the output port P#3.

[0067] Next, the control unit 108 outputs an ON / OFF signal instructing the output port P#3 to be turned off and the output port P#4 to be turned on. The control unit 108 outputs a switching signal to the third SW 153 to switch to the second waveguide 162 side. The control unit 108 outputs a switching signal to the fourth SW 154 to switch to the first waveguide 161 side. The control unit 108 outputs an ON / OFF signal to the third LD 103 to stop outputting the wavelength light Wc. The control unit 108 outputs an ON / OFF signal to the fourth LD 104 to output the wavelength light Wd (step S5). As a result, the input of the wavelength light Wc to the first optical demultiplexer 1 is stopped, and the wavelength light Wd is input to the first optical demultiplexer 1. The wavelength light Wd is also input to the first optical demultiplexer (not shown) of the transceiver unit 159 in the same way. Furthermore, since the output port P#4 of the first optical demultiplexer 1 is switched on, the wavelength light Wd is guided to the output port P#4. In this way, the optical signal with the center wavelength λd can be determined to have an initial optical phase that is guided to the output port P#4.

[0068] Next, the control unit 108 outputs a switching signal to the input optical SWs 156 and 157 to input the wavelength-multiplexed signal light Sz. The control unit 108 outputs an ON / OFF signal to instruct the output port P#4 to be turned off. The control unit 108 outputs a switching signal to the fourth SW 154 to switch to the second waveguide 162 side. The control unit 108 outputs an ON / OFF signal to instruct the fourth LD 104 to stop outputting the wavelength light Wd (step S6). This stops the input of the wavelength light Wd to the first optical demultiplexer 1. Furthermore, by processing steps S2 to S6, the control unit 108 switches the first LD 101 to the fourth LD 104 on and off in order. This causes the control unit 108 to cause the multi-wavelength light output unit L1 to output the wavelength light Wa, Wb, Wc, and Wd sequentially for each wavelength.

[0069] Next, the control unit 108 outputs an ON / OFF signal instructing all output ports P#1 to P#4 to be ON. The control unit 108 outputs an ON / OFF signal instructing each of the first LD 101 to the fourth LD 104 to output the wavelength light Wa, Wb, Wc, and Wd (step S7), and ends the process. As a result, the wavelength light Wa, Wb, Wc, and Wd are guided to the 90-degree hybrid circuits 7a to 7d as local light. Furthermore, due to the above-mentioned initial optical phase, the signal light Sa with the center wavelength λa is output from the output port P#1, and the signal light Sb with the center wavelength λb is output from the output port P#2.

[0070] Similarly, signal light Sc with center wavelength λc is output from output port P#3, and signal light Sd with center wavelength λc is output from output port P#4. Since 90-degree hybrid circuits 7a to 7d are connected to output ports P#1 to P#4, respectively, signal lights Sa, Sb, Sc, and Sd are guided to the 90-degree hybrid circuits 7a to 7d, respectively. This allows the 90-degree hybrid circuits 7a to 7d to perform coherent detection. Furthermore, wavelength lights Wa, Wb, Wc, and Wd are guided to IQ Modulators 8a to 8d, respectively, as transmission lights with center wavelengths λa, λb, λc, and λd. This allows the IQ Modulators 8a to 8d to perform optical modulation.

[0071] As described above, according to the first embodiment, even without employing an electronic circuit including a cross-connect switch, it is possible to uniquely determine the correspondence between the output ports P#1 to P#4 and the wavelengths λa, λb, λc, and λd of the signal lights Sa, Sb, Sc, and Sd through control by the control unit 108. In particular, it is possible to determine such correspondence in the optical transceiver TR1 employing the first optical demultiplexer 1 with one input port. Furthermore, because an electronic circuit including a cross-connect switch is not employed, it is also possible to suppress increases in circuit size and power consumption.

[0072] (Second embodiment) The second embodiment of the present invention will be described with reference to Figures 5 to 7. In Figure 5, the same or corresponding reference numerals are used for the components common to Figure 1, and detailed description thereof will be omitted.

[0073] As shown in Fig. 5, the optical transceiver TR2 includes a first LD 201, a second LD 202, a third LD 203, and a fourth LD 204. The first LD 201 to the fourth LD 204 output wavelength light Wa, Wb, Wc, and Wd having center wavelengths λa to λd spaced at regular wavelength intervals, respectively. The optical transceiver TR2 also includes a PIC 205, optical amplifiers 206, 207, 240, and 241, a control unit 208, and an optical multiplexer 209. The first LD 201, the second LD 202, the third LD 203, the fourth LD 204, the optical multiplexer 209, and the optical amplifier 240 are included in a light source circuit 200 that is independent of the PIC 205. The light source circuit 200 and the optical amplifier 241 are included in a multi-wavelength light output unit L2.

[0074] The optical multiplexer 209 is an example of a multiplexing circuit and includes, for example, an optical combiner. The optical amplifier 240 includes, for example, an SOA (Semiconductor Optical Amplifier). The optical amplifier 241 includes, for example, an EDFA. Each of the optical amplifiers 240 and 241 amplifies one of the wavelength light Wa, Wb, Wc, and Wd or the wavelength-multiplexed wavelength light Wz obtained by multiplexing the wavelength light Wa, Wb, Wc, and Wd. When the optical multiplexer 209 includes an optical combiner, the power of the wavelength light Wa, Wb, Wc, and Wd is reduced by the optical combiner (specifically, by one-fourth depending on the number of wavelengths), but this reduction is compensated for by the optical amplifiers 240 and 241. In particular, by employing the optical amplifier 241, the power of the wavelength-multiplexed wavelength light Wz input to the PIC 205 can be increased compared to when the wavelength light Wa, Wb, Wc, and Wd are input to the PIC 205 using the first through fourth LDs 201 through 204 individually. Furthermore, since the power of the wavelength-multiplexed light Wz can be collectively amplified by one optical amplifier 241, it becomes easier to provide the optical amplifier 241 in the optical transceiver TR2. In other words, since there is one optical amplifier 241, the circuit scale of the optical transceiver TR2 can be reduced, and power consumption can also be reduced.

[0075] The optical multiplexer 209 has four input terminals and one output terminal. The four input terminals of the optical multiplexer 209 are optically connected to the first LD 201, the second LD 202, the third LD 203, and the fourth LD 204, respectively. The output terminal of the optical multiplexer 209 is optically connected to the optical amplifier 240.

[0076] The PIC 205 includes transceivers 258 and 259. Each of the transceivers 258 and 259 has two input terminals and one output terminal. The output terminal of the optical amplifier 241 is connected to one of the input terminals of the transceiver 258. The output terminal of the optical amplifier 206 is connected to the other of the input terminals of the transceiver 258. That is, both the wavelength-multiplexed wavelength light Wz obtained by multiplexing the wavelength lights Wa, Wb, Wc, and Wd and the wavelength-multiplexed signal light Sz are input to the transceiver 258. The transceiver 259 is basically the same as the transceiver 258, and therefore a detailed description thereof will be omitted. Furthermore, as in the first embodiment, the optical transceiver TR2 can also be configured as an optical receiving device by excluding the IQ Modulators 8a to 8d, the optical multiplexer 9, and the DAC from the transceiver 258. The same applies to the third embodiment described below.

[0077] The transmitting / receiving unit 258 includes a second optical demultiplexer 2, 90-degree hybrid circuits 7a to 7d, BPDs 6ai to 6di, 6aq to 6dq, IQ Modulators 8a to 8d, and an optical multiplexer 9. Although not shown, the transmitting / receiving unit 258 includes a DSP, an ADC, a DAC, etc., similar to the first embodiment.

[0078] The second optical demultiplexer 2 has two input ports and eight output ports. One of the input ports of the second optical demultiplexer 2 is connected to one of the input ends of the transceiver 158. The other input port of the second optical demultiplexer 2 is connected to the other input end of the transceiver 158. The second optical demultiplexer 2 demultiplexes the X polarization component of the wavelength-multiplexed wavelength light Wz into wavelength light Wa of wavelength λa, wavelength light Wb of wavelength λb, wavelength light Wc of wavelength λc, and wavelength light Wd of wavelength λd. The second optical demultiplexer 2 also demultiplexes the X polarization component of the wavelength-multiplexed signal light Sz into signal light Sa of wavelength λa, signal light Sb of wavelength λb, signal light Sc of wavelength λc, and signal light Sd of wavelength λd.

[0079] The 90-degree hybrid circuits 7a to 7d are connected to the eight output ports of the second optical demultiplexer 2. Four of the eight output ports output the wavelength light Wa, Wb, Wc, and Wd, respectively, and the remaining four of the eight output ports output the signal light Sa, Sb, Sc, and Sd, respectively. For example, the 90-degree hybrid circuit 7a is connected to output port P#1, which includes an output port that outputs the wavelength light Wa and an output port that outputs the signal light Sa. The 90-degree hybrid circuits 7b to 7d are basically the same as the 90-degree hybrid circuit 7a.

[0080] The output ports for outputting the wavelength light Wa, Wb, Wc, and Wd are also connected to the IQ Modulators 8a to 8d. That is, the output ports for outputting the wavelength light Wa, Wb, Wc, and Wd are connected to the input ends of a waveguide 263 that includes one input end and two output ends. One of the output ends of the waveguide 263 is connected to each of the 90-degree hybrid circuits 7a to 7d, and the other output end is connected to each of the IQ Modulators 8a to 8d.

[0081] The control unit 208 controls the operations of the first LD 201, the second LD 202, the third LD 203, the fourth LD 204, and the second optical demultiplexer 2. For example, the control unit 208 outputs on / off signals to the first LD 201, the second LD 202, the third LD 203, the fourth LD 204, and the second optical demultiplexer 2 to control the operations of the first LD 201, the second LD 202, the third LD 203, the fourth LD 204, and the second optical demultiplexer 2. For example, in the case of the second optical demultiplexer 2, the on / off signal is a signal that switches the output port on and off. Note that the on / off of the output port will be described in detail later.

[0082] The second optical demultiplexer 2 will be described in detail with reference to Fig. 6 and Fig. 7. In Fig. 6, components common to those in Fig. 2 are given the same or corresponding reference numerals, and detailed descriptions thereof will be omitted. In Fig. 7, components common to those in Fig. 6 are given the same reference numerals, and detailed descriptions thereof will be omitted.

[0083] The second optical demultiplexer 2 has a front-stage demultiplexing circuit 21 and back-stage demultiplexing circuits 22 and 23 optically connected to the rear of the front-stage demultiplexing circuit 21. As an example, the second optical demultiplexer 2 demultiplexes signal light Sa, Sb, Sc, and Sd having center wavelengths λa to λd spaced at regular wavelength intervals from wavelength-multiplexed signal light Sz having four wavelengths λa to λd. Also, the second optical demultiplexer 2 demultiplexes wavelength light Wa, Wb, Wc, and Wd having center wavelengths λa to λd spaced at regular wavelength intervals from wavelength-multiplexed wavelength light Wx having four wavelengths λa to λd. The second optical demultiplexer 2 performs demultiplexing processing using each of the front-stage demultiplexing circuit 21 and back-stage demultiplexing circuits 22 and 23 as a unit.

[0084] The second optical demultiplexer 2 has AMZs 2a to 2i connected in multiple stages in a tree configuration. The pre-stage demultiplexing circuit 21 has AMZs 2a to 2c, the post-stage demultiplexing circuit 22 has AMZs 2d to 2f, and the post-stage demultiplexing circuit 23 has AMZs 2g to 2i. In other words, the second optical demultiplexer 2 corresponds to an AMZ-type optical demultiplexer. The AMZs 2a to 2i are connected in multiple stages in a tree configuration. That is, AMZs 2b and 2c are optically connected to the rear of AMZ 2a, AMZs 2d and 2g are optically connected to the rear of AMZ 2b, and AMZs 2d and 2g are optically connected to the rear of AMZ 2c.

[0085] AMZ2e and 2f are optically connected downstream of AMZ2d, and a 90-degree hybrid circuit 7a is optically connected downstream of AMZ2e via output ports P#1 and P#5. A 90-degree hybrid circuit 7b is optically connected downstream of AMZ2f via output ports P#2 and P#6. AMZ2h and 2i are optically connected downstream of AMZ2g, and a 90-degree hybrid circuit 7c is optically connected downstream of AMZ2h via output ports P#3 and P#7. A 90-degree hybrid circuit 7d is optically connected downstream of AMZ2i via output ports P#4 and P#8. One input port of the input coupler Ca of AMZ2b, 2c, 2e, 2f, 2h, and 2i is open.

[0086] The wavelength intervals of the transmission bands of the AMZs 2a to 2i are determined according to the arm length differences, more specifically, the wavelength intervals of the transmission bands of the AMZs 2a to 2i are substantially inversely proportional to the arm length differences.

[0087] The arm length difference between the AMZs 1a to 2c of the pre-demultiplexing circuit 21 is set so that the wavelength interval in the transmission band is the interval Δλ between the center wavelengths λa to λd. Therefore, the pre-demultiplexing circuit 21 transmits and demultiplexes the wavelength-multiplexed signal light Sz and the wavelength-multiplexed wavelength light Wz in the transmission band with the interval Δλ.

[0088] The arm length difference between the AMZs 2d to 2i is set so that the wavelength spacing in the transmission band is twice the central wavelength spacing Δλ (2×Δλ). Therefore, the post-stage demultiplexing circuit 22 transmits and demultiplexes the wavelength-multiplexed signal light Sbd and the wavelength-multiplexed wavelength light Wbd in the transmission band with the spacing Δλ. The post-stage demultiplexing circuit 23 transmits and demultiplexes the wavelength-multiplexed signal light Sac and the wavelength-multiplexed wavelength light Wac in the transmission band with the spacing Δλ.

[0089] Waveguides 210 and 211 extending from one output port of the output coupler Cb of AMZs 2b and 2c intersect at intersection x1 and are connected to one input port of the input coupler Ca of the subsequent AMZs 2g and 2d, respectively. Waveguides 220 and 221 extending from one output port of the output coupler Cb of AMZs 2e and 2f intersect at intersection x2 and are connected to the subsequent 90-degree hybrid circuits 7b and 7a via output ports P#2 and P#1, respectively. Waveguides 230 and 231 extending from one output port of the output coupler Cb of AMZs 2h and 2i intersect at intersection x3 and are connected to the subsequent 90-degree hybrid circuits 7d and 7c via output ports P#4 and P#3.

[0090] In this way, the front-stage demultiplexing circuit 21 and the rear-stage demultiplexing circuits 22, 23 cross their waveguides at crosspoints x1 to x3, so that pairs of signal light Sa to Sd and wavelength light Wa to Wd with matching center wavelengths are input to the 90-degree hybrid circuits 7a to 7d, respectively. For example, a pair of signal light Sd and wavelength light Wd with matching center wavelengths is input to the 90-degree hybrid circuit 7a. The 90-degree hybrid circuits 7b to 7d are basically the same as the 90-degree hybrid circuit 7a.

[0091] Furthermore, the second optical demultiplexer 2 includes monitor circuits Mon#1-#12 that monitor the power of the output light, compensation circuits Dec#1-#3 that decrease the power in accordance with the monitoring results of the output light power, and compensation circuits Inc#1-#6 that increase the power in accordance with the monitoring results of the output light power in order to control the phase shifters Hu and Hd of the AMZs 2a-2i. The compensation circuits Dec#1-#3 and Inc#1-#6 are examples of adjusters. The monitor circuits Mon#1-#12 are realized by, for example, a PD, and the compensation circuits Dec#1-#3 and Inc#1-#6 are realized by, for example, an FPGA or an ASIC.

[0092] Monitor circuits Mon#1 to #4 and compensation circuits Dec#1, Inc#1, #2 are provided in the pre-stage demultiplexing circuit 21. Monitor circuits Mon#1, #2 are optically connected to a pair of output ports of output coupler Cb of AMZ2b via branching coupler CP, respectively. Monitor circuit Mon#1 monitors the power of wavelength-multiplexed signal light Sbd output from AMZ2b to AMZ2d. Monitor circuit Mon#1 notifies compensation circuit Dec#1 of the power result of the monitoring. Monitor circuit Mon#2 monitors the power of wavelength-multiplexed wavelength light Wac output from AMZ2b to AMZ2g. Monitor circuit Mon#2 notifies compensation circuit Inc#1 of the power result of the monitoring.

[0093] The monitor circuits Mon#3 and #4 are optically connected to a pair of output ports of the output coupler Cb of AMZ2c via a branching coupler CP. The monitor circuit Mon#3 monitors the power of the wavelength-multiplexed wavelength light Wbd output from AMZ2c to AMZ2d. The monitor circuit Mon#3 notifies the compensation circuit Inc#2 of the power result of the monitoring. The monitor circuit Mon#4 monitors the power of the wavelength-multiplexed signal light Sac output from AMZ2c to AMZ2g. The monitor circuit Mon#4 notifies the compensation circuit Dec#1 of the power result of the monitoring.

[0094] Compensation circuit Dec#1 controls the amount of optical phase adjustment for phase shifters Hu, Hd of AMZ2a in accordance with the results of monitoring wavelength-multiplexed signal light Sbd, Sac by monitor circuits Mon#1, #4. Compensation circuit Inc#1 controls the amount of optical phase adjustment for phase shifters Hu, Hd of AMZ2b in accordance with the results of monitoring wavelength-multiplexed wavelength light Wac by monitor circuit Mon#2. Compensation circuit Inc#2 controls the amount of optical phase adjustment for phase shifters Hu, Hd of AMZ2c in accordance with the results of monitoring wavelength-multiplexed wavelength light Wbd by monitor circuit Mon#3.

[0095] The monitor circuit Mon#1 is an example of a first monitor that monitors the power of the wavelength-multiplexed signal light Sbd output from AMZ2b to AMZ2d, the monitor circuit Mon#4 is an example of a second monitor that monitors the power of the wavelength-multiplexed signal light Sac output from AMZ2c to AMZ2g, the monitor circuit Mon#2 is an example of a third monitor that monitors the power of the wavelength-multiplexed wavelength light Wac output from AMZ2b to AMZ2g, and the monitor circuit Mon#3 is an example of a fourth monitor that monitors the power of the wavelength-multiplexed wavelength light Wbd output from AMZ2c to AMZ2d.

[0096] The monitor circuits Mon#5-#8 and the compensation circuits Dec#2, Inc#3, #4 are provided in the post-stage demultiplexing circuit 22. The monitor circuits Mon#5, #6 are optically connected to a pair of output ports of the output coupler Cb of the AMZ2e via a branching coupler CP. The monitor circuit Mon#5 monitors the power of the signal light Sd output from the AMZ2e to the 90-degree hybrid circuit 7a. The monitor circuit Mon#5 notifies the compensation circuit Dec#2 of the power result. The monitor circuit Mon#6 monitors the power of the wavelength light Wb output from the AMZ2e to the 90-degree hybrid circuit 7b. The monitor circuit Mon#6 notifies the compensation circuit Inc#3 of the power result.

[0097] The monitor circuits Mon#7 and #8 are optically connected to a pair of output ports of the output coupler Cb of the AMZ2f via a branch coupler CP. The monitor circuit Mon#7 monitors the power of the wavelength light Wd output from the AMZ2f to the 90-degree hybrid circuit 7a. The monitor circuit Mon#7 notifies the compensation circuit Inc#4 of the power result. The monitor circuit Mon#8 monitors the power of the signal light Sb output from the AMZ2f to the 90-degree hybrid circuit 7b. The monitor circuit Mon#8 notifies the compensation circuit Dec#2 of the power result.

[0098] Compensation circuit Dec#2 controls the amount of optical phase adjustment for phase shifters Hu and Hd of AMZ2d in accordance with the monitoring results of monitor circuits Mon#5 and Mon#8. Compensation circuit Inc#3 controls the amount of optical phase adjustment for phase shifters Hu and Hd of AMZ2e in accordance with the monitoring results of monitor circuit Mon#6. Compensation circuit Inc#4 controls the amount of optical phase adjustment for phase shifters Hu and Hd of AMZ2f in accordance with the monitoring results of monitor circuit Mon#7.

[0099] The monitor circuits Mon#9 to #12 and the compensation circuits Dec#3, Inc#5, #6 are provided in the post-stage demultiplexing circuit 23. The monitor circuits Mon#9, #10 are optically connected to a pair of output ports of the output coupler Cb of the AMZ2h via a branching coupler CP, respectively. The monitor circuit Mon#9 monitors the power of the signal light Sc output from the AMZ2h to the 90-degree hybrid circuit 7c. The monitor circuit Mon#9 notifies the compensation circuit Dec#3 of the power of the monitoring result. The monitor circuit Mon#10 monitors the power of the wavelength light Wa output from the AMZ2h to the 90-degree hybrid circuit 7d. The monitor circuit Mon#10 notifies the compensation circuit Inc#5 of the power of the monitoring result.

[0100] The monitor circuits Mon#11 and #12 are optically connected to a pair of output ports of the output coupler Cb of the AMZ2i via a branch coupler CP. The monitor circuit Mon#11 monitors the power of the wavelength light Wc output from the AMZ2i to the 90-degree hybrid circuit 7c. The monitor circuit Mon#11 notifies the compensation circuit Inc#6 of the power result. The monitor circuit Mon#12 monitors the power of the signal light Sa output from the AMZ2i to the 90-degree hybrid circuit 7d. The monitor circuit Mon#12 notifies the compensation circuit Dec#3 of the power result.

[0101] Compensation circuit Dec#3 controls the amount of optical phase adjustment for phase shifters Hu and Hd of AMZ2g in accordance with the monitoring results of monitor circuits Mon#9 and #12. Compensation circuit Inc#5 controls the amount of optical phase adjustment for phase shifters Hu and Hd of AMZ2h in accordance with the monitoring results of monitor circuit Mon#10. Compensation circuit Inc#6 controls the amount of optical phase adjustment for phase shifters Hu and Hd of AMZ2i in accordance with the monitoring results of monitor circuit Mon#11.

[0102] As a result, the front-stage demultiplexing circuit 21 and the rear-stage demultiplexing circuits 22 and 23 can demultiplex the wavelength-multiplexed signal light Sz and the wavelength-multiplexed wavelength light Wz with appropriate power, respectively.

[0103] Here, as shown in Figure 7, it is also possible to input wavelength light of a specific center wavelength from the center wavelengths λa to λd into the second optical demultiplexer 2 and assign the light of the specific center wavelength to any of the output ports P#1 to #4 by operating only the compensation circuits Dec#1 to #3 and Inc#1 to #6 on the path from the input port Pinw to any of the output ports P#1 to #4.

[0104] As an example, consider a technique of assigning output port P#1 to wavelength light Wa with a center wavelength λa. Of the wavelengths λa to λd, only wavelength light Wa with a center wavelength λa is input to input port Pinw. To ensure that wavelength light Wa with a center wavelength λa is output from output port P#1, compensation circuits Dec#1, #2, Inc#2, and #4 on path K connecting input port Pinw and output port P#1 are operated under the control of the control unit 208, while other compensation circuits Dec#3, Inc#1, #3, #5, and #6 are stopped under the control of the control unit 208. Furthermore, to prevent the monitoring results of monitor circuits Mon#4 and #5 on portions other than path K from affecting the control of compensation circuits Dec#1 and #2, the connection between them is cut off under the control of the control unit 208. In the second embodiment, such operation, stop of operation, and disconnection controlled by the control unit 208 are defined as turning on output port P#1 and turning off output ports P#2 to P#4.

[0105] By controlling the optical phase along path K in this way, it is possible to intentionally guide wavelength light Wa with center wavelength λa to output port P#1. Furthermore, by controlling the optical phase of each of the other wavelength lights Wb, Wc, and Wd with center wavelengths λb to λd in the same manner as above, it is possible to assign them to any of output ports P#2 to P#4. That is, by turning on output port P#2 and turning off output ports P#1, P#3 to P#4, wavelength light Wb with center wavelength λb can be guided to output port P#2. By turning on output port P#3 and turning off output ports P#1 to P#2 and P#4, wavelength light Wc with center wavelength λc can be guided to output port P#3. By turning on output port P#4 and turning off output ports P#1 to P#3, wavelength light Wd with center wavelength λd can be guided to output port P#4.

[0106] Therefore, in the second embodiment, by utilizing the above-mentioned method of assigning light of a specific center wavelength to any output port P#1 to #4, the control unit 208 realizes control to uniquely determine the relationship between the output port and the wavelength of the signal light without employing an electronic circuit including a cross-connect switch.

[0107] The operation of the control unit 208 according to the second embodiment will be described with reference to FIG.

[0108] First, the control unit 208 instructs the first LD 201, the second LD 202, the third LD 203, the fourth LD 204, and the second optical demultiplexer 2 to enter an initial state (step S11). More specifically, the control unit 208 outputs an ON / OFF signal to the first LD 201, the second LD 202, the third LD 203, and the fourth LD 204 to stop outputting the wavelength light Wa, Wb, Wc, and Wd. The control unit 208 outputs an ON / OFF signal to the second optical demultiplexer 2 to turn off the output ports P#1 to P#4. This maintains the initial state before the start of the receiving operation of the wavelength multiplexed signal light Sz.

[0109] Next, the control unit 208 outputs an ON / OFF signal to instruct the output port P#1 to be ON. The control unit 208 outputs an ON / OFF signal to instruct the first LD 201 to output the wavelength light Wa (step S12). As a result, the wavelength light Wa is input to the second optical demultiplexer 2. The wavelength light Wa is also input to the second optical demultiplexer (not shown) of the transceiver 259. Furthermore, because the output port P#1 of the second optical demultiplexer 2 is switched ON, the wavelength light Wa is guided to the output port P#1 (see FIG. 7). In this way, the optical signal with the center wavelength λa can be determined to have an initial optical phase to be guided to the output port P#1.

[0110] Next, the control unit 208 outputs an ON / OFF signal instructing the output port P#1 to be turned off and the output port P#2 to be turned on. The control unit 208 outputs an ON / OFF signal instructing the first LD 201 to stop outputting the wavelength light Wa. The control unit 208 outputs an ON / OFF signal instructing the second LD 202 to output the wavelength light Wb (step S13). As a result, the input of the wavelength light Wa to the second optical demultiplexer 2 is stopped, and the wavelength light Wb is input to the second optical demultiplexer 2. The wavelength light Wb is also input to the second optical demultiplexer (not shown) of the transceiver 259. Furthermore, because the output port P#2 of the second optical demultiplexer 2 is switched on, the wavelength light Wb is guided to the output port P#2. In this way, the optical signal with the center wavelength λb can be determined to have an initial optical phase to be guided to the output port P#2.

[0111] Next, the control unit 208 outputs an ON / OFF signal instructing the output port P#2 to be turned off and the output port P#3 to be turned on. The control unit 208 outputs an ON / OFF signal instructing the second LD 202 to stop outputting the wavelength light Wb. The control unit 208 outputs an ON / OFF signal instructing the third LD 203 to output the wavelength light Wc (step S14). As a result, the input of the wavelength light Wb to the second optical demultiplexer 2 is stopped, and the wavelength light Wc is input to the second optical demultiplexer 2. The wavelength light Wc is also input to the second optical demultiplexer (not shown) of the transceiver 259. Furthermore, because the output port P#3 of the second optical demultiplexer 2 is switched on, the wavelength light Wc is guided to the output port P#3. In this way, the optical signal with the center wavelength λc can be determined to have an initial optical phase to be guided to the output port P#3.

[0112] Next, the control unit 208 outputs an ON / OFF signal instructing the output port P#3 to be turned off and the output port P#4 to be turned on. The control unit 208 outputs an ON / OFF signal instructing the third LD 203 to stop outputting the wavelength light Wc. The control unit 208 outputs an ON / OFF signal instructing the fourth LD 204 to output the wavelength light Wd (step S15). As a result, the input of the wavelength light Wc to the second optical demultiplexer 2 is stopped, and the wavelength light Wd is input to the second optical demultiplexer 2. The wavelength light Wd is also input to the second optical demultiplexer (not shown) of the transceiver 259. Furthermore, because the output port P#4 of the second optical demultiplexer 2 is switched on, the wavelength light Wd is guided to the output port P#4. In this way, the optical signal with the center wavelength λd can be determined to have an initial optical phase to be guided to the output port P#4. Furthermore, by the processing of steps S12 to S15, the control unit 208 sequentially switches on and off the first LD 201 to the fourth LD 204. As a result, the control unit 208 causes the multi-wavelength light output unit L2 to sequentially output the wavelength light Wa, Wb, Wc, and Wd for each wavelength.

[0113] Next, the control unit 208 outputs an ON / OFF signal instructing all output ports P#1 to P#4 to be ON. The control unit 208 outputs an ON / OFF signal instructing each of the first LD 201 to the fourth LD 204 to output the wavelength light Wa, Wb, Wc, and Wd (step S16), and ends the process. As a result, the wavelength light Wd, Wc, Wb, and Wa are guided to the 90-degree hybrid circuits 7a to 7d, respectively, as local light. Furthermore, due to the above-mentioned initial optical phase, the signal light Sa with center wavelength λa is output from output port P#8, and the signal light Sb with center wavelength λb is output from output port P#6.

[0114] Similarly, signal light Sc with center wavelength λc is output from output port P#7, and signal light Sd with center wavelength λc is output from output port P#5. Since 90-degree hybrid circuits 7a to 7d are connected to output ports P#5 to P#8, respectively, signal lights Sa, Sb, Sc, and Sd are guided to the 90-degree hybrid circuits 7a to 7d, respectively. This allows the 90-degree hybrid circuits 7a to 7d to perform coherent detection. Furthermore, wavelength lights Wa, Wb, Wc, and Wd are guided to IQ Modulators 8a to 8d, respectively, as transmission lights with center wavelengths λa, λb, λc, and λd. This allows the IQ Modulators 8a to 8d to perform optical modulation.

[0115] As described above, according to the second embodiment, even without employing an electronic circuit including a cross-connect switch, it is possible to uniquely determine the correspondence between the output ports P#1 to P#4 and the wavelengths λa, λb, λc, and λd of the signal lights Sa, Sb, Sc, and Sd through control by the control unit 208. Furthermore, since the second embodiment also does not employ an electronic circuit including a cross-connect switch, it is possible to suppress increases in circuit size and power consumption. In particular, it is sufficient to employ a single optical amplifier 241 to collectively amplify the power of the wavelength-multiplexed wavelength light Wz input to the PIC 205, and it is possible to reduce the circuit size of the optical transceiver TR2.

[0116] (Third embodiment) A third embodiment of the present invention will be described with reference to Fig. 9. In Fig. 9, components common to those in Fig. 5 are denoted by the same or corresponding reference numerals, and detailed descriptions thereof will be omitted. Furthermore, the operation of the control unit 308 according to the third embodiment is basically the same as the operation of the control unit 208 according to the second embodiment, and therefore detailed descriptions thereof will be omitted.

[0117] As shown in FIG. 9, the optical transceiver TR3 includes a first LD 301, a second LD 302, a third LD 303, and a fourth LD 304. The first LD 301 to the fourth LD 304 output wavelength light Wa, Wb, Wc, and Wd having center wavelengths λa to λd spaced at regular wavelength intervals, respectively. The optical transceiver TR3 also includes a PIC 305, optical amplifiers 306 and 307, and a control unit 308. In the third embodiment, the PIC 305 includes an optical multiplexer 351. The optical multiplexer 351 is an example of a multiplexing circuit and includes, for example, a WDM (Wavelength Division Multiplexing) coupler. The optical multiplexer 351 is directly connected to the second optical demultiplexer 2. The first LD 301, the second LD 302, the third LD 303, the fourth LD 304, and the optical multiplexer 351 are included in the multi-wavelength light output unit L3.

[0118] As described above, according to the third embodiment, even without employing an electronic circuit including a cross-connect switch, the correspondence between the output ports P#1 to P#4 and the wavelengths λa, λb, λc, and λd of the signal lights Sa, Sb, Sc, and Sd can be uniquely determined by the control of the control unit 308. Furthermore, since the third embodiment also does not employ an electronic circuit including a cross-connect switch, increases in circuit size and power consumption can be suppressed. In particular, when the optical multiplexer 351 includes a WDM coupler, the power of the wavelength lights Wa, Wb, Wc, and Wd is not reduced as much as when an optical combiner is employed.

[0119] (Fourth embodiment) The fourth embodiment of the present invention will be described with reference to Figures 10 to 15. In Figure 10, the same or corresponding reference numerals are used for the components common to Figure 5, and detailed description thereof will be omitted.

[0120] 10, the optical transceiver TR4 includes an optical frequency comb generator (hereinafter referred to as comb light source) 400. The comb light source 400 outputs an optical frequency comb (hereinafter referred to as optical comb) Oc, in which center wavelengths λa to λh are arranged at equal wavelength intervals. The optical transceiver TR4 also includes a PIC 405, optical amplifiers 406 and 407, and a control unit 408. Unlike the first LD 101 described in the first to third embodiments, the comb light source 400 cannot switch operation for each wavelength.

[0121] The PIC405 includes a first optical comb SW 451, a second optical comb SW 452, transmitters / receivers 458 and 459, eight ATTs (attenuators) 461 to 468, a monitor 470, a first optical demultiplexer 1, and an optical multiplexer 9A. The first optical comb SW 451 has one input terminal and two output terminals. The second optical comb SW 452 has two input terminals and one output terminal. The transmitters / receivers 458 and 459 each have two input terminals and one output terminal. The input terminal of the first optical comb SW 451 is connected to the optical comb light source 400. One of the output terminals of the first optical comb SW 451 is connected to one of the input terminals of the second optical comb SW 452 via a first waveguide 481. The other output terminal of the first optical comb SW 451 is connected to the input port of the first optical demultiplexer 1 via a second waveguide 482.

[0122] Therefore, the optical comb Oc is input to either the second optical comb SW 452 or the first optical demultiplexer 1. When the optical comb Oc is input to the first optical demultiplexer 1, wavelength light Wa with center wavelength λa, wavelength light Wb with center wavelength λb, ..., wavelength light Wh with center wavelength λh are randomly output from the eight output ports of the first optical demultiplexer 1. The other input end of the second optical comb SW 452 is connected to the output port of the optical multiplexer 9A via the third waveguide 483.

[0123] Eight ATTs 461 to 468 are arranged between the first optical demultiplexer 1 and the optical multiplexer 9A. The input terminals of the ATTs 461 to 468 are connected to eight output ports of the first optical demultiplexer 1. Therefore, wavelength light Wa, wavelength light Wb, ..., wavelength light Wh are input to the ATTs 461 to 468. The output terminals of the ATTs 461 to 468 are connected to input ports of the optical multiplexer 9A. Therefore, wavelength light Wa, wavelength light Wb, ..., wavelength light Wh are input to the optical multiplexer 9A.

[0124] The ATTs 461-468 switch between transmitting and blocking the wavelength light Wa, wavelength light Wb, ..., and wavelength light Wh based on an on / off signal output from the control unit 408. For example, when the control unit 408 outputs an on / off signal instructing the ATTs 461-468 to turn on, the ATTs 461-468 transmit the wavelength light Wa, wavelength light Wb, ..., and wavelength light Wh. When the control unit 408 outputs an on / off signal instructing the ATTs 461-468 to turn off, the ATTs 461-468 block the wavelength light Wa, wavelength light Wb, ..., and wavelength light Wh. In other words, the ATTs 461-468 correspond to on / off switches. One output end of the optical multiplexer 9A is connected to the monitor 470. In other words, the waveguide connecting the optical multiplexer 9A and the second optical comb SW 452 branches midway.

[0125] The output end of the second optical comb SW 452 is connected to one of the input ends of the transceiver 458. The output end of the optical amplifier 406 is connected to the other of the input ends of the transceiver 458. That is, the transceiver 458 receives both the wavelength-multiplexed wavelength light Wz obtained by multiplexing wavelength light Wa, wavelength light Wb, . . . , wavelength light Wh, and the wavelength-multiplexed signal light Sz.

[0126] The transceiver unit 459 is basically the same as the transceiver unit 458, and therefore a detailed description thereof will be omitted. As in the first embodiment, the optical transceiver TR4 can also be configured as an optical receiving device by excluding the IQ Modulators 8a-8h, the optical multiplexer 9, and the DAC from the transceiver unit 458. The comb light source 400, the first optical comb SW 451, the second optical comb SW 452, the first optical demultiplexer 1, the optical multiplexer 9A, the ATTs 461-468, and the monitor 470 are included in the multi-wavelength optical output unit L4.

[0127] 11, the monitor 470 includes PDs 471 and 472, a BPF (Band Pass Filter) 473, an electric power detection circuit 474, and an HPF (High Pass Filter) 475. Instead of the HPF 475, an LPF (Low Pass Filter) may be used.

[0128] The PD 471 detects the power of the wavelength-multiplexed light Wz at point (A) in Fig. 11. For example, when the optical comb Oc is output with the control unit 408 turning on any two of the ATTs 461 to 468, the PD 471 may detect power with a small frequency difference or may detect power with a large frequency difference, as shown in Fig. 12(A).

[0129] The BPF 473 uses the frequency of the power on the low frequency side of the power of the electrical signal at point (B) in Figure 11 corresponding to the wavelength-multiplexed wavelength light Wz as a reference frequency, and passes a specific frequency of power that is away from the reference frequency on the high frequency side by an amount equivalent to the adjacent channel. For example, as shown in Figure 12(B), if a specific frequency of power P1 that is away from the reference frequency "0" is included in the passband (transmission band) PB, the BPF 473 passes the specific frequency of power P1. If a specific frequency of power P2 that is away from the reference frequency "0" is not included in the passband (transmission band) PB, the BPF 473 blocks the specific frequency of power P2.

[0130] The electrical power detection circuit 474 detects the power of the electrical signal at point (C) in Fig. 11. If a specific frequency of power P1 is transmitted, the power detected by the electrical power detection circuit 474 will be positive, as shown in Fig. 12(C). This allows the control unit 408 to detect that the wavelengths of the light beams output from any two of the ATTs 461 to 468 that are turned on correspond to adjacent channels. On the other hand, if a specific frequency of power P2 is not transmitted, the power detected by the electrical power detection circuit 474 will be 0 (zero). This allows the control unit 408 to detect that the wavelengths of the light beams output from any two of the ATTs 461 to 468 that are turned on correspond to non-adjacent channels. The electrical power detection circuit 474 outputs the detection result to the control unit 408.

[0131] The HPF 475 outputs high frequency power by removing the low frequency power of the light having the longest wavelength output from any one of the ATTs 461 to 468. The HPF 475 outputs high frequency power by removing the low frequency power of the light having the shortest wavelength output from another one of the ATTs 461 to 468. The PD 472 compares the two high frequency powers output from the HPF 475, determines which wavelength is larger or smaller, and outputs the determination result to the control unit 408.

[0132] The operation of the control unit 408 according to the fourth embodiment will be described with reference to FIGS.

[0133] 13, the control unit 408 instructs the optical frequency comb source 400, the first optical frequency comb switch 451, the second optical frequency comb switch 452, the ATTs 461 to 468, the first optical demultiplexer 1, and the second optical demultiplexer 2 to enter an initial state (step S21). More specifically, the control unit 408 outputs an ON / OFF signal to the optical frequency comb source 400 to instruct it to stop outputting the optical frequency comb Oc. The control unit 408 outputs a switching signal to the first optical frequency comb switch 451 and the second optical frequency comb switch 452 to switch them to the first waveguide 481 side. The control unit 408 outputs an ON / OFF signal to the ATTs 461 to 468 to instruct them to turn off. The control unit 408 outputs an ON / OFF signal to the first optical demultiplexer 1 and the second optical demultiplexer 2 to instruct them to turn off the output ports P#1 to P#4. This maintains the initial state before the start of the receiving operation of the wavelength-multiplexed signal light Sz.

[0134] Next, the control unit 408 switches the first optical comb SW 451 to the second waveguide 482 side (step S22) and turns on the optical comb light source 400 (step S23). Specifically, the control unit 408 outputs a switching signal to the first optical comb SW 451 to switch to the second waveguide 482 side. After outputting the switching signal, the control unit 408 outputs an on / off signal to the optical comb light source 400 to instruct it to output the optical comb Oc. As a result, the optical comb Oc is input to the first optical demultiplexer 1.

[0135] Next, the control unit 408 executes a correspondence relationship specifying process (step S24). The correspondence relationship specifying process is a process for specifying the correspondence relationships between the eight output ports of the first optical demultiplexer 1 and the wavelengths λa to λh.

[0136] Here, the correspondence relationship identifying process will be described in detail with reference to Fig. 14 etc. When the control unit 408 starts the correspondence relationship identifying process, first, it distinguishes between adjacent channels and non-adjacent channels (step S41). For example, the control unit 408 outputs an ON / OFF signal to the ATTs 461 and 462 to instruct them to turn on. As a result, wavelength light of any two arbitrary wavelengths possessed by the optical comb Oc is output from the ATTs 461 and 462 and input to the optical multiplexer 9A, and wavelength-multiplexed wavelength light Wz obtained by multiplexing the two wavelengths is input to the PD 471.

[0137] Based on this wavelength-multiplexed wavelength light Wz, the control unit 408 determines whether the two wavelengths or frequencies of this wavelength-multiplexed wavelength light Wz correspond to adjacent channels or non-adjacent channels, as shown in Figures 12(A) to 12(C). If the two wavelengths or frequencies correspond to adjacent channels, the control unit 408 registers a step ID "S1-1", ATT#1 "ON" that identifies ATT461, ATT#2 "ON" that identifies ATT462, and the adjacent channel "adjacent" in a table in its memory, as shown in Figure 15(A).

[0138] Next, the control unit 408 outputs an ON / OFF signal to the ATT 462 to instruct it to turn off, and outputs an ON / OFF signal to the ATT 463 to instruct it to turn on. As a result, wavelength light of any two arbitrary wavelengths possessed by the optical comb Oc is output from the ATTs 461 and 463 and input to the optical multiplexer 9A, and wavelength-multiplexed wavelength light Wz obtained by multiplexing the two wavelengths is input to the PD 471. As a result, wavelength light of any two arbitrary wavelengths possessed by the optical comb Oc is output from the ATTs 461 and 463 and input to the optical multiplexer 9A, and wavelength-multiplexed wavelength light Wz obtained by multiplexing the two wavelengths is input to the PD 471. By repeating this process, it is possible to distinguish between two combinations of ATTs #1 to #8 corresponding to adjacent channels and two combinations of ATTs #1 to #8 corresponding to non-adjacent channels, as shown in FIG. 15(A).

[0139] After determining whether a channel is adjacent or non-adjacent, the control unit 408 detects the output port that outputs the adjacent channel (step S42). For example, the control unit 408 excludes the adjacent determination "non-adjacent" from the table shown in Figure 15(A) and extracts a table in which the adjacent determination "adjacent" is registered, as shown in Figure 15(B). Then, based on the extracted table, the control unit 408 detects a combination of output ports that output adjacent channels, as shown in Figure 15(C).

[0140] When the output ports are detected, the control unit 408 rearranges the output ports (step S43). For example, the control unit 408 rearranges the output ports by placing combinations of output ports adjacent to each other. As a result, as shown in FIG. 15(D), for example, a first pattern in which port #5 is located at the beginning and port #6 is located at the end, and a second pattern in which port #6 is located at the beginning and port #5 is located at the end are generated. Even when comparing the first pattern and the second pattern, the control unit 408 cannot currently determine whether port #5 or port #6 has the longest wavelength.

[0141] Therefore, after rearranging the output ports, the control unit 408 determines the magnitude relationship of the wavelengths (step S44). For example, when the control unit 408 turns on only the ATT #5 corresponding to port #5, wavelength light with the longest wavelength or the shortest wavelength is output from the output port of port #5. The control unit 408 detects the first power of the wavelength light output from the output port of port #5 after passing through the HPF 475. Next, when the control unit 408 turns off the ATT #5 and turns on only the ATT #6 corresponding to port #6, wavelength light with the longest wavelength or the shortest wavelength is output from the output port of port #6. The control unit 408 detects the second power of the wavelength light output from the output port of port #6 after passing through the HPF 475. Then, the control unit 408 determines the magnitude relationship of the wavelengths based on the magnitude relationship between the first power and the second power. For example, if the second power is greater than the first power, the control unit 408 can determine that the wavelength light output from port #6 has the longest wavelength λh and the wavelength light output from port #5 has the longest wavelength λa. In the fourth embodiment, wavelength λa<wavelength λb<···<wavelength λh.

[0142] After determining the wavelength magnitude relationship, the control unit 408 determines the correspondence between the output port and the wavelength (step S45) and ends the process. As a result, it can be determined that the wavelength light with the minimum wavelength λa is output from output port #5 and the wavelength light with the longest wavelength λh is output from output port #6, as shown in Figure 15(E).

[0143] For wavelengths λb,...,λg located between the minimum wavelength λa and the maximum wavelength λh, the correspondence can be determined according to the order of the output ports. For example, wavelength λb can be associated with output port #4. Wavelength λg can be associated with output port #7. The same applies to the remaining wavelengths λc,...,λf as for wavelengths λb and λg.

[0144] 13, after completing the correspondence relationship identification process, the control unit 408 turns off the optical frequency comb source 400 (step S25) and switches the second optical frequency comb switch 452 to the third waveguide 483 (step S26). Specifically, the control unit 408 outputs an on / off signal to the optical frequency comb source 400 to instruct it to stop outputting the optical frequency comb Oc. After outputting the on / off signal, the control unit 408 outputs a switching signal to the second optical frequency comb switch 452 to switch it to the third waveguide 483.

[0145] Next, the control unit 408 outputs an ON / OFF signal to instruct all of the output ports #1 to #8 of the first optical demultiplexer 1 to be turned on. The control unit 408 outputs an ON / OFF signal to instruct ATT #5 of output port #5 corresponding to the minimum wavelength λa to be turned on. The control unit 408 outputs an ON / OFF signal to instruct output port #1 of the second optical demultiplexer 2 to be turned on (step S27). Then, the control unit 408 turns on the comb light source 400 (step S28). As a result, the optical comb Oc is input to the first optical demultiplexer 1, but because ATT #5 is turned on alone, the wavelength light Wa of the minimum wavelength λa is input to the second optical demultiplexer 2 via the optical multiplexer 9A. Because output port #1 of the second optical demultiplexer 2 is turned on, the wavelength light Wa is output from output port #1 of the second optical demultiplexer 2.

[0146] Next, the control unit 408 turns off ATT #5 corresponding to the minimum wavelength λa and turns on ATT #4 corresponding to the adjacent wavelength λb adjacent to the minimum wavelength λa. The control unit 408 outputs an on / off signal that instructs the second optical demultiplexer 2 to turn off output port #1 and turn on output port #2 (step S29). As a result, wavelength light Wb with wavelength λb is input to the second optical demultiplexer 2 via the optical multiplexer 9A. Because output port #2 of the second optical demultiplexer 2 is on, wavelength light Wb is output from output port #2 of the second optical demultiplexer 2.

[0147] Thereafter, the control unit 408 sequentially executes the same processing, turning off the ATT #7 corresponding to the adjacent wavelength λg and turning on the ATT #6 corresponding to the maximum wavelength λh. The control unit 408 outputs an on / off signal instructing the output port #7 of the second optical demultiplexer 2 to be turned off and the output port #8 to be turned on (step S30). As a result, the wavelength light Wh of wavelength λh is input to the second optical demultiplexer 2 via the optical multiplexer 9A. Because the output port #8 of the second optical demultiplexer 2 is turned on, the wavelength light Wh is output from the output port #8 of the second optical demultiplexer 2. The processing of steps S27 to S30 makes it possible to determine the initial optical phase of the second optical demultiplexer 2. Furthermore, the processing of steps S27 to S30 causes the control unit 108 to sequentially switch on and off the ATTs 461 to 468. As a result, the control unit 408 causes the multi-wavelength light output unit L4 to sequentially output the wavelength light Wa,...,Wh for each wavelength.

[0148] When the process of step S30 is completed, the control unit 408 switches the first optical comb SW 451 to the first waveguide 481 side (step S31) and switches the second optical comb SW 452 to the first waveguide 481 side (step S32). As a result, the optical comb Oc is input to the second optical demultiplexer 2 via the first waveguide 481. When the process of step S32 is completed, the control unit 408 outputs an ON / OFF signal that instructs the second optical demultiplexer 2 to turn on all of the output ports #1 to #8 (step S33) and ends the process. Since the initial optical phase of the second optical demultiplexer 2 has been determined, the optical comb Oc input to the second optical demultiplexer 2 is demultiplexed by the second optical demultiplexer 2. Therefore, the wavelength light Wa to Wh for each wavelength is output from the output ports #1 to #8 of the second optical demultiplexer 2, respectively.

[0149] Thus, according to the fourth embodiment, the correspondence between the output ports P#1 to P#8 and the wavelengths λa, . . . , λh of the optical comb Oc can be uniquely determined by control by the control unit 408, without employing an electronic circuit including a cross-connect switch. Furthermore, since the fourth embodiment also does not employ an electronic circuit including a cross-connect switch, it is possible to determine this correspondence while suppressing increases in circuit size and power consumption. In particular, the fourth embodiment can employ the optical comb light source 400, which cannot switch the operation for each wavelength.

[0150] Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as described in the claims.

[0151] In addition, the following supplementary notes are provided in relation to the above description. (Supplementary Note 1) An optical demultiplexer having an input port and a plurality of output ports, demultiplexing wavelength-multiplexed signal light input from the input port into signal light for each wavelength and outputting the signal light from each of the plurality of output ports, a multi-wavelength optical output unit outputting wavelength light for each wavelength included in the wavelength-multiplexed signal light to the input port of the optical demultiplexer, and a control unit controlling the optical demultiplexer and the multi-wavelength optical output unit, wherein the optical demultiplexer comprises a plurality of asymmetric Mach-Zehnder interferometers each having arm pairs with different lengths, and an optical control unit for controlling the optical control unit in the plurality of asymmetric Mach-Zehnder interferometers and a plurality of adjusters for adjusting phases of the asymmetric Mach-Zehnder interferometers, respectively, wherein the plurality of asymmetric Mach-Zehnder interferometers are connected to one another in a tree configuration so as to connect the input port and the plurality of output ports, and the control unit causes the multi-wavelength optical output unit to output the wavelength light sequentially for each wavelength, and causes the adjusters of the asymmetric Mach-Zehnder interferometers on a path connecting the input port to which the wavelength light from the multi-wavelength optical output unit is input and an output port among the plurality of output ports corresponding to the wavelength of the wavelength light to adjust the optical phase. (Supplementary Note 2) There is one input port, and the wavelength-multiplexed signal light and the wavelength light are selectively input to the input port, and the multi-wavelength light output unit comprises a plurality of single-wavelength light sources, switches the number of which is the same as the number of single-wavelength light sources and switches the output destination of the wavelength light output from each of the plurality of single-wavelength light sources to either a first waveguide or a second waveguide, and an optical coupler that couples each of the first waveguides to one third waveguide, and each of the second waveguides is connected to a plurality of detection circuits for each wavelength that detect the signal light using the wavelength light as local light. 2. The optical receiving device according to claim 1, (Supplementary Note 3) The optical receiving device according to Supplementary Note 1, characterized in that there are two input ports, the wavelength-multiplexed signal light is input to one of the input ports, and wavelength-multiplexed wavelength light obtained by multiplexing the wavelength lights is input to the other input port, and the multi-wavelength light output unit comprises a plurality of single-wavelength light sources and a multiplexing circuit that multiplexes each wavelength light output from the plurality of single-wavelength light sources into the wavelength-multiplexed wavelength light. (Supplementary Note 4) The optical receiving device according to Supplementary Note 3, wherein the multiplexing circuit includes an optical combiner, and an optical amplifier is provided between the optical combiner and the optical demultiplexer. (Supplementary Note 5) The optical receiving device according to Supplementary Note 3, wherein the multiplexing circuit includes a WDM coupler, and the WDM coupler and the optical demultiplexer are directly connected to each other. (Supplementary Note 6) The optical receiving device according to Supplementary Note 1, characterized in that there are two input ports, one of which receives the wavelength-multiplexed signal light and the other of which receives an optical frequency comb including a plurality of wavelengths, and the multi-wavelength optical output unit comprises: an optical frequency comb generator that generates the optical frequency comb; a demultiplexing circuit that demultiplexes the optical frequency comb output from the optical frequency comb generator into wavelength light for each wavelength; and a multiplexing circuit that determines whether the wavelengths are long or short by an on / off switching operation and then multiplexes the wavelength light. (Appendix 7) The optical receiving device described in Appendix 6, characterized in that a plurality of attenuators are provided between the demultiplexing circuit and the multiplexing circuit, and the control unit determines whether the wavelengths are long or short by performing the switching operation on the plurality of attenuators. (Supplementary Note 8) An optical demultiplexer having an input port and a plurality of output ports, demultiplexing wavelength-multiplexed signal light input from the input port into signal light for each wavelength and outputting the signal light from each of the plurality of output ports; a multi-wavelength optical output unit outputting wavelength light for each wavelength included in the wavelength-multiplexed signal light to the input port of the optical demultiplexer; and a control unit controlling the optical demultiplexer and the multi-wavelength optical output unit, wherein the optical demultiplexer has a plurality of asymmetric Mach-Zehnder interferometers each having an arm pair with a different length, and a plurality of adjusters adjusting optical phases in the plurality of asymmetric Mach-Zehnder interferometers, respectively, and the plurality of asymmetric Mach-Zehnder interferometers are connected to each other in a tree shape so as to connect the input port and the plurality of output ports, and the control unit controls the multi-wavelength optical output unit to sequentially output the wavelength light for each wavelength, and adjusts the wavelength light before the wavelength light is input from the multi-wavelength optical output unit. an optical phase is adjusted by the adjuster of the asymmetric Mach-Zehnder interferometer on a path connecting the input port and one of the plurality of output ports corresponding to the wavelength of the wavelength light, the number of the input port being one, the wavelength-multiplexed signal light and the wavelength light being selectively input to the input port, the multi-wavelength light output unit comprising: a plurality of single-wavelength light sources; switches the number of which is equal to the number of the single-wavelength light sources, each of which switches the output destination of the wavelength light output from each of the plurality of single-wavelength light sources to either a first waveguide or a second waveguide; and an optical coupler coupling each of the first waveguides to one third waveguide, and each of the second waveguides is connected to a plurality of detection circuits for each wavelength that detect the signal light using the wavelength light as local light, and a plurality of modulation circuits for each wavelength that optically modulates an electrical signal corresponding to the signal light using the wavelength light as transmission light. [Explanation of symbols]

[0152] 1 1st optical demultiplexer 2 Second optical demultiplexer 1a-1i, 2a-2i AMZ (Asymmetric Mach-Zehnder Interferometer) 101, 201, 301 1st Living Room 102,202 302 2nd LD 103,203,303 3rd LD 104,204 304 4th LD 108,208,308,408 Control unit 155 Optical Coupler 209,351 Optical multiplexer 400 comb light source L1,L2,L3,L4 Multi-wavelength optical output section Inc,Dec compensation circuit TR1, TR2, TR3, TR4 optical transceiver

Claims

1. an optical demultiplexer having an input port and a plurality of output ports, which demultiplexes wavelength-multiplexed signal light input from the input port into signal light of each wavelength and outputs the signal light from each of the plurality of output ports; a multi-wavelength optical output unit that outputs wavelength light for each wavelength included in the wavelength-multiplexed signal light to the input port of the optical demultiplexer; a control unit that controls the optical demultiplexer and the multi-wavelength optical output unit, The optical demultiplexer comprises: a plurality of asymmetric Mach-Zehnder interferometers each having arm pairs of different lengths; a plurality of adjusters for adjusting optical phases in the plurality of asymmetric Mach-Zehnder interferometers, respectively; the plurality of asymmetric Mach-Zehnder interferometers are connected to each other in a tree configuration so as to connect between the input port and the plurality of output ports; The control unit causing the multi-wavelength light output unit to sequentially output the wavelength light for each wavelength; an optical receiving device that controls an adjustment amount of an optical phase for the adjuster of the asymmetric Mach-Zehnder interferometer on a path connecting the input port to which the wavelength light from the multi-wavelength light output unit is input and an output port corresponding to the wavelength of the wavelength light among the plurality of output ports.

2. the number of input ports is one, and the wavelength-multiplexed signal light and the wavelength light are selectively input to the input port; the multi-wavelength light output unit comprises a plurality of single-wavelength light sources, switches the number of which is equal to the number of the single-wavelength light sources and which switch the output destination of the wavelength light output from each of the plurality of single-wavelength light sources to either a first waveguide or a second waveguide, and an optical coupler which couples each of the first waveguides to one third waveguide, each of the second waveguides is connected to a plurality of detection circuits for each wavelength, which detect the signal light using the wavelength light as a local light; 2. The optical receiving device according to claim 1.

3. the number of input ports is two, the wavelength multiplexed signal light is input to one of the input ports, and wavelength multiplexed wavelength light obtained by multiplexing the wavelength lights is input to the other input port; the multi-wavelength light output unit includes a plurality of single-wavelength light sources and a multiplexing circuit that multiplexes the wavelength lights output from the plurality of single-wavelength light sources into the wavelength-multiplexed light; 2. The optical receiving device according to claim 1.

4. the number of input ports is two, the wavelength-multiplexed signal light is input to one of the input ports, and an optical frequency comb including a plurality of wavelengths is input to the other input port; The multi-wavelength light output unit includes an optical frequency comb generator that generates the optical frequency comb, a demultiplexing circuit that demultiplexes the optical frequency comb output from the optical frequency comb generator into wavelength light for each wavelength and outputs the demultiplexed wavelength light to an attenuator, and a multiplexing circuit that performs an on / off switching operation on the attenuator to determine whether the wavelengths are long or short based on the magnitude relationship of the power of the wavelength light, and then multiplexes the wavelength light.

2. The optical receiving device according to claim 1.

5. an optical demultiplexer having an input port and a plurality of output ports, which demultiplexes wavelength-multiplexed signal light input from the input port into signal light of each wavelength and outputs the signal light from each of the plurality of output ports; a multi-wavelength optical output unit that outputs wavelength light for each wavelength included in the wavelength-multiplexed signal light to the input port of the optical demultiplexer; a control unit that controls the optical demultiplexer and the multi-wavelength optical output unit, The optical demultiplexer comprises: a plurality of asymmetric Mach-Zehnder interferometers each having arm pairs of different lengths; a plurality of adjusters for adjusting optical phases in the plurality of asymmetric Mach-Zehnder interferometers, respectively; the plurality of asymmetric Mach-Zehnder interferometers are connected to each other in a tree configuration so as to connect between the input port and the plurality of output ports; The control unit causing the multi-wavelength light output unit to sequentially output the wavelength light for each wavelength; controlling an adjustment amount of an optical phase for the adjuster of the asymmetric Mach-Zehnder interferometer on a path connecting the input port to which the wavelength light from the multi-wavelength light output unit is input and an output port corresponding to the wavelength of the wavelength light among the plurality of output ports; the number of input ports is one, and the wavelength-multiplexed signal light and the wavelength light are selectively input to the input port; the multi-wavelength light output unit comprises a plurality of single-wavelength light sources, switches the number of which is equal to the number of the single-wavelength light sources and which switch the output destination of the wavelength light output from each of the plurality of single-wavelength light sources to either a first waveguide or a second waveguide, and an optical coupler which couples each of the first waveguides to one third waveguide, Each of the second waveguides is connected to a plurality of detection circuits for each wavelength that detect the signal light using the wavelength light as local light, and a plurality of modulation circuits for each wavelength that use the wavelength light as transmission light and optically modulate the transmission light based on an electrical signal corresponding to the signal light. An optical transmitter / receiver characterized by:

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