Optical wavelength tunable filter, its control method, and optical transceiver

Abstract

This invention provides a tunable optical wavelength filter that allows for efficient setting of the transmission bandwidth with a simple configuration, a control method for that filter, and an optical transceiver. [Solution] Multiple optical wavelength filters are connected in a cascade. Multiple photodetectors each detect light transmitted through the multiple optical wavelength filters and output a current signal indicating the intensity of the detected light via two output terminals. An electrode pair includes a first electrode pad connected to one of the two output terminals of each of the multiple photodetectors, and a second electrode pad connected to the other of the two output terminals.

Description

[Technical Field]

[0001] This disclosure relates to an optical wavelength tunable filter, a method for controlling the same, and an optical transceiver. [Background technology]

[0002] In wavelength-division multiplexed optical signal transmission systems, optical wavelength filters are used to control the wavelength of the optical signal. Optical wavelength filters transmit only light within a set transmission band and block optical noise outside of that band. Optical wavelength tunable filters, which can change the transmission band, are widely used in flexible transmission networks (for example, Patent Document 1).

[0003] Waveguide-type ring resonators and Mach-Zehnder interferometers (MZIs) can function as optical wavelength filters by taking advantage of their ability to change the transmission bandwidth. In ring resonators and MZIs, the transmission bandwidth is changed by controlling the temperature of the waveguide using a microheater placed near the waveguide.

[0004] Non-patent document 1 proposes an optical wavelength filter that can achieve a wide transmission bandwidth and cutoff bandwidth by the vernier effect of connecting two ring resonators with different circumference lengths. In this optical wavelength filter, the waveguide is heated by a microheater placed near the waveguide of the ring resonator, thereby changing the resonance characteristics of the ring resonator and thus changing the transmission bandwidth. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2017-15788 [Non-patent literature]

[0006] [Non-Patent Document 1] Haoyan Wang, et al., “Polarization-independent tunable optical filter with variable bandwidth based on silicon-on-insulator waveguides,” Nanophotonics, Vol.7, Issue 8, pp. 1469-1477, 2018. [Overview of the project] [Problems that the invention aims to solve]

[0007] However, Non-Patent Document 1 does not clarify the structure and control method for adjusting the transmission bands of the two ring resonators to a desired band. Therefore, there is a need for a tunable optical wavelength filter that can suitably adjust the transmission bands of multiple cascaded ring resonators with a simple configuration and control method. [Means for solving the problem]

[0008] An optical wavelength tunable filter according to one aspect of the present disclosure comprises a plurality of optical wavelength filters connected in cascade, a plurality of photodetectors that detect light transmitted through the plurality of optical wavelength filters and output a current signal indicating the intensity of the detected light via two output terminals, and an electrode pair including a first electrode pad connected to one of the two output terminals of each of the plurality of photodetectors, and a second electrode pad connected to the other of the two output terminals.

[0009] A control method for a tunable optical wavelength filter, according to one aspect of the present disclosure, comprises a plurality of cascaded optical wavelength filters, a plurality of photodetectors that detect light transmitted through the plurality of optical wavelength filters and output a current signal indicating the intensity of the detected light via two output terminals, and an electrode pair including a first electrode pad connected to one of the two output terminals of each of the plurality of photodetectors and a second electrode pad connected to the other of the two output terminals, wherein the control method for a tunable optical wavelength filter involves inputting light to the foremost optical wavelength filter among the plurality of optical wavelength filters, monitoring a detection signal obtained by summing the plurality of current signals output from the plurality of optical wavelength filters via the electrode pair, and setting the transmission bandwidth of the plurality of optical wavelength filters in order from the foremost optical wavelength filter to the last optical wavelength filter such that the intensity of the light that has passed through each of the plurality of optical wavelength filters is maximized. [Effects of the Invention]

[0010] According to this disclosure, it is possible to provide an optical wavelength tunable filter that can efficiently set the transmission bandwidth with a simple configuration, a control method for the same, and an optical transceiver. [Brief explanation of the drawing]

[0011] [Figure 1] This diagram schematically shows an example configuration of an optical transceiver equipped with a typical optical wavelength tunable filter. [Figure 2] This is a schematic diagram showing the configuration of an optical transmitter. [Figure 3] This diagram schematically shows an example of a typical optical wavelength tunable filter configuration. [Figure 4] This figure schematically shows an example configuration of an optical transceiver equipped with an optical wavelength tunable filter according to one embodiment. [Figure 5] This diagram schematically shows the configuration of an optical transmitter according to one embodiment. [Figure 6] This figure schematically shows the configuration of a tunable optical wavelength filter according to one embodiment. [Figure 7]It is a flowchart of a transmission band control operation of a ring resonator included in an optical wavelength tunable filter according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each drawing, the same elements are denoted by the same reference numerals, and redundant description is omitted as necessary.

[0013] When referred to as one embodiment below, the present invention is applicable to any of the embodiments described below or a combination of two or more embodiments, and this also means that application is not limited to a specific embodiment.

[0014] As a premise for understanding the configuration and operation of the optical wavelength tunable filter according to the embodiment described below, first, the configuration and operation of a general optical wavelength tunable filter provided in an optical transceiver will be described.

[0015] As an example of an optical wavelength tunable filter for precisely filtering the wavelength of light, a configuration in which a plurality of individual filters each including a ring resonator and a Mach-Zehnder interferometer (MZI) are cascaded is known. Hereinafter, for convenience of description, a configuration example in which a ring resonator is applied to individual filters connected in cascade will be described. Needless to say, an MZI may be applied instead of a ring resonator. In an optical wavelength tunable filter in which a plurality of ring resonators are cascaded, periodic transmission wavelength bands appear. Therefore, by cascading a plurality of individually designed filters with different designs as in Non-Patent Document 1, a desired transmission wavelength band and a wide stop wavelength band can be realized. Such a technique is called the vernier effect and is used in various optical wavelength tunable filters.

[0016] Microheaters are placed near the waveguides that make up the ring resonator. By heating the waveguides with the microheaters, the refractive index of the waveguides, and thus the optical path length, can be changed by the thermo-optic effect. This allows the transmission band of each component of the ring resonator to be changed. Therefore, by adjusting the transmission bands of all the individual filters in a tunable optical filter to the desired transmission band, a tunable optical filter can be realized.

[0017] The following describes the general configuration of a tunable optical filter and the adjustment of its transmission bandwidth using specific examples. Figure 1 is a schematic diagram showing an example of the configuration of an optical transceiver equipped with a general tunable optical filter. The optical transceiver 9000 is installed, for example, in an end station device. The optical transceiver 9000 has an optical transmitter 9001, an optical receiver 9002, and a control unit 9010.

[0018] The optical transmitter 9001 transmits an optical signal LT, modulated according to the transmission data signal DT provided to the optical transmitter 9001 from, for example, the terminal device, to the communication partner of the optical transceiver 9000. The optical transmitter 9001 may also output an output signal OUT1, indicating the operating status of the optical transmitter 9001, to the control unit 9010. The optical receiver 9002 demodulates the optical signal LR, input from the communication partner of the optical transceiver 9000, into a received data signal DR. The optical receiver 9002 outputs the received data signal DR to, for example, the terminal device. The optical receiver 9002 may also output an output signal OUT2, indicating the operating status of the optical receiver 9002, to the control unit 9010.

[0019] The control unit 9010 controls the transmission of the optical signal LT by the optical transmitter 9001 by providing a control signal CON1 to the optical transmitter 9001. The control unit 9010 can also determine the operating status of the optical transmitter 9001 based on the output signal OUT1 received from the optical transmitter 9001. In this case, the control unit 9010 may control the transmission of the optical signal LT by the optical transmitter 9001 by providing a control signal CON1 according to the determined operating status of the optical transmitter 9001.

[0020] The control unit 9010 controls the reception of optical signals LR in the optical receiver 9002 by providing a control signal CON2. The control unit 9010 can also determine the operating status of the optical receiver 9002 based on the output signal OUT2 received from the optical receiver 9002. In this case, the control unit 9010 may control the reception of optical signals LR in the optical receiver 9002 by providing a control signal CON2 according to the determined operating status of the optical receiver 9002.

[0021] Figure 2 is a schematic diagram showing the configuration of an optical transmitter. The optical transmitter 9001 includes a tunable light source 901, an optical modulator 902, an optical amplifier 903, and an optical tunable filter 900. The optical tunable filter 900 is an example of a typical optical tunable filter.

[0022] The tunable light source 901 outputs light L1 of a desired wavelength to the optical modulator 902. The tunable light source 901 may be configured as various types of light-emitting elements and light source devices. The tunable light source 901 may be configured such that, for example, light output from a light source element such as an optical amplifier is input to an optical wavelength filter, and light L1 of a desired wavelength that has passed through the optical wavelength filter is output. The optical wavelength filter included in the tunable light source 901 may be provided, for example, in a silicon photonics (SiP) element formed on a silicon substrate.

[0023] The optical modulator 902 outputs an optical signal LT, which is obtained by modulating the optical light L1 output by the tunable light source 901 according to the transmitted data signal DT using a predetermined modulation scheme, to the optical amplifier 903.

[0024] The optical amplifier 903 amplifies the optical signal LT to the desired intensity. The optical amplifier 903 outputs the amplified optical signal LT to the optical wavelength tunable filter 900.

[0025] An example of a typical optical wavelength tunable filter, the optical wavelength tunable filter 900, filters the optical signal LT by wavelength. The optical wavelength tunable filter 900 then outputs the optical signal LT after wavelength filtering. Subsequently, the optical signal LT is transmitted to the communication partner of the optical transceiver 9000 through an optical transmission path (not shown), such as an optical fiber cable.

[0026] The optical wavelength tunable filter 900 will now be described. Figure 3 is a schematic diagram showing a typical configuration of an optical wavelength tunable filter. The optical wavelength tunable filter 900 has multiple ring resonators, multiple photodetectors, and multiple electrode pairs. Hereafter, n will be an integer of 2 or more. Figure 3 shows an example in which the optical wavelength tunable filter 900 has ring resonators R1 to Rn, photodetectors PD1 to PDn, and electrode pairs EP1 to EPn.

[0027] In Figure 3, to show the ports of a ring resonator, the input port P is shown as a representative example for the ring resonator R1. IN , through port P TH Adport P AD and dropport P DR This is what is being displayed. Note that the arrangement of each port is the same for the ring resonator R2~Rn.

[0028] The ring resonators R1 to Rn are cascaded between the input terminal and output terminal of the optical signal LT. In other words, when considering two adjacent ring resonators in R1 to Rn, the drop port, which is the output terminal of the preceding ring resonator, is connected to the input port, which is the input terminal of the following ring resonator. The optical signal LT is input to the input port of the foremost ring resonator R1. The wavelength-filtered optical signal LT is output from the drop port, which is the output terminal of the last ring resonator Rn.

[0029] To monitor the optical signals LT that did not pass through each of the ring resonators R1 to Rn, photodetectors PD1 to PDn are connected to the through ports of the ring resonators R1 to Rn, respectively. This ensures that the optical signals LT that did not pass through each of the ring resonators R1 to Rn are input to the photodetectors PD1 to PDn. For example, photodiodes may be used as the photodetectors PD1 to PDn.

[0030] The photodetectors PD1 to PDn output detection signals S1 to Sn indicating the light intensity of the input light. In this example, the photodetectors PD1 to PDn are configured as photodiodes that output current signals corresponding to the intensity of the received light as detection signals S1 to Sn. Therefore, the anode of each photodetector PD1 to PDn is connected to one of the two electrode pads included in the electrode pair EP1 to EPn, and the cathode is connected to the other of the two electrode pads.

[0031] As a result, for example, the control unit 9010 can receive detection signals S1 to Sn via electrode pairs EP1 to EPn. Here, the detection signals S1 to Sn correspond to the output signal OUT1 described above. The control unit 9010 can set the transmission bandwidth of the ring resonators R1 to Rn to a desired bandwidth by controlling the microheaters H1 to Hn provided in each of the ring resonators R1 to Rn with the control signal CON1 to minimize the detection signals S1 to Sn.

[0032] Note that the figure shows an example where the control signal CON1 is applied to the microheaters H1 to Hn, but this is merely an example. That is, it does not mean that the same signal is applied to the microheaters H1 to Hn; different signals may be applied to drive each of the microheaters H1 to Hn. In addition, each of the microheaters H1 to Hn may be provided with a signal to drive the microheaters H1 to Hn from a drive means controlled by a control means such as the control unit 9010.

[0033] In a typical optical wavelength tunable filter 900, electrode pairs EP1 to EPn are provided, corresponding to each of the ring resonators R1 to Rn. The two electrodes in each electrode pair EP1 to EPn are connected to an external device by wire bonding or the like, and are therefore formed as electrodes of a certain area. Consequently, in an optical wavelength tunable filter 900 with n electrode pairs, the overall dimensions become large, limiting footprint reduction.

[0034] On the other hand, there is a growing demand for further miniaturization of optical transceivers and optical transmitters. Therefore, miniaturization of tunable filters used in optical transceivers is required.

[0035] Furthermore, in a typical tunable optical filter 900, the intensity of light that does not pass through each of the ring resonators R1 to Rn is detected by photodetectors PD1 to PDn connected to the through port. On the other hand, if the transmission bands of each of the ring resonators R1 to Rn are not yet adjusted, the intensity of light input to the downstream ring resonator is expected to be small to begin with. In this case, the intensity of light detected by the photodetector connected to the through port of the downstream ring resonator will also be small. As a result, a situation may arise where the light monitoring by the photodetector does not function adequately.

[0036] The following describes a tunable optical filter that solves the problems of the general tunable optical filters described above.

[0037] Embodiment 1 A tunable wavelength filter according to Embodiment 1 will now be described. Figure 4 is a schematic diagram showing an example of the configuration of an optical transceiver equipped with an optical tunable wavelength filter according to one embodiment. The optical transceiver 1000 is installed, for example, in an end station device. The optical transceiver 1000 has the same configuration as the optical transceiver 9000 shown in Figure 1. That is, the optical transmitter 1001, optical receiver 1002, and control unit 1010 of the optical transceiver 1000 correspond to the optical transmitter 9001, optical receiver 9002, and control unit 9010 of the optical transceiver 9000, respectively.

[0038] Figure 5 is a schematic diagram showing the configuration of an optical transmitter according to one embodiment. Optical transmitter 1001 has the same configuration as optical transmitter 9001 in Figure 2. That is, the tunable light source 101, optical modulator 102, optical amplifier 103, and optical tunable filter 100 of optical transmitter 1001 correspond to the tunable light source 901, optical modulator 902, optical amplifier 903, and optical tunable filter 900 of optical transmitter 9001, respectively.

[0039] The optical wavelength tunable filter 100 according to this embodiment will now be described. The optical wavelength tunable filter 100 wavelength filters the optical signal LT. The optical wavelength tunable filter 100 then outputs the optical signal LT after wavelength filtering. Subsequently, the optical signal LT is transmitted to the communication partner of the optical transceiver 1000 through an optical transmission path (not shown), such as an optical fiber cable.

[0040] Figure 6 is a schematic diagram showing the configuration of a tunable optical filter according to one embodiment. Compared to the tunable optical filter 900, the tunable optical filter 100 has a different configuration in the arrangement of photodetectors PD1 to PDn and the number of electrode pairs. In Figure 6, an example is shown in which the tunable optical filter 100 has ring resonators R1 to Rn, photodetectors PD1 to PDn and electrode pairs EP.

[0041] In Figure 6, to show the ports of a ring resonator, the input port P is shown as a representative example for the ring resonator R1. IN , through port P TH Adport P AD and dropport P DR This is what is being displayed. Note that the arrangement of each port is the same for the ring resonator R2~Rn.

[0042] In the optical wavelength tunable filter 100, the ring resonators R1 to Rn are arranged in the same manner as in the optical wavelength tunable filter 900. Accordingly, the ring resonators R1 to Rn are cascade-connected between the input end of the optical signal LT and the output end of the optical signal LT. When focusing on two adjacent ring resonators among the ring resonators R1 to Rn, the drop port of the preceding-stage ring resonator is connected to the input port of the subsequent-stage ring resonator. The optical signal LT is input to the input port of the foremost-stage ring resonator R1. The optical signal LT after wavelength filtering is output from the drop port of the rearmost-stage ring resonator Rn.

[0043] In order to monitor the optical signal LT transmitted through each of the ring resonators R1 to Rn, the drop port P of the ring resonators R1 to Rn DR is connected to photodetectors PD1 to PDn respectively via branch paths. Accordingly, a part of the optical signal LT output from the drop port P of the ring resonators R1 to Rn DR is branched and input to the photodetectors PD1 to PDn respectively. The photodetectors PD1 to PDn output detection signals S1 to Sn indicating the light intensity of the input optical signal LT. The photodetectors PD1 to PDn are configured as photodiodes that output current signals corresponding to the intensity of received light as the detection signals S1 to Sn. The anode of each of the photodetectors PD1 to PDn is connected to one of two electrode pads included in the electrode pair EP, and the cathode is connected to the other of the two electrode pads. Hereinafter, the anode of each of the photodetectors PD1 to PDn is also referred to as one main output terminal of the two main output terminals, and the cathode is also referred to as the other output terminal.

[0044] As a result, for example, the control unit 1010 can receive a detection signal DET, which is the sum of detection signals S1 to Sn, via the electrode pair EP. Here, the detection signal DET corresponds to the output signal OUT1 described above. Also, one of the two electrode pads of the electrode pair EP is referred to as the first electrode pad, and the other as the second electrode pad. The control unit 1010 controls the microheaters H1 to Hn provided on each of the ring resonators R1 to Rn, and sets the transmission band of the ring resonators R1 to Rn to a desired band by maximizing the intensity of the detection signal DET while sequentially sweeping the transmission band of the ring resonators R1 to Rn.

[0045] The following describes the transmission band control of the ring resonators R1 to Rn in the optical wavelength tunable filter 100. Figure 7 is a flowchart of the transmission band control operation of the ring resonator included in the optical wavelength tunable filter according to one embodiment.

[0046] Step ST0 The control unit 1010 sets the number k, which indicates the ring resonator to be controlled by the transmission band, to its initial value of "1".

[0047] Step ST1 The control unit 1010 controls the tunable light source 101 to input an optical signal LT to the tunable optical filter 100. The control unit 1010 may also control the tunable light source 101 using, for example, a control signal CON1.

[0048] Step ST2 The control unit 1010 monitors the detection signal DET through the electrode pair EP while sweeping the transmission band of the ring resonator Rk by controlling the microheaters H1 to Hn with the control signal CON1.

[0049] Step ST3 The control unit 1010 fixes the transmission band of the ring resonator Rk to the transmission band where the intensity of the detected signal DET is maximized.

[0050] Step ST4 The control unit 1010 determines whether k has reached n. If k has reached n, the control unit 1010 terminates processing.

[0051] Step ST5 If k has not reached n, the control unit 1010 adds "1" to k. Then, the control unit 1010 returns the process to step ST2.

[0052] As explained above, by sequentially adjusting the transmission bandwidth of each ring resonator starting from the upstream ring resonator, the transmission bandwidths of all ring resonators R1 to Rn can be optimally set at the end of the process.

[0053] In this configuration, the detection signals S1 to Sn from photodetectors PD1 to PDn are added together and input to the electrode pair EP. Therefore, as the number of upstream ring resonators whose transmission bandwidth settings have been completed increases, the intensity of the detection signal DET increases. On the other hand, since the transmission bandwidth of each ring resonator is adjusted one by one, the intensity of the detection signal DET during adjustment fluctuates according to the transmission bandwidth sweep of only the ring resonator being adjusted.

[0054] Therefore, with this configuration, the transmission bands of the ring resonators R1 to Rn can be suitably set from the frontmost stage to the backmost stage. By setting all the transmission bands of the ring resonators R1 to Rn, the transmission band of the optical wavelength tunable filter 100 can be suitably set.

[0055] Furthermore, the optical wavelength tunable filter 100 can be configured with only one electrode pair, compared to a typical optical wavelength tunable filter 900. As a result, the optical wavelength tunable filter 100 can reduce the number of electrode pairs and thus the dimensions of the optical wavelength tunable filter compared to a typical optical wavelength tunable filter 900.

[0056] Other embodiments Although the present disclosure has been described above with reference to embodiments, the present disclosure is not limited to the embodiments described above. Various modifications to the structure and details of the present disclosure can be made as can be understood by those skilled in the art within the scope of the present disclosure. Furthermore, each embodiment can be combined with other embodiments as appropriate.

[0057] In the embodiments described above, the transmission bandwidth of the optical wavelength tunable filter was explained as being controlled by a control unit provided on the optical transceiver, but this is merely an example. For example, the transmission bandwidth of the optical wavelength tunable filter may be controlled by any control means provided outside the optical transceiver, such as a control unit provided on the optical transmitter or a higher-level device of the optical transceiver.

[0058] In the above-described embodiment, an example was given in which a ring resonator is used as a standalone filter constituting the optical wavelength tunable filter, but this is merely illustrative. For example, the standalone filter constituting the optical wavelength tunable filter may be an MZI. In this case, a photodetector can be connected to one of the cross port and bar port of the input port of the MZI, and the other end can be left open.

[0059] Although the optical wavelength tunable filter according to the above embodiment has been described as being output from an optical modulator in an optical transceiver and used to wavelength filter the amplified optical signal, its applications are not limited to this. The optical wavelength tunable filter according to the above embodiment may be applied to wavelength filtering of any light. For example, it may be mounted on a wavelength tunable light source included in an optical transceiver and used to control the wavelength of the light output by the wavelength tunable light source. In this case, the transmission bandwidth of the optical wavelength tunable filter according to the above embodiment may be controlled by a control unit provided in the wavelength tunable light source.

[0060] In the embodiments described above, for example, an example was given in which a microheater is used as a means for controlling the transmission band of a ring resonator and a single filter such as an MZI that constitutes an optical wavelength tunable filter. However, this is merely an example. For example, various structures and methods for controlling the transmission band, such as current injection into the optical waveguide that constitutes a ring resonator and a single filter such as an MZI, may be applied.

[0061] Each drawing is merely illustrative to illustrate one or more embodiments. Each drawing may be associated with one or more other embodiments rather than with only one specific embodiment. As those skilled in the art will understand, various features or steps described with reference to any one drawing can be combined with features or steps shown in one or more other drawings, for example, to create embodiments not explicitly shown or described. Not all features or steps shown in any one drawing to illustrate an exemplary embodiment are necessarily required, and some features or steps may be omitted. The order of steps shown in any of the drawings may be changed as appropriate.

[0062] Some or all of the above embodiments may also be described as follows, but are not limited to the following:

[0063] (Note 1) Multiple optical wavelength filters connected in cascade, Multiple photodetectors each detect light transmitted through the multiple optical wavelength filters and output a current signal indicating the intensity of the detected light via two output terminals. The device comprises an electrode pair including a first electrode pad connected to one of the two output terminals of each of the plurality of photodetectors, and a second electrode pad connected to the other of the two output terminals, A tunable optical wavelength filter.

[0064] (Note 2) Of the aforementioned multiple optical wavelength filters, the light that has passed through the preceding optical wavelength filter is input to the subsequent optical wavelength filter. The photodetector that detects the light transmitted through the preceding optical wavelength filter detects the light transmitted through the preceding optical wavelength filter that is branched from between the output terminal of the preceding optical wavelength filter and the input terminal of the subsequent optical wavelength filter. The optical wavelength tunable filter described in Appendix 1.

[0065] (Note 3) When light is input to the foremost optical wavelength filter among the plurality of optical wavelength filters, a detection signal obtained by summing the plurality of current signals output from the plurality of optical wavelength filters is monitored through the electrode pair. The transmission bandwidths of the plurality of optical wavelength filters are set such that the intensity of the light passing through each of the plurality of optical wavelength filters is maximized, from the first optical wavelength filter to the last optical wavelength filter. The optical wavelength tunable filter described in Appendix 2.

[0066] (Note 4) The transmission band of each of the plurality of optical wavelength filters is set so that the intensity of the detection signal is maximized. The optical wavelength tunable filter described in Appendix 3.

[0067] (Note 5) The aforementioned plurality of optical wavelength filters are configured as ring resonators, The output terminal of the preceding optical wavelength filter is the drop port of the ring resonator that constitutes the preceding optical wavelength filter. The input terminal of the subsequent optical wavelength filter is the input port of the ring resonator that constitutes the subsequent optical wavelength filter. A tunable optical wavelength filter as described in any one of the appendices 2 to 4.

[0068] (Note 6) The aforementioned plurality of optical wavelength filters are configured as a Mach-Zehnder interferometer. The output terminal of the preceding optical wavelength filter is the cross port of the Mach-Zehnder interferometer that constitutes the preceding optical wavelength filter. The input terminal of the subsequent optical wavelength filter is the input port of the Mach-Zehnder interferometer that constitutes the subsequent optical wavelength filter. A tunable optical wavelength filter as described in any one of the appendices 2 to 4.

[0069] (Note 7) A tunable light source, An optical modulator that outputs an optical signal obtained by modulating the light output from the aforementioned tunable light source, An amplifier that amplifies the optical signal output from the optical modulator, The system comprises a tunable optical filter as described in Appendix 1 or 2, which wavelength filters the optical signal amplified by the amplifier, Optical transceiver.

[0070] (Note 8) A tunable optical wavelength filter comprising: a plurality of optical wavelength filters connected in cascade; a plurality of photodetectors that detect light transmitted through the plurality of optical wavelength filters and output a current signal indicating the intensity of the detected light via two output terminals; and an electrode pair including a first electrode pad connected to one of the two output terminals of each of the plurality of photodetectors, and a second electrode pad connected to the other of the two output terminals, Among the plurality of optical wavelength filters, light is input to the foremost optical wavelength filter. The detection signal obtained by adding up the multiple current signals output from the multiple optical wavelength filters is monitored through the electrode pair. The transmission bandwidths of the plurality of optical wavelength filters are set sequentially from the first optical wavelength filter to the last optical wavelength filter such that the intensity of the light that has passed through each of the plurality of optical wavelength filters is maximized. A method for controlling a tunable optical wavelength filter. [Explanation of symbols]

[0071] 1000, 9000 optical transceivers 1001, 9001 Optical Transmitters 1002, 9002 Optical receiver 1010, 9010 Control Unit 100, 900 Hz tunable optical wavelength filter 101, 901 wavelength tunable light source 102, 902 Optical modulators 103, 903 Optical Amplifier LT, LR optical signal DET, S1~Sn detection signals DT Transmit Data Signal DR Received Data Signal EP1~EPn electrode pairs OUT1, OUT2 output signals PD1~PDn photodetectors P AD Adport P DR Dropport P IN Input port P TH Through port R1~Rn ring resonator

Claims

1. Multiple optical wavelength filters connected in cascade, Multiple photodetectors each detect light transmitted through the multiple optical wavelength filters and output a current signal indicating the intensity of the detected light via two output terminals, The device comprises an electrode pair including a first electrode pad connected to one of the two output terminals of each of the plurality of photodetectors, and a second electrode pad connected to the other of the two output terminals, A tunable optical wavelength filter.

2. Of the aforementioned multiple optical wavelength filters, the light that has passed through the preceding optical wavelength filter is input to the subsequent optical wavelength filter. The photodetector that detects the light transmitted through the preceding optical wavelength filter detects the light transmitted through the preceding optical wavelength filter that is branched from between the output terminal of the preceding optical wavelength filter and the input terminal of the subsequent optical wavelength filter. The optical wavelength tunable filter according to claim 1.

3. When light is input to the foremost optical wavelength filter among the plurality of optical wavelength filters, a detection signal obtained by summing the plurality of current signals output from the plurality of optical wavelength filters is monitored through the electrode pair. The transmission bandwidths of the plurality of optical wavelength filters are set such that the intensity of the light passing through each of the plurality of optical wavelength filters is maximized, from the first optical wavelength filter to the last optical wavelength filter. The optical wavelength tunable filter according to claim 2.

4. The transmission band of each of the plurality of optical wavelength filters is set so that the intensity of the detection signal is maximized. The optical wavelength tunable filter according to claim 3.

5. The aforementioned plurality of optical wavelength filters are configured as ring resonators, The output terminal of the preceding optical wavelength filter is the drop port of the ring resonator that constitutes the preceding optical wavelength filter. The input terminal of the subsequent optical wavelength filter is the input port of the ring resonator that constitutes the subsequent optical wavelength filter. The optical wavelength tunable filter according to claim 2 or 3.

6. The aforementioned plurality of optical wavelength filters are configured as a Mach-Zehnder interferometer. The output terminal of the preceding optical wavelength filter is the cross port of the Mach-Zehnder interferometer that constitutes the preceding optical wavelength filter. The input terminal of the subsequent optical wavelength filter is the input port of the Mach-Zehnder interferometer that constitutes the subsequent optical wavelength filter. The optical wavelength tunable filter according to claim 2 or 3.

7. A tunable light source, An optical modulator that outputs an optical signal obtained by modulating the light output from the aforementioned tunable light source, An amplifier that amplifies the optical signal output from the optical modulator, The optical wavelength tunable filter according to claim 1 or 2, which wavelength filters the optical signal amplified by the amplifier, is provided. Optical transceiver.

8. A tunable optical wavelength filter comprising: a plurality of optical wavelength filters connected in cascade; a plurality of photodetectors that detect light transmitted through the plurality of optical wavelength filters and output a current signal indicating the intensity of the detected light via two output terminals; and an electrode pair including a first electrode pad connected to one of the two output terminals of each of the plurality of photodetectors, and a second electrode pad connected to the other of the two output terminals, Among the plurality of optical wavelength filters, light is input to the foremost optical wavelength filter. The detection signal obtained by adding up the multiple current signals output from the multiple optical wavelength filters is monitored through the electrode pair. The transmission bandwidths of the plurality of optical wavelength filters are set sequentially from the first optical wavelength filter to the last optical wavelength filter such that the intensity of the light that has passed through each of the plurality of optical wavelength filters is maximized. A method for controlling a tunable optical wavelength filter.

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