Optical transceiver, optical transceiver device using the same, and method for controlling the wavelength of a light source

Abstract

To improve the efficiency of frequencies while suppressing increase in size and cost of an optical transceiver.SOLUTION: An optical transceiver includes: an optical transceiver circuit; a light source device configured to multiplex light rays emitted from light source elements having different wavelengths and output multiplexed light; a demultiplexer to demultiplex the light output from the light source device into wavelengths to supply the wavelengths to the optical transceiver circuit; monitors configured to monitor the wavelengths at output ports of the demultiplexer, respectively; and a wavelength controller configured to control the wavelengths of the light source elements, based on monitoring results of the monitors. The demultiplexer includes a plurality of unit circuits in each of which three asymmetric Mach-Zehnder interferometers having a predetermined arm length difference are cascaded in a tree shape. Each of the monitors is arranged at an output waveguide of an asymmetric Mach-Zehnder interferometer at an end of the cascaded tree, to be connected to the wavelength controller via a signal line.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] This disclosure relates to an optical transceiver, an optical transceiver using the same, and a method for controlling the wavelength of a light source. [Background technology]

[0002] One method for increasing communication capacity is Wavelength Division Multiplexing (WDM), which multiplexes light of multiple wavelengths. WDM increases communication capacity by multiplexing multiple channels assigned to multiple optical transceiver modules onto a single optical fiber and transmitting them. Dense WDM, which multiplexes many wavelengths closely together to improve the efficiency of optical spectrum utilization, has also been put into practical use. On the receiving side of the optical transceiver module, a demultiplexer is used to separate the multiplexed light of each wavelength (see, for example, Patent Documents 1 and 2). A configuration of a demultiplexer has been proposed in which multiple unit circuits formed by three asymmetric Mach-Zehnder (AMZ) interferometers with the same arm length difference are connected (see, for example, Patent Document 3).

[0003] On the other hand, subcarrier transmission, which uses multiple subcarriers for frequency multiplexing between a pair of optical transceiver modules, is known. In subcarrier transmission, a technique is required to control the wavelength spacing to be equal so that each subcarrier can be accurately separated on the receiving side of the optical transceiver. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 9-261181 [Patent Document 2] Japanese Patent Publication No. 2016-225923 [Patent Document 3] Japanese Patent Publication No. 2019-135524 [Overview of the project] [Problems that the invention aims to solve]

[0005] In subcarrier transmission systems, a light source device is used that has multiple laser elements that output light of different wavelengths. To control the wavelength spacing to be dense and equally spaced using laser elements corresponding to the number of subcarriers, a wavelength monitor or wavelength rocker is provided for each laser element. The size of the light source device increases in proportion to the number of multiplexed subcarriers, leading to an increase in the size and cost of the optical transceiver. One aspect of the present invention aims to improve frequency utilization efficiency while suppressing the increase in the size and cost of the optical transceiver. [Means for solving the problem]

[0006] In one embodiment, the optical transceiver is Optical transceiver circuit, A light source device that combines and outputs light emitted from multiple light source elements of different wavelengths, A demultiplexer that splits the light output from the light source device into multiple wavelengths and supplies them to the optical transmitting and receiving circuit, A monitor that monitors each of the plurality of wavelengths at the output port of the demultiplexer, A wavelength controller that controls the wavelengths of the plurality of light source elements based on the monitoring results of the monitor, It has, The demultiplexer has multiple unit circuits in which three asymmetric Mach-Zehnder interferometers having a predetermined difference in arm length are connected in a tree-like manner, and the multiple unit circuits are cascaded in a tree-like manner, and the monitor is placed in the output waveguide of the asymmetric Mach-Zehnder interferometer at the end of the cascaded tree and connected to the wavelength controller by a signal line. [Effects of the Invention]

[0007] This allows for improved frequency utilization efficiency while keeping the size and cost of optical transceivers down. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic diagram of an optical transmission device to which this disclosure applies. [Figure 2] This is a schematic diagram illustrating the application of subcarrier transmission to WDM. [Figure 3] This is a schematic diagram of a subcarrier-type optical transceiver. [Figure 4] This is a schematic diagram of the optical transceiver of the first embodiment. [Figure 5] Figure 4 is a schematic diagram of a demultiplexer used in an optical transceiver. [Figure 6] Figure 4 is a schematic diagram of light source wavelength control using the monitoring function of the demultiplexer. [Figure 7] This figure shows the initial state of the light source wavelength and the transmission characteristics of the demultiplexer. [Figure 8] This figure shows an example of port assignment for each wavelength. [Figure 9] This figure shows an example of port assignment for each wavelength. [Figure 10] This figure shows an example of port assignment for each wavelength. [Figure 11] This figure shows an example of port assignment for each wavelength. [Figure 12] This diagram shows the wavelength correction process. [Figure 13] This diagram shows the wavelength correction process. [Figure 14] This diagram shows the wavelength correction process. [Figure 15] This figure shows the final light source wavelength settings. [Figure 16A] This figure shows the changes in each wavelength during control. [Figure 16B] This figure shows the change in each wavelength interval during control. [Figure 17] This is a schematic diagram of the optical transceiver of the second embodiment. [Figure 18] Figure 17 is a schematic diagram of light source wavelength control using the monitoring function of the demultiplexer. [Figure 19] This figure shows the initial state of the light source wavelength and the transmission characteristics of the demultiplexer. [Figure 20] This figure shows an example of port assignment for each wavelength. [Figure 21]This figure shows an example of port assignment for each wavelength. [Figure 22] This figure shows an example of port assignment for each wavelength. [Figure 23] This diagram shows the light source wavelength correction excluding the reference wavelength. [Figure 24] This figure shows wavelength correction using heater control. [Figure 25] This figure shows the final light source wavelength settings. [Figure 26A] This figure shows the changes in each wavelength during control. [Figure 26B] This figure shows the change in each wavelength interval during control. [Figure 27] This figure shows the effect of controlling the light source wavelength in the second embodiment in comparison with the comparative example. [Modes for carrying out the invention]

[0009] Figure 1 is a schematic diagram of an optical transmission device 100 to which this disclosure applies. The optical transmission device 100 is used, for example, as a network node in a WDM transmission system. The optical transmission device 100 has a plurality of transponders 130-1 to 130-n (collectively referred to as "transponder 130" as appropriate), an optical multiplexer / demultiplexer 140, an optical amplifier 160, and a control unit 150. The control unit 1501 is implemented with a processor and memory and controls the operation of each transponder 130, the optical multiplexer / demultiplexer 140, and the optical amplifier 160. The transponder 130 is, for example, a transponder for subcarrier transmission and is an example of an optical transceiver.

[0010] Signals from client devices such as routers are converted into a frame format for optical transmission by transponders 130-1 to 130-n, and a subcarrier signal containing multiple subcarriers is generated by the corresponding optical transceivers 10-1 to 10-n (collectively referred to as "optical transceiver 10" as appropriate). The subcarrier signal generated by optical transceiver 10 is wavelength-multiplexed by the multiplexer ("MUX") 140M of the optical multiplexer / demultiplexer 140, amplified by the optical amplifier 160T, and output to the transmission path on the network side. The light received from the network is amplified by the optical amplifier 160R, then demultiplexed into each channel by the optical demultiplexer ("DEMUX") 140D, and supplied to each transponder 130. The optical signal received by each transponder 130 contains multiple subcarriers. The optical transceiver 10 of transponder 130 demultiplexes the received optical signal into subcarriers and detects them.

[0011] Figure 2 is a schematic diagram illustrating the application of subcarrier transmission to WDM. In WDM communication, the wavelength band assigned to each transponder 130 (or optical transceiver 10) is denoted as W. A single wavelength band W contains multiple subcarriers λ1, λ2, ..., λn. Each subcarrier λ1, λ2, ..., λn is subjected to intensity modulation, such as quaternary pulse amplitude modulation (PAM4). One optical transceiver 10 uses wavelength band Wi, and another optical transceiver 10 uses the adjacent wavelength band Wj. Signals from numerous wavelength bands W, each containing multiple subcarriers λi, are multiplexed and transmitted as a WDM signal. If each subcarrier is intensity-modulated on the transmitting side, the receiving side separates the signals into subcarriers at regular wavelength intervals, and the power of each subcarrier is detected by a photodetector.

[0012] Figure 3 is a schematic diagram of an optical transceiver 10 of an embodiment. The optical transceiver includes a light source device 11, an optical integrated circuit (PIC: Photonic Integrated Circuit) 15, and a processor 19. The light source device 11 includes a plurality of light source elements 12-1 to 12-n (collectively referred to as "light source elements 12" as appropriate) and a multiplexer 13. In this example, the light source elements 12 are laser diodes and are denoted as "LD" in the figure. The optical integrated circuit 15 includes a demultiplexer 20 and an optical transceiver circuit 17. The optical transceiver circuit 17 includes a transmit circuit 171 and a receive circuit 172. The demultiplexer 20 and the optical transceiver circuit 17 are integrated on the same substrate, for example, using silicon photonics technology. Of the output light from the demultiplexer 20, the light incident on the transmit circuit 171 is modulated and emitted as a modulated light signal. The light incident on the receive circuit 172 from the demultiplexer 20 is used as locally oscillated light (LO).

[0013] In this embodiment, when controlling the transmission characteristics of the demultiplexer 20 based on the monitoring results of the light of each wavelength demultiplexed by the demultiplexer 20, the wavelength of each light source element 12 of the light source device 11 is controlled by the processor 19 using the monitoring results. Even if the oscillation wavelengths of multiple light source elements 12 are designed to be equally spaced, they often deviate from the designed oscillation wavelengths due to manufacturing variations, environmental changes, and changes over time. For this reason, a wavelength monitor or wavelength rocker is generally provided to monitor and control the wavelength of each light source element. In contrast, in this embodiment, by controlling the oscillation wavelength of each light source element 12 in parallel with controlling the transmission characteristics of the demultiplexer 20, an evenly designed wavelength spacing can be obtained without installing a wavelength monitor or wavelength rocker for each light source element 12. When we say "even wavelength spacing," it does not mean strictly identical wavelength spacing, but may include errors within the range allowed in subcarrier transmission. Subcarrier transmission improves frequency utilization efficiency by densely arranging narrowband orthogonal subcarriers, so it is important to maintain an even wavelength spacing. The "orthogonality" of subcarriers refers to a mathematical meaning where the signal equations carried by adjacent subcarriers can be combined and separated from each other, and is different from the orthogonality of optical phases. Below, a configuration in which the wavelength spacing is controlled uniformly (first embodiment) and a configuration in which the absolute value of the wavelength is controlled along with the uniform wavelength spacing (second embodiment) will be described in detail.

[0014] <First Embodiment> Figure 4 is a schematic diagram of the optical transceiver 10A of the first embodiment. The optical transceiver 10A includes a light source device 11A, an optical integrated circuit 15A, and a wavelength controller 191A. The wavelength controller 191A is implemented by the functions of the processor 19. The optical integrated circuit 15A includes a demultiplexer 20 and an optical transceiver circuit 17A. The demultiplexer 20 and the optical transceiver circuit 17A may be formed on a single substrate, for example, by silicon photonics technology. The receiving circuit 172 of the optical transceiver circuit 17A includes an optical demultiplexer 176 and a plurality of photodetectors (indicated as "PD" in the figure) 174-1, 174-2, ..., 174-n (collectively referred to as "photodetector 174" as appropriate). The transmitting circuit 171 includes a plurality of optical modulators 173-1, 173-2, ..., 173-n (collectively referred to as "optical modulator 173" as appropriate) and an optical multiplexer 175.

[0015] The light source device 11A has n light source elements 12 (where n is an integer greater than or equal to 2). Each light source element 12 oscillates at different wavelengths λ1, λ2, ..., λn. The light of multiple wavelengths is combined by a multiplexer 13 such as an optical coupler and output from the light source device 11A. The light output from the light source device 11A is incident on the optical integrated circuit 15A. The demultiplexer 20 formed in the optical integrated circuit 15A has optical path length controllers 201-1, 201-2, ..., 201-n (collectively referred to as "optical path length controller 201" as appropriate) corresponding to the number of wavelengths, and photodetectors 202-1, 202-2, ..., 202-n for monitoring provided at the output port Pout. The photodetectors 202-1, 202-2, ..., 202-n for monitoring are designated PD1, PD2, ..., PD2 to distinguish them from the photodetector 174 of the receiving circuit 172. n This is how it is written. Hereafter, photodetectors 202-1, 202-2, ..., 202-n will be referred to as monitor PD202-1, 202-2, ..., 202-n, and will be collectively referred to as "monitor PD202" as appropriate.

[0016] The optical path length controllers 201-1 to 201-n control the effective optical path length of the optical waveguide formed in the demultiplexer 20. The optical path length controllers 201-1 to 201-n are an example of a control mechanism that controls the effective optical path length or optical phase by changing the refractive index of the optical waveguide by heating, voltage application, etc. The control mechanism controls the transmission characteristics of the demultiplexer 20 by changing the optical phase, and demultiplexes light of multiple wavelengths incident on the demultiplexer 20. The light of each wavelength demultiplexed by the demultiplexer 20 is monitored by monitors PD202-1, 202-2, ..., 202-n.

[0017] The outputs of monitors PD202-1 to 201-n are fed back to the wavelength controller 191A via the feedback signal line 200. The monitoring results are used by the wavelength controller 191A to control the oscillation wavelengths of each light source element 12-1 to 12-n of the light source device 11A. Using the monitoring results from the demultiplexer 20, the light source device 11A is controlled so that the oscillation wavelengths λ1, λ2, ..., λn of each light source element 12-1 to 12-n are at predetermined optical frequency intervals. As will be described later, the control of the oscillation wavelength of the light source device 11A is performed in parallel with the control of the transmission characteristics of the demultiplexer 20 by the optical path length controllers 201-1 to 201-n.

[0018] In the first embodiment, light of each wavelength emitted from the light source device 11A is intensity-modulated by the transmission circuit 171 and transmitted. At the receiving end, subcarriers are demultiplexed at regular intervals and power is detected, so uniform wavelength spacing is required, but absolute wavelength values ​​are not. Even if the absolute values ​​of the wavelengths are slightly shifted, since the wavelength spacing is uniformly controlled, the same amount of shift in the center wavelength in the same direction can be absorbed by coherent signal processing, including a digital signal processor, between the opposing pair of optical transceivers.

[0019] Control of the transmission characteristics of the demultiplexer 20 and the wavelength spacing of the light source device 11A are performed when a new transponder 130 is installed in the optical transmission device 100, or when the optical transceiver 10A or transponder 130 is restarted. In addition to when the optical transceiver 10A is started up, the transmission characteristics of the demultiplexer 20 and the wavelength spacing of the light source device 11A may be controlled periodically or irregularly during operation.

[0020] FIG. 5 is a schematic diagram of the demultiplexer 20 of FIG. 4. The demultiplexer 20 includes unit circuits 21-1, 21-2, and 21-3 that are cascade-connected in a tree shape. Each of the unit circuits 21-1, 21-2, and 21-3 is formed of three Asymmetric Mach-Zehnder (AMZ) interferometers 25 that are cascade-connected in a tree shape. This demultiplexer configuration is called CAT (Cascaded AMZ Triplet).

[0021] In the example of FIG. 5, to demultiplex four wavelengths λ1, λ2, λ3, and λ4, a two-stage CAT is used in which unit circuits 21-2 and 21-3 are respectively connected to two outputs of the leading unit circuit 21-1 of the demultiplexer 20. When separating more wavelengths, another unit circuit may be further connected to each output of the second-stage unit circuits 21-2 and 21-3, so that eight wavelengths can be separated by a three-stage CAT.

[0022] The leading unit circuit 21-1 includes three AMZs 25 having the same arm length difference ΔL 11 , 25 12 , and 25 13 . When the arm length difference is described as "the same", it means that the designed effective arm length difference is the same, and in an actual product, this is intended to include allowable errors, manufacturing variations, and the like. Each of the asymmetric optical waveguides of the AMZ 25 11 , 25 12 , and 25 13 is provided with a heater H 11 , H 12 , and H 13 , respectively.

[0023] The output of the AMZ 25 11 is split into two, which are respectively connected to an input of the AMZ 25 12 and an input of the AMZ 25 13 . The output of the AMZ 25 12 is split into two, a monitor 1A UP is connected to one output waveguide, and the monitor 1A lоwIt is connected. Monitor 1A UP The output waveguide to which it is connected becomes port (a) connected to the second-stage unit circuit 21-2. Similarly, AMZ25 13 The output is split into two, and one of the output waveguides is connected to Monitor 1B UP The other output waveguide is connected to Monitor 1B lоw It is connected. Monitor 1B UP The output waveguide to which it is connected becomes port (b) connected to the second-stage unit circuit 21-3.

[0024] Monitor 1A UP and Monitor 1B UP The monitoring results are supplied to control circuit 23-1. Control circuit 23-1 controls monitor 1A UP and Monitor 1B UP In the direction of increasing power detected by heater H 11 Power P 11 It controls the following. For this reason, control circuit 23-1 is labeled "Inc" in the diagram. Monitor 1A lоw The monitoring results are supplied to control circuit 22a and monitor 1B lоw The monitoring results are supplied to control circuit 22b. Control circuit 22a monitors 1A lоw Heater H 12 Power P 12 Controls the monitor 1B. The control circuit 22b controls the monitor 1B. lоw Heater H 13 Power P 13 This controls the following. For this reason, control circuits 22a and 22b are labeled "Dec" in the diagram. The dotted lines connecting each monitor to control circuit 23 or 22, and between control circuit 22 or 23 and heater H, indicate electrical control lines.

[0025] The transmission characteristics of the first-stage unit circuit 21-1 are controlled by control circuit 23-1 and control circuits 22a and 22b. Control circuits 23-1, 22a, and 22b, and heater H 11 H 12 , and H 13 This is an example of the optical path length controller 201 shown in Figure 4. Heater H 11H 12 , and H 13 Instead, AMZ25 11 ,twenty five 12 ,twenty five 13 Another configuration (such as applying an electric field) may be used to control the optical phase by changing the refractive index of the asymmetric waveguide. Of the wavelengths λ1, λ2, λ3, and λ4 incident on unit circuit 21-1, λ1 and λ3 are transmitted to the second-stage unit circuit 21-2, and λ2 and λ4 are transmitted to the second-stage unit circuit 21-3.

[0026] Three AMZ25s form the second stage unit circuit 21-2 21 ,twenty five 22 , and 25 23 This is the first stage unit circuit 21-1 with three AMZ25 11 ,twenty five 12 , and 25 13 It has an arm length difference of half the arm length difference ΔL. Similarly, three AMZ25 form the second stage unit circuit 21-3. 31 ,twenty five 32 , and 25 33 This is the first stage unit circuit 21-1 with three AMZ25 11 ,twenty five 12 , and 25 13 It has an arm length difference of half the arm length difference ΔL. When the third stage unit circuit is cascaded, each AMZ of the third stage unit circuit has an arm length difference of half the arm length difference of the AMZs of the second stage unit circuits 21-2 and 21-3.

[0027] AMZ25 of Unit Circuit 21-2 21 ,twenty five 22 , and 25 23 Heater H is placed in each of the asymmetric optical waveguides. 21 H 22 , and H 23 A unit circuit 21-3 AMZ25 is provided. 31 ,twenty five 32 , and 25 33 Heater H is placed in each of the asymmetric optical waveguides. 31 H 32 , and H 33 A system is in place.

[0028] AMZ25 22 the output is branched into two, and monitor 1A UP is connected to one output waveguide, and monitor 2A lоw is connected to the other output waveguide. Monitor 2A UP connected output waveguide serves as output port (c) for wavelength λ1. The output of AMZ25 23 is branched into two, and monitor 2B UP is connected to one of the two output waveguides, and monitor 2B lоw is connected to the other output waveguide. Monitor 2B UP connected output waveguide serves as output port (d) for wavelength λ3.

[0029] Monitor 2A UP and monitor 2B UP provide their monitoring results to control circuit 23-2. Control circuit 23-2 controls power P UP of heater H UP in the direction that increases the power detected by monitor 2A 21 and monitor 2B 21 . For this reason, control circuit 23-2 is labeled "Inc" in the drawing. The monitoring result of monitor 2A lоw is supplied to control circuit 22c, and the monitoring result of monitor 2B lоw is supplied to control circuit 22d. Control circuit 22c controls power P lоw of heater H 22 in the direction that decreases the power detected by monitor 2A 22 . Control circuit 22d controls power P lоw of heater H 23 in the direction that decreases the power detected by monitor 2B 22 . For this reason, control circuits 22c and 22d are labeled "Dec" in the drawing.

[0030] For AMZ25 of unit circuit 21-3, 32 the output is branched into two, monitor 3A UP is connected to one output waveguide, and monitor 3A lоw is connected to the other output waveguide. Monitor 3A UPThe connected output waveguide serves as an output port (e) for wavelength λ2. AMZ25 33 output is split into two branches, and monitor 3B is provided on one output waveguide UP is connected, and monitor 3B is connected to the other output waveguide lоw is connected. Monitor 3B UP The connected output waveguide serves as the output port (f) for λ4.

[0031] Monitor 3A UP and monitor 3B UP monitoring results are supplied to the control circuit 23-3. The control circuit 23-3 controls such that the monitor 3A UP and monitor 3B UP the power detected at increases the power of the heater H 31 power P 31 is controlled. For this reason, the control circuit 23-3 is labeled "Inc" in the drawing. Monitor 3A lоw monitoring result is supplied to the control circuit 22e, and monitor 3B lоw monitoring result is supplied to the control circuit 22f. The control circuit 22e controls such that the power detected by the monitor 3A lоw decreases the power of the heater H 32 power P 32 is controlled. The control circuit 22f controls such that the power detected by the monitor 3B lоw decreases the power of the heater H 33 power P 33 is controlled. For this reason, the control circuits 22e and 22f are labeled "Dec" in the drawing.

[0032] The transmission characteristic of the second-stage unit circuit 21-2 is controlled by the control circuit 23-2 and the control circuits 22c and 22d. The transmission characteristic of the unit circuit 21-3 is controlled by the control circuit 23-3 and the control circuits 22e and 22f. The control circuits 23-2, 23-3, 22c, 22d, 22e, and 22f, and the heater H 21 , H 22 , H 23 , H 31 , H 32 , and H 33This is an example of the optical path length controller 201 shown in Figure 4. As mentioned above, a different optical path length control mechanism may be used instead of the heater.

[0033] In the CAT configuration of the demultiplexer 20 shown in Figure 5, variations in the manufacturing of the optical waveguides of each AMZ 25 and variations in refractive index due to temperature fluctuations are compensated for, and each AMZ can be controlled to the optimal condition for the input signal wavelength. By configuring the unit circuit 21 with three AMZ 25s, it is possible to determine whether the transmission characteristics of each wavelength are optimally controlled from the monitor values ​​tapped at each output port. Based on the monitoring results of each tap, individual control becomes possible, such as increasing the power of the wavelength of interest and decreasing the power of unnecessary wavelengths. However, if the output wavelengths of each light source element 12 of the light source device 11A are not uniform, even if the transmission characteristics are controlled with optimal power control for each wavelength, the wavelengths will be separated by non-uniform optical frequency intervals. Therefore, the wavelengths λ1, λ2, λ3, and λ4 output from ports (c), (d), (e), and (f) are monitored by the monitor PD202 as shown in Figure 4, and the monitoring results are fed back to the wavelength controller 191A to control the oscillation wavelength of each light source element 12 of the light source device 11A. Instead of providing a separate monitor PD202, monitor 2A of the splitter 20 is used. UP , 2B UP , 3A UP , and 3B UP The monitoring results may be used for wavelength control of the light source device 11A.

[0034] Figure 6 is a schematic diagram of light source wavelength control using the monitoring function of the demultiplexer 20. In Figure 6, monitor 2A is used for controlling the transmission characteristics of the demultiplexer 20. UP , 2B UP , 3A UP , and 3B UP The output is connected to the input of the wavelength controller 191A via the feedback signal line 200. As described above, monitor 2A UP , 2B UP , 3A UP , and 3B UPThe output represents the monitoring results for each wavelength of interest. Based on the monitoring results, the wavelength controller 191A controls the oscillation wavelengths λ1, λ2, λ3, and λ4 of each light source element 12-1, 12-2, 12-3, and 12-4 of the light source device 11A so that they are equally spaced. The specific control procedure is described below with reference to Figures 7 to 15.

[0035] During actual operation, the light output from each light source element 12-1, 12-2, 12-3, and 12-4 is combined by the optical coupler 13A and incident on the demultiplexer 20. The light of each wavelength demultiplexed by the demultiplexer 20 is modulated by the corresponding optical modulator 173 of the transmission circuit 171. When controlling the transmission characteristics of the demultiplexer 20, one wavelength at a time is input to the demultiplexer 20, and the transmission characteristics of the demultiplexer 20 are controlled based on the monitoring results in the optical waveguide through which the light of that wavelength passes. With the output light of all light source elements 12-1 to 12-4 incident on the demultiplexer 20, the wavelength spacing of each light source element 12-1 to 12-4 is controlled by the wavelength controller 191A in parallel with the control of the transmission characteristics of the demultiplexer 20 (using the monitoring results for transmission characteristic control).

[0036] Figure 7 shows the initial state of the light source wavelength and the transmission characteristics of the demultiplexer. The wavelengths and transmission characteristics at ports (a), (b), (c), (d), (e), and (f) in Figure 5 are shown, respectively. The dotted wavelengths λ1, λ2, λ3, and λ4 are the center wavelengths of the subcarriers set at equal intervals. λ'1, λ'2, λ'3, and λ'4 are the wavelengths contained in the light output from the light source device 11A and incident on the demultiplexer 20. λ'1, λ'2, and λ'4 are shifted to the lower frequency side (longer wavelength side) from λ1, λ2, and λ4, while λ'3 is shifted to the higher frequency side (shorter wavelength side) from λ3.

[0037] In the first stage, AMZ25-1, we want to align the transmission spectrum peaks at λ'1 and λ'3 in port (a) and at λ'2 and λ'4 in port (b). In the second stage, AMZ25-2, we want to align the transmission spectrum peak at λ'1 in port (c) and at λ'3 in port (d). In the second stage, AMZ25-3, we want to align the transmission spectrum peak at λ'2 in port (e) and at λ'4 in port (f).

[0038] Figures 8 to 11 show an example of wavelength assignment to each port. Port assignment for each wavelength is done by injecting light into the demultiplexer 20 one wavelength at a time, adjusting the transmission characteristics of the demultiplexer 20, and sequentially assigning the wavelength to the corresponding port. In Figure 8, the light source element 12-1 is turned on (active) and wavelength λ'1 is injected into the demultiplexer 20. At port (a), monitor 1A UP Monitor results increased, Monitor 1A lоw The monitor results show that the heater H is decreasing. 11 and H 12 Power P 11 and P 12 This controls the transmission spectrum to shift it. At this time, port (b) is monitored by monitor 1B UP and 1B lоw There is no feedback from (hereinafter referred to collectively as Monitor 1B), but Power P 11 The transmission spectrum shifts due to the influence of the control.

[0039] On port (c), Monitor 2A UP The monitoring results for Monitor 2A increased. lоw The monitoring results show a decrease in power P 21 and P 22 This controls the transmission spectrum to shift it. At this time, there is no feedback from monitor 2B at port (d), but power P 21 The transmission spectrum shifts due to the influence of the control. At ports (e) and (f), there is no optical input to the unit circuit 21-3, so the transmission spectrum hardly changes.

[0040] Next, in Figure 9, light source element 12-2 is turned on to add wavelength λ'2. Light source elements 12-1 and 12-2 are in the active state. Monitor 1A is on port (a). UP Monitor results increased, Monitor 1A lоw The monitoring results show a decrease in power P 11 and P 12 Control this to shift the transmission spectrum. At port (b), monitor 1B UP The monitoring results for monitor 1B increased, lоw The monitoring results show a decrease in power P 11 and P 13 Control this to adjust the transmission spectrum.

[0041] On port (c), Monitor 2A UP The monitoring results for Monitor 2A increased. lоw The monitoring results show a decrease in power P 21 and P 22 This controls the power P and adjusts the transmission spectrum. At this time, port (d) controls the power P 21 The amount of control is very small, Power P 21 The control has almost no effect. On port (e), monitor 3A UP The monitoring results increased, Monitor 3A lоw The monitoring results show a decrease in power P 31 and P 32 The transmission spectrum is adjusted by controlling the power P. At this time, there is no feedback from monitor 3B at port (f), but power P 31 The transmission spectrum shifts due to the influence of the control.

[0042] Next, in Figure 10, light source element 12-3 is turned on to add wavelength λ'3. Light source elements 12-1, 12-2, and 12-3 are in the active state. Monitor 1A is on port (a). UP Monitor results increased, Monitor 1A lоw The monitoring results show a decrease in power P 11 and P 12 Control this to shift the transmission spectrum. At port (b), monitor 1B UP The monitoring results for monitor 1B increased,lоw The monitoring results show a decrease in power P 11 and P 13 Control the transmission spectrum to adjust it.

[0043] On port (c), Monitor 2A UP The monitoring results for Monitor 2A increased. lоw The monitoring results show a decrease in power P 21 and P 22 Control this to adjust the transmission spectrum. On port (d), monitor 2B UP The monitoring results for Monitor 2B have increased. lоw The monitoring results show a decrease in power P 21 and P 23 The transmission spectrum is adjusted by controlling this. At ports (e) and (f), the optical input to the unit circuit 21-3 is only light of wavelength λ'2, so the transmission spectrum hardly changes.

[0044] Finally, in Figure 11, light source element 12-4 is turned on to add wavelength λ'4. All light source elements 12-1 to 12-4 are in the active state. Monitor 1A on port (a). UP Monitor results increased, Monitor 1A lоw The monitoring results show a decrease in power P 11 and P 12 Control this to adjust the transmission spectrum. On port (b), monitor 1B UP The monitoring results for monitor 1B increased, lоw The monitoring results show a decrease in power P 11 and P 13 Control the transmission spectrum to adjust it.

[0045] On port (c), Monitor 2A UP The monitoring results for Monitor 2A increased. lоw The monitoring results show a decrease in power P 21 and P 22 Control this to adjust the transmission spectrum. On port (d), monitor 2B UP The monitoring results for Monitor 2B have increased. lоw The monitoring results show a decrease in power P 21 and P23 Control and adjust the transmission spectrum. On port (e), monitor 3A UP The monitoring results increased, Monitor 3A lоw The monitoring results show a decrease in power P 31 and P 32 Control this to adjust the transmission spectrum. On port (f), monitor 3B UP Monitor results increased, Monitor 3B lоw The monitoring results show a decrease in power P 31 and P 33 This controls the transmission spectrum to adjust it. This completes the assignment of wavelengths to each port.

[0046] In the state shown in Figure 11, at ports (c), (d), (e), and (f), the peaks of the transmission spectrum are near the corresponding wavelengths λ'1, λ'2, λ'3, and λ'4, respectively, indicating that the transmission characteristics are controlled, but the wavelength spacing is non-uniform. Therefore, the oscillation wavelength of the light source device 11A and the transmission characteristics of the demultiplexer 20 are further controlled to correct the optical frequency spacing of each wavelength λ'1, λ'2, λ'3, and λ'4 to be uniform.

[0047] Figure 12 shows the process of wavelength correction by light source control. With all four wavelengths incident on the demultiplexer 20, the wavelength controller 191A controls the wavelengths λ'1, λ'2, λ'3, and λ'4 of the light source elements 12-1 to 12-4 of the light source device 11A as follows. Monitor 2A at port (c) of unit circuit 21-2. UP The monitoring results for Monitor 2A increased. lоw The oscillation wavelength λ'1 of the light source element 12-1 is controlled in a direction that decreases the monitoring result. At port (d), monitor 2B UP The monitoring results for Monitor 2B have increased. lоw The oscillation wavelength λ'3 of the light source element 12-3 is controlled in a direction that decreases the monitoring result. Monitor 3A at port (e) of unit circuit 21-3. UP The monitoring results increased, Monitor 3A lоw The oscillation wavelength λ'2 of the light source element 12-2 is controlled in a direction that decreases the monitoring result. Monitor 3B on port (f). UP Monitor results increased, Monitor 3B lоwThe oscillation wavelength λ'4 of the light source element 12-4 is controlled in a direction that decreases the monitoring result.

[0048] Next, in Figure 13, the heater of the demultiplexer 20 is controlled again to adjust the transmitted spectrum at each port. At port (a), monitor 1A UP Monitor results increased, Monitor 1A lоw The monitoring results show a decrease in power P 11 and P 12 Control this to shift the transmission spectrum. At port (b), monitor 1B UP The monitoring results for monitor 1B increased, lоw The monitor results show that the heater H is decreasing. 11 and H 13 Power P 11 and P 13 This controls the transmission spectrum to shift it.

[0049] On port (c), Monitor 2A UP The monitoring results for Monitor 2A increased. lоw The monitoring results show a decrease in power P 21 and P 22 Control this to shift the transmission spectrum. On port (d), monitor 2B UP The monitoring results for Monitor 2B have increased. lоw The monitoring results show a decrease in power P 21 and P 23 This controls the transmission spectrum to shift it. On port (e), monitor 3A UP The monitoring results increased, Monitor 3A lоw The monitoring results show a decrease in power P 31 and P 32 Control this to adjust the transmission spectrum. Port (f) is Monitor 3B UP Monitor results increased, Monitor 3B lоw The monitoring results show a decrease in power P 31 and P 33 Control the transmission spectrum to adjust it.

[0050] Next, in Figure 14, the wavelength controller 191A controls the oscillation wavelengths λ'1, λ'2, λ'3, and λ'4 of the light source elements 12-1 to 12-4 of the light source device 11A again. Monitor 2A is located at port (c) of the unit circuit 21-2. UP The monitoring results for Monitor 2A increased. lоw The oscillation wavelength λ'1 of the light source element 12-1 is controlled in a direction that decreases the monitoring result. Monitor 2B at port (d). UP The monitoring results for Monitor 2B have increased. lоw The oscillation wavelength λ'3 of the light source element 12-3 is controlled in a direction that decreases the monitoring result. At port (e) of the unit circuit 21-3, monitor 3A UP The monitoring results increased, Monitor 3A lоw The oscillation wavelength λ'2 of the light source element 12-2 is controlled in a direction that decreases the monitoring result. At port (f), monitor 3B UP Monitor results increased, Monitor 3B lоw The oscillation wavelength λ'4 of the light source element 12-4 is controlled in a direction that decreases the monitoring result.

[0051] The final state shown in Figure 15 is reached by repeatedly and alternately correcting the oscillation wavelengths of each light source element 12-1 to 12-4 of the light source device 11A and adjusting the transmission characteristics of the demultiplexer 20. In the controlled state shown in Figure 15, assuming the wavelengths of each subcarrier are λ''1, λ''2, λ''3, and λ''4, the peaks of the transmission spectrum of port (a) of the first-stage unit circuit 21-1 coincide with wavelengths λ''1 and λ''3, and the peaks of the transmission spectrum of port (b) coincide with wavelengths λ''2 and λ''4. The peak of the transmission spectrum of port (c) of the second-stage unit circuit 21-2 coincides with wavelength λ''1, and the peak of the transmission spectrum of port (d) coincides with wavelength λ''3. The peak of the transmission spectrum of port (e) of the second-stage unit circuit 21-3 coincides with wavelength λ''2, and the peak of the transmission spectrum of port (f) coincides with wavelength λ''4.

[0052] In this state, λ''1 is not the same as the set wavelength λ1 (λ''1 ≠ λ1), but the intervals between each wavelength, λ''1-λ'2, λ''2-λ''3, and λ''3-λ''4, are the same (λ''1-λ'2 = λ''2-λ''3 = λ''3-λ''4). By feeding back the monitoring results at the output stage of each wavelength of the demultiplexer 20 to the wavelength controller 191A, the oscillation wavelengths of each light source element 12 of the light source device 11A can be made equal and matched to the transmission characteristics of the demultiplexer 20. As a result, the wavelength spacing of the light source device 11A can be controlled with high precision using the monitoring results of the transmission characteristic control.

[0053] Figure 16A shows the change in each wavelength during light source wavelength control in the first embodiment. Figure 16B shows the change in the wavelength intervals during light source wavelength control. Figures 16A and 16B show that eight wavelengths are decoupled using a CAT configuration unit circuit cascaded in three stages, and the wavelength intervals of the light source device are controlled to be equal. In the horizontal direction, the process progresses from the initial state to port assignment, and then to light source wavelength correction. During the port assignment period, the transmission characteristics of the decoupler 20 are controlled based on the monitoring results present from the incident end of the decoupler 20 to the output port of the wavelength of interest. Laser wavelength correction is performed by adjusting the oscillation wavelength of the corresponding light source element 12 so that the monitoring results of the monitors provided at the output ports of each wavelength increase, and the monitoring results of the monitors connected to the optical waveguide on the opposite side of that output port decrease. The output ports are one of the two output waveguides of the AMZ25 at the end of the cascaded tree, and the other output waveguide is the optical waveguide on the opposite side of the output port. In the first embodiment, the wavelength spacing is controlled to be relatively uniform, so the wavelengths of all light sources fluctuate, but ultimately all wavelengths (i.e., optical frequencies) converge to equal intervals.

[0054] The effective optical path length difference of each AMZ25 of the demultiplexer 20 and the light source wavelength are controlled in parallel so that the monitor power is maximized at ports (c), (d), (e), and (f) of the demultiplexer 20 and minimized at the output waveguide on the opposite side of these ports. As a result, multiple wavelengths converge to the optimal state shown in Figures 16A and 16B, and this converged state is maintained.

[0055] The heater power can be controlled by adding a slight intensity fluctuation (dither ±Δ) to the heater current and detecting the direction of change in the monitor output. The control circuit 23 for "Inc" increases the heater power by one step if the monitor current I+ when dither +Δ is greater than the monitor current I- when dither -Δ is greater, indicating that the control direction is correct. The control circuit 23 for "Dec" decreases the heater power by one step if the monitor current I+ when dither +Δ is less than the monitor current I- when dither -Δ is greater, indicating that the control direction is correct.

[0056] The light source wavelength is controlled by adjusting the oscillation frequency of each light source element 12-1 to 12-2. For example, a slight offset (dither ±Δ) may be added to the oscillation wavelength of each light source element 12, and the oscillation frequency may be raised or lowered from the direction of change in the monitor output. The configuration and light source wavelength control of the first embodiment make it possible to improve frequency utilization efficiency while suppressing increases in the size and cost of the optical transceiver 10A.

[0057] <Second Embodiment> Figure 17 is a schematic diagram of the optical transceiver 10B of the second embodiment. In the second embodiment, the absolute value of the wavelength is controlled along with the wavelength spacing of the multiple subcarriers. A wavelength monitor or wavelength rocker is provided on only one of the multiple light source elements to control the absolute value of all wavelengths and the wavelength spacing.

[0058] The optical transceiver 10B includes a light source device 11B, an optical integrated circuit 15B, and a wavelength controller 191B. The wavelength controller 191A is implemented by the functions of the processor 19 (see Figure 3). The optical integrated circuit 15B includes a demultiplexer 20 and an optical transceiver circuit 17B. The receiving circuit 172B of the optical transceiver circuit 17A includes an optical demultiplexer 176, a plurality of balanced photodiodes (indicated as "BPD" in the figure) 175-1, 175-2, ..., 175-n (collectively referred to as "BPD175" as appropriate), and a plurality of 90° hybrid optical mixers 177-1, 177-2, ..., 177-n (collectively referred to as "90° hybrid optical mixer 177" as appropriate). The transmitting circuit 171B of the optical transmitting / receiving circuit 17B has a plurality of optical modulators 173-1, 173-2, ..., 173-n (collectively referred to as "optical modulator 173" as appropriate) and an optical multiplexer 175. The optical modulator 173 is, for example, an IQ modulator.

[0059] The optical transceiver circuit 17B is a front-end circuit for a digital coherent transceiver, and the receiving circuit 172B uses a portion of the output light from the light source device 11B as local light emission to detect the received optical signal with the 90° hybrid optical mixer 177. Therefore, the multiple light source elements 12 used in the light source device 11B require both uniform wavelength spacing and a uniform absolute value of wavelength.

[0060] To accurately determine the absolute value of the wavelength, a wavelength monitor 125 is provided on one light source element 12 (for example, light source element 12-1) in the light source device 11B, but wavelength monitors are not required for the other light source elements 12. By using the oscillation wavelength of light source element 12-1, which has the wavelength monitor 125, as the reference wavelength, and controlling the oscillation wavelengths of the other light source elements 12-2 to 12-n at equal intervals from the reference wavelength, a uniform wavelength spacing and the absolute value of the wavelength can be correctly obtained.

[0061] The monitoring results of the light separated by the demultiplexer 20 are used to control the wavelength interval and the absolute value of the wavelength. By using a CAT-configured demultiplexer 20, the heater power can be optimally controlled for each wavelength to optimize the transmission characteristics. Monitors PD202-1, 202-2, ..., 202-n may be provided for monitoring light of each wavelength, or the monitoring function of the demultiplexer 20 may be used.

[0062] Figure 18 is a schematic diagram of light source wavelength control using the monitoring function of the demultiplexer 20. The demultiplexer 20 is a CAT configuration demultiplexer, similar to the first embodiment. Monitor 2A for controlling the transmission characteristics of the demultiplexer 20. UP , 2B UP , 3A UP , and 3B UP The output is connected to the input of the wavelength controller 191B via the feedback signal line 200. Based on the monitoring results, the wavelength controller 191B controls the absolute values ​​and wavelength spacing of the oscillation wavelengths λ1, λ2, λ3, and λ4 of each light source element 12-1, 12-2, 12-3, and 12-4 of the light source device 11B.

[0063] Figure 19 shows the initial state of the light source wavelength and the transmission characteristics of the demultiplexer. The wavelengths and transmission characteristics at ports (a), (b), (c), (d), (e), and (f) in Figure 18 are shown, respectively. The dotted lines indicate wavelengths λ1, λ2, λ3, and λ4, which are the center wavelengths of each subcarrier set at equal intervals. λ'1, λ'2, λ'3, and λ'4 are the wavelengths contained in the light output from the light source device 11B and incident on the demultiplexer 20. λ'1, λ'2, and λ'4 are shifted to the lower frequency side (longer wavelength side) from λ1, λ2, and λ4, while λ'3 is shifted to the higher frequency side (shorter wavelength side) from λ3.

[0064] Figures 20-22 show examples of port assignments for each wavelength. In Figure 20, the light source element 12-1 is turned on (activated), and the output light from the light source element 12-1 is incident on the demultiplexer 20. At this time, the wavelength monitor 125 of the light source device 11B is used to fix the oscillation wavelength λ'1 of the light source element 12-1 to λ1. Light of wavelength λ1 passes through ports (a) and (c), but the peak of the transmission spectrum does not coincide with λ1.

[0065] In Figure 21, port (a) is connected to monitor 1A. UP Monitor results increased, Monitor 1A lоw The monitoring results show a decrease in power P 11 and P 12This controls the transmission spectrum to shift it. At this time, there is no feedback from monitor 1B at port (b), but power P 11 The transmission spectrum shifts due to the influence of the control.

[0066] On port (c), Monitor 2A UP The monitoring results for Monitor 2A increased. lоw The monitoring results show a decrease in power P 21 and P 22 This controls the transmission spectrum to shift it. At this time, there is no feedback from monitor 2B at port (d), but power P 21 The transmission spectrum shifts due to the influence of the control. At ports (e) and (f), there is no optical input to the unit circuit 21-3, so the transmission spectrum hardly changes.

[0067] Next, similar to the first embodiment, light source element 12-2 is turned on to add wavelength λ'2. Light source elements 12-1 and 12-2 become active. At ports (a) to (f), the heater power is adjusted so that the monitoring result of the monitor connected to the control circuit of "Inc" increases and the monitoring result of the monitor connected to the control circuit of "Dec" decreases. Then, wavelength λ'3 is added. At ports (a) to (f), the heater power is adjusted so that the monitoring result of the monitor connected to the control circuit of "Inc" increases and the monitoring result of the monitor connected to the control circuit of "Dec" decreases.

[0068] In Figure 22, the last wavelength λ'4 is added to control the transmission spectrum. Monitor 1A on port (a). UP Monitor results increased, Monitor 1A lоw The monitoring results show a decrease in power P 11 and P 12 Control this to shift the transmission spectrum. At port (b), monitor 1B UP Monitor results increased, Monitor 1B lоw The monitor results show that the heater H is decreasing. 11 and H 13 Power P 11 and P 13Control this to shift the transmission spectrum. Monitor 2A on port (c) UP The monitoring results for Monitor 2A increased. lоw The monitoring results show a decrease in power P 21 and P 22 Controls the Monitor2B on port (d). UP The monitoring results for Monitor 2B have increased. lоw The monitoring results show a decrease in power P 21 and P 23 Controls the monitor 3A on port (e). UP The monitoring results increased, Monitor 3A lоw The monitoring results show a decrease in power P 31 and P 32 It controls the monitor 3B on port (f). UP Monitor results increased, Monitor 3B lоw The monitoring results show a decrease in power P 31 and P 33 Control.

[0069] In the state shown in Figure 22, the peaks and wavelengths of the transmission spectrum match at ports (c), (d), (e), and (f), but only the reference wavelength λ1 matches the wavelengths designed to be equally spaced. Therefore, the light source device 11B adjusts the oscillation wavelengths of light source elements 12-2, 12-3, and 12-4, excluding light source element 12-1. The oscillation wavelength of light source element 12-1 is locked to λ1 by the wavelength monitor 125.

[0070] Figure 23 shows the correction of the light source wavelength. Monitor 2B at port (d) of the unit circuit 21-2 of the demultiplexer 20. UP The monitoring results for Monitor 2B have increased. lоw The oscillation wavelength λ'3 of the light source element 12-3 is controlled in a direction that decreases the monitoring result. At port (e) of the unit circuit 21-3, monitor 3A UP The monitoring results increased, Monitor 3A lоw The oscillation wavelength λ'2 of the light source element 12-2 is controlled in a direction that decreases the monitoring result. At port (f), monitor 3B UP Monitor results increased, Monitor 3B lоwThe oscillation wavelength λ'4 of the light source element 12-4 is controlled in a direction that decreases the monitoring result.

[0071] Next, in Figure 24, the heater of the demultiplexer 20 is controlled again to adjust the transmitted spectrum at each port. At port (a), monitor 1A UP Monitor results increased, Monitor 1A lоw The monitoring results show a decrease in power P 11 and P 12 Control this to shift the transmission spectrum. At port (b), monitor 1B UP The monitoring results for monitor 1B increased, lоw The monitor results show that the heater H is decreasing. 11 and H 13 Power P 11 and P 13 This controls the transmission spectrum to shift it.

[0072] On port (c), Monitor 2A UP The monitoring results for Monitor 2A increased. lоw The monitoring results show a decrease in power P 21 and P 22 Control this to shift the transmission spectrum. On port (d), monitor 2B UP The monitoring results for Monitor 2B have increased. lоw The monitoring results show a decrease in power P 21 and P 23 This controls the transmission spectrum to shift it. On port (e), monitor 3A UP The monitoring results increased, Monitor 3A lоw The monitoring results show a decrease in power P 31 and P 32 Control this to adjust the transmission spectrum. Port (f) is Monitor 3B UP Monitor results increased, Monitor 3B lоw The monitoring results show a decrease in power P 31 and P 33 Control the transmission spectrum to adjust it.

[0073] Next, the wavelength controller 191B controls the oscillation wavelengths λ'2, λ'3, and λ'4 of the light source elements 12-2, 12-3, and 12-4 of the light source device 11B again. By repeatedly correcting the oscillation wavelengths of the light source elements 12-2, 12-3, and 12-4 of the light source device 11B and adjusting the transmission characteristics of the demultiplexer 20 alternately, the final state shown in Figure 25 is reached. In Figure 25, light with wavelengths matching the equally spaced wavelengths λ1, λ2, λ3, and λ4 passes through ports (c), (d), (e), and (f) at maximum power. This achieves both uniform wavelength spacing and uniform absolute wavelengths.

[0074] Figure 26A shows the change in each wavelength during light source wavelength control in the second embodiment, and Figure 26B shows the change in each wavelength interval during light source wavelength control. In Figures 26A and 26B, the horizontal axis shows the transition from the initial state to port assignment and then to light source wavelength correction. In the second embodiment, the wavelength of light source element 12-1 is locked to λ1 by the wavelength monitor 125, so the wavelength of LD1 remains constant throughout the control process. After port assignment, the oscillation wavelengths of light source elements 12 other than LD1 are adjusted such that the monitoring result at the output port connected to one output waveguide of the AMZ25 at the end of the cascaded tree increases, and the monitoring result at the monitor connected to the optical waveguide on the opposite side of the AMZ25 decreases.

[0075] The light source wavelength is adjusted in parallel with the control of the transmission characteristics of the demultiplexer 20 based on monitoring results between the incident end of the demultiplexer 20 and the output port for each wavelength. This ensures that multiple subcarriers are maintained at the absolute value of the set wavelength and converge to the optimal state shown in Figures 26A and 26B.

[0076] In Figure 26B, the control method of the embodiment causes the frequency intervals of the eight different wavelengths of light to converge to around 75 GHz, with a variation of only ±0.9 GHz. As will be described later, the optical frequency accuracy (variation) when wavelength control is performed by providing a wavelength monitor or wavelength rocker for each light source element 12 in a typical configuration is ±1.5 GHz, so the control accuracy of the embodiment is high. In the second embodiment, the size and cost of the light source device 11B or optical transceiver 10B can be significantly reduced while improving frequency utilization efficiency with higher accuracy than conventional methods.

[0077] Figure 27 shows the effect of light source wavelength control in the second embodiment in comparison with a comparative example. In Figure 27(A), using the configuration of the embodiment, only the oscillation wavelength λ1 of the light source element 12-1 is locked by the wavelength monitor 125, and the other wavelengths λ2, λ3, and λ4 are controlled by the wavelength controller 191B. The variation in the center wavelength of λ1 locked by the wavelength monitor 125 is ±1.5 GHz, but the variation in the center wavelengths of λ2, λ3, and λ4 adjusted by the method of the embodiment is 0.9 GHz. Even when the center wavelengths of adjacent subcarriers (for example, λ2 and λ3) vary in opposite directions, the gap is a maximum of 1.8 GHz.

[0078] In contrast, in the comparative configuration of Figure 27(B), a wavelength monitor is placed on each light source element 12, and the oscillation wavelength of each light source element 12 is locked by the wavelength monitor. In this case, a variation of 1.5 GHz occurs in all light source elements, and the spacing between adjacent subcarriers (for example, λ2 and λ3) when their center wavelengths vary in opposite directions can reach a maximum of 3 GHz. By controlling the light source wavelength in this embodiment, the optical frequency spacing of the subcarriers is controlled uniformly and densely, thereby increasing the efficiency of spectral utilization.

[0079] Through the first and second embodiments, a light source device 11 including multiple light source elements 12 can accurately control the spacing between multiple wavelengths to be equally spaced, either without using a wavelength monitor or wavelength rocker, or using only a single wavelength monitor or wavelength rocker. This improves frequency utilization efficiency while suppressing increases in size and cost of the light source device 11 or optical transceiver 10. The configuration and light source wavelength control method of the embodiments can also be applied to configurations that separate two wavelengths using one unit circuit 21, configurations that separate eight wavelengths by cascading three unit circuits 21, and configurations that separate sixteen wavelengths by cascading four unit circuits 21. In these cases as well, the spacing between multiple wavelengths can be maintained equally and closely spaced regardless of manufacturing variations in the PIC, manufacturing variations in each light source element of the light source device, environmental fluctuations, and aging.

[0080] The following additional information is provided in response to the above description. (Note 1) Optical transceiver circuit, A light source device that combines and outputs light emitted from multiple light source elements of different wavelengths, A demultiplexer that splits the light output from the light source device into multiple wavelengths and supplies them to the optical transmitting and receiving circuit, A monitor that monitors each of the plurality of wavelengths at the output port of the demultiplexer, A wavelength controller that controls the wavelengths of the plurality of light source elements based on the monitoring results of the monitor, It has, The demultiplexer has multiple unit circuits in which three asymmetric Mach-Zehnder interferometers having a predetermined arm length difference are connected in a tree-like manner, and the multiple unit circuits are cascaded in a tree-like manner, and the monitor is placed in the output waveguide of the asymmetric Mach-Zehnder interferometer at the end of the cascaded tree and connected to the wavelength controller by a signal line. Optical transceiver. (Note 2) The light source device has a wavelength monitor or wavelength rocker only for the first light source element among the plurality of light source elements. The wavelength controller fixes the wavelength of the first light source element using the wavelength monitor or the wavelength rocker, and controls the wavelengths of the light source elements other than the first light source element based on the monitoring results. The optical transceiver described in Appendix 1. (Note 3) The wavelength controller controls the wavelengths of the plurality of light source elements so that the plurality of wavelengths are equally spaced. The optical transceiver described in Appendix 1. (Note 4) The wavelength controller controls the wavelengths of the plurality of light source elements so that the plurality of wavelengths have a predetermined absolute value and are equally spaced. The optical transceiver described in Appendix 2. (Note 5) The output waveguide of the aforementioned terminal asymmetric Mach-Zehnder interferometer is branched into two. The demultiplexer has a first monitor connected to one output waveguide of the terminal asymmetric Mach-Zehnder interferometer to monitor light of the corresponding wavelength, and a second monitor connected to the other output waveguide. The wavelength controller controls the wavelengths of the plurality of light source elements in a direction that increases the first monitoring result of the first monitor and decreases the second monitoring result of the second monitor. The optical transceiver described in Appendix 1. (Note 6) The demultiplexer has a control mechanism that controls the transmission characteristics of the demultiplexer based on the first monitor result and the second monitor result. The wavelength controller controls the wavelengths of the plurality of light source elements in parallel with the control of the transmission characteristics by the control mechanism. The optical transceiver described in Appendix 5. (Note 7) The control mechanism includes a first control circuit that controls the effective optical path length of the leading asymmetric Mach-Zehnder interferometer of a unit circuit including the terminal asymmetric Mach-Zehnder interferometer so that the first monitoring result increases, and a second control circuit that controls the effective optical path length of the terminal asymmetric Mach-Zehnder interferometer so that the second monitoring result decreases. The optical transceiver described in Appendix 6. (Note 8) An optical transceiver for subcarrier transmission, equipped with an optical transceiver as described in any of the appendices 1 to 7. (Note 9) Prepare a light source device having multiple light source elements of different wavelengths, Multiple unit circuits, each consisting of three asymmetrical Mach-Zehnder interferometers with predetermined arm length differences connected in a tree-like structure, are cascaded in a tree-like structure to form a demultiplexer into which light of multiple wavelengths is incident from the light source device. The light of the multiple wavelengths separated by the demultiplexer is monitored at the output port of the demultiplexer. Based on the monitoring results, the wavelengths of the multiple light source elements are controlled by the wavelength controller. A method for controlling the wavelength of a light source. (Note 10) The first wavelength of the first light source element among the plurality of light source elements is fixed, The wavelength controller controls the wavelengths of the light source elements, excluding the first light source element. The method for controlling the wavelength of the light source as described in Appendix 9. (Note 11) The wavelength controller controls the oscillation wavelengths of the multiple light source elements so that the multiple wavelengths are equally spaced. The method for controlling the wavelength of the light source as described in Appendix 9. (Note 12) The wavelength controller controls the oscillation wavelengths of the plurality of light source elements so that the plurality of wavelengths have a predetermined absolute value and are equally spaced. The method for controlling the wavelength of the light source as described in Appendix 10. (Note 13) A first monitor is connected to monitor the light of the wavelength corresponding to one of the two output waveguides of the asymmetric Mach-Zehnder interferometer at the end of the cascaded tree, and a second monitor is connected to the other waveguide. The wavelength controller controls the oscillation wavelength of the corresponding light source element in a direction that increases the first monitoring result of the first monitor and decreases the second monitoring result of the second monitor. The method for controlling the wavelength of the light source as described in Appendix 9. [Explanation of Symbols]

[0081] 1A UP , 1A low , 1B UP , 1B low monitor 2A UP , 2B UP , 3A UP , 3B UP Monitor (First Monitor) 2A low , 2B low , 3A low , 3B low Monitor (Second Monitor) 10, 10A, 10B Optical Transceivers 11, 11A, 11B Light source device 12, 12-1~12n light source element 13 Multiplexer 13A, 13B Optical Coupler 15, 15A, 15B Optical Integrated Circuits (PICs) 17 Optical Transceiver Circuit 171 Transmitter Circuit 172 Receiving Circuit 19 processors 191A, 191B Wavelength Controller 20 duplexer 21-1, 21-2, 21-3 Unit Circuits 22a~22f Control circuit (Second control circuit) 23-1, 23-2, 23-3 Control circuits (First control circuit) 25, 25 11 ,twenty five 12 ,twenty five 13 ,twenty five 21 ,twenty five 22 ,twenty five 23 ,twenty five 31 ,twenty five 32 ,twenty five 33 AMZ (Asymmetric Mach-Zehnder Interferometer) 100 Optical transmission device 130-1~130n transponder (optical transceiver) 200 Feedback signal line 201-1~201-n Optical Path Length Controller (Control Mechanism) 202-1~202-n Monitor PD (Monitor)

Claims

1. Optical transceiver circuit, A light source device that combines and outputs light emitted from multiple light source elements of different wavelengths, A demultiplexer that splits the light output from the light source device into multiple wavelengths and supplies them to the optical transmitting and receiving circuit, A monitor that monitors each of the plurality of wavelengths at the output port of the demultiplexer, A wavelength controller that controls the wavelengths of the plurality of light source elements based on the monitoring results of the monitor, It has, The demultiplexer has a plurality of unit circuits in which three asymmetric Mach-Zehnder interferometers having a predetermined difference in arm length are connected in a tree-like manner, and the plurality of such unit circuits are cascaded in a tree-like manner, and the monitor is placed in the output waveguide of the asymmetric Mach-Zehnder interferometer at the end of the cascaded tree and connected to the wavelength controller by a signal line. Optical transceiver.

2. The light source device is equipped with a wavelength monitor or wavelength rocker only for the first light source element among the plurality of light source elements. The wavelength controller fixes the wavelength of the first light source element using the wavelength monitor or the wavelength rocker, and controls the wavelengths of the light source elements other than the first light source element based on the monitoring results. The optical transceiver according to claim 1.

3. The wavelength controller controls the wavelengths of the plurality of light source elements so that the plurality of wavelengths are equally spaced. The optical transceiver according to claim 1.

4. The wavelength controller controls the wavelengths of the plurality of light source elements so that the plurality of wavelengths have a predetermined absolute value and are equally spaced. The optical transceiver according to claim 2.

5. The output waveguide of the aforementioned terminal asymmetric Mach-Zehnder interferometer is branched into two. The demultiplexer has a first monitor connected to one output waveguide of the terminal asymmetric Mach-Zehnder interferometer to monitor light of the corresponding wavelength, and a second monitor connected to the other output waveguide. The wavelength controller controls the wavelengths of the plurality of light source elements in a direction that increases the first monitoring result of the first monitor and decreases the second monitoring result of the second monitor. The optical transceiver according to claim 1.

6. The demultiplexer has a control mechanism that controls the transmission characteristics of the demultiplexer based on the first monitoring result and the second monitoring result. The wavelength controller controls the wavelengths of the plurality of light source elements in parallel with the control of the transmission characteristics by the control mechanism. The optical transceiver according to claim 5.

7. An optical transceiver for subcarrier transmission, comprising an optical transceiver according to any one of claims 1 to 6.

8. The light source device synthesizes and outputs light emitted from multiple light source elements of different wavelengths, A demultiplexer, in which multiple unit circuits, each consisting of three asymmetric Mach-Zehnder interferometers with a predetermined difference in arm length, are connected in a tree-like manner, cascades in a tree-like manner to split the light output from the light source device into multiple wavelengths and supplies them to the optical transmission / reception circuit. The wavelength controller monitors the multiple wavelengths of light separated by the demultiplexer at the output port of the demultiplexer and controls the wavelengths of the multiple light source elements based on the monitoring results of a monitor located in the output waveguide of an asymmetric Mach-Zehnder interferometer at the end of a cascaded tree and connected to the wavelength controller by a signal line. A method for controlling the wavelength of a light source.

9. The wavelength controller fixes the first wavelength of the first light source element among the plurality of light source elements, The wavelength controller controls the wavelengths of the light source elements excluding the first light source element. The method for controlling the wavelength of a light source according to claim 8.

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