JP2010193363A - Subscriber-side backup response device, subscriber-side apparatus and optical path inspection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To facilitate management of an apparatus for detecting a fault on an optical path. <P>SOLUTION: A subscriber-side backup response device comprises: an optical receiving device 110 for extracting and receiving a control signal of a predetermined wavelength included in an optical signal transmitted from a station side via an optical fiber; an optical switch 112 capable of selectively connecting an optical path from the station side to one terminal, to which a subscriber-side apparatus is connected, and to another terminal different from the one terminal; a control section 114 which causes the optical switch 112 to select the terminal to connect the optical path thereto in accordance with the control signal received by the optical receiving device 110; and e.g., a grating fiber 115 as a response section connected to the other terminal and capable of transmitting an optical signal to the station side. The subscriber-side backup response device is provided correspondingly to each of ONUs 8-10. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a technique for inspecting whether or not a failure has occurred in an optical line in an optical network in which one station-side device and a plurality of home-side devices are connected via an optical line including an optical fiber.

  An OTDR (Optical Time Domain Reflectometer) is installed on the station side to monitor the optical line in an optical network in which one station side device and multiple home side devices are connected via an optical line including an optical fiber. A monitoring system in which a grating fiber is provided on the home side has been proposed (see, for example, Patent Documents 1 and 2). OTDR enters pulse ratio light into a ratio measurement optical fiber network, and measures the weak reflected light returning to the incident end in the time domain to determine the connection loss and return loss of the optical fiber, the distance to the point, etc. It is a measuring instrument to measure. In this monitoring system, the test light output from the OTDR reaches the home side via the optical line and is reflected by the grating fiber. Then, the reflected light and the backscattered light of the test light generated in the middle of the optical line are detected as return light by the OTDR through the optical line.

  If there is no failure in the optical line, return light having a substantially constant intensity is detected stably, and conversely, if a failure such as an optical fiber break occurs in the optical line, the intensity of the return light sharply decreases. Therefore, the failure of the optical line can be detected by always monitoring the intensity of the return light with OTDR.

JP 2000-295185 A (FIG. 1) JP 2000-354008 A (FIG. 1)

  In order to apply the method of monitoring an optical line failure using an OTDR and a grating fiber as described above to a large number of optical lines branched by a coupler, a grating fiber is provided at each end of the large number of optical lines. Will be monitored by one OTDR. In this case, it is necessary to devise to distinguish each return light from each other. For example, return light having a different wavelength is obtained for each optical line on the house side (see FIG. 5 of Patent Document 2). For this purpose, each grating fiber needs to have different profiles. However, if there are as many types of grating fibers as the number of home-side devices, management becomes complicated and costs increase.

  In view of such a conventional problem, an object of the present invention is to facilitate management of a device that detects a failure in an optical line.

  The home side standby response device of the present invention includes an optical receiving device that extracts and receives a control signal of a predetermined wavelength included in an optical signal transmitted from the station side via an optical fiber, and a station side. To the one terminal to which the home-side device is connected, and the optical switch that can be selectively connected to another terminal different from the terminal, and the control signal received by the optical receiving device. Accordingly, the optical switch includes a control unit that selects a terminal to be connected, and a response unit that is connected to the other terminal and can transmit an optical signal to the station side.

  In the home side standby response device configured as described above, the optical switch is normally used in a state where the optical line from the station side is connected to the home side device. On the other hand, in response to the control signal, when the optical switch connects the optical line to another terminal, that is, the response unit, the response unit can transmit an optical signal to the station side. If there is no failure in the optical line, the control signal for switching the connection of the optical switch from the home side device to the response unit reaches the home side standby response device, and the optical signal from the response unit reaches the station side. It turns out that it is not a malfunction. Conversely, if there is no response even when the above control signal is given, it is understood that the optical line is faulty. Such a home-side standby response device is not always ready to respond, but when it receives an instruction, it responds by switching the connection of the optical switch. It is possible to give an instruction and respond to only the device.

In the above-mentioned home side preliminary response device, the response unit may be a grating fiber that reflects the test light transmitted from the station-side OTDR with a unique profile.
In this case, a grating fiber having a common profile can be used as a response unit in all the home-side preliminary response devices.

In the above-mentioned home side standby response device, the response unit may be a preliminary home side device that can communicate with the station side device.
In this case, a standardized inexpensive home-side device can be used as a response unit of the home-side standby response device.

Further, in the above-mentioned home side standby response device, when the optical switch is connected to one terminal, it is preferable that the standby home side device is in an off state.
In this case, when communication is normally performed between the station-side device and the home-side device, the standby home-side device can be turned off to save power consumption.

Further, in the above-mentioned home-side standby response device, the response unit may be an optical transmitter that transmits an optical signal that can be detected by a predetermined optical receiver provided on the station side.
In this case, the optical transmitter can select a wavelength in an available wavelength region.

Moreover, in the said home side preliminary response apparatus, when the optical switch has connected with the one terminal, it is preferable that an optical transmitter is an OFF state.
In this case, when communication is normally performed between the station-side device and the home-side device, the standby home-side device can be turned off to save power consumption.

On the other hand, the present invention may be a home-side device on which any of the home-side preliminary response devices described above is mounted.
In this case, it is possible to provide a home device that integrally has the function of the home side preliminary response device.

  Further, the present invention provides a plurality of optical switches that switch by a control signal whether to connect an optical line from a station side including an optical fiber to a home side device or to connect to a response unit different from the home side device. An inspection method of an optical line in a system provided for each home-side device, (1) when communication between the station-side device and the home-side device is interrupted, the connection destination of the optical line from the home-side device A control signal for switching to the response unit is transmitted from the station side to the home side as an optical signal of a predetermined wavelength. (2) The optical switch switches the connection destination of the optical line from the home side device to the response unit, (3) The response unit transmits an optical signal, (4) If the optical signal from the response unit can be received on the station side, it is not a failure of the optical line, and if the optical signal cannot be received, It is assumed that it is a failure.

  In the optical line inspection method as described above, the optical switch is normally used in a state where the optical line from the station side is connected to the home apparatus. On the other hand, when communication between the station side device and the home side device is interrupted, the optical switch connects the optical line to the response unit according to the control signal, and the response unit transmits the optical signal to the station side. Can do. If there is no failure in the optical line, the control signal for switching the connection of the optical switch from the home side device to the response unit reaches the home side standby response device, and the optical signal from the response unit reaches the station side. It turns out that it is not a malfunction. Conversely, if there is no response even when the above control signal is given, it is understood that the optical line is faulty.

According to the home-side standby response device of the present invention, by providing a common home-side standby response device corresponding to each of the plurality of home-side devices, it is possible to detect a failure in the optical line, and thus management is easy. It is.
Further, according to the optical line inspection method of the present invention, when necessary, it is possible to inspect the presence or absence of a failure in the optical line from the station side to any home-side device, and in a common method, all Since the optical line can be inspected, management is easy.

It is a block diagram which shows the optical network between OLT-ONU containing the residential side preliminary response apparatus which concerns on 1st Embodiment of this invention. It is a block diagram which shows the optical network between OLT-ONU including the residential side preliminary response apparatus which concerns on 2nd Embodiment of this invention. It is a block diagram which shows the optical network between OLT-ONU containing the residential side preliminary response apparatus which concerns on 3rd Embodiment of this invention.

  FIG. 1 is a block diagram showing an optical network between an OLT (station side device) and an ONU (home side device) including the home side standby response device according to the first embodiment of the present invention. A connection line represented by a solid line between the blocks means an optical signal line using an optical fiber, and a connection line represented by a broken line means an electric signal line. In the figure, on the station side of this optical network, an OLT 1, a video distribution unit 2 that distributes video, an OTDR 3 that transmits and receives test light, a switching instruction device 4 that transmits a control signal for switching instructions, and a wavelength WDM couplers 5 to 7 for multiplexing different optical signals are provided.

  Wavelength λ1 is used for uplink data communication from a plurality (3 in this example) of ONUs 8 to 10 to OLT1, and conversely, wavelength λ2 is used for downlink data communication from OLT1 to ONUs 8 to 10. The wavelength λ3 is used for the video distribution in the downward direction by the video distribution unit 2. The wavelength λ4 is used for the test light output from the OTDR3. The wavelength λ5 is used for the control signal output from the switching instruction device 4.

Here, specific examples of each wavelength are as follows.
λ1 = 1310 μm
λ2 = 1490μm
λ3 = 1550 μm
λ4 = 1630μm
λ5 = 1650 μm
Thus, the wavelength λ5 of the control signal (switching instruction) is the longest wavelength. As for downlink communication from the OLT 1, an optical signal having a shorter wavelength is multiplexed at the upper level, and a control signal having the longest wavelength is multiplexed last. Conversely, for upstream communication, the longer wavelength is extracted first.

  The optical fiber F0 connected to the WDM coupler 7 branches into a plurality of (in this example, three) lines F1 to F3 via the power coupler 14. The optical fibers F0 to F3 together with the power coupler 14 constitute a main optical line between the OLT and the ONU.

  On the other hand, on the home side of the optical network, in addition to the ONUs 8 to 10, home side standby response devices 11 to 13 are provided at the nearest higher levels corresponding to the ONUs 8 to 10, respectively. Specifically, for example, it is housed in an independent housing and installed in the vicinity of the ONU 8, built in an optical outlet provided on the wall of the room, or anywhere in the house, whether indoors or outdoors. Provided. As the power source of the home side standby response devices 11 to 13, similarly to the ONUs 8 to 10, a commercial AC power source drawn into each home is used. Although it can be provided outside the house, for example, on a pillar, installation in the house is preferable in consideration of the convenience of power supply.

  The internal configurations of the home side standby response devices 11 to 13 are all the same. As a typical example, the internal configuration of the home side standby response device 11 will be described. A WDM coupler 111, an optical switch 112, an optical receiver 113, A control unit 114 and a grating fiber 115 are provided. The WDM coupler 111 extracts only an optical signal having a wavelength λ5, and allows optical signals having other wavelengths to pass through both upstream and downstream. The optical switch 112 is a device that can selectively connect the optical line from the station side to one terminal to which the ONU 8 is connected and to another terminal that is different from the terminal. A connection is established and transmission / reception signals between the OLT 1 and the ONU 8 are passed. As long as communication between the OLT 1 and the ONU 8 is normally performed, this state continues.

On the other hand, the OLT 1 is provided corresponding to the ONU 8 by sending an electrical signal to the switching instruction device 4 when the OLT 1 grasps that the communication has been interrupted due to no longer receiving the signal periodically received from the ONU 8. The home side standby response device 11 is instructed to switch the optical switch 112. At the same time, the OLT 1 operates the OTDR 3. Here, as a cause of communication interruption, failure of the optical line, mainly disconnection of the optical fibers F0 to F3 can be considered. In addition to the failure of the optical line, for example, a failure of the ONU 8 can be considered.
Note that the OTDR 3 and the switching instruction device 4 may be operated by a manual operation without depending on the instruction of the OLT 1.

  Here, it is assumed that the cause of the communication interruption is other than the failure of the optical line, that is, the case where there is no failure in the optical line. In this case, when a control signal of wavelength λ5 instructing switching of the optical switch 112 is transmitted from the switching instruction device 4, the WDM coupler 111 extracts the control signal of wavelength λ5 included in the optical signal, Is received by the optical receiver 113. That is, the WDM coupler 111 and the optical receiver 113 constitute an optical receiving device 110 that extracts and receives a control signal having a wavelength λ5. Moreover, the identification code for each of the home side preliminary response devices 11 to 13 is given to the control signal, and only the optical receiver 113 with the matching identification code can receive the control signal. Here, only the optical receiver 113 of the home side standby response device 11 corresponding to the ONU 8 can receive the control signal.

  When the optical receiving unit 113 receives the control signal, the control unit 114 instructs the optical switch 112 to switch the switch. Thereby, the optical switch 112 cuts off the connection with the ONU 8 and selects the connection to the grating fiber 115. On the other hand, the station-side OTDR 3 transmits test light having a wavelength λ4. This test light reaches the grating fiber 115, and reflects the test light having the wavelength λ4 based on the unique profile. That is, the grating fiber 115 functions as a response unit that transmits a response signal (reflected light) to the test light. By receiving this reflected light by the OTDR 3, the fact that there is no failure in the optical line is revealed.

  On the other hand, when the optical line is broken, typically, when the optical fiber is broken, the control signal from the switching instruction device 4 does not reach the home side standby response device 11. Therefore, the optical switch 112 is not switched. Also, the test light of OTDR3 does not reach the home side standby response device 11. That is, it can be seen that a failure has occurred in the optical line due to the fact that there is no response even though there should be a response from the home side standby response device 11.

  Since the above-mentioned home side preliminary response devices 11 to 13 are not always ready to respond, but are devices that respond by switching the connection of the optical switch 112 when receiving an instruction. Therefore, it is possible to give an instruction and respond to only an arbitrary device on the home side. Therefore, by providing the common home side standby response devices 11 to 13 corresponding to each of the plurality of home side devices 8 to 10, a failure of the optical line can be detected, and management is easy. In particular, it is convenient in that the grating fiber 115 having a common profile can be used as a response unit in all the home-side preliminary response apparatuses 11 to 13. Similarly, according to such an optical line inspection method, it is possible to inspect whether there is a failure in the optical line from the station side to any of the home-side devices 11 to 13 when necessary. Moreover, since all the optical lines can be inspected by a common method, management is easy.

  FIG. 2 is a block diagram showing an OLT-ONU optical network including a home side standby response apparatus according to the second embodiment of the present invention. The same parts as those in FIG. On the station side, the OTDR 3 (FIG. 1) of the first embodiment is not provided in this embodiment. Further, regarding the configuration in the home side standby response device 11 (12, 13 is also the same), a dummy ONU 116 is used instead of the grating fiber 115 in the first embodiment.

  The dummy ONU 116 is configured in the same manner as the ONUs 8 to 10 with respect to main functions, and can be regarded as a preliminary or simple ONU. By using such a dummy ONU 116 as a response unit of the home side preliminary response device 11, standardized and inexpensive hardware and software of the home side device can be used as they are.

  In FIG. 2, the wavelength λ1 is used for uplink data communication from a plurality (three in this example) of ONUs 8 to 10 to OLT1, and conversely, wavelength λ2 is used for downlink data communication from OLT1 to ONUs 8 to 10. used. The wavelength λ3 is used for the video distribution in the downward direction by the video distribution unit 2. The wavelength λ5 is used for the control signal output from the switching instruction device 4.

Here, specific examples of each wavelength are as follows.
λ1 = 1310 μm
λ2 = 1490μm
λ3 = 1550 μm
λ5 = 1650 μm
Thus, the wavelength λ5 of the control signal (switching instruction) is the longest wavelength. As for downlink communication from the OLT 1, an optical signal having a shorter wavelength is multiplexed at the upper level, and a control signal having the longest wavelength is multiplexed last.

  The optical switch 112 of the home side standby response device 11 is normally connected to the ONU 8 and passes transmission / reception signals between the OLT 1 and the ONU 8. As long as communication between the OLT 1 and the ONU 8 is normally performed, this state continues. When communication is normally performed between the OLT 1 and the ONU 8, the dummy ONU 116 is in an off state (shutdown state). Thereby, useless power consumption can be saved.

On the other hand, the OLT 1 is provided corresponding to the ONU 8 by sending an electrical signal to the switching instruction device 4 when the OLT 1 grasps that the communication has been interrupted due to no longer receiving the signal periodically received from the ONU 8. The home side standby response device 11 is instructed to switch the optical switch 112.
Note that the switching instruction device 4 may be operated by a manual operation without depending on the instruction of the OLT 1.

  Here, it is assumed that the cause of the communication interruption is other than the failure of the optical line, that is, the case where there is no failure in the optical line. In this case, when a control signal of wavelength λ5 instructing switching of the optical switch 112 is transmitted from the switching instruction device 4, the WDM coupler 111 extracts the control signal of wavelength λ5 included in the optical signal, Is received by the optical receiver 113. That is, the WDM coupler 111 and the optical receiver 113 constitute an optical receiving device 110 that extracts and receives a control signal having a wavelength λ5.

  The control signal is given an identification code for each of the home side preliminary response devices 11 to 13, and only the optical receiver 113 having the same identification code can receive the control signal. Here, only the optical receiver 113 of the home side standby response device 11 corresponding to the ONU 8 can receive the control signal.

  When the optical receiving unit 113 receives the control signal, the control unit 114 instructs the optical switch 112 to switch the switch. Thereby, the optical switch 112 cuts off the connection with the ONU 8 and selects the connection with the dummy ONU 116. Like the ONU 8, the dummy ONU 116 can communicate with the OLT 1 at the upstream wavelength λ1 and the downstream wavelength λ2. Therefore, the optical signal transmitted from the dummy ONU 116 is received by the OLT 1. Thus, the fact that there is no failure in the optical line is revealed by receiving the optical signal by the OLT 1.

  On the other hand, when the optical line is broken, typically, when the optical fiber is broken, the control signal from the switching instruction device 4 does not reach the home side standby response device 11. Therefore, the optical switch 112 is not switched, and there is no opportunity for the dummy ONU 116 to transmit an optical signal. That is, it can be seen that a failure has occurred in the optical line due to the fact that there is no response even though there should be a response from the home side standby response device 11.

  As in the first embodiment, the home-side preliminary response devices 11 to 13 are not always ready to respond, but respond by switching the connection of the optical switch 112 when receiving an instruction. Therefore, it is possible to give an instruction and give a response only to an arbitrary device on the home side from the station side. Therefore, by providing the common home side standby response devices 11 to 13 corresponding to each of the plurality of home side devices 8 to 10, a failure of the optical line can be detected, and management is easy. In particular, a standardized inexpensive dummy ONU 116 can be used as a response unit of the home side preliminary response device. Similarly, according to such an optical line inspection method, it is possible to inspect whether there is a failure in the optical line from the station side to any of the home-side devices 11 to 13 when necessary. Moreover, since all the optical lines can be inspected by a common method, management is easy.

  FIG. 3 is a block diagram showing an OLT-ONU optical network including a home side standby response apparatus according to the third embodiment of the present invention. The same parts as those in FIG. On the station side, the OTDR 3 (FIG. 1) of the first embodiment is not provided in this embodiment. On the other hand, in this embodiment, a switching instruction / response confirmation device 15 is provided. The apparatus 15 includes a switching instruction unit 151 that outputs a control signal for switching instructions, an optical transmitter 152 that transmits the control signal as an optical signal with a wavelength λ5, an optical signal with a wavelength λ4 extracted by a WDM coupler 153, and a WDM coupler 153. And a response confirmation unit 155 that confirms the presence / absence of a response based on the signal received by the optical reception unit 154.

Further, regarding the configuration in the home side standby response device 11 (12, 13 is also the same), an optical transmitter 117 is used instead of the grating fiber 115 in the first embodiment.
In FIG. 3, the wavelength λ1 is used for uplink data communication from a plurality (3 in this example) of ONUs 8 to 10 to OLT1, and conversely, wavelength λ2 is used for downlink data communication from OLT1 to ONUs 8 to 10. used. The wavelength λ3 is used for the video distribution in the downward direction by the video distribution unit 2. The optical transmitter 152 in the switching instruction / response confirmation device 15 transmits an optical signal having a wavelength λ5. The optical transmitter 117 on the home side transmits an optical signal having a wavelength λ4, and the optical receiver 154 on the station side can receive this optical signal.

Here, specific examples of each wavelength are as follows.
λ1 = 1310 μm
λ2 = 1490μm
λ3 = 1550 μm
λ4 = 1570-1630 μm
λ5 = 1650 μm
Thus, the wavelength λ5 of the control signal (switching instruction) is the longest wavelength. As for downlink communication from the OLT 1, an optical signal having a shorter wavelength is multiplexed at the upper level, and a control signal having the longest wavelength is multiplexed last. Conversely, for upstream communication, the longer wavelength is extracted first. Further, as λ4, the wavelength can be selected in the above-mentioned wavelength range that is vacant.

  The optical switch 112 of the home side standby response device 11 is normally connected to the ONU 8 and passes transmission / reception signals between the OLT 1 and the ONU 8. As long as communication between the OLT 1 and the ONU 8 is normally performed, this state continues. When communication is normally performed between the OLT 1 and the ONU 8, the optical transmitter 117 is in an off state. Thereby, useless power consumption can be saved.

On the other hand, the OLT 1 sends an electrical signal to the switching instruction unit 151 when it is determined that the communication has been interrupted due to the loss of the signal periodically received from the ONU 8. As a result, the switching instruction unit 151 causes the optical transmitter 152 to transmit a control signal as an optical signal having the wavelength λ5, and switches the optical switch 112 to the home side standby response device 11 provided corresponding to the ONU 8. Instruct.
Note that the switching instruction unit 151 may be manually operated without depending on the instruction of the OLT 1.

  Here, it is assumed that the cause of the communication interruption is other than the failure of the optical line, that is, the case where there is no failure in the optical line. In this case, when a control signal of wavelength λ5 instructing switching of the optical switch 112 is transmitted from the optical transmitter 152, the WDM coupler 111 extracts the control signal of wavelength λ5 included in the optical signal, Is received by the optical receiver 113. That is, the WDM coupler 111 and the optical receiver 113 constitute an optical receiving device 110 that extracts and receives a control signal having a wavelength λ5.

  The control signal is given an identification code for each of the home side preliminary response devices 11 to 13, and only the optical receiver 113 having the same identification code can receive the control signal. Here, only the optical receiver 113 of the home side standby response device 11 corresponding to the ONU 8 can receive the control signal.

  When the optical reception unit 113 receives the control signal, the control unit 114 instructs the optical switch 112 to switch the switch and turns on the optical transmitter 117. Thereby, the optical switch 112 cuts off the connection with the ONU 8 and selects the connection to the optical transmitter 117. Accordingly, the optical signal transmitted from the optical transmitter 117 is received by the optical receiver 154. When the response confirmation unit 155 confirms this response, the fact that it is not a failure of the optical line is revealed. The optical signal transmitted from the optical transmitter 117 may not be modulated, and the optical receiver 154 only needs to be able to detect the optical signal transmitted from the optical transmitter 117.

  On the other hand, when the optical line is broken, typically, when the optical fiber is disconnected, the control signal from the optical transmitter 152 does not reach the home side standby response device 11. Therefore, the optical switch 112 is not switched, and there is no opportunity for the optical transmitter 117 to transmit an optical signal. That is, it can be seen that a failure has occurred in the optical line due to the fact that there is no response even though there should be a response from the home side standby response device 11.

  As in the first embodiment, the home-side preliminary response devices 11 to 13 are not always ready to respond, but respond by switching the connection of the optical switch 112 when receiving an instruction. Therefore, it is possible to give an instruction and give a response only to an arbitrary device on the home side from the station side. Therefore, by providing the common home side standby response devices 11 to 13 corresponding to each of the plurality of home side devices 8 to 10, a failure of the optical line can be detected, and management is easy. Similarly, according to such an optical line inspection method, it is possible to inspect whether there is a failure in the optical line from the station side to any of the home-side devices 11 to 13 when necessary. Moreover, since all the optical lines can be inspected by a common method, management is easy.

  In addition, in each said embodiment, although the home side preliminary response apparatuses 11-13 were provided separately from ONU8-10, it is good also as a home side apparatus carrying a home side preliminary response apparatus. In that case, it is possible to provide a high-function home-side device that integrally has the function of the home-side preliminary response device.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined not by the above-mentioned meaning but by the scope of claims for patent, and is intended to include all modifications within the scope and meaning equivalent to the scope of claims for patent.

1 OLT (Station side equipment)
3 OTDR
8-10 ONU (home-side equipment)
11-13 Residential side preliminary response device 15 Switching instruction / response confirmation device 110 Optical receiving device 112 Optical switch 114 Control unit 115 Grating fiber (response unit)
116 Dummy ONU (Response section)
117 Optical transmitter (response section)
F0 to F3 optical fiber

Claims (8)

An optical receiver that extracts and receives a control signal of a predetermined wavelength included in an optical signal transmitted from the station side via an optical fiber;
An optical switch that can selectively connect the optical line from the station side to one terminal to which the home-side device is connected, and another terminal different from the terminal,
A control unit that causes the optical switch to select a terminal to be connected in accordance with the control signal received by the optical receiver;
A home-side preliminary response device, comprising: a response unit connected to the other terminal and capable of transmitting an optical signal to the station side.   The home-side preliminary response device according to claim 1, wherein the response unit is a grating fiber that reflects the test light transmitted from the station-side OTDR with a unique profile.   The home-side standby response device according to claim 1, wherein the response unit is a preliminary home-side device capable of communicating with a station-side device.   4. The home side standby response device according to claim 3, wherein when the optical switch is connected to the one terminal, the preliminary home side device is in an off state.   2. The home side preliminary response apparatus according to claim 1, wherein the response unit is an optical transmitter that transmits an optical signal that can be detected by a predetermined optical receiver provided on the station side.   6. The home side preliminary response device according to claim 5, wherein the optical transmitter is in an off state when the optical switch is connected to the one terminal.   A home-side device on which the home-side preliminary response device according to any one of claims 1 to 6 is mounted. An optical switch that switches whether to connect the optical line from the station side including the optical fiber to the home side device or to connect to a response unit different from the home side device is provided for each of the home side devices. A method for inspecting an optical line in a system,
When communication between the station side device and the home side device is interrupted, a control signal for switching the connection destination of the optical line from the home side device to the response unit is transmitted from the station side to the home side as an optical signal of a predetermined wavelength. Send
The optical switch switches the connection destination of the optical line from the home device to the response unit,
The response unit transmits an optical signal,
A method of inspecting an optical line, characterized in that when the optical signal from the response unit can be received on the station side, it is not a failure of the optical line, and if it cannot be received, it is a failure of the optical line.

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