JP5475710B2 - Optical fiber measuring device, optical fiber measuring method, and line switching work method - Google Patents

Description

  The present invention relates to a core line contrast technique for specifying an optical fiber and an OTDR (Optical Time Domain Reflectometer) technique for evaluating an optical fiber.

  In recent years, with the increase in optical access services and the expansion of the optical service area, the amount of optical facilities has increased, and there has been an increase in obstruction relocation works that change cable routes associated with road construction and the like. In the troubled relocation work, after laying the cable at the relocation destination outdoors, the relocation source optical fiber is identified, the core wire is cut and the reciprocation operation is performed to connect to the relocation destination optical fiber, and the connection is tested correctly. (For example, refer nonpatent literature 1.).

On the other hand, a core wire contrast technique has been proposed to specify an optical fiber (see, for example, Non-Patent Document 2). In Non-Patent Document 2 core control technology, as shown in FIG. 14, it is inserted from the communication facility building 91, the modulated light L _K modulated from the long wavelength side wavelength of communication light L _S to the optical fiber 100. Outdoor communications facilities building 91, bending the optical fiber 100 to the extent that the modulated light L _K leaks, determines the presence or absence of modulated light L _K from leaking light. Thus, without affecting the communication light L _S of the optical fiber 100, to identify the optical fiber 100 by inserting the modulated light L _K. Further, the modulated light _{L K} is 270Hz modulation is often used at a wavelength of 1650nm band.

Masahito Ari, Yuji Higashi, Tomotaka Enomoto, Katsaki Suzuki, Noriyuki Araki, Shigenori Uruno, Tsuneichi Watanabe, “Optical Media Network Operation Technology to Support the Expanding Optical Access Network”, NTT Technology Journal, December 2006, pp . 58-61 Suzuki Katsuaki, Yamamoto Motoshi, Natsume Arata, “Optical Fiber Contrast Technology for R15 Core”, NTT Technical Journal, April 2007, pp. 54-55

  When performing optical cable switching work such as obstacle relocation work, specify the optical fiber to be switched by contrast control, disconnect the target optical fiber, confirm the disconnection by OTDR measurement, connect to the transfer destination optical fiber, by OTDR measurement The work procedure is to check the connection of the destination optical fiber.

FIG. 15 shows an equipment configuration for carrying out optical cable switching work. An optical coupler 56 is installed in the communication equipment building 91, an OLT (Optical Line Terminal) 51 is connected to the α port of the optical coupler 56, and the communication equipment building 91 is laid outside from the communication equipment building 91. The optical fiber 100 is connected. This figure is an example for switching the core wire of the optical fiber in the section between the outdoor point P _X and the point P _Y, transfer source of the optical fiber is 100a, relocation of the optical fiber is 100b. When performing the contrast control or the OTDR measurement, one of the modulation light source 54 and the OTDR measurement device 53 is selected according to the measurement contents, and the measurement is performed by connecting to the β port of the optical coupler 56. Here, both the modulation light source 54 and the OTDR measurement device 53 use a 1650 nm band different from the communication light wavelength so as not to affect the communication. The light that has entered the optical coupler 56 from the β port of the optical coupler 56 is not output to the α port, but is output only to the γ port. In addition, light incident on the γ port from the optical fiber 100 is emitted to both the α port and the β port. Furthermore, the incident light from the α port is emitted to the γ port without being emitted to the β port. Therefore, it is possible to perform cord contrast and OTDR measurement without cutting the communication line from the OLT 51 to the ONU 52.

However, as shown in FIG. 15, when performing core control with respect to the optical fiber 100, the modulated light source 54 to the incident modulated light L _K in the optical fiber 100 connected to the β port and the optical fiber When performing OTDR measurement on 100, it is necessary to connect the OTDR measurement device 53 to the β port.

  In this way, since separate devices are used for the contrast control and the OTDR measurement, the worker in the communication facility building 91 communicates with the outdoor worker by telephone or the like, and the optical coupler 56 according to the work situation. The device connected to the β port of was replaced. For this reason, when carrying out the optical cable switching work such as the obstacle relocation work, it is necessary for the worker to always stand by in the communication equipment building 91.

Further, trouble transferring construction becomes possible to perform the work at the same time two or more points outdoors (e.g., point P _X and the point P _Y). Therefore, for example, for the point _{P X} which may the OTDR measurement, wants to point _{P Y} in core control. In such a case, since only one device can be connected to the β port of the coupler 56 in the communication facility building, OTDR measurement and core line contrast cannot be performed at the same time. I had to wait. For this reason, the work time for trouble relocation work has become longer, and there has been a problem that the service interruption time associated with switching is prolonged.

  Therefore, in order to solve the above-described problems, an object of the present invention is to provide an optical fiber measurement device, an optical fiber measurement method, and a combined light generation method capable of simultaneously performing OTDR measurement and core line contrast.

  In order to achieve the above object, an optical fiber measurement device, an optical fiber measurement method, and a combined light generation method according to the present invention modulate a pulsed light generated from one light source at a constant period, thereby controlling a cord. It was decided to generate combined light having both light and OTDR test light components.

  Specifically, in the optical fiber measurement device according to the present invention, a light output unit that generates combined light obtained by modulating pulse light of a pulse train having a predetermined cycle with a modulation period longer than the predetermined cycle, and the light output unit generates A light receiving unit that enters the combined light into one end of the optical fiber to be inspected and measures the time-to-light intensity of the return light based on the combined light output from the one end of the optical fiber.

  This optical fiber measurement device generates combined light obtained by modulating pulse light of a pulse train having a predetermined period with a modulation period longer than the predetermined period. For this reason, this optical fiber measuring device can generate both the core wire contrast light and the OTDR test light with a single light source. Therefore, the present invention can provide an optical fiber measurement device and a combined light generation method capable of simultaneously performing OTDR measurement and core line contrast.

  The optical output unit of the optical fiber measuring device according to the present invention includes a pulsed light generation circuit that generates the pulsed light and a pulse drive circuit that controls generation and stop of the pulsed light. The combined light generation method according to the present invention is characterized in that the combined light is generated by driving a pulsed light generation circuit that generates the pulsed light to control generation and stop of the pulsed light.

  The optical output unit of the optical fiber measurement device according to the present invention includes: a pulsed light generation circuit that generates the pulsed light; and an optical switch that repeatedly transmits and blocks the pulse train of the pulsed light through the path of the pulsed light. It is characterized by having. The combined light generation method according to the present invention is characterized in that the combined light is generated by repeatedly transmitting and blocking the pulse train of the pulsed light.

  Specifically, in the optical fiber measurement method according to the present invention, one end of one specific optical fiber of a plurality of optical fibers is obtained by combining combined light obtained by modulating pulse light of a pulse train having a predetermined period with a modulation period longer than the predetermined period. And detecting the light of the modulation period leaking from the side surface of the optical fiber, and the specific optical fiber that has received the combined light in the combined light incident procedure among a plurality of optical fibers. Loss for measuring a loss in an optical path formed by the specific optical fiber by measuring time-to-light intensity of return light based on the modulated light detection procedure to be specified and the combined light output from the one end of the specific optical fiber And a measurement procedure.

  In this optical fiber measurement method, combined light having components of both the core-line control light and the OTDR test light is incident on the optical fiber. Therefore, the present invention can provide an optical fiber measurement method capable of simultaneously performing OTDR measurement and core line contrast.

  In the loss measurement procedure of the optical fiber measurement method according to the present invention, the fluctuation of the position where the combined light is reflected by Fresnel reflection is confirmed from the light intensity of the return light, and the optical fiber measured on the optical path of the specific optical fiber The switching operation is monitored.

  The present invention can provide an optical fiber measurement device, an optical fiber measurement method, and a combined light generation method capable of simultaneously performing OTDR measurement and core line contrast.

It is a figure explaining the system containing the optical fiber measuring device concerning the present invention. (A) It is a figure explaining the combined light produced | generated by the combined light production | generation method based on this invention. (B) It is a figure which expands and demonstrates a part of combined light. It is a figure explaining the optical output part with which the optical fiber measuring device concerning the present invention is provided. It is a figure explaining the optical output part with which the optical fiber measuring device concerning the present invention is provided. It is a figure explaining the optical fiber measuring method which concerns on this invention. It is a figure explaining the optical fiber measuring method which concerns on this invention. It is a figure explaining the optical fiber measuring method which concerns on this invention. It is a figure explaining the optical fiber measuring method which concerns on this invention. It is a figure explaining the optical fiber measuring method which concerns on this invention. It is a figure explaining the optical fiber measuring method which concerns on this invention. It is a figure explaining the optical fiber measuring method which concerns on this invention. It is a figure explaining the optical fiber measuring method which concerns on this invention. It is a figure explaining the optical fiber measuring method which concerns on this invention. It is a figure explaining the core line contrast technique described in the nonpatent literature 2. FIG. It is a figure explaining optical cable switching construction. (A) It is a figure explaining the modulation period which modulates pulsed light. (B) It is a figure explaining the combined light produced | generated by the combined light production | generation method based on this invention.

  Embodiments of the present invention will be described with reference to the drawings. In the present specification and drawings, the same reference numerals denote the same components.

  FIG. 1 shows an example of the configuration of an optical fiber measurement system according to this embodiment. The optical fiber measurement system according to this embodiment includes an optical fiber measurement device 11, a modulated light receiver 13, and a reflection filter 14.

Optical fiber measuring device 11 outputs a pulse light L _P modulated light L _K multiplexed light L _F that modulated created period of 2 to the optical fiber 100a. With reference to FIG. 2, the light output unit 21 is generated, for explaining the waveform of the pulse light L _P modulated light L _K modulation period is created multiplexed light L _F of. Here, (a) represents, modulates the emission cycle of the pulse light L _P, represents the modulated light L _K multiplexed light L _F containing elements, (b) is an enlarged part of the combined light L _F , representing the pulse light _{L P.} In both figures, the vertical axis represents light level and the horizontal axis represents time. In OTDR measurement, the pulse width 0.1~1μs is often used, the period of the pulse light _{L P} is about 200 [mu] s. On the other hand, as in FIG. 16, but 270Hz is often used as a period of the modulated light _{L K,} 1 cycle of this case becomes 3700Myuesu, it is a period of non-light emission with a period that is emitting light for each 1850μs repeated. Pulse light _{L P} is about 10 times with 1850μs the emission to have a period of _{L K,} so that the light emission. Here, (a) in FIG. 16 represents the modulated light _{L K,} (b) represents the combined light _{L F.}

Pulse light _{L P} to receive the reflected return light _{L B} in the optical fiber 100a. Demultiplexer 12, is inserted the combined light _{L F} from the optical output unit 21 to the optical fiber 100a, separates the reflected by the optical fiber 100a returning light _{L B} in the light-receiving unit 22. Modulated light receiving unit 13 receives the multiplexed light L _F leaking from the outside of the optical fiber 100a. Multiplexed light L _F leaked from the mantle, because it contains elements of the modulated light L _K, modulated light receiving unit 13 determines that the equivalent modulated light L _K. Reflection filter 14 is installed at the ends of the ONU (Optical Network Unit) side of the optical fiber 100a, and reflects the pulse light _{L P.} When the pulse light L _P reaches the reflective filter 14, reflected light of the reflection filter 14 becomes return light L _B by the Fresnel reflection.

Because it contains elements of the modulated light L _K in multiplexed light L _F, it is possible to perform the core control using modulated light photodetector 13. Since the multiplexed light L _F contains pulse light L _P, it is possible to perform OTDR measurements by receiving the return light L _B in the optical fiber measuring device 11. Therefore, the optical fiber measurement system according to the present embodiment can simultaneously perform OTDR measurement and core contrast using the same light output unit.

The optical fiber measurement device 11 includes an optical multiplexer / demultiplexer 12, a light output unit 21, a light receiving unit 22, and a calculation unit 23. The light output unit 21 generates a combined light L _F including the modulated light L _K by changing the light emission period of the pulse light L _P. Wavelength of the modulated light L _K and the pulse light L _P is the same, but different from the communication light L _S.

Receiving unit 22, pulse light _{L P} generated by the optical output unit 21 receives the returning light _{L B} reflected by the optical fiber 100a. Receiving unit 22, similarly to the conventional OTDR measuring device, received in accordance with the output to the period of the pulsed light L _P. Calculation unit 23 measures the time until the light level and the pulse light L _P of the return light L _B for receiving the light-receiving unit 22 receives the returning light L _B from the output of the optical fiber 100a. Thereby, the optical fiber measuring device 11 performs OTDR measurement.

FIG. 3 shows a first example of the light output unit 21. The first example of the light output unit includes a pulsed light generation unit 34 and a pulse drive circuit 33. By pulse drive circuit 33 causes the light emission at regular intervals with a pulse light L _P, to generate a modulated light L _K. Thus, the multiplexed light L _F is output.

FIG. 4 shows a second example of the light output unit. The second example of the optical output unit includes a pulse drive circuit 33, a pulsed light generation unit 34, an optical switch 35, and a modulation signal generation unit 36. Pulsed light generation unit 34 emits pulse light _{L P,} the modulation signal generator 36 to emit combined light _{L F} which multiplexes the modulated light _{L K} and the pulse light _{L P} by turning ON / OFF the optical switch 35 be able to.

OTDR measurement, pulsed light L _P from the optical output unit 21 emits, by the Rayleigh scattering light generated in the optical fiber 100a observes and received by the light receiving unit 22, the loss or the connection with a optical fiber 100a interval Measure the point loss. Further, Fresnel reflection occurs from the refractive index difference at the connection point, and the amount of reflection at the connection point can be observed. Receiving unit 22, a return light L _B of the Rayleigh scattered light and Fresnel reflection light or the like generated in the optical fiber 100a is measured, the arithmetic unit 23 calculates the distance in time to the return light L _B returns .

On the other hand, when the core wire controls, bending the optical fiber 100a at the point P _X and the point P _Y is added, the modulated light L _K leaked from the optical fiber 100a receives a modulated optical light receiver 13, to be disconnected The core wire, that is, the optical fiber 100a is specified. The modulated light receiving unit 13 includes a circuit for detecting the modulated light, it is possible to detect a plurality of pulse light L _P multiplexed light L _F that is created by modulating the as-modulated light L _K.

  FIG. 5 is a flowchart showing an example of the optical fiber switching connection work according to the present embodiment. The optical fiber measurement method according to this embodiment includes a combined light incident procedure S101, a modulated light detection procedure S102, an optical fiber cutting procedure S103, and an optical fiber connection procedure S104 in this order.

In the multiplexed light incident steps S101 shown in FIG. 5, the multiplexed light _{L F} modulated light _{L K} and the pulse light _{L P} are superimposed, is input to one end of the continuous optical fiber 100a. The output of the multiplexed light _{L F} is modulated light detection procedure S102, over the optical fiber cutting steps S103 and optical fiber connection procedure S104, continuously performed.

Multiplexed light L _F is, for example, using a light output section 21 shown in FIGS. 3 and 4, and outputs a waveform modulated light L _K and the pulse light L _P are superimposed.

FIG. 6 shows a state of the optical fiber measurement system in the combined light incident procedure S101. Multiplexed light L _F which is modulated with a period of the pulse light L _P modulated light L _K from the optical fiber measuring device 11 is emitted to the optical fiber 100a to be measured. Since the multiplexed light L _F is containing the components of the pulsed light L _P, is reflected by the reflective filter 14 disposed in front of the ONU 52 (point P _R), the reflected return light L _B is the optical multiplexer 12 Incident to the γ port. incident on the γ port return light L _B is emitted from the β port, and enters the optical fiber measuring device 11. Then, the optical fiber measurement device 11 performs the OTDR measurement using the pulsed light _{L P} and the returning light _{L B} is an element of the multiplexed light _{L F.}

FIG. 7 shows an example of the OTDR waveform in the combined light incident procedure S101. By measuring the light level of the optical fiber measuring device 11 is returned light L _B, it can be confirmed that the Fresnel reflection occurs at a distance of the point P _R.

In the modulated light detection procedure S102 shown in FIG. 5, for receiving the combined light _{L F} at any position of the optical fiber 100a. For example, in outdoor locations _{P X} and the point _{P Y,} by bending the optical fiber 100a for receiving the combined light _{L F} from among the leakage light. Since the multiplexed light L _F includes the element of the modulated light L _K , it is possible to perform the optical fiber 100a for the work to be performed or to perform the core line contrast.

In the optical fiber cutting procedure S103 shown in FIG. 5, to cut the optical fiber 100a which has received the modulated light _{L K} in the modulated light detection procedure S102 in the middle point _{P Y} of the optical fiber 100a. In this case, accidentally while confirming the modulated light L _K in cord control so as not to cut the other optical fiber, cutting the optical fiber 100a.

8 shows a state of the optical fiber measurement system when the optical fiber 100a is cut at the point P _Y. In this state, it receives returned to one end of the optical fiber 100a pulsed light L _P of the multiplexed light L _F output by the multiplexed light incident steps S101 is reflected by the optical fiber 100a return light L _B. Pulse light L _P is the Fresnel reflection occurs at the point P _Y, the reflected return light L _B is incident on the optical fiber measuring device 11.

Figure 9 shows an example of the OTDR measurement waveform when the optical fiber 100a is cut at the point _{P Y.} When measuring the light level of the optical fiber measuring device 11 is returned light L _B, Fresnel reflection occurs at a distance of the point P _Y, appears broken waveform. By measuring the Fresnel reflection, it is possible to the optical fiber 100a to determine whether or not cut at a distance of the point P _Y.

In the optical fiber cutting procedure S103 shown in FIG. 5, further cutting the optical fiber 100a which has received the modulated light _{L K} multiplexed light _{L F} that contains the elements of the modulation light detection procedure S102 in the middle of the point _{P X} of the optical fiber 100a To do. At this time, while confirming the other modulated light L _K multiplexed light L _F containing elements in the core wire control so as not to cut the optical fiber accidentally cutting the optical fiber 100a.

10 shows a state of the optical fiber measurement system when the optical fiber 100a is cut at the point P _X. In this state, it receives returned to one end of the optical fiber 100a pulsed light L _P of the multiplexed light L _F output by the multiplexed light incident steps S101 is reflected by the optical fiber 100a return light L _B. Pulse light L _P is the Fresnel reflection occurs at the point P _X, reflected return light L _B is incident on the optical fiber measuring device 11.

Figure 11 shows an example of OTDR waveform when the optical fiber 100a is cut at the point _{P X.} When measuring the light level of the optical fiber measuring device 11 is returned light L _B, Fresnel reflection occurs at a distance of the point P _X, appears broken waveform. By measuring the Fresnel reflection, it is possible to the optical fiber 100a to determine whether or not cut at a distance of the point P _X.

In the optical fiber connection procedure S104 shown in FIG. 5, the optical fiber 100a close to one end on the optical multiplexer / demultiplexer 12 side of the optical fiber 100a cut in the optical fiber cutting procedure S103 is connected to the other optical fiber 100b. For example, described in Figure 15, after the optical fiber 100a is cut at the point _{P X} and the point _{P Y,} is first connected to 100b of 100a and B section of the A interval, then the B section 100b and section C 100a Connect.

FIG. 12 shows the state of the optical fiber measurement system in the optical fiber connection procedure S104. In this state, reflected by the optical fiber 100a pulsed light _{L P} is the point _{P Y} from the point _{P X} is switched connected to the optical fiber 100b of the multiplexed light _{L F} output by the multiplexed light incident steps S101 to optical fiber 100a receiving returned to end the return light L _B. Pulse light L _P is the Fresnel reflection occurs at the point P _R, the reflected return light L _B is incident on the optical fiber measuring device 11.

FIG. 13 shows an example of an OTDR measurement waveform in the optical fiber connection procedure S104. By measuring the light level of the optical fiber measuring device 11 is returned light L _B, determines the connection state of point P _X and the point P _Y. For example, it reads the connection loss of the point P _X and the point P _Y, if the connection loss was prescribed value or less for a predetermined, may be determined to be a normal connection state.

Also, when measuring the light level of the optical fiber measuring device 11 is returned light L _B, Fresnel reflection occurs at a distance of a point P _R, appears broken waveform. By measuring this Fresnel reflection, it can be determined whether or not the optical fiber 100a is connected to the optical fiber 100b.

  According to the present invention, in trouble relocation work, it is not necessary to communicate the work progress sequentially by telephone etc. between the worker in the communication equipment building and the outdoor worker, and it is not necessary to perform the work that matches the timing at multiple work points, Since it is possible to proceed with different tasks, it is possible to reduce the total work time.

In the present embodiment, the modulated light L _K for core controls were described embodiment also output in the optical fiber connection procedure S104, but is not limited thereto. For example, if it is not necessary to carry out the core control after it is confirmed the completion of the cutting operation of the optical fiber 100a at the point P _X, it may stop the output of the modulated light L _K from the modulation light source 54. Thus, the modulated light L _K is because it is no longer reflected by the far end or the like of the connector connection point or an optical fiber 100a of the optical fiber 100a enters the OTDR measurement device 53, to reduce the noise superimposed on the OTDR measurement waveform be able to. Therefore, the measurement accuracy in OTDR measurement can be increased.

(effect)
The optical fiber measurement apparatus according to the present invention can simultaneously perform OTDR measurement and core contrast. Therefore, when conducting a core contrast in a communication facility building, since the core contrast and OTDR measurement can be performed at the same wavelength using the same light source, contact the person in charge at the relocation destination who is working outdoors by telephone or the like. However, it is not necessary to change the connection of the measuring device according to the work procedure.

Although trouble transferring construction becomes possible to perform the work at two or more positions simultaneously, the point P _X in OTDR measurement, since it is possible to perform a point P _Y in the core control simultaneously, without having to wait for the operator work Can proceed.

  Furthermore, since there is no need to switch the measuring device according to the field work, the worker does not have to wait for the switching work outdoors in the communication equipment building during the trouble relocation work, and the OTDR device and the light source for contrast control 2 There is no need to prepare different types of measuring instruments.

11: Optical fiber measuring device 12: Optical multiplexer / demultiplexer 13: Modulated light receiver 14: Reflection filter 21: Light output unit 22: Light receiving unit 23: Calculation unit 33: Pulse drive circuit 34: Pulsed light generation unit 35: Optical switch 36: Modulation signal generator 51: OLT
52: ONU
53: OTDR measuring device 54: modulated light source 56: optical coupler 57: PD
59: Connection point 91: Communication equipment building 100a, 100b: Optical fiber

Claims (6)

A light output unit that generates combined light obtained by modulating pulse light of a pulse train of a predetermined period with a modulation period longer than the predetermined period;
A light receiving unit that measures the light intensity of the return light based on the combined light that is output from the one end of the optical fiber, incident on one end of the optical fiber to be inspected, and the combined light generated by the light output unit;
An optical fiber measuring device. The light output unit is
A pulsed light generating circuit for generating the pulsed light;
A pulse driving circuit for controlling generation and stop of the pulsed light;
The optical fiber measuring device according to claim 1, wherein The light output unit is
A pulsed light generating circuit for generating the pulsed light;
An optical switch that repeatedly transmits and blocks the pulse train of the pulsed light in the path of the pulsed light;
The optical fiber measuring device according to claim 1, wherein A combined light incident procedure in which combined light obtained by modulating pulse light of a pulse train of a predetermined period with a modulation period longer than the predetermined period is incident on one end of one specific optical fiber of the plurality of optical fibers;
By detecting light of the modulation period leaking from the side surface of the optical fiber, a modulated light detection procedure for identifying the specific optical fiber that has entered the combined light in the combined light incident procedure among a plurality of optical fibers;
A loss measurement procedure for measuring the time-to-light intensity of the return light based on the combined light output from the one end of the specific optical fiber, and confirming the loss in the optical path formed by the specific optical fiber;
An optical fiber measurement method. The loss measurement procedure includes:
5. The optical fiber switching operation performed on the optical path of the specific optical fiber is monitored by confirming a change in the position where the combined light is reflected by Fresnel from the light intensity of the return light. Optical fiber measurement method. A line switching work method for performing an optical cable switching work using the optical fiber measurement method according to claim 4,
  While confirming the loss of the optical path by the loss measurement procedure, the specific optical fiber is specified and cut at the first location by the modulated light detection procedure, and the first optical fiber is confirmed to be cut. Cutting procedure;
  While identifying the loss of the optical path by the loss measurement procedure, the specific optical fiber is identified and cut by the modulated light detection procedure at the second location closer to the one end of the specific optical fiber than the first location, and the identification is performed. A second cutting procedure for confirming that the optical fiber has been cut;
  While confirming the loss of the optical path by the loss measurement procedure, one end of the transfer destination optical fiber is connected to the cutting point of the specific optical fiber on the one end side at the second location, and the specific optical fiber and the transfer destination optical fiber are connected. A first connection procedure for confirming that the connection with is completed;
  While confirming the loss of the optical path by the loss measurement procedure, the other end of the transfer destination optical fiber is connected to the cutting point of the specific optical fiber opposite to the one end at the first location, and the specific optical fiber and the transfer A second connection procedure for confirming that the connection with the first optical fiber is completed;
The track switching work method characterized by performing in order.

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