JPH0865268A - Reference wavelength distributing system - Google Patents

Abstract

PURPOSE: To freely design the configuration of a reference wavelength generating part and an interface by making usable a wavelength to be used for the interface between a wavelength generating part and a receiving part even when that wavelength is different from a reference wavelength. CONSTITUTION: Respective wavelength measuring parts 11 and 51 of a reference wavelength generator 1 and a reference wavelength receiver 2 measure the wavelength difference of the reference wavelength and a transmission wavelength. This wavelength difference measured on the side of the reference wavelength generator 1 is transmitted to the reference wavelength receiver 2, and a data processing part 54 calculates the wavelength difference between the reference wavelengths of both the devices from two kinds of wavelength difference. This wavelength difference of reference wavelengths is used for wavelength control on the side of the reference wavelength receiver 2. Thus, even when the transmission wavelength to be used for the interface between the reference wavelength generator 1 and the reference wavelength receiver 2 is different from the reference wavelength of the reference wavelength generator 1, the reference wavelength can be distributed. Therefore, even when the reference wavelength is changed, the interface between the reference wavelength generator 1 and the reference wavelength receiver 2 can be used as it is.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reference wavelength distribution system used in wavelength multiplexing transmission for multiplexing a large number of wavelengths on a single optical fiber cable.

[0002]

2. Description of the Related Art In optical communication, the communication capacity is expanded by wavelength multiplexing of light. In this wavelength division multiplexing, in order for each device to transmit and receive optical signals arranged in high density on the wavelength axis, it is necessary to distribute a reference wavelength signal indicating an optical wavelength serving as a reference for each optical signal. The reference frequency of an electric signal is
It is distributed to all nodes by a subordinate synchronization network consisting of one master node and slave nodes synchronized with it.
In the node, the reference frequency is distributed to each device by a device having a distribution function such as a clock distribution device. With this network configuration, all devices can communicate at the reference frequency with the same accuracy. With the same network configuration, the reference wavelength can be distributed to each device. An optical signal from a reference wavelength light source installed in the master node can be distributed to each node and each device by an optical fiber cable.

[0003]

In the prior art, when the reference wavelength is distributed, the wavelength used by the interface on the wavelength generator side matches the reference wavelength. As a result, the wavelength receiving section has an advantage that the reference wavelength can be regenerated by receiving the optical signal. However, on the wavelength transmitting side, a circuit for synchronizing the wavelength of the laser used by the interface with the reference wavelength is required. In order to synchronize, it is also necessary to select a laser capable of wavelength synchronization. Even if a reference light source with higher wavelength stability is developed, if the wavelength is different, the conventional interface may not be usable.

Further, in the wavelength receiving section, the internal light source is synchronized with the distributed reference signal, but conventionally there has been no means for grasping the synchronization characteristic. The present invention has been made in view of the above points, and an object thereof is to make it possible to use a wavelength different from the reference wavelength for the wavelength used by the interface between the wavelength generation unit and the reception unit. And to be able to freely design the interface configuration. Further, it is to provide a means for grasping the synchronization characteristic of the reference wavelength on the wavelength receiving section side.

[0005]

In order to solve the above-mentioned problems, the invention according to claim 1 provides a first reference wavelength generator for generating a first reference wavelength and the first reference wavelength. A reference wavelength generation device comprising a first wavelength measurement unit that measures a wavelength as a reference, and a first interface unit that superimposes a measurement result from the first wavelength measurement unit on transmission data and transmits the reference data. , A second reference wavelength generating section for generating a second reference wavelength, a second wavelength measuring section for measuring a wavelength based on the second reference wavelength, and receiving the reference signal, the measurement result Reference signal distribution including a reference wavelength receiving device including a second interface unit that separates and a first data processing unit, and a transmission medium that connects the first interface unit and the second interface unit In the method, the reference wavelength In the raw device, the first wavelength measuring unit measures a first wavelength difference which is a difference between a transmission wavelength transmitted by the first interface unit to the transmission medium and the first reference wavelength, and A transmission wavelength and the first wavelength difference are transmitted to the transmission medium, and in the reference wavelength receiving device, the second interface unit receives the transmission wavelength and the first wavelength difference, and the second The wavelength measuring unit measures a second wavelength difference which is a difference between the second reference wavelength and the transmission wavelength, and in the first data processing unit, the first wavelength difference and the second wavelength. The third wavelength difference, which is the difference between the first reference wavelength and the second reference wavelength, is obtained from the difference.

According to a second aspect of the present invention, in the reference wavelength distribution system according to the first aspect, the reference wavelength generator is provided with a second data processing section, and the reference wavelength generator and the reference wavelength receiver are provided. Is connected by a transmission medium capable of bidirectional transmission, and in the reference wavelength generating device, from the second wavelength difference transmitted from the first wavelength difference and the reference wavelength receiving device, the second wavelength difference The fourth wavelength difference, which is the difference between the reference wavelength and the first reference wavelength, is obtained by the second data processing unit, and again, from the reference wavelength generation device, through the first interface unit, the A fourth wavelength difference is transmitted to the transmission medium, the reference wavelength receiving device receives the fourth wavelength difference by the second interface unit, and the third wavelength difference is received by the first data processing unit. Wavelength difference, ratio of the fourth wavelength difference To have and outputs the result.

[0007]

According to the first aspect of the invention, the wavelength difference between the reference wavelength and the transmission wavelength used by the reference wavelength generator and the reference wavelength receiver is measured in each wavelength measuring section. This wavelength difference measured on the reference wavelength generating device side is transmitted to the reference wavelength receiving device, and the data processing unit on the reference wavelength receiving device side obtains the wavelength difference between the reference wavelengths of both devices from these two wavelength differences. The wavelength difference between the reference wavelengths is used for wavelength control on the reference wavelength receiving device side. Thus, even if the transmission wavelength used by the interface between the reference wavelength generating device and the reference wavelength receiving device is different from the reference wavelength of the reference wavelength generating device, the reference wavelength can be distributed. Therefore, even if the reference wavelength is changed, the interface between the reference wavelength generating device and the reference wavelength receiving device can be used as it is. further,
Since it is not necessary to control the wavelength of the light source used for the interface between the reference wavelength generation device and the reference wavelength reception device, the wavelength selection of the light source becomes unnecessary, and the cost can be reduced.

According to the second aspect of the invention, the reference wavelength generating device side is based on the wavelength difference between the reference wavelength of the device and the transmission wavelength measured by the reference wavelength generating device and the reference wavelength receiving device. The data processing unit determines the wavelength difference between the reference wavelengths of both devices. The reference wavelength generator sends this wavelength difference back to the reference wavelength receiver. The data processing unit of the reference wavelength receiving device compares the wavelength difference between the reference wavelengths of the reference wavelength generating device and the reference wavelength receiving device, which are obtained by the reference wavelength receiving device and the reference wavelength receiving device. Thereby, it is possible to judge whether the reference wavelength used internally by the reference wavelength receiving device is accurately synchronized with the reference wavelength of the reference wave generating device.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an apparatus according to the reference wavelength distribution system according to this embodiment. In the figure, a reference wavelength generator 1 and a reference wavelength receiver 2
Are connected by bidirectional transmission lines 3 and 4. The reference wavelength generation device 1 includes a reference wavelength generation unit M10 and a wavelength measurement unit M1.
1, an interface unit M transmission unit 12, an interface unit M reception unit 13, a data processing unit M14, a multiplexing unit 15, and a demultiplexing unit 16. Further, the reference wavelength receiving device 2 is
A reference wavelength generating section S50, a wavelength measuring section S51, an interface section S transmitting section 52, an interface section S receiving section 53,
The data processing unit S54, the multiplexing unit 55, and the demultiplexing unit 56 are included.

FIG. 2 shows the structure of the reference wavelength generator. The reference wavelength generator is a laser 100, a molecular absorption cell 1
01, the detector 102, and the control unit 103. The laser 100 has two outputs, one of which serves as the output 104 of the reference wavelength generator, and the other one 105 is used for wavelength stabilization. The laser output 105 is input to the molecular absorption cell 101, and the output optical signal 106 is converted into an electric signal 107 in the detector 102. Due to the absorption characteristics of light at the specific wavelength indicated by the molecular absorption cell 101,
The electrical signal 107 varies with the wavelength of the laser 100. Based on this change, the control unit 103 controls the wavelength of the laser 100 to the peak wavelength of the absorption characteristic. By this control, the wavelength of the laser 100 is stabilized at the specific wavelength indicated by the molecular absorption cell 101. The laser output 104 becomes the output of the reference wavelength generation unit. In FIG. 1, the reference wavelength generator is
The reference wavelength generator M10 or the reference wavelength generator S50. In the figure, the laser output 104 is the reference wavelength M1.
7, corresponding to the reference wavelength S57.

FIG. 3 shows the configuration of the wavelength measuring section.
The wavelength measurement unit includes an optical coupler 120, a sweeping Fabry-Perot filter 121, a detector 122, a control unit 123, a sweep signal generator 124, and an optical switch 125. One of the signals under measurement 126 is selected by the two-input optical switch 125 by the control signal 130 from the control section 123. Selected measured signal 127 and reference wavelength signal 12
8 is multiplexed by the optical coupler 120 to become an optical signal 129,
It is input to the sweeping type Fabry-Perot filter 121. The sweep signal generator 124 controls the control signal 1 from the control unit 123.
Controlled by 32, the sweep signal 131 changes the optical output 133 of the sweeping Fabry-Perot filter 121. The detector 122 converts this light output 133 into an electrical signal 134. Based on the electrical signal 134, the control unit 123 selects the measured signal 127 selected with respect to the reference wavelength signal 128.
Is calculated and output as the measured value 135. In FIG. 1, the wavelength measuring unit is the wavelength measuring unit M11 or the wavelength measuring unit S51. In the same figure, the signal under measurement 126
Is the transmission wavelength 18 and the reception wavelength 19, and the transmission wavelength 5
8 and the reception wavelength 59, and the reference wavelength signal 128 corresponds to the reference wavelength M17 and the reference wavelength S57. Further measured value 13
5 is the output 20 of the wavelength measuring unit M11 and the wavelength measuring unit S51.
Corresponding to the output 60 of

FIG. 4 shows the structure of the interface transmission unit. The interface transmitter includes a laser control / modulation signal receiver 140, a laser 141, and an optical coupler 1.
It is composed of 42. Upon receiving the modulation signal 143, the laser control / modulation signal receiving unit 140 outputs the modulation signal 144 of the laser 141, and the laser 141 outputs the optical signal 145 according to the modulation signal 144. The optical signal 145 is branched by the optical coupler 142, and becomes the output 146 of the interface transmission unit and the signal 147 to the wavelength measurement unit. In FIG. 1, the interface unit transmission unit is the interface unit M transmission unit 12 or the interface unit S transmission unit 52. Further, in the figure, the modulated signal 143 corresponds to the output 22 of the multiplexing unit 15 and the output 64 of the multiplexing unit 55, and the signal 147 to the wavelength measuring unit corresponds to the transmission wavelengths 18 and 58. The output 146 of the interface transmitter is transmitted to the transmission line 3 in the reference wavelength generator 1 and to the transmission line 4 in the reference wavelength receiver 2.
Connected to.

FIG. 5 shows the configuration of the interface section receiving section. The interface section receiving section includes an optical receiving and demodulating section 150 and an optical coupler 151. The optical signal 152 is branched by the optical coupler 151 and becomes an output 153 to the optical receiving and demodulating section 150 and a signal 154 to the wavelength measuring section. The optical receiving and demodulating section 150 uses the optical coupler output 15
3 and outputs the demodulated signal 155. In FIG.
The interface unit receiving unit is the interface unit M receiving unit 1.
3 or the interface unit S reception unit 53. Further, in the figure, the signal 154 to the wavelength measuring unit is the reception wavelength 19,
Corresponds to 59. The demodulated signal 155 corresponds to the input 23 of the separation unit 16 and the input 61 of the separation unit 56. Optical signal 1
Reference numeral 52 is connected to the transmission line 4 in the reference wavelength generating device 1 and to the transmission line 3 in the reference wavelength receiving device 2.

FIG. 6 shows the structure of the multiplexing unit. The multiplexing unit includes memory writing circuits 160 and 161, a digital memory 162, and a memory reading circuit 163. The multiplexed signals 164 and 165 are written in the digital memory 162 by the memory writing circuits 160 and 161, respectively, and are accumulated in one signal series. The accumulated signal is read by the memory reading circuit 163 and becomes the multiplexed output 166. In FIG. 1, the multiplexing unit is the multiplexing unit 15 or the multiplexing unit 55. The multiplexed output 166 corresponds to 22 and 64 in FIG. FIG. 7 shows the configuration of the separation unit. The separation unit includes the memory reading circuits 170 and 171, the digital memory 1
72 and a memory writing circuit 173. The demodulated signal 176 is written in the digital memory 172 by the memory writing circuit 173 and accumulated in two signal sequences. The accumulated signal is stored in the memory reading circuit 170,
171, respectively, and output by the separation unit 17
It becomes 4,175. In FIG. 1, the separation unit is the separation unit 16
Alternatively, it is the separation unit 56. Also, demodulated signal 1 which is the input
76 corresponds to 23 and 61 in FIG.

FIG. 8 shows the configuration of the data processing section. The data processing unit includes a processing circuit 180, input interfaces 181, 182, and an output interface 183. The data 184 from the wavelength measuring unit and the data 185 from the separating unit are input interface 18 respectively.
The data is input to the processing circuit 180 via 1, 182. The processing circuit 180 is composed of a microprocessor (not shown) and a memory (not shown), and the processing result is data 186 to the separation unit via the output interface 183. In FIG. 1, the data processing units are a data processing unit M14 and a data processing unit S54.

Next, the operation of the reference wavelength distribution system having the above configuration will be described with reference to FIG. The wavelength measuring unit M11
With reference to the reference wavelength M17 (wavelength λ _M ) from the reference wavelength generator M10, the transmission wavelength 18 (wavelength λ _T1 ) used in the interface M transmitter 12 and the reception wavelength received in the interface M receiver 13 are used. 19 (wavelength λ _T2 ) is measured. As a result, the measurement result Δλ _T1M (= λ _T1 −λ _M ) of the transmission wavelength 18 and the measurement result Δλ _T2M (= λ _T2 −λ _M ) of the reception wavelength 19 are obtained at the output 20 of the wavelength measuring unit M11. On the other hand, the wavelength measurement unit S51 uses the reference wavelength S57 (wavelength λ _S ) from the reference wavelength generation unit S50 as a reference, and the transmission wavelength 58 (wavelength λ _T2 ) and the interface unit S reception used in the interface unit S transmission unit 52. Part 5
The reception wavelength 59 (wavelength λ _T1 ) received at 3 is measured.
As a result, the measurement result of the transmission wavelength 58 Δλ _T2S (= λ _T2 −
λ _S ), the measurement result of the reception wavelength 59 Δλ _T1S (= λ _T1 −
λ _S ) is obtained at the output 60 of the wavelength measuring unit S51.

The measurement result Δλ _T1M of the transmission wavelength 18 is sent to the multiplexing unit 15 via the data processing unit M14 and multiplexed with other data 21. Output 22 of multiplexer 15
Is converted into an optical signal by the interface section M transmitter 12 and transmitted to the reference wavelength receiver 2 via the transmission line 3. The measurement result Δλ _T1M of the transmission wavelength 18 transmitted to the reference wavelength receiving device 2 is converted into an electric signal by the interface section S receiving section 53 and becomes an input 61 of the separating section 56. The separating unit 56 measures the measurement result Δλ of the transmission wavelength 18 from the electric signal 61.
_T1M is separated, and the input 62 of the data processing unit S54 is output. The data processing unit S54 calculates the following equation based on the transmitted measurement result Δλ _T1M of the transmission wavelength 18 and the measurement result Δλ _T1S of the reception wavelength 59 measured by the wavelength measurement unit S51. Δλ _T1M −Δλ _T1S = (λ _T1 −λ _M ) − (λ _T1 −λ _S ) = λ _S −λ _M (1) = Δλ _SM

By executing the equation (1), the reference wavelength S57 from the reference wavelength generating section S50 is based on the reference wavelength M17 (wavelength λ _M ) from the reference wavelength generating section M10.
The wavelength difference of (wavelength λ _S ) and Δλ _SM can be obtained.
By controlling the wavelength of the reference wavelength receiving device 2 using this Δλ _SM , it is possible to perform communication by wavelength multiplexing of light. The measurement result Δλ _T2S of the transmission wavelength 58 is sent to the multiplexing unit 55 via the data processing unit S54 and multiplexed with other data 63. The output 64 of the multiplexer 55 is converted into an optical signal by the interface S transmitter 52 and transmitted to the reference wavelength generator 1 via the transmission line 4. The measurement result Δλ _T2S of the transmission wavelength 58 transmitted to the reference wavelength generation device 1 is converted into an electric signal by the interface unit M reception unit 13 and becomes the input 23 of the separation unit 16. The separation unit 16 receives the electric signal 23.
From the measurement result Δλ _T2S of the transmission wavelength 58, and outputs the input 24 of the data processing unit M14.

In the data processing unit M14, the measurement result Δλ _T2S of the transmitted transmission wavelength 58 and the wavelength measuring unit M11 are transmitted.
From the measurement result Δλ _T2M of the reception wavelength 19 measured in
The following formula is calculated. Δλ _T2M −Δλ _T2S = (λ _T2 −λ _M ) − (λ _T2 −λ _S ) = λ _S −λ _M (2) = Δλ _SM ′ By executing the equation (2), the reference wavelength generator M10
It is possible to obtain the wavelength difference Δλ _SM ′ of the reference wavelength S57 (wavelength λ _S ) from the reference wavelength generator S50 with reference to the reference wavelength M17 (wavelength λ _M ). This wavelength difference Δ
λ _SM 'is transmitted again to the reference wavelength receiving device 2 via the data processing unit M14, the multiplexing unit 15, the interface unit M transmitting unit 12, and the transmission line 3, and the interface unit S receiving unit 5
3, the data is transferred to the data processing unit S54 via the separation unit 56. In the data processing unit S54, the wavelength difference Δ obtained first
comparing the lambda _SM, the [Delta] [lambda] _SM 'measured at a reference wavelength generator 1. If the two measured values match, the reference wavelength generator S
It can be confirmed that the reference wavelength S57 at 50 is normally maintained.

[0020]

As described above, according to the first aspect of the invention, the transmission wavelength used by the interface between the reference wavelength generating device and the reference wavelength receiving device is independent of the reference wavelength of the reference wavelength generating device. Can be set. Therefore, even if the reference wavelength is changed, the interface between the reference wavelength generating device and the reference wavelength receiving device can be used as it is. Further, it is not necessary to control the wavelength of the light source used for the interface between the reference wavelength generating device and the reference wavelength receiving device, which eliminates the need to select the wavelength of the light source, and has the effect of reducing the cost. According to the second aspect of the present invention, there is an effect that the reference wavelength receiving device can determine whether or not the reference wavelength used internally by the reference wavelength receiving device is operating normally.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an apparatus according to a reference wavelength distribution system according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a reference wavelength generation unit M10 or a reference wavelength generation unit S50 according to the embodiment.

FIG. 3 is a block diagram showing a configuration of a wavelength measuring unit M11 or a wavelength measuring unit S51 according to the same embodiment.

FIG. 4 is an interface unit M transmission unit 12 according to the embodiment.
Alternatively, it is a block diagram showing a configuration of an interface unit S transmission unit 52.

FIG. 5 is an interface unit M receiving unit 13 according to the embodiment.
Alternatively, it is a block diagram showing the configuration of the interface unit S reception unit 53.

FIG. 6 is a block diagram showing a configuration of a multiplexing unit 15 or a multiplexing unit 55 according to the embodiment.

FIG. 7 is a separation unit 16 or a separation unit 56 according to the embodiment.
FIG. 3 is a block diagram showing the configuration of FIG.

FIG. 8 is a block diagram showing a configuration of a data processing unit M14 or a data processing unit S54 according to the embodiment.

[Explanation of symbols]

1 ... Reference wavelength generator, 2 ... Reference wavelength receiver, 3, 4
... bidirectional transmission path, 10 ... reference wavelength generating section M, 11 ... wavelength measuring section M, 12 ... interface section M transmitting section, 13 ... interface section M receiving section, 14 ... data processing section M, 15
... Multiplexing unit, 16 ... Separation unit, 17 ... Reference wavelength M, 18 ...
Transmitting wavelength, 19 ... Receiving wavelength, 20 ... Output of wavelength measuring unit M11, 21 ... Other data, 22 ... Output of multiplexing unit 23, 23 ... Input of demultiplexing unit 16, 24 ... Data processing unit M1
4 input, 50 ... Reference wavelength generating section S, 51 ... Wavelength measuring section S, 52 ... Interface section S transmitting section, 53 ... Interface section S receiving section, 54 ... Data processing section S, 55 ... Multiplexing section, 56 ... Separation unit, 57 ... Reference wavelength S, 58 ... Transmission wavelength, 59 ... Reception wavelength, 60 ... Output of wavelength measurement unit S51,
61 ... Input of separation unit 56, 62 ... Input of data processing unit S54, 63 ... Other data, 64 ... Output of multiplexing unit 55, 100 ... Laser, 101 ... Molecular absorption cell, 102 ...
Detector, 103 ... Control unit, 104, 105 ... Laser output, 106 ... Optical signal, 107 ... Electrical signal, 120 ... Optical coupler, 121 ... Sweep type Fabry-Perot filter, 122
... detector, 123 ... control unit, 124 ... sweep signal generator,
125 ... Optical switch, 126 ... Signal under measurement, 127 ... Selected signal under measurement, 128 ... Reference wavelength signal, 129 ...
Optical signal, 130 ... Control signal from control unit 123, 131
... sweep signal, 132 ... control signal from control unit 123, 1
33 ... Optical output, 134 ... Electrical signal, 135 ... Measured value, 1
40 ... Laser control and modulation signal receiving section, 141 ... Laser, 142 ... Optical coupler, 143 ... Modulation signal, 144 ... Laser 141 modulation signal, 145 ... Optical signal, 146 ... Interface section transmitting section output, 147 ... Wavelength measurement To the unit, 150 ... Optical receiving and demodulating unit, 151 ... Optical coupler,
152 ... Optical signal, 153 ... Optical reception and output to demodulation section 150, 154 ... Wavelength measurement section signal, 155 ... Demodulated signal, 160, 161, ... Memory writing circuit, 162 ... Digital memory, 163 ... Memory reading circuit, 16
4, 165 ... Multiplexed signals, 166 ... Multiplexed outputs,
170, 171 ... Memory reading circuit, 172 ... Digital memory, 173 ... Memory writing circuit, 174, 1
75 ... Separator output, 176 ... Demodulated signal, 180 ... Processing circuit, 181, 182 ... Input interface, 183 ... Output interface, 184 ... Data from wavelength measuring section,
185 ... Data from separation unit, 186 ... Data to separation unit

Claims (2)

[Claims] 1. A first reference wavelength generating section for generating a first reference wavelength, a first wavelength measuring section for measuring a wavelength with reference to the first reference wavelength, and the first wavelength measuring section. A reference wavelength generator comprising a first interface unit for superimposing the measurement result from the transmission data and transmitting it as a reference signal; a second reference wavelength generating unit for generating a second reference wavelength; A second wavelength measuring unit for measuring a wavelength with reference to the reference wavelength, a second interface unit for receiving the reference signal and separating the measurement result, and a first data processing unit, receiving a reference wavelength. In a reference signal distribution system comprising a device and a transmission medium that connects the first interface unit and the second interface unit, in the reference wavelength generation device, in the first wavelength measurement unit,
The first interface section measures a first wavelength difference which is a difference between a transmission wavelength transmitted to the transmission medium and the first reference wavelength, and the transmission wavelength and the first wavelength difference are the transmission medium. In the reference wavelength receiving device, the second interface unit receives the transmission wavelength and the first wavelength difference,
In the second wavelength measurement unit, to measure a second wavelength difference that is the difference between the second reference wavelength and the transmission wavelength, in the first data processing unit, the first wavelength difference and the A reference wavelength distribution system, wherein a third wavelength difference, which is a difference between the first reference wavelength and the second reference wavelength, is obtained from a second wavelength difference. 2. The reference wavelength distribution system according to claim 1, wherein the reference wavelength generating device is provided with a second data processing unit, and bidirectional transmission is possible between the reference wavelength generating device and the reference wavelength receiving device. Connected by a medium, in the reference wavelength generator, from the first wavelength difference and the second wavelength difference transmitted from the reference wavelength receiving device, the second reference wavelength and the first reference The fourth wavelength difference, which is the difference in wavelength, is obtained by the second data processing unit,
Again, from the reference wavelength generation device, via the first interface unit, the fourth wavelength difference is transmitted to the transmission medium, in the reference wavelength receiving device, the second interface unit, by the second interface unit. A reference wavelength distribution system, wherein four wavelength differences are received, and the first data processing unit compares the third wavelength difference and the fourth wavelength difference and outputs the result.