JP2017053908A - Wavelength selection module and optical switch control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the influence of crosstalk.SOLUTION: The wavelength selection module comprises: an optical switch for receiving inputs of signal lights having N kinds of different wavelengths to output one of the signal lights having N kinds of wavelengths; and an optical switch control part for controlling the optical switch. The optical switch includes a plurality of sub optical switches for inputting two or more signal lights having wavelengths adjacent to each other when the N kinds of different wavelengths are arranged in the wavelength axis direction, to output a signal light having one wavelength. The sub optical switches are connected in multi stages so as to output one of the signal lights having the N kinds of different wavelengths, and the optical switch control part controls the sub optical switches so as to output the signal light having a wavelength farther separated in the wavelength axis direction than the wavelength of one signal light output from the optical switch.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a technology of a wavelength selection element used in optical communication.

  In recent years, with the rapid spread of the Internet, there has been a demand for increasing the capacity, sophistication, and economy of optical access systems. Research on PON (Passive Optical Network) is underway as a method for realizing such a system. In PON, transmission lines extending to locations of a plurality of users are concentrated in a single transmission line. An optical passive element such as an optical power splitter is used for the concentrator. With such a technique, a transmission path between the center apparatus and the optical passive element can be shared by a plurality of users. Therefore, it is possible to provide an economically advantageous optical access communication system.

  In present Japan, GE-PON (Gigabit Ethernet [registered trademark] -PON) is introduced. In GE-PON, 1 Gbps class line capacity is shared by time division multiplexing (TDM) with a maximum of 32 users. With such a configuration, an FTTH (Fiber To The Home) service has begun to be provided at a realistic price for users.

  As a next-generation optical access system capable of meeting the needs for further increase in capacity, research on 10 Gbps-class 10G-EPON is underway. In 2009, IEEE standardization of 10G-EPON was completed. In 10G-EPON, due to an increase in the bit rate of the optical transceiver, it is possible to increase the capacity while using the same transmission line as the existing GE-PON. However, depending on the service, it may be possible to increase the capacity beyond the 10 Gbps class. However, in order to further increase the bit rate of the transceiver (40 or 100 Gbps class), a significant increase in cost of the transceiver has been a problem.

  As a means to realize an economically large capacity, it is possible to add wavelength tunability to the optical transceiver so that the optical transceiver in the station side device can be added in stages according to the bandwidth requirement. Proposed. More specifically, a wavelength tunable WDM / TDM-PON combining TDM and wavelength division multiplexing (WDM: Wavelength Division Multiplexing) has been reported (for example, see Patent Document 1).

Japanese Patent Laid-Open No. 11-252046

  In the wavelength tunable WDM / TDM-PON, an optical transmitter / receiver having wavelength variability is required for a subscriber apparatus or a station side apparatus. A signal light (hereinafter referred to as “wavelength multiplexed light”) in which N wavelengths are wavelength-multiplexed is demultiplexed into signal light of each wavelength by a wavelength filter, and then a PD (Photo Diode) corresponding to each wavelength. Thus, the signal light is photoelectrically converted into an electric signal. Thereafter, an electrical signal corresponding to the signal light having a desired wavelength is selected by the electrical switch. Such processing is realized by a wavelength tunable receiver.

Such a wavelength tunable receiver converts signal light of any one wavelength from input wavelength multiplexed light into an electrical signal. At this time, there may be a crosstalk phenomenon in which the wavelengths that are adjacent to each other in the wavelength order remain in the wavelength of the signal light converted into the electrical signal.
In view of the above circumstances, an object of the present invention is to provide a technique capable of reducing the influence of crosstalk.

  According to one aspect of the present invention, an optical switch that receives input of signal light having N different wavelengths and outputs one signal light from signal light having N wavelengths, and optical switch control that controls the optical switch The optical switch includes a plurality of sub-optical switches that input a plurality of adjacent wavelength signal lights and output a single wavelength signal light when N different wavelengths are arranged in the wavelength axis direction. And the sub optical switch is connected in multiple stages so that one signal light is output from among the N types of signal light having different wavelengths, and the optical switch control unit outputs one signal light from the optical switch. It is a wavelength selection module that controls the sub optical switch so that signal light having a wavelength farther apart in the wavelength axis direction than the wavelength of one signal light is output.

  One aspect of the present invention is the above-described wavelength selection module, in which, when N is 4, the optical switch includes a first signal light having the longest wavelength and a signal light having the next longest wavelength. A second signal light, a first optical switch that outputs one of the first signal light and the second signal light, and a second signal light having a wavelength next to the second signal light. A second optical switch that inputs three signal lights and a fourth signal light having the shortest wavelength among the four signal lights, and outputs one of the third signal light and the fourth signal light; A signal light output from one optical switch and a signal light output from the second optical switch, and a third optical switch that outputs one of them, and the optical switch control unit includes: When the first signal light is output from the optical switch, the first optical switch Controls to output the first signal light, controls the second optical switch to output the fourth signal light, and outputs the first signal light to the third optical switch. To be controlled.

  One aspect of the present invention is an optical switch control method for controlling an optical switch that receives input of signal light having N different wavelengths and outputs one signal light from signal light having N wavelengths. The optical switch includes a plurality of sub-optical switches that input a plurality of signal lights having adjacent wavelengths when N different wavelengths are arranged in the wavelength axis direction and output a signal light having one wavelength, and the sub-optical switch Are connected in multiple stages so that one signal light is output from among the N types of signal light of different wavelengths, and more in the wavelength axis direction than the wavelength of one signal light output from the optical switch. And a control step of controlling the sub optical switch so that signal light having a wavelength greatly separated is output.

  According to the present invention, the influence of crosstalk can be reduced.

It is a schematic block diagram showing the function structure of the wavelength selection module used for a wavelength variable receiver. FIG. 5 is a diagram illustrating a specific example of control of the optical switch control unit 30. It is a figure which shows the specific example of the input light in each sub optical switch, or output light in case output signal light is signal light of wavelength (lambda) 1. It is a figure which shows the specific example of the input light or output light in each sub optical switch when output signal light is wavelength (lambda) 2. It is a figure which shows the specific example of the input light in each sub optical switch, or output light in case an output signal light is wavelength (lambda) 3. It is a figure which shows the specific example of the input light or output light in each sub optical switch in case output signal light is wavelength (lambda) 4. Wavelength demultiplexer 101, optical switch 102, and optical switch of a wavelength selection module to which wavelength multiplexed light in which eight wavelengths (λ1, λ2, λ3, λ4, λ5, λ6, λ7, λ8) are multiplexed is input 3 is a schematic block diagram illustrating a functional configuration of a control unit 30. FIG. FIG. 5 is a diagram illustrating a specific example of control of the optical switch control unit 30.

FIG. 1 is a schematic block diagram showing a functional configuration of a wavelength selection module used in a wavelength tunable receiver. The wavelength selection module is mounted in Package10. The package 10 includes a mount 20 and an optical switch control unit 30. The mount 20 includes a PLC (Planar Lightwave Circuit) 40, a photoelectric conversion unit 50, and an amplification unit 60. The mount 20 may be constructed as a terrace made of, for example, SiO ₂ . The optical switch control unit 30 controls an optical switch provided in the PLC 40.

  The PLC 40 receives the wavelength multiplexed light input to the wavelength selection module, and outputs one signal light among a plurality of signal lights multiplexed on the wavelength multiplexed light.

  The photoelectric conversion unit 50 is configured using, for example, a PD (PhotoDiode). More specifically, the photoelectric conversion unit 50 may be configured using an APD (Avalanche PhotoDiode). The photoelectric conversion unit 50 performs photoelectric conversion based on the signal light output by the PLC 40. The photoelectric conversion unit 50 outputs an electrical signal generated by photoelectric conversion.

  The amplification unit 60 is configured using, for example, a TIA (Trans Impedance Amplifier). The amplifying unit 60 amplifies the electric signal output by the photoelectric conversion unit 50. The amplification unit 60 outputs the amplified electrical signal.

  Next, the PLC 40 will be described in more detail. The PLC 40 includes a wavelength demultiplexer 101 and an optical switch 102. The wavelength demultiplexer 101 receives the wavelength multiplexed light input to the wavelength selection module and demultiplexes the wavelength multiplexed light. The wavelength demultiplexer 101 outputs signal light of each wavelength that has been multiplexed with the input wavelength multiplexed light. In this embodiment, signal light having four wavelengths (λ1, λ2, λ3, λ4) is multiplexed in the wavelength multiplexed light. Therefore, the wavelength demultiplexer 101 outputs signal light with wavelength λ1, signal light with wavelength λ2, signal light with wavelength λ3, and signal light with wavelength λ4. Wavelength λ1 is the longest, then wavelength λ2 is the longest, wavelength λ3 is the longest, and wavelength λ4 is the shortest. The wavelength demultiplexer 101 may be configured using, for example, an AWG (Arrayed Waveguide Grating). The wavelength demultiplexer 101 may be configured by arranging, for example, a TFF (Thin Film Filter) in a groove-like trench formed on the PLC. An advantage of using AWG is that it can be monolithically integrated with TOSW described later. That is, the optical alignment between the optical output port of the AWG and the input port of the optical switch is not required, which is advantageous for downsizing and economy. Furthermore, the temperature dependence of the transmission center wavelength of the AWG can be made extremely small by making the AWG an Thermal AWG having a very small temperature dependence. Furthermore, there is no need to mount a temperature adjustment element such as a thermoelectric semiconductor element in the package. Therefore, it is advantageous for further miniaturization and economy.

  The optical switch 102 receives the signal light of each wavelength demultiplexed by the wavelength demultiplexer 101. The optical switch 102 outputs signal light of one wavelength among the signal light of each wavelength according to the control by the optical switch control unit 30. The optical switch 102 is composed of a multi-stage optical switch, and outputs signal light of one wavelength from among m kinds of wavelength signal light at each stage. With such a configuration, the optical switch 102 finally outputs signal light of one wavelength.

  In the present embodiment, the optical switch 102 includes three sub optical switches (a first optical switch 201, a second optical switch 202, and a third optical switch 203). Each sub optical switch may be configured using, for example, a thermo-optic switch (TOSW: Thermo-Optic SWitch). The first optical switch 201 receives the signal light having the wavelength λ1 and the signal light having the wavelength λ2. The second optical switch 202 receives the signal light having the wavelength λ3 and the signal light having the wavelength λ4. The third optical switch 203 receives the signal light output from the first optical switch 201 and the signal light output from the second optical switch 202. The first optical switch 201, the second optical switch 202, and the third optical switch 203 each output signal light according to a control signal output from the optical switch control unit 30. Although not shown in the figure, the control signal uses the optical switch 102 to change the reception wavelength designated by the OLT (the carrier station terminal device) to the ONU (subscriber terminal device) by the control circuit in the ONU. Is converted into a control signal for driving.

  FIG. 2 is a diagram illustrating a specific example of the control of the optical switch control unit 30. The optical switch control unit 30 controls each sub optical switch in accordance with the signal light output from the optical switch 102 (hereinafter referred to as “output signal light”). More specifically, the optical switch control unit 30 outputs the output target signal light for the sub optical switch to which the signal light having the same wavelength as the output signal light (hereinafter referred to as “output target signal light”) is input. To be controlled. On the other hand, for the sub optical switch to which only signal light having a wavelength different from the output signal light is input, control is performed so that signal light having a wavelength farther apart in the wavelength axis direction than the wavelength of the output signal light is output. .

  For example, when the output signal light is the signal light having the wavelength λ1, the first optical switch 201 is controlled so that the signal light having the wavelength λ1, which is the output target signal light, is output. The second optical switch 202 is controlled so that the signal light having the wavelength λ4, which is the signal light having a wavelength farther from the wavelength λ1, is output because the signal light having the wavelength λ1 that is the output target signal light is not input. . The third optical switch 203 is controlled so that the signal light of λ1 that is the output target signal light is output.

  For example, when the output signal light is the signal light having the wavelength λ2, the first optical switch 201 is controlled so that the signal light having the wavelength λ2 that is the output target signal light is output. The second optical switch 202 is controlled so that the signal light having the wavelength λ4, which is the signal light having a wavelength farther from the wavelength λ2, is output because the signal light having the wavelength λ2 that is the target signal light is not input. . The third optical switch 203 is controlled so that the signal light of λ2, which is the output target signal light, is output.

  For example, when the output signal light is the signal light having the wavelength λ3, the signal light having the wavelength λ3 that is the output target signal light is not input to the first optical switch 201. Therefore, control is performed so that the signal light having the wavelength λ1, which is the signal light having a wavelength farther from the wavelength λ3, is output. The second optical switch 202 is controlled so that the signal light having the wavelength λ3, which is the output target signal light, is output. The third optical switch 203 is controlled so that the signal light of λ3, which is the output target signal light, is output.

  For example, when the output signal light is the signal light having the wavelength λ4, the signal light having the wavelength λ4 that is the output target signal light is not input to the first optical switch 201. For this reason, control is performed so that signal light of wavelength λ1, which is signal light having a wavelength far from wavelength λ4, is output. The second optical switch 202 is controlled so that signal light having a wavelength λ4, which is output target signal light, is output. The third optical switch 203 is controlled so that the signal light of λ4 that is the output target signal light is output.

  FIG. 3 is a diagram illustrating a specific example of input light or output light in each sub optical switch when the output signal light is signal light having a wavelength λ1. Wavelength multiplexed light obtained by multiplexing four signal lights of wavelength λ1, wavelength λ2, wavelength λ3, and wavelength λ4 is input to the wavelength demultiplexer 101. The first optical switch 201 receives signal light having wavelengths λ1 and λ2. Neither signal intensity is attenuated so much at this point. To the second optical switch 202, signal lights having wavelengths λ3 and λ4 are input. Neither signal intensity is attenuated so much at this point. The first optical switch 201 outputs signal light having a wavelength λ1. In this case, the first optical switch 201 attenuates signal light that is not output. Specifically, the signal light of wavelength λ2 is attenuated. The second optical switch 202 outputs signal light having a wavelength λ4. Similarly, in this case, the second optical switch 202 attenuates signal light that is not output. Specifically, the signal light of wavelength λ3 is attenuated. The signal light output from the first optical switch 201 and the signal light output from the second optical switch 202 are input to the third optical switch 203. The third optical switch 203 outputs signal light having a wavelength λ1. In this case, the third optical switch 203 attenuates the signal light having the wavelength λ2, the signal light having the wavelength λ3, and the signal light having the wavelength λ4, which are signal lights that are not output. As a result, the signal light illustrated as the third optical switch output light is output. In the third optical switch output light, the intensity of the signal light having the wavelength λ3 is smaller than the intensity of the signal light having the wavelength λ4. The signal light of wavelength λ3 is closer in wavelength to the signal light of wavelength λ1, which is the output target signal light, than the signal light of wavelength λ4. For this reason, the signal light with the wavelength λ3 is easier to crosstalk with the signal light with the wavelength λ1 that is the output target signal light than the signal light with the wavelength λ4. In this embodiment, since the signal light (wavelength λ4) having a wavelength farther than the wavelength (λ1) of the output target signal light is output from the second optical switch 202, the influence of crosstalk on the output target signal light is reduced. Is possible. FIG. 3 shows the third optical switch output light when the second optical switch 202 outputs the signal light having the wavelength λ3 as a comparative example. Compared to such a comparative example, the third optical switch output light in this embodiment is less affected by crosstalk.

  For example, in each sub optical switch, signal light having a wavelength controlled to be output is output without being attenuated, and signal light having a wavelength controlled not to be output is output with an intensity of −20 dB as compared with the input time. Assume that When the output target optical signal is a signal light having a wavelength λ1, the signal light output from the first optical switch 201 includes an unattenuated signal light having a wavelength λ1 and a signal having a wavelength λ2 having an intensity of −20 dB. Includes light. The signal light output from the second optical switch 202 includes signal light having a wavelength λ3 having an intensity of −20 dB and signal light having a wavelength λ4 that is not attenuated. The signal light output from the third optical switch 203 includes the signal light having the wavelength λ1 that is not attenuated, the signal light having the wavelength λ2 having an intensity of −20 dB, and the intensity of −40 dB by the second attenuation. The signal light having the wavelength λ3 and the signal light having the wavelength λ4 having an intensity of −20 dB are included.

  4 to 6 are diagrams illustrating specific examples of input light or output light in each sub optical switch when the output signal light has wavelengths λ2 to 4, respectively. Detailed description of FIGS. 4 to 6 will be omitted.

  FIG. 7 shows a wavelength demultiplexer 101 of a wavelength selection module, an optical switch to which wavelength multiplexed light into which 8 types of wavelengths (λ1, λ2, λ3, λ4, λ5, λ6, λ7, λ8) are multiplexed is input. It is a schematic block diagram which shows the function structure of 102 and the optical switch control part 30. The wavelength demultiplexer 101 includes a signal light having a wavelength λ1, a signal light having a wavelength λ2, a signal light having a wavelength λ3, a signal light having a wavelength λ4, a signal light having a wavelength λ5, a signal light having a wavelength λ6, a signal light having a wavelength λ7, and a wavelength. The signal light of λ8 is output. Wavelength λ1 is the longest, then wavelength λ2 is longest, then wavelength λ3 is long, then wavelength λ4 is long, then wavelength λ5 is long, then wavelength λ6 is long, then wavelength λ7 is long, wavelength λ8 Is the shortest. The wavelength demultiplexer 101 may be configured using, for example, AWG. The wavelength demultiplexer 101 may be configured by arranging, for example, a TFF in a groove-like trench formed on a PLC. An advantage of using AWG is that it can be monolithically integrated with TOSW described later. That is, the optical alignment between the optical output port of the AWG and the input port of the optical switch is not required, which is advantageous for downsizing and economy. Furthermore, the temperature dependence of the transmission center wavelength of the AWG can be made extremely small by making the AWG an Thermal AWG having a very small temperature dependence. Furthermore, there is no need to mount a temperature adjustment element such as a thermoelectric semiconductor element in the package. Therefore, it is advantageous for further miniaturization and economy.

  The optical switch 102 receives the signal light of each wavelength demultiplexed by the wavelength demultiplexer 101. The optical switch 102 outputs signal light of one wavelength among the signal light of each wavelength according to the control by the optical switch control unit 30. The optical switch 102 is composed of a multi-stage optical switch, and outputs signal light of one wavelength from among m kinds of wavelength signal light at each stage. With such a configuration, the optical switch 102 finally outputs signal light of one wavelength.

  In the present embodiment, the optical switch 102 includes seven sub optical switches (first optical switch 201, second optical switch 202, third optical switch 203, fourth optical switch 204, fifth optical switch 205, and sixth optical switch. 206 and a seventh optical switch 207). Each sub optical switch may be configured using, for example, a thermo-optic switch (TOSW: Thermo-Optic SWitch). The first optical switch 201 receives the signal light having the wavelength λ1 and the signal light having the wavelength λ2. The second optical switch 202 receives the signal light having the wavelength λ3 and the signal light having the wavelength λ4. The third optical switch 203 receives the signal light output from the first optical switch 201 and the signal light output from the second optical switch 202. The fourth optical switch 204 receives the signal light having the wavelength λ5 and the signal light having the wavelength λ6. The fifth optical switch 205 receives the signal light having the wavelength λ7 and the signal light having the wavelength λ8. The sixth optical switch 206 receives the signal light output from the fourth optical switch 204 and the signal light output from the fifth optical switch 205. The seventh optical switch 207 receives the signal light output from the third optical switch 203 and the signal light output from the sixth optical switch 206. The first optical switch 201, the second optical switch 202, the third optical switch 203, the fourth optical switch 204, the fifth optical switch 205, the sixth optical switch 206, and the seventh optical switch 207 are respectively supplied from the optical switch control unit 30. Signal light is output according to the output control signal. Although not shown, the control signal is supplied after converting the reception wavelength designated from the OLT to the ONU into a control signal for driving the optical switch 102 by the control circuit in the ONU.

  FIG. 8 is a diagram illustrating a specific example of the control of the optical switch control unit 30. The optical switch control unit 30 controls each sub optical switch according to the signal light (output signal light) output from the optical switch 102. More specifically, the optical switch control unit 30 controls the sub optical switch to which signal light having the same wavelength as the output signal light (output target signal light) is input so that the output target signal light is output. . On the other hand, for the sub optical switch to which only signal light having a wavelength different from the output signal light is input, control is performed so that signal light having a wavelength farther apart in the wavelength axis direction than the wavelength of the output signal light is output. .

  For example, when the output signal light is the signal light having the wavelength λ1, the first optical switch 201 is controlled so that the signal light having the wavelength λ1, which is the output target signal light, is output. The second optical switch 202 is controlled so that the signal light having the wavelength λ4, which is the signal light having a wavelength farther from the wavelength λ1, is output because the signal light having the wavelength λ1 that is the output target signal light is not input. . The third optical switch 203 is controlled so that the signal light of λ1 that is the output target signal light is output. The fourth optical switch 204 is controlled so that the signal light having the wavelength λ6 that is a signal light having a wavelength farther from the wavelength λ1 is output because the signal light having the wavelength λ1 that is the target signal light is not input. . The fifth optical switch 205 is controlled so that the signal light having the wavelength λ8, which is the signal light having a wavelength far away from the wavelength λ1, is output because the signal light having the wavelength λ1 that is the output target signal light is not input. . The sixth optical switch 206 is controlled so that the signal light having the wavelength λ8, which is the signal light having a wavelength farther from the wavelength λ1, is output because the signal light having the wavelength λ1 that is the output target signal light is not input. . The seventh optical switch 207 is controlled so that the signal light of λ1, which is the output target signal light, is output.

  The control contents when the output signal light is signal light with wavelengths λ2 to λ8 are as shown in FIG.

  In the wavelength selection module configured as described above, signal light having a wavelength farther apart in the wavelength axis direction than the wavelength of output signal light is output in each sub optical switch. Therefore, signal light having a wavelength closer to the wavelength axis direction than the wavelength of output signal light is attenuated at an earlier timing. As a result, the influence of crosstalk can be suppressed.

<Modification>
The signal light input to the wavelength selection module may be signal light that is not multiplexed. For example, in the embodiment shown in FIG. 1, each signal light of wavelength λ1 to wavelength λ4 may be input to the wavelength channel selector receiver module in a state where it is demultiplexed in advance. In that case, the wavelength selection module may not include the wavelength demultiplexer 101.

  The wavelength selection module described above may be used as a part of a communication device in PON, or may be used in a wavelength-multiplexed network such as WDM-PON and WDM / TDM-PON.

  You may make it implement | achieve the optical switch control part 30 in embodiment mentioned above with a computer. The optical switch control unit 30 is controlled based on the reception wavelength designated from the OLT. In that case, a program for realizing this function may be recorded on a computer-readable recording medium, and the program recorded on this recording medium may be read into a computer system and executed. Here, the “computer system” includes an OS and hardware such as peripheral devices. The “computer-readable recording medium” refers to a storage device such as a flexible medium, a magneto-optical disk, a portable medium such as a ROM and a CD-ROM, and a hard disk incorporated in a computer system. Furthermore, the “computer-readable recording medium” dynamically holds a program for a short time like a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line. In this case, a volatile memory inside a computer system serving as a server or a client in that case may be included and a program held for a certain period of time. Further, the program may be a program for realizing a part of the above-described functions, and may be a program capable of realizing the functions described above in combination with a program already recorded in a computer system. You may implement | achieve using programmable logic devices, such as FPGA (Field Programmable Gate Array).

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes designs and the like that do not depart from the gist of the present invention.

DESCRIPTION OF SYMBOLS 10 ... Package, 20 ... Mount, 30 ... Optical switch control part, 40 ... PLC, 50 ... Photoelectric conversion part, 60 ... Amplification part, 101 wavelength demultiplexer, 102 ... Optical switch, 201 ... First optical switch, 202 ... Second optical switch, 203 ... Third optical switch, 204 ... Fourth optical switch, 205 ... Fifth optical switch, 206 ... Sixth optical switch, 207 ... Seventh optical switch

Claims (3)

An optical switch that receives input of signal light of N different wavelengths and outputs one signal light out of the signal light of N types of wavelengths;
An optical switch control unit for controlling the optical switch,
The optical switch includes a plurality of sub-optical switches that input a plurality of signal lights having adjacent wavelengths when N different wavelengths are arranged in the wavelength axis direction and output a signal light having one wavelength, and the sub-optical switch Are connected in multiple stages so that one signal light is output from the N kinds of signal lights of different wavelengths,
The optical switch control unit controls the sub optical switch so that signal light having a wavelength farther apart in the wavelength axis direction than the wavelength of one signal light output from the optical switch is output. Selection module. When N is 4, the optical switch is
The first signal light having the longest wavelength and the second signal light having the next longest wavelength are input, and one of the first signal light and the second signal light is output. One light switch,
The third signal light having the next longest wavelength after the second signal light and the fourth signal light having the shortest wavelength among the four signal lights are input, and the third signal light and the first signal light are input. A second optical switch that outputs one of the four signal lights;
A signal light output from the first optical switch and a signal light output from the second optical switch, and a third optical switch that outputs one of them,
The optical switch controller is
When the first signal light is output from the optical switch, the first optical switch is controlled to output the first signal light, and the fourth optical signal is output to the second optical switch. The wavelength selection module according to claim 1, wherein the third optical switch is controlled so that the first signal light is output. An optical switch control method for receiving an input of signal light of N different wavelengths and controlling an optical switch that outputs one signal light among signal light of N types of wavelengths,
The optical switch includes a plurality of sub-optical switches that input a plurality of signal lights having adjacent wavelengths when N different wavelengths are arranged in the wavelength axis direction and output a signal light having one wavelength, and the sub-optical switch Are connected in multiple stages so that one signal light is output from the N kinds of signal lights of different wavelengths,
An optical switch control method comprising: a control step of controlling the sub optical switch so that signal light having a wavelength farther apart in the wavelength axis direction than the wavelength of one signal light output from the optical switch is output. .

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