JP4855435B2 - Optical fiber core contrast method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To allow contrasting cores for respective optical fibers between an optical splitter and an ONU in a PON system and contrasting cores for optical fibers which does not bring about leaked light in bending the optical fibers. <P>SOLUTION: In the method of contrasting cores of optical fiber being a work target out of a plurality of optical fibers, such a configuration is provided that pulse test light is sent from one end of the work target optical fiber with a prescribed sending period T and the reception intensity of a prescribed polarized component of return light reflected on the other end and returned after a prescribed time. Polarization fluctuation is given to the pulse test light and the return light at the other end of the work target optical fiber, and the reception intensity of the prescribed polarization component of the return light returned the prescribed time after having sent the pulse test light is detected, and it is detected whether or not the reception intensity is varied due to the polarization fluctuation to specify the optical fiber in which the polarization fluctuation has been given to the pulse test light. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an optical fiber core comparison method and apparatus for specifying an optical fiber to be worked during construction or maintenance work of an optical line.

  The conventional optical fiber core line contrast device enters the test light into the optical fiber to be worked, observes the test light leaked by bending applied to the optical fiber, and if the test light is detected, the optical fiber is operated. The configuration was specified as the target. This is called “heart-line contrast”.

FIG. 8 shows a configuration example of a conventional optical fiber core wire contrast device (Patent Document 1, Patent Document 2).
In the figure, a station-side terminator OLT (Optical Line Terminal) and a user-side terminator ONU (Optical Network Unit) are connected via an optical fiber cable 50 in which optical fibers are bundled. Test light is incident on the work target optical fiber 51 from the optical fiber 51 on the optical fiber 51 via the OLT-side optical coupler 52 and is bent using the bending portion 54 on the ONU side of the optical fiber 51. The test light leaking due to the bending is detected by a photodetector (PD) 55. Here, the test light having a wavelength longer than that of the communication light between the OLT and the ONU is used, and the test light is blocked by the test light blocking filter 56 disposed at the far end of the optical fiber 51 (input end of the ONU). Therefore, it is possible to perform the contrast control using the test light without affecting the communication light.

The optical fiber core wire contrast device includes an optical coupler 52 and a core wire contrast test light source 53 as an in-house device, and a bending portion 54 and a photodetector 55 as external devices. The operator enters the test light into the optical fiber 51 to be worked using the in-house device, detects the test light leaking from the optical fiber 51 using the outside device, and the communication light is being transmitted. You can also perform heart contrast without interrupting service.
Japanese Patent Laid-Open No. 01-237509 Japanese Patent Laid-Open No. 02-001632

  By the way, the conventional optical fiber core line contrast device has no problem in the optical network system in which the OLT and the ONU are connected one-to-one, but a PON (Passive Optical) that accommodates a plurality of ONUs in one OLT via an optical splitter. Problems arise with Network) systems. The test light incident on one optical fiber from the test light source for controlling the core wire is evenly distributed to the plurality of optical fibers via the optical splitter. There is no contrast.

  Further, in recent years, in order to improve the workability of optical fiber operation, an optical fiber is used in which loss fluctuation hardly occurs with respect to bending, that is, leakage light due to bending does not easily occur. As such an optical fiber, a hole assist fiber or the like in which holes are provided around an optical fiber core and a strong light confinement effect is realized by a low refractive index cladding layer has been developed. The conventional method of observing leaked light due to bending with respect to this optical fiber cannot perform contrast control.

  The present invention relates to an optical fiber core contrast method that enables a core contrast for each of a plurality of optical fibers between an optical splitter and an ONU in a PON system, and a core contrast for an optical fiber that does not generate leakage light with respect to bending. And an object to provide an apparatus.

In the first invention, one optical fiber and another optical fiber having different optical fiber lengths are connected via an optical splitter, pulse test light is transmitted from one end of the one optical fiber, and the other plural optical fibers are transmitted. when reflected respectively at the other end of the optical fiber returns to the one end of the hand of the optical fiber, the other of the plurality of optical fibers is determined in accordance with the time position of the return beam, a predetermined relative time position of the return beam In the optical fiber core-line contrast method for detecting the received light intensity of the polarization component of the optical fiber and identifying the optical fiber to be worked out from the other plurality of optical fibers, the pulse test light is converted into one optical fiber and the other plurality of light. sending the longest optical fiber transmission cycle is set longer than the light reciprocating time combined T of the fiber, in addition to lateral pressure or bending or twisting at the other end of the work target of the optical fiber, pulse trial Polarization fluctuations at a modulation frequency set lower than 1 / (2T) and higher than 20 Hz with respect to the transmission period T of the pulse test light are given to the light and the return light, and the pulse test is performed at one end of one optical fiber. After the light is sent out, the received light intensity of the predetermined polarization component of the return light at the time position corresponding to the work optical fiber is sampled a plurality of times at the send cycle T, the time variation of the received light intensity is frequency-analyzed, and the work light and detecting the presence or absence of the components of the modulation frequency of the polarization fluctuation given to fiber to identify the optical fiber gave polarization fluctuation.

In the second invention, one optical fiber and the other optical fibers having different optical fiber lengths are connected via an optical splitter, and pulse test light is transmitted from one end of the one optical fiber, and the other plural optical fibers are transmitted. when reflected respectively at the other end of the optical fiber returns to the one end of the hand of the optical fiber, the other of the plurality of optical fibers is determined in accordance with the time position of the return beam, a predetermined relative time position of the return beam In the optical fiber core-line contrast device that detects the received light intensity of the polarization component of the optical fiber and identifies the optical fiber to be worked from among the other optical fibers, the pulse test light is transmitted to one optical fiber and the other optical fibers. lateral pressure or bending also at the other end of the longest pulse test light transmitting means for transmitting a long, set transmission period T than the light reciprocating time combined optical fiber, work target of the optical fibers of the fiber Added twist, the pulsed test light and return light, and means for providing 1 / (2T) than the low relative transmission period T of the pulse test light, and a polarization fluctuation of the set high modulation frequency from 20 Hz, whereas After receiving the pulse test light at one end of the optical fiber, the received light intensity of the predetermined polarization component of the return light at the time position corresponding to the work optical fiber is sampled a plurality of times at the transmission period T, and the time of the received light intensity And a core line contrast means for analyzing the frequency of the fluctuation and detecting the presence / absence of a modulation frequency component of the polarization fluctuation given to the work target optical fiber to identify the optical fiber given the polarization fluctuation.

  The present invention provides a light receiving time of return light from the far ends of a plurality of optical fibers branched by an optical splitter of a PON system, and a predetermined polarization component of the return light when polarization fluctuation is given to the optical fiber to be worked on. By detecting a change in the received light intensity, it is possible to perform a core contrast with respect to the optical fiber to be worked.

  In the present invention, the light reception time of the return light from the far ends of a plurality of optical fibers branched by the optical splitter of the PON system, and the polarization of the return light when a polarization fluctuation of a predetermined modulation frequency is given to the optical fiber to be worked on. By detecting the modulation frequency component from the time variation of the received light intensity of a predetermined polarization component, it is possible to perform a core contrast with respect to the optical fiber to be worked.

  In addition, since the present invention observes the received light intensity of a predetermined polarization component of the return light, it is possible to perform a core contrast with respect to an optical fiber that does not generate leakage light with respect to bending.

(First embodiment)
FIG. 1 shows a first embodiment of the optical fiber core wire contrast device of the present invention.
In the figure, in the PON system, an optical fiber 11 connected to an OLT and optical fibers 13-1 to 13-m connected to a plurality of m ONUs are connected via an m-branch optical splitter 12. It is a configuration. An optical coupler 14 is inserted into the optical fiber 11 that connects the OLT and the optical splitter 12, and the optical fiber reference internal device 20 is connected to the test port of the optical coupler 14. The core wire control in-house device 20 outputs pulse test light having a wavelength different from that of the communication light between the OLT and the ONU. The pulse test light enters the optical fiber 11 from the optical coupler 14 and propagates, and is distributed by the optical splitter 12 to the optical fibers 13-1 to 13-m. A test light blocking filter 15 that transmits communication light and blocks and reflects pulse test light is inserted at the far end (input end of each ONU) of the optical fibers 13-1 to 13-m. An external device 30 for contrasting the core that gives polarization fluctuation to the light propagating through the optical fiber is attached to an optical fiber (13-m in this case) that performs the core contrast.

  The intracenter device 20 for controlling the core wire includes a light source 21 that outputs pulse test light having a large polarization extinction ratio, an optical coupler 22, a polarizer 23, a photodetector (PD) 24, a signal control / processing unit 25, and a database 26. Is done. The pulse test light output from the light source 21 enters the optical fiber 11 via the optical coupler 22 and the optical coupler 14, and the return light reflected by the test light blocking filter 15 is the optical coupler 14, the optical coupler 22, and the polarizer 23. Is input to the photodetector 24. The polarizer 23 transmits a predetermined polarization component of the return light, and the photodetector 24 receives the return light of the predetermined polarization component. The signal control / processing unit 25 controls the transmission period T (second) of the pulse test light output from the light source 21, and monitors the light reception time and light reception intensity of the return light of the predetermined polarization component detected by the photodetector 24. And it is the structure which performs a core line contrast process.

  Here, the pulse test light incident on the optical fiber 11 from the optical fiber reference device 20 is reflected at the connector connection point in the optical line to the ONU, the far end, etc., and returns to the optical fiber reference device 20. The return loss at the connector connection point is about 40 dB. Therefore, the main return light detected by the photodetector 24 of the intracardiac contrast device 20 is the return loss generated by the test light blocking filter 15 provided at the far end of the optical fibers 13-1 to 13-m. 0-14 dB Fresnel reflected light.

The optical fiber lengths L _{1 to} L _m of the optical fibers 13-1 to 13 -m connecting the optical splitter 12 and the ONUs of the respective user houses are registered in the database 26 in association with the respective core numbers. Reference can be made from the control / processing unit 25. Here, for the sake of simplicity, the length becomes longer in the order of L ₁ , L ₂ ,..., L _m , and the optical fiber length L _m of the optical fiber 13- _m is the longest. When the optical fiber length of the optical fiber 11 was set to L _F, the distance between the core wire control for house device 20 and the longest optical fiber test light blocking filter 15 connected to the far end of the 13-m L is
L = L _F + L _m
It becomes. At this time, it is necessary to set the transmission period T of the pulse test light output from the optical fiber reference device 20 longer than the time 2 L / v for reciprocating the distance to the far end of the longest optical fiber 13-m. . v is the speed of the pulse test light in the optical fiber.

The optical fiber lengths L _{1 to} L _m of the optical fibers 13-1 to 13-m are different from each other, and the relationship between the minimum optical fiber length difference (resolution) Lr and the pulse width w of the pulse test light is
Lr> w · v / 2
It is necessary to set. 2 (1) and 2 (2) show time charts of the pulse test light and the return light based on the above settings.

The pulse test light transmitted from the core wire control in-house device 20 at time nT propagates through the optical fiber 11 and is branched into m by the optical splitter 12, and propagates through the optical fibers 13-1 to 13-m to block the test light. Reflected by the filter 15, each return light follows the reverse path and is received by the light detector 24 via the polarizer 23 of the intracardiac contrast device 20. The received light intensity of each return light is P _{1n to} P _mn . The time for each return light to be received depends on the respective round-trip propagation delay time,
nT + 2 (L _F + L ₁ ) / v
nT + 2 (L _F + L ₂ ) / v
...
nT + 2 (L _F + L _m ) / v
It becomes. The signal control / processing unit 25 monitors the light reception time and the light reception intensities P _{1n to} P _mn of the return light from the far ends of the optical fibers 13-1 to 13-m. Note that the photodetector 24 is configured to detect the received light intensity of a predetermined polarization component that passes through the polarizer 23, and the polarization state of each return light is not necessarily the same, as shown in FIG. 2 (2). In addition, the received light intensity P _{1n to} P _mn of each return light varies.

Based on the above premise, the external device 30 for controlling the core wire is attached to the working optical fiber 13-m and a lateral pressure is applied, and the cross-sectional shape of the optical fiber is changed as shown in FIG. Then, the mode speeds in the x direction and the y direction change, and the polarization of the pulse test light and return light propagating through the optical fiber 13-m fluctuates. This polarization fluctuation appears as a change in the received light intensity P _mn when the return light is received by the photodetector 24 via the polarizer 23 of the optical fiber reference device 20, and the signal control / processing unit 25 To monitor.

On the other hand, the signal control / processing unit 25 refers to the database 26, associates the optical fiber lengths L _{1 to} L _m from the time positions of the respective return lights, and further supports the core numbers of the optical fibers 13-1 to 13-m. Let When the change in the received light intensity P _xn of the return light with respect to the pulse test light transmitted at time nT is detected, the optical fiber to which the side pressure is applied by the external device 30 for contrast control is the optical fiber 13-x. Identify. In the example of this embodiment, when a side pressure is applied to the optical fiber 13-m using the external device 30 for controlling the core wire, if a change is _detected in the received light intensity P _mn of the return light, the optical fiber It is identified as 13-m plus lateral pressure. In this way, it is possible to perform a core contrast for the optical fibers 13-1 to 13-m below the optical splitter 12 of the PON system and an optical fiber that does not generate leakage light with respect to bending.

(Second Embodiment)
In the first embodiment, the return light corresponding to the optical fiber for contrasting the cores is not compared with the received light intensity of the return light corresponding to the other optical fibers, but the offset given by the external device 30 for controlling the cores is not used. In this configuration, a change in received light intensity due to wave fluctuation is detected. That is, as shown in FIG. 2 (2), the return light whose received light intensity is changing is identified from the variations in the received light intensity P _{1n to} P _mn of the predetermined polarization component of each return light, and the corresponding light is dealt with. There was a need to identify the optical fiber.

  In addition, it is known that the optical fiber cable through which the pulse test light propagates fluctuates, so that the polarization in the optical fiber fluctuates gently, and the frequency component of the fluctuation is about 20 Hz or less (Fujikura Technical Report 108 No., pp.14-18, http://www.fujikura.co.jp/00/gihou/gihou.html). Accordingly, the received light intensity of the return light in the intra-center apparatus 20 for core-line contrast may include an error due to a gradual change in polarization, and the core-line contrast is performed while removing the frequency component of about DC to 20 Hz. There is a need to do.

  Based on the above situation, in order to reliably detect the change in the received light intensity due to the polarization fluctuation given by the core contrast external device 30, the lateral pressure applied to the optical fiber by the core contrast external device 30 is set to the frequency. A method of modulating with f and detecting the component of the modulation frequency f from the received light intensity of the return light with the intracardiac contrast in-house device 20 is effective. The method will be described below.

In the intracardiac contrast center apparatus 20, the received light intensity of the return light at the time position corresponding to the optical fiber 13-m is kth when the pulse test light is incident N times (N is an integer of 2 or more) at intervals of T seconds. When the received light intensity of the return light with respect to the pulse test light (k is an integer of 1 to N) is P _mk , the received light intensity P _mk of the return light is sampled at a period T, and the N times of received light intensity P _mk The integrated value is ΣP _mk (k is 1 to N)
It can be expressed as FIG. 4 shows the time series change of the received light intensity P _mk . Note that it is not necessary to perform the averaging process on the integrated value of the N received light intensities P _mk of the return light corresponding to the optical fiber 13-m.

When the time series change of the received light intensity P _mk is envelope-detected and the frequency component is analyzed using an FFT (Fourier transform circuit), the side pressure applied to the optical fiber 13-m by the external device 30 for contrast control is adjusted. The frequency f can be detected. That is, as shown in FIG. 5, when the component of the modulation frequency f is detected in the received light intensity P _mk , the optical fiber 13-m can be compared with the optical fiber 13-m to which a lateral pressure is applied. The received light intensity P _mk of the return light includes a frequency component (20 Hz or less) of polarization fluctuation due to fluctuation of the optical fiber cable as shown in FIG. 5, but this frequency component can be removed if necessary. That's fine.

Here, the component of the modulation frequency f of the received light intensity can be sampled at a period T at which the pulse test light is transmitted and detected up to a frequency of 1 / (2T). The shorter the sampling period T, the shorter the measurement time and the higher frequency modulation can be detected. As described above, the transmission period T of the pulse test light is longer than the time 2 L / v during which light travels back and forth through the longest optical fiber. The modulation frequency f is limited by the line length L of the longest optical fiber,
20Hz <f <1 / (2.2L / v)
Set within the range. For example, when the line length is 20 km, the modulation frequency f may be set in the range of 20 Hz to 2.5 kHz.

(Modification of the first and second embodiments)
The external device 30 for contrasting the core wire may be configured to bend or twist, for example, as long as it is a configuration that similarly changes the polarization instead of applying a side pressure to the optical fiber. Further, even in a conventional optical fiber in which leakage light is generated by bending, the polarization changes due to side pressure, bending, twisting, and the like, so that the cords can be controlled by the method and apparatus of the present invention.

  The optical fiber line contrast according to the first and second embodiments can be applied to an optical line configuration that does not include the optical splitter 12 in which the OLT and the ONU are connected on a one-to-one basis.

  When the optical line is not in service, the optical fiber 11 may be directly connected to the optical fiber reference device 20 without using the optical coupler 14.

  When there is no distance information of the optical fibers 13-1 to 13-m, that is, when there is no information indicating from which optical fiber each return light shown in FIG. The external device 30 for contrasting the core wire is arranged in the very vicinity of the far end, and the correspondence relationship with the delay time of the return light of each optical fiber in advance using the technique of the first and second embodiments, that is, the optical fiber What is necessary is just to obtain | require the distance information of 13-1 to 13-m. Further, distance information of the optical fibers 13-1 to 13-m may be acquired by performing an OTDR test or the like from the ONU side.

(Third embodiment)
FIG. 6 shows a third embodiment of the optical fiber core line contrast device of the present invention. Here, the description will be made based on the work procedure when the operator performs the core contrast on site, but the basic principle of the core contrast is the same as in the first and second embodiments, and FIG. Components corresponding to those of the optical fiber core wire contrast device shown are denoted by the same reference numerals and description thereof is omitted.

  In FIG. 6, a plurality of optical fibers 11-1 to 11-3 are connected to the OLT, and an optical coupler 14 is inserted into each of them. Although not shown in the drawing, an optical splitter 12 is connected to each of the plurality of optical fibers 11-1 to 11-3, and an ONU is connected to each of the plurality of optical fibers 13. The intracardiac contrast device 20 includes an optical switch 27 that inputs the pulse test light output from the light source 21 to one of the optical couplers 14 inserted into each of the plurality of optical fibers 11-1 to 11-3. . The optical switch 27 switches connection destinations under the control of the signal control / processing unit 25. In addition, the optical switch 27 may be provided outside the in-house device 20 for controlling the core wire, or may be operated by a person in the in-house. The signal control / processing unit 25 of the intracardiac contrast device 20 and the communication / display unit 31 of the core contrast external device 30 include a function of performing communication via the communication network 32. In addition, the communication form of the core wire contrast in-house device 20 and the core wire contrast external device 30 is not particularly limited, and an existing public wireless communication system or the like can be used.

  The operator gives a polarization fluctuation to the optical fiber (13-m in this case) that is connected to the optical fiber 11-1 in the field using the external apparatus 30 for controlling the optical fiber, An operation of transmitting optical fiber information and test instructions for optical fiber contrast is performed from the communication / display unit 31 via the communication network 32 to the signal control / processing unit 25 of the intra-cardiac optical device 20. When the signal control / processing unit 25 of the intracardiac contrast device 20 receives a signal from the core contrast external device 20 via the communication network 32, the signal control / processing unit 25 is inserted into the optical fibers 11-1 to 11-3. By referring to the database 26 having correspondence information between the test port of the optical coupler 14 and the port of the optical switch 27, the optical fiber 11-1 to which the pulse test light is input based on the information of the optical fiber 13-m of the core line contrast In particular, the optical switch 27 is controlled to control the pulse test light to be input to the optical fiber 11-1.

  Next, as described in the first and second embodiments, the signal control / processing unit 25 of the intracardiac contrast device 20 performs, for example, a frequency analysis example of the received light intensity of the return light illustrated in FIG. Then, the return light in which the received light intensity varies is detected, the length of the optical fiber in which the return light is generated is determined from the time from when the pulse test light is sent to when the return light is detected. To obtain the core number of the corresponding optical fiber 13-m. The information of the core number is transferred from the signal control / processing unit 25 of the intra-core device 20 for core-line comparison to the communication / display unit 31 of the external device 30 for core-line control via the communication network 32, and the optical fiber 13. -M core number is displayed. As a result, the operator can identify the optical fiber 13-m having the polarization fluctuation by using the external device 30 for controlling the core wire.

  In addition, when an operator performs the optical fiber 13-m connected to the optical fiber 11-1, the optical fiber 13-m is mistakenly given, for example, a polarization fluctuation is given to the optical fiber connected to the optical fiber 11-2. When the optical fiber 13-m connected to the fiber 11-1 is notified to the in-core device 20 for core line control as the core wire reference, the following is performed. The signal control / processing unit 25 of the cord-line contrast in-house device 20 sends pulse test light to the optical fiber 11-2, and monitors the variation of the received light intensity of the return light. However, the operator gives a polarization fluctuation to the optical fiber 13-m connected to the optical fiber 11-1, and gives no polarization fluctuation to the optical fiber connected to the optical fiber 11-2. Therefore, as shown in FIG. 7 (2), the intracenter device 20 for contrast control cannot observe the return light whose received light intensity varies. In this case, the in-core device 20 for controlling the core wire notifies the out-of-device device 30 for checking the core wire that there is no optical fiber for controlling the core wire in the optical line subjected to the test.

The figure which shows 1st Embodiment of the optical fiber core wire contrast apparatus of this invention. The figure which shows pulse test light and return light. The figure which shows the modification of the optical fiber by a side pressure. The figure which shows the example of the time fluctuation | variation of the light reception intensity | strength of the return light in the 2nd Embodiment of this invention. The figure which shows the frequency analysis example of the light reception intensity | strength of the return light in the 2nd Embodiment of this invention. The figure which shows 3rd Embodiment of the optical fiber core wire contrast apparatus of this invention. The figure which shows the frequency analysis example of the light reception intensity | strength of the return light in the 3rd Embodiment of this invention. The figure which shows the structural example of the conventional optical fiber core wire contrast apparatus.

Explanation of symbols

OLT Station-side terminator ONU User-side terminator 11, 13 Optical fiber 12 Optical splitter 14 Optical coupler 15 Test light blocking filter 20 Optical fiber reference device 21 Light source 22 Optical coupler 23 Polarizer 24 Photo detector (PD)
25 Signal Control / Processing Unit 26 Database 27 Optical Switch 30 External Device for Control of Core Wire 31 Communication / Display Unit 32 Communication Network

Claims (2)

One optical fiber and another optical fiber having different optical fiber lengths are connected via an optical splitter, and pulse test light is transmitted from one end of one optical fiber, and the other end of the other optical fibers is returning to one end of the hand of the optical fiber and reflected respectively, in accordance with the time position of the return light when the other of the plurality of optical fibers is determined, the received light intensity of the predetermined polarization component to the time position of the return beam In the optical fiber core contrast method for detecting the optical fiber and identifying the optical fiber to be worked from among the other plurality of optical fibers,
The pulse test light is transmitted at a transmission period T set longer than an optical reciprocation time of the longest optical fiber of the one optical fiber and the other plurality of optical fibers,
A lateral pressure, bending, or twisting is applied to the other end of the optical fiber to be worked, and the pulse test light and the return light are lower than 1 / (2T) with respect to the transmission period T of the pulse test light and 20 Hz. Gives the polarization fluctuation of the modulation frequency set higher,
At one end of the one optical fiber, after receiving the pulse test light, the received light intensity of a predetermined polarization component of the return light at a time position corresponding to the work optical fiber is sampled a plurality of times at the transmission period T. , that the frequency analysis of the time variation of the received light intensity, identifying the optical fiber gave Kihen wave fluctuations before checking for possible component of the modulation frequency of the polarization fluctuation given to the work object optical fiber An optical fiber core contrast method characterized. One optical fiber and another optical fiber having different optical fiber lengths are connected via an optical splitter, and pulse test light is transmitted from one end of one optical fiber, and the other end of the other optical fibers is returning to one end of the hand of the optical fiber and reflected respectively, in accordance with the time position of the return light when the other of the plurality of optical fibers is determined, the received light intensity of the predetermined polarization component to the time position of the return beam In the optical fiber core-line contrast device that detects the optical fiber to be worked from among the other plurality of optical fibers,
A pulse test light sending means for sending the pulse test light at a sending cycle T set longer than an optical reciprocation time of the longest optical fiber of the one optical fiber and the other plurality of optical fibers;
A lateral pressure, bending, or twisting is applied to the other end of the optical fiber to be worked, and the pulse test light and the return light are lower than 1 / (2T) with respect to the transmission period T of the pulse test light and 20 Hz. Means for providing polarization fluctuations at a higher modulation frequency;
At one end of the one optical fiber, after receiving the pulse test light, the received light intensity of a predetermined polarization component of the return light at a time position corresponding to the work optical fiber is sampled a plurality of times at the transmission period T. , core wire that frequency analysis of the time variation of the received light intensity, identifying the optical fiber gave Kihen wave fluctuations before checking for possible component of the modulation frequency of the polarization fluctuation given to the work object optical fiber An optical fiber optical fiber contrast device comprising: a contrast means.

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