JP2009253735A - Wavelength error detector, wavelength error detection method using the same and multiplex optical communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain detection of the temporal changes in a wavelength error signal in an optical multiplex communication, to enable the wavelength error signal to be identified for each user in a time division multiplexing signal, and to attain simplification of a user-side device and reduction of costs. <P>SOLUTION: A wavelength error signal detector includes: a light beam splitter (BS); a first photodetector for receiving one output of the BS; an amplifier connected to the first photodetector; an optical filter for giving a wavelength reference to another output of the BS; a second photodetector for receiving the output of the optical filter; a subtractor for subtracting the output of the amplifier from the output of the second photodetector; and an AD converter connected to the subtractor. When the optical signal of a desired wavelength is inputted, the gain of the amplifier is adjusted so that the output of the subtractor becomes 0. Thus, a wavelength error signal from the desired wavelength of the input optical signal can be obtained, from the output of the subtractor. According to a sampling trigger signal given to the AD converter, the output of the subtractor can be monitored at arbitrary time intervals, so that a temporal change in the wavelength error signal can be observed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a wavelength error signal detector for a time division multiplexed optical signal, a wavelength error signal detection method using the same, a wavelength error signal detection circuit, a time division multiplexed optical communication system, and a wavelength division multiplexed optical communication system.

  As an uplink signal multiplexing method in an access optical communication system, a time division multiplexing method as shown in FIG. 12 is widely used. Here, a signal transmitted from the user side device 1000 to the station side device 1010 is referred to as an uplink signal. In this method, N user apparatuses (N is an integer of 2 or more) 1001-1 to 1001-N are optical transmitters 1003-1 to 1003-N and optical signal transmission timing for each user, as user-side apparatuses 1000, respectively. Are provided to a receiver 1011 with a reception timing controller 1013 as a station side device 1010 via an optical coupler (optical multiplexer) 1006 and an optical fiber 1009. Connected.

In this conventional system, as shown in FIG. 13, all N users use the same communication wavelength λ ₁ , assign a communicable time for each user, and control the transmission timing and the reception timing. It can be performed. This conventional method has the advantage of low cost because a single type of user side device can be used, but there is a difficulty that control of transmission timing and reception timing becomes difficult as the transmission speed increases. .

As another uplink signal multiplexing method, a wavelength division multiplexing method as shown in FIG. 14 has been proposed. In this method, the user device 1000 includes an optical transmitter 1003-1～1003-N for transmitting different wavelengths lambda ₁ to [lambda] _N respectively to N user 1001-1～1001-N, the wavelength for each user Are multiplexed using a wavelength multiplexer 1008 such as a dielectric multilayer filter or an arrayed waveguide diffraction grating, and the multiplexed signal is wavelength-multiplexed by a single optical fiber 1009, After being demultiplexed into N wavelengths using the wavelength demultiplexer 1021 of the station side device 1020, the signals are received by the corresponding receivers 1023-1 to 1023 -N for each wavelength.

In this conventional method, as shown in FIG. 15, since different wavelengths λ _{1 to} λ _N are assigned to _N users, there is an advantage that services can be provided independently for each user. The demultiplexer 1008 and the wavelength demultiplexer 1021 are expensive, and N types of optical transmitters 1003-1 to 1003-N and N receivers 1023-1 to 1023-N that transmit different wavelengths for each user are included. There is a drawback that it is necessary.

In this conventional method, particularly in the high-density wavelength division multiplexing method, it is important to stabilize all wavelengths to a predetermined wavelength (λ _{1 to} λ _N ). This will be described with reference to FIG. In FIG. 16, δλ _i (i = 1 to N) represents a wavelength drift amount with respect to the wavelength λ _i . In the wavelength division multiplexing system, when a certain signal wavelength drifts from a predetermined wavelength, not only the optical power of the signal wavelength itself is attenuated but also crosstalk to adjacent wavelengths, so that transmission quality deteriorates. In order to prevent this, as shown in FIG. 14, wavelength error signal detectors 1005-1 to 1005-N for detecting δλ _i are provided for N optical transmitters 1003-1 to 1003-N, respectively. The wavelength error signal obtained by these wavelength error signal detectors is used to correct the transmission wavelength of the corresponding optical transmitter.

Further, as shown in FIGS. 17 and 18, by using M waves (λ _{i to} λ _M ) for N users as shown in FIG. A hybrid configuration that combines the advantages of time division multiplexing and wavelength division multiplexing is conceivable. FIG. 17 shows a configuration multiplexed by the optical coupler 1006, and FIG. 18 shows a configuration in which wavelength division multiplexing is performed by the wavelength multiplexer 1008 after time division multiplexing by the optical couplers 1006 and 1007. In these configurations, even if the same wavelength is used, different wavelength drifts occur for each user.

FIG. 20 shows an example of an optical spectrum when 4 users are accommodated per wavelength. Here, δλ _{i, j} (i = 1 to M, M ≦ N) represents a wavelength drift from the wavelength λ _i of the transmission wavelength of the j-th user to which the wavelength λ _i is assigned. Even in these configurations, it is necessary to stabilize the signal wavelength to a predetermined wavelength when performing high-density wavelength multiplexing.

(First prior art)
FIG. 21 shows an example of the configuration of a conventional wavelength error signal detection circuit described in Non-Patent Document 1 as the first conventional technique. The wavelength error signal detection circuit detects a wavelength error signal for each of N optical transmitters having different transmission wavelengths. The wavelength error signal detection circuit of FIG. 21 is connected to one of the outputs of the optical beam splitter 2103 and the optical beam splitter 2103 for splitting the optical power of the optical signal input 2101 and the first light reception for monitoring the reference optical power. Connected to the other output of the optical beam splitter 2103, the optical filter 2105 serving as a wavelength reference, and connected to the output of the optical filter 2105. A second light receiver 2107 for monitoring the filter output optical power and a subtractor 2113 for subtracting the output of the amplifier 2111 from the output of the second light receiver 2107 are provided. An etalon filter or the like is used as the optical filter 2105.

  The operation principle of the conventional circuit when an etalon filter is used as the optical filter 2105 will be described with reference to FIG. FIG. 22 shows the wavelength dependence of the received light power in the second light receiver 2107 and the first light receiver 2109. Here, the gain of the amplifier 2111 disposed at the subsequent stage of the first light receiver 2109 is adjusted so that the output of the subtractor 2113 becomes 0 at the target wavelength (wavelength multiplexer transmission center wavelength). At this time, when the optical signal 2101 drifted from the target wavelength is input, a wavelength error signal 2119 corresponding to the drift amount is obtained as an output of the subtractor 2113.

(Second prior art)
FIG. 23 shows an example of the configuration of a conventional wavelength error signal detection circuit described in Patent Document 1 as the second prior art. This wavelength error signal detection circuit is configured to perform wavelength stabilization by sharing some components for the optical transmitters 2311-1 to 2311 -N that transmit N different wavelengths. This configuration includes an optical coupler 2301 that branches the wavelength multiplexed optical signal multiplexed by the wavelength multiplexer 2307, a Mach-Zehnder filter 2303 that is connected to one of the branched optical signals and serves as a wavelength reference, and a transmission center frequency of the Mach-Zehnder filter 2303. Oscillator 2305, wavelength demultiplexer 2309 for demultiplexing N wavelengths, N light receivers 2313-1 to 2313 -N and N multipliers 2315 for monitoring the optical power of the demultiplexed N wavelengths, respectively. -1 to 2315-N, and N low-pass filters (LPFs) 23171-1 to 2317-N.

  The operation principle of the conventional circuit of FIG. 23 will be described with reference to FIG. FIG. 24 shows the wavelength dependence of the received light power in a certain light receiver (for example, the second light receiver 2313-2). By perturbing the transmission center wavelength of the Mach-Zehnder filter 2303 with a sine wave, the received light power of the optical signal demultiplexed by the wavelength demultiplexer 2309 oscillates at the perturbation frequency with an amplitude proportional to the amount of wavelength drift. This signal is subjected to synchronous detection with respect to N wavelengths and the respective LPF outputs are detected, whereby wavelength error signals of the transmission wavelengths of N optical transmitters 2311-1 to 2311 -N can be obtained.

A Highly Stable and Reliable Wavelength Monitor Integrated Laser Module Design ”, J. Lightwave Technol., Vol.22, pp1344-1351, May 2004 JP-A-9-261181

  However, when the first prior art as shown in FIG. 21 is applied to the user side, the wavelength error signal detection circuit is provided for each optical transmitter because the wavelength error signal is detected for each optical transmitter. There is a problem that it is necessary to provide such a device, and it is necessary to use expensive optical components on the user side.

  In the second prior art as shown in FIG. 23, the wavelength control circuit can be shared by N optical transmitters as compared to the first prior art, but N multipliers and N Therefore, there is a problem that the configuration is complicated.

  Furthermore, neither of the first and second prior arts considers application to an optical signal time-division multiplexed at the same wavelength, and from which optical transmitter the obtained wavelength error signal originates There was a problem to be solved that could not be identified.

  The present invention has been made to solve these problems of the prior art, and an object of the present invention is to provide a wavelength error signal detector capable of detecting a time change of the wavelength error signal, and to provide the wavelength error signal detector. To provide a wavelength error signal detection method and circuit capable of identifying a wavelength error signal for each user in a used time division multiplexed signal, and to perform wavelength error signal detection in a time division multiplexed optical signal on the station side, thereby providing a user side device. Can provide a time division multiplexing optical communication system that can simplify the process, and in a system that performs time division multiplexing for each M wave, the wavelength error signal detector can be shared by the M wave, thereby further reducing the cost. Another object of the present invention is to provide a wavelength division multiplexing optical communication system.

  In order to achieve the above object, a wavelength error signal detector according to the first aspect of the present invention includes an optical beam splitter that branches an optical signal power of an input optical signal that is a time division multiplexed optical signal, and one output of the optical beam splitter. A first optical receiver for monitoring the output, an amplifier connected to the output of the first optical receiver, an optical filter disposed downstream of the other output of the optical beam splitter to provide a wavelength reference, and the optical filter A second light receiver for monitoring the output of the second light receiver, a subtractor for subtracting the output of the amplifier from the output of the second light receiver, and an analog-digital conversion circuit connected to the output of the subtractor; And the amplifier has a gain adjusted so that an output of the subtractor becomes 0 when an optical signal having a desired wavelength is input, and the analog-digital conversion circuit includes a sampling trigger. Trust Characterized by monitoring the output of the subtractor at arbitrary time intervals by.

  In order to achieve the above object, a wavelength error signal detector according to the present invention of claim 2 includes a reference light source that generates a wavelength reference light serving as a wavelength reference, an input optical signal that is a time-division multiplexed optical signal, and the wavelength reference light. An optical coupler that combines the output light of the optical coupler, a filter that photoelectrically converts the output light of the optical coupler, and a filter that is connected to the output of the optical receiver and has a frequency dependency in which the transmittance changes as the frequency increases. An analog-to-digital conversion circuit connected to the output of the filter, and the input optical signal and the wavelength reference light are heterodyne-detected by the light receiver, and the filter includes the input optical signal and the wavelength reference light. The beat frequency is converted into an intensity, and the analog-digital conversion circuit monitors the output of the filter at an arbitrary time interval by a sampling trigger signal.

In order to achieve the above object, a wavelength error signal detector according to a third aspect of the present invention includes a reference pulse light source that generates a wavelength reference light serving as a wavelength reference, an input optical signal that is a time-division multiplexed optical signal, and the wavelength reference. An optical coupler for combining light, a photoreceiver for photoelectrically converting the output light of the optical coupler, and a filter having a frequency dependency that is connected to the output of the photoreceiver and whose transmittance changes as the frequency increases And an analog-to-digital conversion circuit connected to the output of the filter, and the input optical signal and the wavelength reference light are heterodyne-detected by the light receiver, and the filter is connected to the input optical signal and the wavelength reference light. The reference pulse light source outputs an optical pulse as the wavelength reference light at an arbitrary time interval by a sampling trigger signal.

  In order to achieve the above object, a wavelength error signal detection circuit according to a fourth aspect of the present invention includes the wavelength error signal detector according to any one of the first to third aspects and N users (N is an integer of 2 or more). A reception timing signal selector that gives a signal reception time of any one user when a time division multiplexed optical signal is input, and the wavelength error signal detector receives the signal received by the reception timing signal selector By detecting the wavelength error with respect to the input optical signal at the time, the wavelength error signal of the transmission wavelength of any one of the N users is detected.

  In order to achieve the above object, a wavelength error signal detection circuit according to a fifth aspect of the present invention includes the wavelength error signal detector according to any one of the first to third aspects and N users (N is an integer of 2 or more). When a time division multiplexed optical signal is input, a sampling trigger signal having a repetition frequency of a detection period capable of detecting a wavelength error signal at least once for the optical signal of the N user is generated and supplied to the wavelength error signal detector. A sampling trigger signal generator; and a memory for storing time-series data of wavelength error signals obtained by the wavelength error signal detector; and the time-series data of wavelength error signals stored in the memory It is characterized in that the wavelength error signal of each of the transmission wavelengths of the N users is detected by corresponding to the reception time for each of the N users.

  In order to achieve the above object, the time division multiplexing optical communication system according to the present invention of claim 6 includes N optical transmitters of N users (N is an integer of 2 or more) and each of the optical transmitters of the N users. N transmission timing controllers for controlling the transmission timing of the optical signals, an optical multiplexer for generating a time division multiplexed optical signal by multiplexing the optical signals transmitted from the N optical transmitters, and the time division multiplexing An optical receiver that receives an optical signal, and a wavelength error signal detection circuit according to claim 4 or 5 that receives the time division multiplexed optical signal and detects a wavelength error signal, and the wavelength error signal. The detection circuit is arranged in the vicinity of the optical receiver.

  In order to achieve the above object, the wavelength division multiplexing optical communication system of the present invention according to claim 7 includes N optical transmitters of N users (N is an integer of 2 or more), each of which is an M wave (M N is an integer greater than or equal to 2) N optical transmitters that transmit optical signals of any one of the wavelengths, and N transmission timing controllers that control the transmission timing of the optical transmitters of the N users, An optical multiplexer that multiplexes the optical signals of the M waves transmitted from the N optical transmitters to generate a time-division multiplexed optical signal, and demultiplexes the M-wave time-division multiplexed optical signals. A wavelength demultiplexer, M optical receivers that respectively receive the M-wave optical signals demultiplexed by the wavelength demultiplexer, and M × 1 light disposed at the subsequent stage of the wavelength demultiplexer SW (switch) and a control signal for selecting one of the M waves are sent to the M × 1 optical SW. A wavelength error signal detection circuit according to claim 4 or 5, wherein the wavelength error signal detection circuit receives the M wave optical signal and detects a wavelength error signal, and the wavelength error signal detection circuit includes the M wave signal. The wavelength error signal detector is shared by the M wave by connecting the wavelength error signal detection circuit to the output of the M × 1 light SW.

  In order to achieve the above object, the wavelength division multiplexing optical communication system according to the present invention of claim 8 includes N optical transmitters of N users (N is an integer of 2 or more), each of which includes M waves (M N is an integer greater than or equal to 2) N optical transmitters that transmit optical signals of any one of the wavelengths, and N transmission timing controllers that control the transmission timing of the optical transmitters of the N users, An optical multiplexer that multiplexes optical signals of the M waves transmitted from the N optical transmitters to generate a time-division multiplexed optical signal, and the M wave transmitted through a transmission path A wavelength demultiplexer that demultiplexes the division multiplexed optical signal, M optical receivers that respectively receive the M-wave optical signals demultiplexed by the wavelength demultiplexer, and a front stage of the wavelength demultiplexer An optical coupler arranged and branching a part of the optical signal in the transmission line, and after the optical coupler A wavelength selector that selects one of the M waves of the wavelength-multiplexed optical signal branched by the optical coupler, a controller that controls wavelength selection of the wavelength selector, and the M wave And a wavelength error signal detection circuit according to claim 4, wherein the wavelength error signal detection circuit detects the wavelength error signal and receives the M wave. In contrast, the wavelength error signal detector is shared by M waves by connecting the wavelength error signal detection circuit to the output of the wavelength selector.

  To achieve the above object, the wavelength error signal detection method of the present invention according to claim 9 includes the step of branching the optical signal power of the input optical signal which is a time division multiplexed optical signal by the optical beam splitter, and the first optical receiver. Converting one of the branched output optical signal powers into an electrical signal power, amplifying the electrical signal power with an amplifier, and a wavelength with respect to the one of the branched output optical signal powers with an optical filter. A step of providing a reference, a step of converting an output optical signal power of the optical filter into an electric signal power by a second light receiver, and an output power of the amplifier from an output power of the second light receiver by a subtractor. Subtracting, converting the output of the subtractor into a digital signal by an analog-to-digital converter circuit, When the signal is input, the gain of the amplifier is adjusted so that the output of the subtractor becomes 0, and the analog-digital conversion circuit is driven at an arbitrary time interval by a sampling trigger signal; It is characterized by including. In order to achieve the above object, the wavelength error signal detection method of the present invention according to claim 10 includes a step of generating wavelength reference light serving as a wavelength reference from a reference light source, and an input optical signal which is a time division multiplexed optical signal by an optical coupler. And the wavelength reference light, a step of heterodyne detecting the input optical signal and the wavelength reference light by an optical receiver, and the input optical signal and the wavelength reference light by a filter having frequency dependency. And converting the beat frequency of the filter into an intensity, and driving the analog-digital conversion circuit with a sampling trigger signal to monitor the output of the filter at an arbitrary time interval.

  In order to achieve the above object, the wavelength error signal detection method of the present invention according to claim 11 includes a step of generating a wavelength reference optical pulse serving as a wavelength reference from a reference light source at an arbitrary time interval by a sampling trigger signal, and an optical coupler. A step of multiplexing the input optical signal that is a time-division multiplexed optical signal and the wavelength reference optical pulse, a step of performing heterodyne detection of the input optical signal and the wavelength reference optical pulse by an optical receiver, and frequency dependence. The method includes a step of converting a beat frequency of the input optical signal and the wavelength reference optical pulse into an intensity by a filter having an intensity, and a step of monitoring the output of the filter.

  Here, a reception timing signal selector generates a reception timing signal that gives a signal reception time of any one user when a time division multiplexed optical signal is input by N users (N is an integer of 2 or more); A step of detecting a wavelength error signal of a transmission wavelength of an arbitrary one of the N users by detecting a wavelength error with respect to an input optical signal at a signal reception time given by a reception timing signal. Can be characterized.

  In addition, when a time division multiplexed optical signal is input by N users (N is an integer of 2 or more), a sampling trigger signal having a repetition frequency of a detection period capable of detecting a wavelength error signal at least once for the optical signal of the N user. Generating time series data of the wavelength error signal obtained by using the sampling trigger signal in a memory, and time series data of the wavelength error signal stored in the memory for each of the N users. And a step of detecting a wavelength error signal of each of the N user's transmission wavelengths.

  With the above configuration, according to the present invention, a wavelength error signal detector capable of detecting a time change of the wavelength error signal and a method for identifying a wavelength error signal for each user in a time division multiplexed signal using the wavelength error signal detector are provided. it can. In addition, it is possible to provide a time division multiplexing optical communication system that enables simplification of the user side apparatus by performing wavelength error signal detection in the time division multiplexing optical signal on the station side. Furthermore, according to the present invention, there is provided a wavelength division multiplexing optical communication system capable of further reducing the cost by sharing the wavelength error signal detector with M waves in a system that performs time division multiplexing for each of the M waves. Can be provided.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
(First embodiment)
FIG. 1 shows a circuit configuration of a wavelength error signal detector according to the first embodiment of the present invention. The solid line in the figure indicates an optical signal, and the broken line indicates an electrical signal. The wavelength error signal detector of this embodiment includes an optical beam splitter 103 that branches the power of the optical signal 101, a first light receiver 105 for monitoring that photoelectrically converts one output of the optical beam splitter 103, and a first light receiver 105. An amplifier 111 connected to the output of the optical beam splitter, an optical filter 107 disposed after the other output of the optical beam splitter to give a wavelength reference, and a second light receiving device for monitoring that photoelectrically converts the output of the optical filter 107 109, a subtractor 113 for subtracting the output of the amplifier 111 from the output of the second light receiver 109, and an analog-digital conversion circuit (AD converter) 117 connected to the output of the subtractor 113.

  By adjusting the gain of the amplifier 111 in advance so that the output of the subtractor 113 becomes 0 when the optical signal 101 having a desired wavelength is input, the desired output of the input optical signal 101 is determined by the output of the subtractor 113. A wavelength error signal 119 can be obtained from these wavelengths.

  The AD converter 117 includes a sampling trigger terminal to which the sampling trigger signal 115 is applied. By monitoring the output of the subtractor 113 at an arbitrary time interval by the sampling trigger signal 115, it has not been measured in the prior art. The time change of the wavelength error signal with respect to the input optical signal can be observed at arbitrary time intervals.

(Second Embodiment)
FIG. 2 shows a circuit configuration of a wavelength error signal detector according to the second embodiment of the present invention. The solid line in the figure indicates an optical signal, and the broken line indicates an electrical signal. The wavelength error signal detector of the present embodiment includes a reference light source 201 that generates a wavelength reference light serving as a wavelength reference, an optical coupler 205 that combines the time-division multiplexed optical signal 101 and the wavelength reference light, and outputs of the optical coupler 205. Are connected to the output of the light receiver 207, have a wavelength dependency filter 209 whose transmittance changes with increasing frequency, and an AD converter 117 connected to the output of the filter 209. The AD converter 117 includes a sampling trigger terminal to which the sampling trigger signal 115 is applied.

  The time division multiplexed optical signal 101 and the wavelength reference light are subjected to heterodyne detection in the light receiver 207. The filter 209 converts the beat frequency of the time division multiplexed optical signal 101 and the wavelength reference light into intensity. The AD converter 117 monitors the output of the filter 209 at an arbitrary time based on the sampling trigger signal, so that the time change of the wavelength error signal with respect to the time division multiplexed optical signal 101 can be observed at an arbitrary time interval.

  The operation principle of the wavelength error signal detector of the present embodiment will be described with reference to FIGS. 3 (A) and 3 (B). In the following, for simplicity of description, the optical frequency is represented by f using f = c / λ (c represents the speed of light). A broken line a in FIG. 3A indicates reference light, and a solid line b indicates signal light.

As shown in FIG. 3 (A), the light receiver 207, a wavelength reference light optical frequency f _L generated by the reference light source 201 as a local light source, with respect to optical frequency f _c of the target f _c -f _L = By performing heterodyne detection on the time division multiplexed light 101 having the optical frequency of Δf and the optical frequency f _S = f _c + δf _i , an intermediate frequency signal f _S -f _L between the wavelength reference light and the signal light is obtained. Therefore, with respect to optical frequency f _C of the target, resulting intermediate frequency signal f _S from -f _L, the optical signal with respect to frequency f _C of the target f _S + wavelength drift amount δf _i δf _i = f _S -f _L- Δf can be detected. Further, the obtained wavelength drift frequency (δf _i ) is passed through a filter 209 whose transmittance changes as the frequency increases, so that the change amount of the intensity signal corresponding to the target optical frequency f _C is obtained. Since it can be converted, the wavelength error signal 119 can be obtained as the output of the AD converter 117.

  As such a filter 209, for example, a filter whose transmittance decreases uniformly with an increase in frequency as shown in FIG. 3B can be used. The AD converter 117 is provided with a sampling trigger terminal. By monitoring the output of the filter 209 at an arbitrary time, the time change of the wavelength error signal 119 can be observed.

In the present embodiment, the wavelength error signal 119 can be detected with high sensitivity by sufficiently increasing the light intensity of the output light of the reference light source 201 with respect to the light intensity of the signal light 101. Here, as shown in FIG. 3B, the wavelength error signal corresponds to the amount of change in the intensity signal corresponding to the signal light 101 with respect to the intensity signal corresponding to the target optical frequency f _C.

(Third embodiment)
FIG. 4 shows a circuit configuration of a wavelength error signal detector according to the third embodiment of the present invention. The wavelength error signal detector of the present embodiment includes a reference pulse light source 203 that generates wavelength reference light serving as a wavelength reference, an optical coupler 205 that combines the time-division multiplexed light 101 and the wavelength reference light, and outputs of the optical coupler 205. Are connected to the output of the light receiver 207, the filter 209 having a frequency dependency in which the transmittance changes as the frequency increases, and the AD converter 117 connected to the output of the filter 209. The reference pulse light source 203 includes a sampling trigger terminal to which a sampling trigger signal 202 is applied.

  The reference pulse light source 203 outputs an optical pulse as wavelength reference light at an arbitrary time in response to the sampling trigger signal 202. The time division multiplexed light 101 and the wavelength reference light are subjected to heterodyne detection in the light receiver 207. The filter 209 converts the beat frequency of the time division multiplexed light 101 and the wavelength reference light into intensity.

  Similar to the configuration of FIG. 3, the wavelength of the time division multiplexed light and the wavelength reference light through the light receiver 207, the filter 209, and the AD converter 117 by the heterodyne detection of the time division multiplexed light 101 using the wavelength reference light as a local light source. A wavelength error signal 119 corresponding to the error is obtained. At this time, the reference pulse light source 203 is provided with a pulse oscillation trigger terminal. A sampling trigger signal 202 is applied to the pulse oscillation trigger terminal, and an optical pulse is output from the reference pulse light source 203 to the optical coupler 205 at an arbitrary time. As a result, the time change of the wavelength error signal 119 can be observed on the output side of the AD converter 117. That is, the time change of the wavelength error signal 119 is observed on the output side of the AD converter 117 by driving the reference pulse light source 203 at the output time of the sampling trigger signal 202 output from the reception timing control circuit (not shown). Can do.

  In the present embodiment, as in the case of the second embodiment of the present invention described above, the light intensity of the light pulse generated from the reference pulse light source 203 is sufficiently increased with respect to the intensity of the signal light 101, thereby The wavelength error signal can be detected with sensitivity, and the reference light pulse light source 203 can be driven at a higher speed than the AD converter 117, so that the wavelength error signal can be detected at an extremely high speed.

(Fourth embodiment)
FIG. 5 shows a circuit configuration of a wavelength error signal detection circuit using the above-described wavelength error signal detector according to the present invention in the fourth embodiment of the present invention. The wavelength error signal detection circuit of the present embodiment is a circuit for identifying the wavelength error signal for each user in the time division multiplexed optical signal, and the wavelength error signal detection shown in any one of FIGS. And a reception timing signal selector 507 for selecting the reception time of one user among the reception timing signals 505. A sampling trigger signal 509 is output from the reception timing signal selector 507 to the wavelength error signal detector 503 at the timing of the selected time.

  When a time division multiplexed signal is input as the optical signal input 501, the error signal is detected by the wavelength error signal wavelength detector 503 at the reception time corresponding to one user by the reception timing signal selector 507, so that N The wavelength error signal 511 of one user among users (N is an integer of 2 or more) can be identified. Such a reception timing signal 505 is generally generated in the media access control sublayer (MAC layer) when the time division multiplexed signal is separated, and this MAC layer function can be used in this embodiment.

The operation of the wavelength error signal detection circuit of this embodiment will be described with reference to the timing chart of FIG. In FIG. 6, the horizontal axis represents time, and the vertical axis represents wavelength. It is assumed that N (N is an integer of 2 or more) optical transmitters (not shown) each transmit an optical signal having a wavelength λ ₁ but have different wavelength errors. FIG. 6 shows a case where N = 4, and each wavelength error signal is represented by δλ _i (i = 1 to 4). Further, t _i (i = 1 to 4) represents the reception timing and is given by the above-described MAC layer function. Since the reception time of the time-division multiplexed optical signal input 501 is known in advance, the wavelength error signal detector 503 uses the timing signal 505 at the reception timing of a signal of one user arbitrarily selected. By detecting the wavelength error signal 511, the wavelength error signal 511 corresponding to a certain user can be obtained from the time-divided optical signal 501.

(Fifth embodiment)
FIG. 7 shows another circuit configuration of the wavelength error signal detection circuit using the wavelength error signal detector according to the present invention in the fifth embodiment of the present invention. The wavelength error signal detection circuit of the present embodiment is a circuit for identifying the wavelength error signal for each user in the time division multiplexed optical signal, and the wavelength error signal detection shown in any one of FIGS. 705, a sampling trigger signal generator 701 for supplying a sampling trigger signal 703 having a repetition frequency fs to the wavelength error signal detector 705, and time series data of the wavelength error signal 707 obtained by the wavelength error signal detector 705 are stored. A memory 709 is included.

The operation of the wavelength error signal detection circuit of this embodiment will be described with reference to the timing chart of FIG. The meanings of symbols in FIG. 8 are the same as those in FIG. As shown in FIG. 8, when a time division multiplexed optical signal 501 is input by N users (N is an integer of 2 or more), a wavelength error signal 707 is detected at least once for the optical signal 501 of N users. The sampling trigger signal generator 701 is driven at a possible detection cycle f _S , and the sampling trigger signal 703 of the detection cycle fs output from the sampling trigger signal generator 701 is input to the wavelength error signal detector 705. As a result, the wavelength error signal 707 is output from the wavelength error signal detector 705 and sequentially stored in the memory 709.

  Since the reception time of the time division multiplexed signal 501 is known in advance, the wavelength error signal 707 stored in the memory 709 is input by inputting the reception timing signal 711 corresponding to the reception time for each of the N users into the memory 709 as a read signal. Can be read in correspondence with the reception time for each of the N users, and the wavelength error signal 511 of each N user's transmission wavelength can be obtained from the memory 709.

(Sixth embodiment)
FIG. 9 shows a circuit configuration of a time division multiplexing optical communication system using the wavelength error signal detection circuit according to the present invention in the sixth embodiment of the present invention. The time division multiplexing optical communication system of the present embodiment is a time division multiplexing optical communication system in which a wavelength error signal detector of a user output signal can be detected on the station side by arranging a wavelength error signal detector on the station side. Control the transmission timing of each of the optical transmitters 903-1 to 903-N and optical transmitters 903-1 to 903-N in the user devices 901-1 to 901-N (N is an integer of 2 or more). Transmission timing controllers 905-1 to 905-N, a first optical coupler 907 for multiplexing the outputs of N optical transmitters, an optical fiber 909, a second optical coupler 911, a receiver 913, and FIG. A wavelength error signal detection circuit 915 shown in FIG. 7 and a reception timing controller 917 that generates the above-described reception timing signal 505 or 711 are included. Here, the user devices 901-1 to 901-N and the first optical coupler 907 are the user-side device 900. The second optical coupler 911, the receiver 913, the wavelength error signal detection circuit 915, and the reception timing controller 917 are the station side device 910.

From the N optical transmitters 903-1 to 903-N, optical signals of wavelength λ ₁ whose transmission timing is controlled by the transmission timing controllers 905-1 to 905-N are output, respectively, and the first optical coupler 907 is output. Is sent out. These optical signals having the wavelength λ ₁ are combined by the first optical coupler 907 to generate a time division multiplexed signal. After the time division multiplexed signal is transmitted through the optical fiber 909, a part of the optical power is input to the wavelength error signal detection circuit 915 by the second optical coupler 911, and the remaining optical power is input to the receiver 913.

  Here, by arranging the wavelength error signal detection circuit 915 in the station side device 920, the user side optical transmitters 903-1 to 903-1 are installed without installing expensive optical components necessary for detecting the wavelength error signal on the user side. A transmission wavelength error of 903-N can be detected.

  Further, the upstream signal light intensity is greatly attenuated due to transmission path loss, loss due to the optical couplers 907 and 911 at the time of reception, etc., but the wavelength error signal detector 503 or 705 constituting the wavelength error signal detection circuit 915 is particularly shown in FIG. A wavelength error signal can be obtained with high sensitivity by using the wavelength error detector according to the present invention shown in FIG.

(Seventh embodiment)
FIG. 10 shows a circuit configuration of a wavelength division multiplexing optical communication system configured based on the time division multiplexing optical communication system shown in FIG. 9 according to the present invention in the seventh embodiment of the present invention. The wavelength division multiplexing optical communication system of this embodiment is a wavelength division multiplexing optical communication system in which a wavelength error signal detection circuit is shared by an optical switch (SW), and N (N is an integer of 2 or more) user devices 901. -1 to 901-N, transmission timing controllers 905-1 to 905-N for controlling the transmission timing of the optical transmitters 903-1 to 903-N and optical transmitters 903-1 to 903-N, M waves demultiplexed by the first optical coupler 907, the optical fiber 909, the wavelength demultiplexer 921, and the wavelength demultiplexer 921 that multiplex N optical transmitter outputs (M is an integer of 2 or more) (N ≧ M) M optical couplers 922-1 to 922 -M, M receivers 923-1 to 923 -M, and M reception timing controllers 924-1 to 924 that branch out a part of each optical power. -M, M × 1 optical switch (SW 925, having a wavelength error signal detection circuit 929 shown in FIG. 5 or FIG. 7 according to the controller 927, and the present invention. Here, the user devices 901-1 to 901-N and the first optical coupler 907 are the user-side device 900. Further, a wavelength demultiplexer 921, optical couplers 922-1 to 922-M, receivers 923-1 to 923-N, reception timing controllers 924-1 to 924-M, M × 1 optical switch (SW) 925, The controller 927 and the wavelength error signal detection circuit 929 are the station side device 920.

  Among the N optical transmitters 903-1 to 903 -N, M optical transmitters 903-1 to 903 -M each have an optical signal whose transmission timing is controlled at any one of M wavelengths (N ≧ M). And these optical signals are combined by the optical coupler 907 to generate a time division multiplexing / wavelength division multiplexing hybrid signal. The time division multiplex / wavelength division multiplex hybrid signal is transmitted through the optical fiber 909, and then is demultiplexed into M waves by the wavelength demultiplexer 921 of the station side device 920. The demultiplexed M waves are respectively optical couplers 922. Part of the optical power is input to M × 1 optical SW 925 by −1 to 922-M, and the remaining optical power is input to M receivers 923-1 to 923-M, respectively.

  The output of the M × 1 light SW 925 is input to the wavelength error signal detection circuit 929. Here, it is assumed that the wavelength error signal detection circuit has the same performance with respect to the M wave. In general, wavelengths are arranged at equal intervals in a wavelength division multiplexing optical transmission system. In order to obtain equivalent performance for such M waves arranged at equal intervals, an optical device that provides an equivalent wavelength reference for M waves in a wavelength error signal detector used in a wavelength error signal detection circuit is provided. Use it. In the wavelength error signal detector shown in the first embodiment, an etalon filter, a Mach-Zehnder type filter, or the like having a periodic wavelength dependency of transmittance can be used as an optical filter. In the wavelength error signal detector shown in the second and third embodiments, a multi-wavelength light source or a mode-locked laser that outputs wavelengths arranged at equal intervals is used as a reference light source and a reference pulse light source. Can be used. When the M waves have arbitrary wavelengths, the wavelength error signal detector shown in the first embodiment can use a wavelength tunable optical filter as an optical filter. In the wavelength error signal detector shown in the third embodiment, a wavelength variable light source can be used as the reference light source and the reference pulse light source.

  In receivers 923-1 to 923 -M, signals for each user are identified by reception timing control signals from reception timing controllers 924-1 to 924 -M for each of the M waves. Reception timing control signals generated by the M reception timing controllers 924-1 to 924 -M are also input to the controller 927.

In the controller 927, the wavelength λ _{i (i} = 1~M) when detecting a wavelength error signal for, and sets the output of the M × 1 optical SW925 to the wavelength lambda _i, a receiver for receiving the wavelength lambda _i The wavelength error signal for the wavelength λ _i is detected by driving the wavelength error signal detection circuit 929 using the reception timing control signal generated in the reception timing controller 924-i connected to the 923-i. With this configuration, in the wavelength division multiplexing optical communication system using a plurality of M waves, the wavelength error signal detection circuit 929 can be integrated into one, that is, the wavelength error signal detector can be integrated into one.

  In the present embodiment, the case where a single optical coupler 907 is used for multiplexing user signals has been described. However, the present invention is not related to this, and for example, as shown in FIG. 18 described in the background art section. After such time division multiplexing using a plurality of optical couplers, wavelength division multiplexing may be performed using a wavelength multiplexer.

(Eighth embodiment)
FIG. 11 shows a circuit configuration of still another wavelength division multiplexing optical communication system configured based on the time division multiplexing optical communication system shown in FIG. 9 according to the present invention in the eighth embodiment of the present invention. The wavelength division multiplexing optical communication system of this embodiment is a wavelength division multiplexing optical communication system in which a wavelength error signal detection circuit is shared by a wavelength selector, and the wavelength division multiplexing optical communication of the seventh embodiment of the present invention shown in FIG. The difference from the system is that M optical couplers 922-1 to 922 -M and M × 1 optical SW 925 that are arranged in the subsequent stage (output side) of the wavelength demultiplexer 921 of the station side device 920 in FIG. A single optical coupler 911 that demultiplexes a part of the optical signal of the transmission line 909 is installed in the previous stage (input side) of the wavelength demultiplexer 921 of the station side device 930, and the output of the optical coupler 911 is controlled. The wavelength selector 935 is connected to the detector 927, and the output of the wavelength selector 935 is input to the wavelength error signal detection circuit 929 shown in FIG. 5 or 7 according to the present invention.

In the controller 927, when a wavelength error signal is detected for the wavelength λ _i (i = 1 to M), the reception timing controller 924-i connected to the receiver 923-i that receives the wavelength λ _i is used. By using the generated reception timing control signal to select the wavelength λ _i as the output timing of the wavelength selector 935, the wavelength error signal for the wavelength λ _i that is one of the M waves is converted into a wavelength error signal detection circuit. 929 to detect.

  In this way, by selecting one of the M waves by the wavelength selector 930, a wavelength error signal can be obtained from the wavelength error signal detection circuit 929 without loss by the wavelength demultiplexer 921, and the wavelength demultiplexer 921. The wavelength error signal can be obtained from the wavelength error signal detection circuit 929 without depending on the transmission band.

(Other embodiments)
In the above, the preferred embodiment of the present invention has been described by way of example. However, the embodiment of the present invention is not limited to the above-described example, and the constituent members thereof are within the scope of the claims. Various modifications such as replacement, change, addition, increase / decrease in number, change in shape design, etc. are all included in the embodiments of the present invention. Further, the present invention may be applied to a system constituted by a plurality of devices, or may be applied to an apparatus having one device.

It is a block diagram which shows the circuit structure of the wavelength error signal detector in 1st Embodiment of this invention. It is a block diagram which shows the circuit structure of the wavelength error signal detector in 2nd Embodiment of this invention. It is a figure explaining the operating principle of the wavelength error signal detector in 2nd Embodiment of this invention, (A) is a characteristic figure which shows the relationship between a wavelength and the transmittance | permeability of a filter, (B) is a wavelength. It is. It is a block diagram which shows the circuit structure of the wavelength error signal detector in 3rd Embodiment of this invention. It is a block diagram which shows the circuit structure of the wavelength error signal detection circuit in 4th Embodiment of this invention. It is a timing diagram explaining the identification principle of the wavelength error signal regarding the time division multiplexing optical signal in 4th Embodiment of this invention. It is a block diagram which shows the circuit structure of the wavelength error signal detection circuit in 5th Embodiment of this invention. It is a timing diagram explaining the identification principle of the wavelength error signal regarding the time division multiplexing optical signal in 5th Embodiment of this invention. It is a block diagram which shows the circuit structure of the time division multiplexing optical communication system in 6th Embodiment of this invention. It is a block diagram which shows the circuit structure of the wavelength division multiplexing optical communication system in 7th Embodiment of this invention. It is a block diagram which shows the circuit structure of the wavelength division multiplexing optical communication system in 8th Embodiment of this invention. It is a block diagram which shows the circuit structure of the time division multiplexing system in a prior art. It is a timing diagram explaining a time division multiplexed optical signal. It is a block diagram which shows the circuit structure of the wavelength division multiplexing system in a prior art. It is a timing diagram explaining a wavelength division multiplexing signal. It is a characteristic view explaining the wavelength error at the time of wavelength division multiplexing. It is a block diagram which shows the circuit structure of a time division multiplexing and a wavelength division multiplexing system. It is a block diagram which shows the other circuit structure of a time division multiplexing and a wavelength division multiplexing system. It is a timing diagram explaining a time division multiplexing / wavelength division multiplexing hybrid signal. It is a characteristic view explaining the wavelength error at the time of time division multiplexing and wavelength division multiplexing. It is a block diagram which shows the circuit structure of the wavelength error signal detection circuit in a 1st prior art. It is a characteristic view explaining the identification principle of the wavelength error signal of the wavelength error signal detection circuit in the first prior art. It is a block diagram which shows the circuit structure of the wavelength error signal detection circuit in the 2nd prior art. It is a characteristic figure explaining the identification principle of the wavelength error signal of the wavelength error signal detection circuit in the 2nd prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Optical signal, Time division multiplexed optical signal 103 Optical beam splitter 105 1st light receiver 107 Optical filter 109 2nd light receiver 111 Amplifier (amplifier)
113 Subtractor 115 Sampling trigger signal 117 Analog-digital conversion circuit (AD converter)
119 Wavelength error signal 201 Reference light source 203 Reference pulse light source 205 Optical coupler 207 Light receiver 209 Filter 501 Optical signal input, time division multiplexed signal 503 Wavelength error signal detector 507 Reception timing signal selector 509 Sampling trigger signal 701 Sampling trigger signal generator 703 Sampling trigger signal 705 Wavelength error signal detector 707 Wavelength error signal 709 Memory 900 User side device 901-1 to 901-N User device 903-1 to 903-N Optical transmitter 905-1 to 905-N Transmission timing controller 907 First optical coupler 909 Optical fiber 910 Station side device 911 Second optical coupler 913 Receiver 915 Wavelength error signal detection circuit 917 Reception timing controller 920 Station side device 921 Wavelength demultiplexer 922-1 to 922-M light Plastic 923-1~923-M receivers 924-1~924-M controller 925 M × 1 optical switch (SW)
927 Controller 929 Wavelength error signal detection circuit 930 Station side device 935 Wavelength selector

Claims (13)

An optical beam splitter that branches the optical signal power of the input optical signal that is a time-division multiplexed optical signal;
A first receiver for monitoring one output of the light beam splitter;
An amplifier connected to the output of the first receiver;
An optical filter disposed downstream of the other output of the optical beam splitter to provide a wavelength reference;
A second light receiver for monitoring the output of the optical filter;
A subtractor for subtracting the output of the amplifier from the output of the second light receiver;
An analog-to-digital conversion circuit connected to the output of the subtractor, and the amplifier is configured so that the output of the subtractor becomes 0 when an optical signal having a desired wavelength is input. The gain is adjusted,
The wavelength-error signal detector, wherein the analog-digital conversion circuit monitors the output of the subtractor at an arbitrary time interval by a sampling trigger signal. A reference light source for generating a wavelength reference light serving as a wavelength reference;
An optical coupler for combining the input optical signal which is a time division multiplexed optical signal and the wavelength reference light;
A light-receiving device that photoelectrically converts the output light of the optical coupler;
A filter having a frequency dependency that is connected to the output of the light receiver and whose transmittance changes as the frequency increases;
An analog-digital conversion circuit connected to the output of the filter, and the input optical signal and the wavelength reference light are heterodyne-detected in the light receiver,
The filter converts the beat frequency of the input optical signal and the wavelength reference light into intensity,
The wavelength error signal detector, wherein the analog-digital conversion circuit monitors the output of the filter at an arbitrary time interval by a sampling trigger signal. A reference pulse light source for generating a wavelength reference light serving as a wavelength reference;
An optical coupler for combining the input optical signal which is a time division multiplexed optical signal and the wavelength reference light;
A light-receiving device that photoelectrically converts the output light of the optical coupler;
A filter having a frequency dependency that is connected to the output of the light receiver and whose transmittance changes as the frequency increases;
An analog-digital conversion circuit connected to the output of the filter, and the input optical signal and the wavelength reference light are heterodyne-detected in the light receiver,
The filter converts the beat frequency of the input optical signal and the wavelength reference light into intensity,
The wavelength error signal detector, wherein the reference pulse light source outputs an optical pulse as the wavelength reference light at an arbitrary time interval by a sampling trigger signal. A wavelength error signal detector according to any one of claims 1 to 3,
A reception timing signal selector that gives a signal reception time of any one user at the time of input of time division multiplexed optical signals by N users (N is an integer of 2 or more), and the wavelength error signal detector includes A wavelength error signal of a transmission wavelength of an arbitrary one of the N users is detected by detecting a wavelength error with respect to an input optical signal at a signal reception time given by a reception timing signal selector. Wavelength error signal detection circuit. A wavelength error signal detector according to any one of claims 1 to 3,
When a time-division multiplexed optical signal is input by N users (N is an integer of 2 or more), a sampling trigger signal having a repetition frequency of a detection period capable of detecting a wavelength error signal at least once for the optical signal of the N user is generated. A sampling trigger signal generator to be supplied to the wavelength error signal detector;
A memory for storing time-series data of wavelength error signals obtained by the wavelength error signal detector, and
A wavelength error signal for detecting the wavelength error signal of each of the N users is detected by associating the time series data of the wavelength error signal stored in the memory with the reception time for each of the N users. Detection circuit. N optical transmitters of N users (N is an integer of 2 or more);
N transmission timing controllers for controlling the transmission timing of each of the N optical transmitters of the N users;
An optical multiplexer that multiplexes optical signals transmitted from the N optical transmitters to generate a time-division multiplexed optical signal;
An optical receiver for receiving the time division multiplexed optical signal;
The wavelength error signal detection circuit according to claim 4, wherein the wavelength error signal detection circuit receives the time division multiplexed optical signal and detects a wavelength error signal, and the wavelength error signal detection circuit is in the vicinity of the optical receiver. A time division multiplex optical communication system characterized by being arranged in N optical transmitters of N users (N is an integer of 2 or more), each of which transmits an optical signal of any wavelength of M waves (M is an integer of 2 or more) An optical transmitter;
N transmission timing controllers for controlling the transmission timing of each of the N optical transmitters of the N users;
An optical multiplexer that multiplexes optical signals of the M waves transmitted from the N optical transmitters to generate a time-division multiplexed optical signal;
A wavelength demultiplexer for demultiplexing the M-wave time-division multiplexed optical signal;
M optical receivers respectively receiving the M-wave optical signals demultiplexed by the wavelength demultiplexer;
M × 1 optical SW (switch) arranged at the subsequent stage of the wavelength demultiplexer;
A controller for sending a control signal for selecting one of the M waves to the M × 1 optical SW;
The wavelength error signal detection circuit according to claim 4, wherein the wavelength error signal detection circuit receives the M wave optical signal and detects a wavelength error signal, and the wavelength error signal detection circuit is equivalent to the M wave. Has characteristics,
A wavelength division multiplexing optical communication system characterized in that the wavelength error signal detector is shared by M waves by connecting the wavelength error signal detection circuit to the output of the M × 1 optical SW. N optical transmitters of N users (N is an integer of 2 or more), each of which transmits an optical signal of any wavelength of M waves (M is an integer of 2 or more) An optical transmitter;
N transmission timing controllers for controlling the transmission timing of each of the N optical transmitters of the N users;
An optical multiplexer that multiplexes optical signals of the M waves transmitted from the N optical transmitters to generate a time-division multiplexed optical signal;
A wavelength demultiplexer for demultiplexing the M-wave time-division multiplexed optical signal transmitted through the transmission line;
M optical receivers respectively receiving the M-wave optical signals demultiplexed by the wavelength demultiplexer;
An optical coupler that is arranged in front of the wavelength demultiplexer and branches a part of the optical signal in the transmission path;
A wavelength selector that selects one of the M waves of the wavelength-multiplexed optical signal that is arranged downstream of the optical coupler and branched by the optical coupler;
A controller for controlling wavelength selection of the wavelength selector;
6. The wavelength error signal detection circuit according to claim 4, further comprising: a wavelength error signal detection circuit according to claim 4, wherein the wavelength error signal detection circuit receives one optical signal of the M waves and detects a wavelength error signal. Has equivalent characteristics to the M wave,
A wavelength division multiplexing optical communication system characterized in that the wavelength error signal detector is shared by M waves by connecting the wavelength error signal detection circuit to the output of the wavelength selector. Branching the optical signal power of the input optical signal which is a time-division multiplexed optical signal by the optical beam splitter;
Converting one output optical signal power branched by the first light receiver into an electric signal power;
Amplifying the electrical signal power by an amplifier;
Providing a wavelength reference for the one output optical signal power branched by an optical filter;
Converting the output optical signal power of the optical filter into electric signal power by a second light receiver;
Subtracting the output power of the amplifier from the output power of the second light receiver by a subtractor;
Converting the output of the subtractor into a digital signal by an analog-digital conversion circuit;
Adjusting the gain of the amplifier so that the output of the subtractor becomes 0 when an optical signal of a desired wavelength is input;
And a step of driving the analog-digital conversion circuit at an arbitrary time interval by a sampling trigger signal. Generating wavelength reference light as a wavelength reference from a reference light source;
Combining an input optical signal that is a time-division multiplexed optical signal and the wavelength reference light by an optical coupler;
Heterodyne detection of the input optical signal and the wavelength reference light by an optical receiver;
Converting the beat frequency of the input optical signal and the wavelength reference light into intensity by a filter having frequency dependence;
Monitoring the output of the filter at arbitrary time intervals by driving an analog-digital conversion circuit with a sampling trigger signal. Generating a wavelength reference light pulse to be a wavelength reference from a reference light source at an arbitrary time interval by a sampling trigger signal;
Combining an input optical signal that is a time-division multiplexed optical signal and the wavelength reference optical pulse by an optical coupler;
Heterodyne detection of the input optical signal and the wavelength reference optical pulse by an optical receiver;
Converting the beat frequency of the input optical signal and the wavelength reference optical pulse into an intensity by a filter having frequency dependence;
Monitoring the output of the filter. A method of detecting a wavelength error signal, comprising: Generating a reception timing signal that gives a signal reception time of an arbitrary user when a time division multiplexed optical signal is input by N users (N is an integer of 2 or more) by a reception timing signal selector;
Detecting a wavelength error signal of a transmission wavelength of any one of the N users by detecting a wavelength error with respect to an input optical signal at a signal reception time given by the reception timing signal. 12. The wavelength error signal detection method according to claim 9, wherein the wavelength error signal is detected. When a time-division multiplexed optical signal is input by N users (N is an integer of 2 or more), a sampling trigger signal having a repetition frequency of a detection period capable of detecting a wavelength error signal at least once for the optical signal of the N user is generated. And steps to
Storing time-series data of the wavelength error signal obtained using the sampling trigger signal in a memory;
Detecting the wavelength error signal of each of the N users' transmission wavelengths by associating the time series data of the wavelength error signal stored in the memory with the reception time for each of the N users. The wavelength error signal detection method according to claim 9.

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