Optical transmission device and optical transmission system

Abstract

When the distance between optical transmission devices increases, an OTDR (Optical Time Domain Reflectometer) is used to measure the distance between the optical transmission devices. [Solution] The optical transmission device is an optical transmission device that faces another optical transmission device via a transmission path having a predetermined transmission path loss, and comprises: a first transmitting / receiving unit that transmits a first measurement light based on OTDR to the transmission path and receives a first return light based on the reflection of the first measurement light from the transmission path; a measuring unit that measures a first optical loss in the transmission path based on the first measurement light and the first return light; a receiving unit that receives predetermined information regarding a second optical loss in the transmission path from the other optical transmission device; and a calculation unit that calculates the distance between the optical transmission device and the other optical transmission device based on the first optical loss, the second optical loss and the transmission path loss.

Description

Technical Field

[0001] This invention relates to an optical transmission device and an optical transmission system.

Background Art

[0002] An OTDR (Optical Time Domain Reflectometer) including a laser light source that emits a laser beam into a device under test and a connection port for connecting to an end of the device under test is known. It is also known that an OTDR operates in conjunction with another OTDR to measure the fiber length of an optical fiber (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, when measuring the distance between opposing optical transmission devices via a transmission path such as an optical fiber using an OTDR mounted on the optical transmission device, it may be difficult to measure the distance. For example, when the distance between the optical transmission devices is long, if the optical power of the measurement light is reduced below the limit of the measurement sensitivity even when the measurement light based on the OTDR is input into the transmission path, there is a risk that the distance cannot be measured over the entire length.

[0005] Therefore, on one aspect, an object is to provide an optical transmission device and an optical transmission system that measure the distance between optical transmission devices using an OTDR when the distance between the optical transmission devices increases.

Means for Solving the Problems

[0006] In one embodiment, the optical transmission device is an optical transmission device facing another optical transmission device via a transmission path having a predetermined transmission path loss, and includes: a first transmitting / receiving unit that transmits a first measurement light based on OTDR to the transmission path and receives a first return light based on the reflection of the first measurement light from the transmission path; a measuring unit that measures a first optical loss in the transmission path based on the first measurement light and the first return light; a receiving unit that receives predetermined information regarding a second optical loss in the transmission path from the other optical transmission device; and a calculation unit that calculates the distance between the optical transmission device and the other optical transmission device based on the first optical loss, the second optical loss and the transmission path loss. [Effects of the Invention]

[0007] When the distance between optical transmission devices increases, the distance between them can be measured using an OTDR. [Brief explanation of the drawing]

[0008] [Figure 1] This is an example of a block diagram for an optical transmission system. [Figure 2] This is a flowchart illustrating an example of how an optical transmission system works. [Figure 3] (a) is an example of a U / D loss distribution. (b) is an example of a D / U loss distribution. [Figure 4] This figure illustrates an example of transforming the U / D loss distribution. [Figure 5] (a) is an example of calculating distance #1. (b) is an example of calculating distance #2. (c) is an example of calculating the distance between devices. [Modes for carrying out the invention]

[0009] The following will explain the implementation of this project with reference to the drawings.

[0010] As shown in Figure 1, the optical transmission system ST includes two opposing optical transmission devices 100 and 200. Optical transmission device 100 is an example of a first optical transmission device. Optical transmission device 200 is an example of a second optical transmission device. Optical transmission devices 100 and 200 include, for example, ROADM (Reconfigurable Optical Add / Drop Multiplexer).

[0011] Optical transmission devices 100 and 200 are connected via two parallel transmission paths T1 and T2. Optical transmission device 100 is connected to one end of each transmission path T1 and T2. Optical transmission device 200 is connected to the other end of each transmission path T1 and T2. Both transmission paths T1 and T2 contain optical fibers. The type of optical fiber is not particularly limited. The optical fiber may be an SMF (Single Mode Fiber) or a DSF (Dispersion Shifted Fiber). Both transmission paths T1 and T2 have a predetermined transmission path loss.

[0012] First, the optical transmission device 100 will be described. The optical transmission device 100 includes an OTDR (Optical Time Domain Reflectometer) unit 101, an OSC transmitting / receiving unit 102, and optical amplifiers 103 and 104. The OTDR unit 101 is an example of a first transmitting / receiving unit and a measurement unit. The OSC transmitting / receiving unit 102 is an example of a second transmitting / receiving unit.

[0013] Furthermore, the optical transmission device 100 includes WDM couplers 106, 108, a branch coupler 109, a control unit (indicated as CTRL in Figure 1) 110, optical transmission units 112, 113, and optical reception units 114, 115. The control unit 110 is an example of a reception unit and calculation unit. The optical transmission units 112, 113 and the optical reception units 114, 115 each include connectors.

[0014] The optical amplifier 103, WDM couplers 106 and 108, optical transmitter 112, and optical receiver 115 are connected by the optical fiber 116 of the optical transmission device 100. The optical amplifier 104, branch coupler 109, optical transmitter 113, and optical receiver 114 are connected by the optical fiber 117 of the optical transmission device 100.

[0015] The OTDR unit 101 is optically connected to the WDM coupler 106. The OTDR unit 101 transmits a pulsed light Lp1 as a first measurement light to the transmission line T1 via the optical fiber 116 and receives a return light Lr1 as a first return light based on the reflection of the pulsed light Lp1. The reflection includes, for example, Rayleigh scattering and Fresnel reflection. By receiving the return light Lr1, the OTDR unit 101 can generate a loss distribution that represents the distribution of optical loss in the longitudinal direction of the transmission line T1. In this way, the OTDR unit 101 can measure the magnitude of the optical loss of the transmission line T1.

[0016] The OSC transceiver 102 is optically connected to the WDM coupler 108 and the branch coupler 109. The OSC transceiver 102 transmits a first control signal light Lo1 based on the OSC (Optical Supervisory Channel) to the optical transmission device 200. The first control signal light Lo1 is an example of a first signal light. The OSC transceiver 102 receives a second control signal light Lo2 output from the optical transmission device 200. The second control signal light Lo2 is an example of a second signal light. The second control signal light Lo2 may or may not include span loss as transmission path loss in the transmission path T1.

[0017] The optical amplifier 103 amplifies and outputs the WDM signal light Lw1 received by the optical transmission device 100 via the optical reception unit 115. The optical amplifier 103 is a post-amplifier realized by, for example, an EDFA (Erbium Doped Fiber Amplifier) and a circuit board for controlling the gain of the EDFA. Note that the post-amplifier is an amplifier provided at the subsequent stage or downstream of a WSS (Wavelength Selective Switch) (not shown) provided between the optical amplifier 103 and the optical reception unit 115. The WDM signal light Lw1 output by the optical amplifier 103 is transmitted to the transmission line T1 via the optical transmission unit 112.

[0018] The optical amplifier 104 amplifies and outputs the WDM signal light Lw2 received by the optical transmission device 100 via the optical reception unit 114. The optical amplifier 104 is a pre-amplifier realized by, for example, an EDFA and a circuit board for controlling the gain of the EDFA. Note that the pre-amplifier is an amplifier provided at the previous stage or upstream of a WSS (not shown) provided between the optical amplifier 104 and the optical transmission unit 113. The WDM signal light Lw2 output by the optical amplifier 104 is transmitted via the optical transmission unit 113.

[0019] The control unit 110 is electrically connected to the OTDR unit 101, the OSC transceiver unit 102, and the optical amplifiers 103 and 104. The control unit 110 includes a processor such as a CPU (Central Processing Unit) and memories such as a RAM (Random Access Memory) and a ROM (Read Only Memory). The control unit 110 may include an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit). The control unit 110 controls the operations of the OTDR unit 101, the OSC transceiver unit 102, and the optical amplifiers 103 and 104.

[0020] For example, the control unit 110 can request the OTDR unit 101 to output the pulsed light Lp1. The control unit 110 can request the OSC transceiver unit 102 to output the first control signal light Lo1. The control unit 110 can adjust the gains of the optical amplifiers 103 and 104.

[0021] Next, the optical transmission device 200 will be described. The optical transmission device 200 includes an OTDR unit 201, an OSC transceiver unit 202, and optical amplifiers 203 and 204. Further, the optical transmission device 200 includes WDM couplers 206 and 208, a branching coupler 209, a control unit 210, optical transmitters 212 and 213, and optical receivers 214 and 215.

[0022] The optical amplifier 203, the WDM coupler 208, the optical transmitter 212, and the optical receiver 215 are connected by the optical fiber 216 of the optical transmission device 200. The optical amplifier 204, the WDM coupler 206, the branching coupler 209, the optical transmitter 213, and the optical receiver 214 are connected by the optical fiber 217 of the optical transmission device 200.

[0023] Thus, the optical transmission device 200 basically has the same configuration as the optical transmission device 100. Therefore, the details of the optical transmission device 200 will be omitted. For example, the OTDR unit 201 transmits the pulsed light Lp2 as the second measurement light to the transmission path T1 via the optical fiber 217, and receives the return light Lr2 as the second return light based on the reflection of the pulsed light Lp2. The OSC transceiver unit 202 outputs the second control signal light Lo2 based on the OSC toward the optical transmission device 100. The optical transmitter 212 transmits the second control signal light Lo2 toward the optical transmission device 100. Thereby, the second control signal light Lo2 propagates through the transmission path T2.

[0024] Referring to FIGS. 2 to 5, the operation of the optical transmission system ST will be described.

[0025] First, as shown in Figure 2, the OTDR unit 101 of the optical transmission device 100 measures the optical loss #1 of the transmission path T1 (step S1). Optical loss #1 is an example of the first optical loss. More specifically, the OTDR unit 101 transmits pulsed light Lp1 of wavelength λ1 to the transmission path T1 and receives return light Lr1 of wavelength λ1 from the transmission path T1.

[0026] In other words, the OTDR unit 101 receives the return light Lr1 of the pulsed light Lp1 transmitted from the optical transmission device 100 located upstream of the transmission path T1 to the optical transmission device 200 located downstream of the transmission path T1. Based on the pulsed light Lp1 and the return light Lr1, the OTDR unit 101 measures the magnitude of the optical loss #1 in the transmission path T1. As a result, as shown in Figure 3(a), the OTDR unit 101 can generate an U / D (Upstream / Downstream) loss distribution including the optical loss #1 when a pulsed light Lp1 of wavelength λ1 is transmitted from upstream to downstream. Such a U / D loss distribution corresponding to wavelength λ1 is an example of the first optical loss.

[0027] Once optical loss #1 is measured, the OTDR unit 201 of the optical transmission device 200 measures optical loss #2 of the transmission path T1 (step S2). Optical loss #2 is an example of a second optical loss. More specifically, the OTDR unit 201 transmits a pulsed light Lp2 as a second measurement light with a wavelength λ2, which is longer than wavelength λ1, to the transmission path T1, and receives a return light Lr2 as a second return light from the transmission path T1.

[0028] In other words, the OTDR unit 201 receives the return light Lr2 of the pulsed light Lp2 transmitted from the optical transmission device 200 to the optical transmission device 100. Based on the pulsed light Lp2 and the return light Lr2, the OTDR unit 201 measures the magnitude of the optical loss #2 in the transmission path T1. As a result, as shown in Figure 3(b), the OTDR unit 201 can generate a D / U (Downstream / Upstream) loss distribution that includes the optical loss #2 when a pulsed light Lp2 with wavelength λ2 is transmitted from downstream to upstream. Such a D / U loss distribution corresponding to wavelength λ2 is an example of a second optical loss.

[0029] When the optical loss #2 is measured, the control unit 110 calculates the span loss (indicated as S / L in Figure 2) (step S3). More specifically, the control unit 110 requests the OSC transceiver 102 to transmit the first control signal light Lo1. The OSC transceiver 102 then transmits the first control signal light Lo1. The first control signal light Lo1 propagates through the transmission path T1 and reaches the optical transmission device 200.

[0030] The OSC transceiver 202 of the optical transmission device 200 receives the first control signal light Lo1. When the OSC transceiver 202 receives the first control signal light Lo1, the control unit 210 measures the optical power of the first control signal light Lo1 as the received optical power and requests the OSC transceiver 202 to transmit the second control signal light Lo2, which includes the received optical power. As a result, the OSC transceiver 202 transmits the second control signal light Lo2. The second control signal light Lo2 propagates through the transmission path T2 and reaches the optical transmission device 100.

[0031] The OSC transceiver 102 of the optical transmission device 100 receives the second control signal light Lo2. When the OSC transceiver 102 receives the second control signal light Lo2, the control unit 110 calculates the span loss based on the difference between the transmitted optical power of the first control signal light Lo1 and the received optical power included in the second control signal light Lo2.

[0032] If the span loss of the transmission line T1 is specified in advance by the specifications, the processing in step S3 may be omitted. In this case, the control unit 110 only needs to store the span loss of the transmission line T1 in advance. Alternatively, the OSC transceiver 102 may transmit the first control signal light Lo1, which includes the transmitted optical power of the first control signal light Lo1. In this case, when the OSC transceiver 202 receives the first control signal light Lo1, the control unit 210 can calculate the span loss based on the difference between the transmitted optical power included in the first control signal light Lo1 and the received optical power of the first control signal light Lo1. Furthermore, not limited to such a difference, for example, the control unit 210 may calculate the span loss based on the difference between the transmitted optical power and the received optical power of the WDM signal light Lw1 when the WDM signal light Lw1 is transmitted.

[0033] Once the span loss is calculated, the control unit 110 aggregates the optical loss #2 measured by the OTDR unit 201 to the optical transmission device 100 (step S4). For example, once the control unit 110 calculates the span loss, it requests the OSC transceiver unit 102 to transmit a first control signal optical Lo1 requesting the transmission of optical loss #2. As a result, the OSC transceiver unit 102 transmits the first control signal optical Lo1.

[0034] The OSC transceiver 202 of the optical transmission device 200 receives the first control signal light Lo1. When the control unit 210 hears the first control signal light Lo1 from the OSC transceiver 202, it requests the OSC transceiver 202 to transmit the second control signal light Lo2, which includes optical loss #2. As a result, the OSC transceiver 202 transmits the second control signal light Lo2, which includes optical loss #2. If the control unit 210 has calculated the span loss, the OSC transceiver 202 may transmit the second control signal light Lo2, which includes both optical loss #2 and the span loss.

[0035] The OSC transceiver 102 of the optical transmission device 100 receives the second control signal light Lo2. Upon receiving the second control signal light Lo2, the OSC transceiver 102 converts it into electrical control information. The control information is an example of predetermined information. After converting the second control signal light Lo2 into control information, the OSC transceiver 102 transmits the control information to the control unit 110. As a result, the control unit 110 receives control information regarding optical loss #2 from the optical transmission device 200. In other words, the control unit 110 aggregates the optical loss #2 measured by the OTDR unit 201 to the optical transmission device 100. Alternatively, the control unit 210 may aggregate the optical loss #1 measured by the OTDR unit 101 to the optical transmission device 200.

[0036] After aggregation, the control unit 110 compares the span loss and the optical loss #2 (step S5) and determines whether the span loss is less than or equal to the optical loss #2 (step S6). More specifically, when the control unit 110 receives control information, it can calculate the optical loss #2 based on the control information. After calculating the optical loss #2, the control unit 110 determines whether the span loss corresponding to the wavelength λ2 is less than or equal to the total loss of the optical loss #2. If the span loss is less than or equal to the optical loss #2 (step S6: YES), the control unit 110 displays the distance between devices based on the optical loss #2 alone (step S7) and terminates the process.

[0037] More specifically, the control unit 110 displays the distance of the transmission path T1 on a display device connected to the optical transmission device 100 using only the optical loss #2, and then terminates the process. In this way, if the span loss of the transmission path T1 is less than or equal to the optical loss #2, the control unit 110 can measure the inter-device distance between the optical transmission devices 100 and 200 over the entire length.

[0038] On the other hand, if the span loss is greater than the optical loss #2 (step S6: NO), the control unit 110 determines whether the pulsed light Lp1 and Lp2 have the same wavelength (step S8). If they do not have the same wavelength (step S8: NO), the control unit 110 converts either the U / D loss distribution or the D / U loss distribution (step S9). For example, as shown in Figure 4, the control unit 110 converts the U / D loss distribution corresponding to wavelength λ1 to a U / D loss distribution corresponding to wavelength λ2. Such a U / D loss distribution corresponding to wavelength λ2 is an example of the third optical loss. The control unit 110 can convert the U / D loss distribution based on the ratio of the first loss coefficient corresponding to pulsed light Lp1 and the second loss coefficient corresponding to pulsed light Lp2.

[0039] Similarly, the control unit 110 may convert the D / U loss distribution corresponding to wavelength λ2 to a D / U loss distribution corresponding to wavelength λ1. Also, if the wavelengths are the same (step S8: YES), the control unit 110 skips the processing in step S9. For example, if the control unit 110 can confirm that the wavelengths of pulsed light Lp1 and Lp2 are the same via network controllers connected to the optical transmission devices 100 and 200 respectively, the control unit 110 can skip the processing in step S9.

[0040] When either the U / D loss distribution or the D / U loss distribution is converted, the control unit 110 calculates distance #1 (step S10). Distance #1 is an example of a first distance. For example, as shown in Figure 5(a), the control unit 110 calculates half of the span loss corresponding to the intermediate position of the transmission line T1 based on the U / D loss distribution corresponding to the wavelength λ2, and calculates distance #1 which corresponds to half of the span loss. Note that the intermediate position is an example of a specific position.

[0041] Once distance #1 is calculated, the control unit 110 calculates distance #2 (step S11). Distance #2 is an example of a second distance. For example, as shown in Figure 5(b), the control unit 110 calculates half of the span loss corresponding to the intermediate position of the transmission line T1 based on the D / U loss distribution corresponding to the wavelength λ2, and calculates distance #2 which corresponds to half of the span loss.

[0042] Once distance #2 is calculated, the control unit 110 calculates the distance between the devices (step S12). For example, as shown in Figure 5(c), the control unit 110 adds distance #1 and distance #2 to calculate the distance between the devices. As described above, if the wavelengths are not the same, the control unit 110 converts the U / D loss distribution corresponding to wavelength λ1 to a U / D loss distribution corresponding to wavelength λ2, so it can calculate the distance between the devices by adding distance #2 to distance #1, which is calculated based on the U / D loss distribution corresponding to wavelength λ2.

[0043] In this way, the control unit 110 switches the calculation method for calculating the inter-device distance based on the comparison result of span loss and optical loss #2. Once the inter-device distance is calculated, the control unit 110 displays the inter-device distance (step S13) and terminates the process.

[0044] As described above, the optical transmission device 100 comprises an OTDR unit 101 and a control unit 110. The OTDR unit 101 transmits a pulsed light Lp1 with wavelength λ1 based on OTDR to the transmission path T1 and receives a return light Lr1 with wavelength λ1 based on the reflection of the pulsed light Lp1 from the transmission path T1. Upon receiving the return light Lr1, the OTDR unit 101 measures the optical loss #1 in the transmission path T1 based on the pulsed light Lp1 and the return light Lr1, and generates a U / D loss distribution including the optical loss #1.

[0045] The control unit 110 receives control information regarding optical loss #2 in the transmission path T1 from the optical transmission device 200 via the second control signal optical Lo2, and calculates the distance between the devices based on optical loss #1, optical loss #2, and span loss. This allows the distance between optical transmission devices 100 and 200 to be measured using the OTDR regardless of the length of that distance. In other words, even if the distance between optical transmission devices 100 and 200 is large, the distance between them can be measured using the OTDR.

[0046] In the embodiments described above, the intermediate position of the transmission line T1 was explained as an example of a specific position, but the specific position is not limited to the intermediate position. The specific position may be a position located at a distance equivalent to one-third of the transmission line T1 from either the optical transmission device 100 or 200. In this case, the control unit 110 can calculate the distance between the devices by adding distance #1, which is equivalent to one-third of the span loss, and distance #2, which is equivalent to two-thirds of the span loss. Thus, distances #1 and #2 may be calculated using different calculation methods depending on the ratio of span loss.

[0047] Furthermore, the control unit 110 may calculate the span latency in the transmission path T1 based on the speed of light, the distance between devices, the refractive index of the transmission path T1, and a predetermined calculation formula. Latency is an example of propagation delay time. The predetermined calculation formula is defined, for example, as (optical loss #1 × refractive index) / speed of light + (optical loss #2 × refractive index) / speed of light.

[0048] Although preferred embodiments of the present invention have been described in detail above, the present invention is not limited to specific embodiments, and various modifications and changes are possible within the scope of the gist of the invention as described in the claims.

[0049] For example, in the embodiment described above, it was explained that the OSC transceiver 202 transmits a second control signal optical Lo2 including optical loss #2. However, if the optical transmission devices 100, 200 are connected to a network controller that controls the optical transmission devices 100, 200, the optical loss #2 may be transmitted from the optical transmission device 200 to the optical transmission device 100, via the network controller. In other words, the optical loss #2 may be transmitted by electrical transmission instead of optical transmission.

[0050] Furthermore, the following additional information is disclosed regarding the above explanation. (Note 1) An optical transmission device facing another optical transmission device via a transmission path having a predetermined transmission path loss, comprising: a first transmitting / receiving unit that transmits a first measurement light based on OTDR to the transmission path and receives a first return light based on the reflection of the first measurement light from the transmission path; a measuring unit that measures a first optical loss in the transmission path based on the first measurement light and the first return light; a receiving unit that receives predetermined information regarding a second optical loss in the transmission path from the other optical transmission device; and a calculation unit that calculates the distance between the optical transmission device and the other optical transmission device based on the first optical loss, the second optical loss and the transmission path loss. (Note 2) The optical transmission device according to Note 1, characterized in that the calculation unit calculates a first distance from the optical transmission device to a specific location in the transmission path based on a portion of the first optical loss, calculates a second distance from another optical transmission device to the specific location based on a portion of the second optical loss, and calculates the distance based on the first distance and the second distance. (Note 3) The optical transmission apparatus according to Note 1 or 2, characterized in that the calculation unit switches the calculation method for calculating the distance based on the comparison result of the first optical loss or the second optical loss and the transmission path loss. (Note 4) The optical transmission device according to Note 1 or 2, characterized in that, when the second optical loss is measured by the other optical transmission device based on a second measurement light having a second wavelength different from the first wavelength of the first measurement light and a second return light from the transmission path based on the reflection of the second measurement light, the calculation unit converts the first optical loss into a third optical loss corresponding to the second wavelength based on the ratio of a first loss coefficient corresponding to the first measurement light and a second loss coefficient corresponding to the second measurement light, and calculates the distance based on the second optical loss, the third optical loss and the transmission path loss. (Note 5) The optical transmission device according to Note 1 or 2, characterized in that the calculation unit calculates the second optical loss based on the predetermined information. (Appendix 6) An optical transmission device according to Appendix 1 or 2, comprising a second transmitting / receiving unit that transmits a first signal light toward another optical transmission device and receives a second signal light including the received optical power of the first signal light received by the other optical transmission device, wherein the calculation unit calculates the transmission path loss based on the difference between the transmitted optical power of the first signal light and the received optical power included in the second signal light. (Note 7) The optical transmission device according to Note 1 or 2, characterized in that the calculation unit calculates a specific propagation delay time in the transmission path based on the speed of light, the distance, the refractive index of the transmission path, and a predetermined calculation formula for calculating the propagation delay time. (Note 8) The optical transmission device according to Note 1 or 2, characterized in that the optical transmission device is connected to one end of the transmission line, and the other optical transmission device is connected to the other end of the transmission line. (Note 9) An optical transmission system comprising a first optical transmission device and a second optical transmission device facing each other via a transmission path having a predetermined transmission path loss, wherein the first optical transmission device transmits a first measurement light based on OTDR to the transmission path, receives a first return light based on the reflection of the first measurement light from the transmission path, measures a first optical loss in the transmission path based on the first measurement light and the first return light, the second optical transmission device transmits a second measurement light based on OTDR to the transmission path, receives a second return light based on the reflection of the second measurement light from the transmission path, measures a second optical loss in the transmission path based on the second measurement light and the second return light, the first optical transmission device receives predetermined information regarding the second optical loss from the second optical transmission device, and calculates the distance between the first optical transmission device and the second optical transmission device based on the first optical loss, the second optical loss and the transmission path loss. [Explanation of Symbols]

[0051] ST Optical Transmission Systems 100,200 Optical transmission devices 101,201 OTDR Department 102,202 OSC Transceiver 110,210 Control Unit

Claims

1. An optical transmission device that faces another optical transmission device via a transmission path having a predetermined transmission path loss, A first transmitting and receiving unit transmits a first measurement light based on an OTDR (Optical Time Domain Reflectometer) to the transmission path and receives a first return light based on the reflection of the first measurement light from the transmission path, A measuring unit that measures the first optical loss in the transmission line based on the first measurement light and the first return light, A receiving unit that receives predetermined information regarding the second optical loss in the transmission line from another optical transmission device, A calculation unit that calculates the distance between the optical transmission device and the other optical transmission device based on the first optical loss, the second optical loss, and the transmission path loss, An optical transmission device having the following features.

2. The calculation unit calculates a first distance from the optical transmission device to a specific location in the transmission path based on a portion of the first optical loss, calculates a second distance from another optical transmission device to the specific location based on a portion of the second optical loss, and calculates the distance based on the first distance and the second distance. The optical transmission device according to feature 1.

3. The calculation unit switches the calculation method for calculating the distance based on the comparison result between the first optical loss or the second optical loss and the transmission path loss. The optical transmission device according to claim 1 or 2.

4. The calculation unit, when the second optical loss is measured by the other optical transmission device based on a second measurement light having a second wavelength different from the first wavelength of the first measurement light and a second return light from the transmission path based on the reflection of the second measurement light, converts the first optical loss into a third optical loss corresponding to the second wavelength based on the ratio of a first loss coefficient corresponding to the first measurement light and a second loss coefficient corresponding to the second measurement light, and calculates the distance based on the second optical loss, the third optical loss and the transmission path loss. The optical transmission device according to claim 1 or 2.

5. It includes a second transmitting / receiving unit that transmits a first signal light toward the other optical transmission device and receives a second signal light including the received optical power of the first signal light received by the other optical transmission device, The calculation unit calculates the transmission path loss based on the difference between the transmitted optical power of the first signal light and the received optical power included in the second signal light. The optical transmission device according to claim 1 or 2.

6. An optical transmission system including a first optical transmission device and a second optical transmission device facing each other via a transmission path having a predetermined transmission path loss, The first optical transmission device is A first measurement light based on an OTDR (Optical Time Domain Reflectometer) is transmitted to the transmission path, a first return light based on the reflection of the first measurement light is received from the transmission path, and a first optical loss in the transmission path is measured based on the first measurement light and the first return light. The second optical transmission device is A second measurement light based on OTDR is transmitted to the transmission path, a second return light based on the reflection of the second measurement light is received from the transmission path, and the second optical loss in the transmission path is measured based on the second measurement light and the second return light. The first optical transmission device is The system receives predetermined information regarding the second optical loss from the second optical transmission device, and calculates the distance between the first optical transmission device and the second optical transmission device based on the first optical loss, the second optical loss, and the transmission path loss. An optical transmission system characterized by the following:

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