JP2005147871A - Analytical method for optical path characteristic, and optical path test monitoring system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an analytical method for an optical path characteristic capable of measuring an optical characteristic of an optical path without generating a measuring incapable section, and an optical path test monitoring system. <P>SOLUTION: A waveform in a tailing portion of Fresnel reflection A is substituted with a rear scattering light level just before Fresnel reflection B (substituted waveform W1), in an OTDR waveform appearing with the Fresnel reflections A, B in distances laterally symmetric each other around Fresnel reflection of a termination filter 22 as the center, the rear scattering light level is corrected thereafter in the waveform W1 by a DL of a path loss (level-corrected waveform W2), and a waveform W3 obtained by inverting the waveform W2 to be conformed with a measuring direction (level-inverted waveform W3) is further substituted with that in the same section in the waveform A. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for analyzing optical line characteristics of an optical communication facility and an optical line test monitoring system.

  The optical line test monitoring system is a system that tests and monitors an optical fiber cable that is an optical line without affecting optical communication services. FIG. 10 is a schematic configuration diagram of a conventional optical line test monitoring system (see Patent Document 1 below). Hereinafter, the configuration of a conventional optical line test monitoring system will be described with reference to FIG.

  As shown in the figure, the conventional optical line test monitoring system includes a communication facility building 1 in which telecommunications facilities are installed, a facility management center 6 that manages facility information of the communication facility building 1, and a user building 3. Each building has the following facilities.

  In the communication facility building 1, a transmission device 2, an optical termination 14 and an optical testing device 15 are installed. The optical termination 14 is a core selection device (FS) for selecting an optical fiber core to be tested. ) 16 and an optical coupler module 12 that multiplexes and demultiplexes the test light into the optical fiber 5 and blocks the test light from entering the optical fiber 5, and the optical test apparatus 15 includes the equipment management center 6. Functions of a test control device 19 that receives test instructions from the operation terminal 8 and transmits test results to the facility management center 6, an optical pulse tester (OTDR), a loss test light source, a core-line control light source, and a power meter And an optical measuring device / test rack selecting device (FTES) 17 for selecting the optical measuring device 18 and the core wire selecting device 16.

  The facility management center 6 is provided with an optical line facility database 7 and an operation terminal 8 for remotely operating the optical testing device 15 of the communication facility building 1. The user building 3 has a transmission device 4 that transmits and receives an optical signal facing the transmission device 2 and is installed immediately before the transmission device 4 to transmit the communication light and block the test light, and to reflect Fresnel reflection at the open end. And a termination filter 13 that generates a larger reflection of the test light. The transmission device 2 and the transmission device 4 are connected by an optical fiber 5, and the equipment management center 6 and the communication equipment building are connected by a communication network 9.

  FIG. 11 is a schematic configuration diagram of an optical coupler module installed on the optical termination. As shown in the figure, the optical coupler module 12 includes an optical coupler 10 that multiplexes and demultiplexes test light and communication light and couples them to the optical fiber 5, and an optical filter 11 that transmits the communication light and blocks the test light. And has four ports A to D. The A port is connected to the transmission device 2 side, the B port is a communication light port connected to the optical fiber 5 side, the C port is the optical fiber 5 and transmission device 4 side, and the D port is the transmission device 2 side test. This is a test light port to which a measuring device for connecting is connected.

  Below, the example which detects the failure of an optical line using the conventional optical line monitoring test system shown in FIG. 10 is demonstrated. Based on the database 7 installed in the facility management center 6, a test command is issued from the operation terminal 8 to the optical test apparatus 15. In accordance with this command, the test control device 19 of the optical test device 15 selects the optical measuring device 18 by the FTES 17 and also the core selection device 16 that accommodates the test light input / output ports C and D of the optical coupler module 12. Thus, the test light input port C or D of the optical coupler module 12 to which the designated optical fiber is connected is selected.

  Since the optical filter 11 and the termination filter 13 are respectively installed in front of the transmission devices 2 and 4, the test light from the optical measuring device 18 does not affect the optical communication service. Thereby, the in-service test of the optical fiber designated from the optical test apparatus 15 becomes possible.

  Moreover, in order to distinguish the failure of the transmission device 2 or the transmission device 4 from the failure in the optical line section (optical fiber 5), the termination filter 13 is designed to reflect the test light to be larger than the Fresnel reflection at the open end. Has been. Usually, the Fresnel reflection at the open end of the optical fiber is about -15 dB. For example, when the reflection of the test light of the termination filter is set to −12 dB or more, and the reflection is reduced to −15 dB or less, it is understood that the optical line is broken (broken).

  Next, the case where the OTDR test is performed in the in-service test in the optical line monitoring test system shown in FIG. 10 will be described. The description will be made assuming that the test wavelength is 1.65 μm. Conventionally, a dielectric multilayer optical filter is generally used as the optical filter 11 installed in the optical coupler module 12.

  A dielectric multilayer film has a multilayer structure in which dozens or hundreds of thin films with different refractive indexes are laminated on quartz glass, etc., and is inserted into an optical fiber, waveguide, or optical connector part at a specific angle. By doing so, it is possible to reflect only a specific wavelength on the clad, and to adjust the transmission / cutoff wavelength band and the reflection amount of the cutoff wavelength.

  FIG. 12A is a graph showing the optical characteristics of the optical filter 11 using this dielectric multilayer film. As shown in the figure, the transmission loss is 1.0 dB or less in the band of 1.26 μm to 1.58 μm, and the transmission loss gradually increases in the band of 1.58 to 1.64 μm. It can be seen that a certain 1.65 μm has a blocking amount of about 40 dB. The return loss of the test light can be set to 40 dB or more by adjusting the insertion angle of the dielectric multilayer filter.

  On the other hand, as the termination filter 13 installed in the user building 3, a dielectric multilayer film filter or a fiber Bragg grating (hereinafter referred to as FBG) in which the reflection of the test light is adjusted to -12 dB or more by adjusting the insertion angle is used. .

  The FBG type optical filter is formed by irradiating an optical fiber with ultraviolet rays to form tens of thousands of gratings having different refractive indexes in the longitudinal direction of the core of the optical fiber or in the longitudinal direction of the core and the clad. By forming the refractive index modulation so as to satisfy the Bragg reflection condition, only a specific wavelength is reflected, and other wavelengths are transmitted.

  FIG. 12B is a graph showing the optical characteristics of the termination filter 13 using the FBG type optical filter. As shown in the figure, in the band of 1.26 μm to 1.625 μm, the transmission loss is 0.8 dB or less, and the transmission loss increases rapidly from 1.625 μm to 1.645 μm. It can be seen that the cutoff amount is 20 dB at a certain 1.65 μm. Further, the test light is reflected at about -1 dB.

  In the conventional optical line test monitoring system, as described above, the optical characteristics of the optical line are measured from the communication facility building 1 side using an optical test means such as an optical pulse tester (OTDR). We are conducting testing and monitoring. Here, when measuring backscattered light and Fresnel reflection using OTDR, if the backscattered light just before the measurement point is large or if there is Fresnel reflection, the electrical system (amplifier circuit) becomes saturated, As a result, a weak signal located behind may not be normally detected. (See Non-Patent Document 1 below.)

  In general, Fresnel reflection has a considerably higher power level than backscattered light. Therefore, in normal 0TDR measurement, if there is Fresnel reflection at the incident end of an optical pulse or Fresnel reflection due to connector connection in the middle of an optical fiber cable, the OTDR electrical system (amplifier circuit) is saturated due to Fresnel reflection. Become.

  FIG. 13 is a graph showing an OTDR waveform when the optical characteristics of the optical line are measured. As shown in the figure, as the optical fiber 5, an optical fiber having two optical fibers 5a and 5b connected by connectors and having an optical connector 21 at the end is used. The incident end side of the optical fiber 5 from the connector connection point 20 is referred to as an optical fiber 5a, and the optical connector 21 side of the terminal end from the connector connection point 20 is referred to as an optical fiber 5b.

  As shown in the figure, Fresnel reflection occurs at the incident end, the connector connection point 20, and the terminal optical connector 21, and a reflection tail appears, and the backscattered light of the optical fiber cannot be accurately measured after the Fresnel reflection. There is a section (this section is called “unmeasurable section”).

  This is defined by JIS-C6185 (Optical Time Domain Reflectometer (OTDR) test method) as dead zone (loss measurement dead zone) and spatial resolution (loss measurement resolution). And the interval until the difference between the received light level of the backscattered light becomes 0.1 dB or less.

  In order to remove the influence of these Fresnel reflections, an optical switch (A / O switch) or the like that switches the optical path using the acousto-optic effect is used only at the moment when the Fresnel reflection returns to the measurement end. It is possible to prevent the reflected light from entering the OTDR light receiving device. This is called mask setting, and the position and width of the mask can be set according to the pulse width of the OTDR test light and the position where Fresnel reflection appears.

  FIG. 14 is a graph showing an OTDR waveform when the optical characteristics of the optical line are measured, and shows a case where a mask is set. As shown in the figure, the OTDR waveform when the mask is set does not cause Fresnel reflection and its tailing at the connector connection point 20 in the middle of the optical fiber 5, and measurement becomes impossible when the mask is not set. In some cases, the backscattered light can be accurately measured even in the interval.

Japanese Patent Laid-Open No. 2-1632 (pages 4-9, FIGS. 1-8) Supervised by Atsushi Ishihara, “Points of optical fiber technology 200 useful for practical use (Revised 2nd edition)”, Telecommunications Association, June 25, 2001, p.283-284

  However, since the optical line is switched by the optical switch by setting a mask to remove the influence of Fresnel reflection, light enters the OTDR light receiving device at least for a time longer than the pulse width of the OTDR test light. Thus, the OTDR waveform cannot be acquired in the interval corresponding to this time. In practice, depending on the response speed of the optical switch, the section in which the OTDR waveform cannot be acquired further increases.

  In addition, most OTDRs currently on the market do not have a mask (optical mask) setting function using an optical switch for the purpose of downsizing and cost reduction. Therefore, when there is an optical connector connection or the like in the middle of the optical line, there is always an unmeasurable section on the OTDR waveform due to the tailing of Fresnel reflection that occurs due to the connector connection or the like.

  As described above, in the section where the OTDR waveform cannot be acquired due to the mask setting and the section where the OTDR waveform cannot be measured, even if loss due to bending or the like occurs in the optical fiber section, the optical characteristics of the optical line are accurately measured. I can't. For this reason, when there is a large loss in these unmeasurable sections, the OTDR test from one side cannot distinguish between the connector connection loss and the optical fiber section loss. There was a problem that the cause of the failure could not be determined.

  Therefore, in order to eliminate these unmeasurable sections, the OTDR test must be performed from both ends of the optical line, and the sections located behind the Fresnel reflection at the connector connection point must be measured.

  The present invention has been made in view of the above situation, and in an optical pulse test from one end, even if there is a connector connection point in the middle of the optical line, the optical line without an unmeasurable section due to Fresnel reflection tailing, etc. It is an object of the present invention to provide an optical line characteristic analysis method and an optical line test monitoring system capable of measuring the optical characteristic of the optical line with high accuracy.

An optical line characteristic analysis method according to the present invention that solves the above problems is as follows.
In the optical line characteristic analysis method for analyzing the optical characteristic in the optical line from one end of the optical line to the test light reflecting means (termination filter or the like) provided in the optical line by the test light incident from the one end,
Before the test light reflected by the test light reflecting means returns to the one end, the backscattered light and Fresnel reflection measurement data generated by the test light and reflected by the test light reflecting means are used. do it,
An optical line characteristic analysis method comprising analyzing the optical characteristic of the optical line.

In addition, another optical line characteristic analysis method according to the present invention that solves the above problems is
In the optical line characteristic analysis method for analyzing the optical characteristics in the optical line from one end of the optical line to the test light reflecting means provided in the optical line by the test light incident from the one end,
First measurement data of backscattered light and Fresnel reflection generated before the incident test light reaches the test light reflecting means,
Second measurement data of backscattered light and Fresnel reflection generated by the test light and reflected by the test light reflecting means until the test light reflected by the test light reflecting means returns to the one end. To convert,
An optical line characteristic analysis method comprising analyzing the optical characteristic of the optical line.

Also, in the method for analyzing optical line characteristics,
The conversion of the first measurement data using the second measurement data is as follows:
A first section located behind the Fresnel reflection in the first measurement data,
In the second measurement data, the conversion is performed by replacing with a second section located in front of the Fresnel reflection measured at a distance symmetrical to the first section with the measurement data in the test light reflecting means as the center. This is a method for analyzing optical line characteristics.

Also, in the method for analyzing optical line characteristics,
The transformation for replacing the first interval with the second interval is:
The measurement data of the second section is replaced with the measurement data of the first section, the level correction of the measurement data of the second section, and the inversion corresponding to the measurement direction of the measurement data of the second section. This is a method for analyzing the characteristics of an optical line.

Also, in the method for analyzing optical line characteristics,
The first section is a method for analyzing optical line characteristics, characterized in that the backscattered light located behind the Fresnel reflection is a dead zone where measurement is impossible.

Also, in the method for analyzing optical line characteristics,
The first section is a section calculated based on a function consisting of the pulse width of the test light, the light intensity of the backscattered light before and after the Fresnel reflection, the intensity of the Fresnel reflection, and the response characteristic of the light receiving unit of the optical test means. This is an optical line characteristic analysis method characterized by the above.

Also, in the method for analyzing optical line characteristics,
A part of measurement data of Fresnel reflection in the first measurement data is left.

An optical line test monitoring system according to the present invention that solves the above problems is as follows.
In the optical line test monitoring system for analyzing the optical characteristics of the optical line from one end of the optical line to the test light reflecting means provided in the optical line by analyzing the test light incident from the one end, and monitoring the optical line,
Means for injecting test light from one end of the optical line (such as OTDR);
First measurement data of backscattered light and Fresnel reflection generated before the incident test light reaches the test light reflecting means;
Second measurement data of backscattered light and Fresnel reflection generated by the test light and reflected by the test light reflecting means until the test light reflected by the test light reflecting means returns to the one end. Means for measuring (OTDR, etc.);
Means for converting the first measurement data by using the second measurement data.

In the optical line test monitoring system,
The means for converting the first measurement data includes:
A first section located behind the Fresnel reflection in the first measurement data,
The second measurement data is a means for replacing the second measurement data with a second section located in front of the Fresnel reflection measured at a distance symmetrical to the first section with the measurement data in the test light reflecting means as the center. It is an optical line test monitoring system.

In the optical line test monitoring system,
The means for replacing the first section with the second section is:
A means for replacing the measurement data of the second section with the measurement data of the first section, a level correction means for the measurement data of the second section, and an inversion means corresponding to the measurement direction of the measurement data of the second section; It is comprised from these. The optical line test monitoring system characterized by the above-mentioned.

In the optical line test monitoring system,
In the optical line test and monitoring system, the first section is a dead zone located behind the Fresnel reflection and incapable of measuring backscattered light.

In the optical line test monitoring system,
The first section is a section calculated based on a function consisting of the pulse width of the test light, the light intensity of the backscattered light before and after the Fresnel reflection, the intensity of the Fresnel reflection, and the response characteristic of the light receiving unit of the optical test means. An optical line test monitoring system characterized by the above.

In the optical line test monitoring system,
The optical line test monitoring system further comprises means for leaving a part of measurement data of Fresnel reflection in the first measurement data.

Another optical line characteristic analysis method according to the present invention that solves the above problems is as follows.
Inserting an optical coupling / branching means for inputting / outputting test light in the vicinity of one transmission device of the optical line whose both ends are connected to the transmission device,
A test light reflecting means that transmits the communication light and reflects the test light is inserted immediately before the other transmission device,
The test light from the optical test means for measuring the optical characteristics consisting of the distance and light intensity of the optical line is incident on the optical line through the optical coupling / branching means,
Backscattered light and Fresnel reflected light intensity generated by the test light until reaching the test light reflecting means, and the test light reflected by the test light reflecting means, and further reflected by the test light reflecting means The light intensity of the backscattered light and the Fresnel reflection is measured by the light test means,
In the measurement data measured by the optical test means, the first section located behind the Fresnel reflection is positioned in front of the Fresnel reflection measured at a symmetrical distance with the measurement data in the test light reflection means as the center. By replacing the measurement data of two sections and analyzing the backscattering level,
An optical line characteristic analysis method characterized in that the optical characteristic composed of the distance and light intensity of the optical line is analyzed without an unmeasurable interval.

Also, in the method for analyzing optical line characteristics,
The first section is a section calculated based on a function consisting of the pulse width of the test light, the light intensity of the backscattered light before and after the Fresnel reflection, the intensity of the Fresnel reflection, and the response characteristic of the light receiving unit of the optical test means. This is an optical line characteristic analysis method characterized by the above.

Another optical line test and monitoring system according to the present invention that solves the above problems is as follows.
Optical coupling / branching means for inserting and outputting test light, both ends of which are inserted in the vicinity of one transmission device of an optical line connected to the transmission device,
A test light reflecting means that is inserted immediately before the other transmission device and transmits the communication light and reflects the test light;
In an optical line test monitoring system having an optical test means for measuring optical characteristics consisting of a distance and light intensity of the optical line,
The test light from the optical test means is incident on the optical line via the optical coupling / branching means,
Backscattered light and Fresnel reflected light intensity generated by the test light until reaching the test light reflecting means, and the test light reflected by the test light reflecting means, and further reflected by the test light reflecting means The light intensity of the backscattered light and the Fresnel reflection is measured by the light test means,
In the measurement data measured by the optical test means, the first section located behind the Fresnel reflection is positioned in front of the Fresnel reflection measured at a symmetrical distance with the measurement data in the test light reflection means as the center. By replacing the measurement data of two sections and analyzing the backscattering level,
An optical line test monitoring system characterized in that the optical line is monitored by analyzing an optical characteristic composed of a distance and light intensity of the optical line without an unmeasurable interval.

In the optical line test monitoring system,
The first section is a section calculated based on a function consisting of the pulse width of the test light, the light intensity of the backscattered light before and after the Fresnel reflection, the intensity of the Fresnel reflection, and the response characteristic of the light receiving unit of the optical test means. An optical line test monitoring system characterized by the above.

  Another optical line test and monitoring system that solves the above-described problems includes an optical characteristic analysis means for the optical line, and an operation means (operation terminal) that is operated remotely via a communication network, and an operation means. And a test control means for controlling various test apparatuses and transmitting the test result of the optical test means to the operation means.

According to the present invention described above,
Optical characteristics such as a connection loss at a connection point of an optical fiber that is an optical line and a loss in an optical fiber section can be calculated without an unmeasurable section.

  In addition, by defining the section calculated based on the function consisting of the pulse width of the test light, the light intensity of the backscattered light, the intensity of Fresnel reflection, and the response characteristic of the light receiving unit of the optical test means as an unmeasurable section. By replacing an appropriate section according to the response characteristic of the measuring instrument, it becomes possible to more optimally measure the optical characteristic composed of the distance and the light intensity of the optical line without an unmeasurable section.

  In addition, even when there is a connector connection point in the middle of the optical line in an optical pulse test from one end of the optical line (including the case where the optical coupler is interposed in the middle of the optical line and incident from the middle of the optical line) In addition, it is possible to measure the optical characteristics including the distance and the light intensity of the optical line with high accuracy by eliminating the section where the OTDR waveform cannot be acquired due to the mask setting and the section where measurement cannot be performed due to the tailing of Fresnel reflection.

  As a result, in the optical pulse test at the time of optical fiber cable construction work or failure occurrence, compared to the conventional one-end measurement, it is possible to eliminate the unmeasurable section due to the tailing of the Fresnel reflection, etc. It is possible to more accurately determine the quality of the loss in the optical fiber section. Moreover, it is not necessary to perform an optical test from both ends of the optical fiber cable.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a graph showing an OTDR waveform when an optical characteristic of an optical line is measured in association with a position in an optical fiber. As shown in the figure, as the optical fiber 5, an optical line in which two optical fibers 5a and 5b are connected by connectors and a termination filter 22 using an FBG type optical filter is installed at a far end is used. . The incident end side of the optical fiber 5 with respect to the connector connection point 20 is defined as an optical fiber 5a, and the termination filter 22 side of the connector connection point 20 is defined as an optical fiber 5b.

  Two waveforms, waveform A (first measurement data) in section A and waveform B (second measurement data) in section B, appear around termination filter 22. A waveform A is a waveform in which the back scattered light of the light pulse incident from the OTDR and the Fresnel reflection at the incident end and the connector connection point 20 are measured.

  The waveform B is a waveform obtained by receiving and measuring the backscattered light of the light pulse once reflected by the termination filter 22 by the OTDR after being reflected again by the termination filter 22. Therefore, on the time axis, the fiber reaches the OTDR with a deviation of the length of the measured optical fiber, so that the fiber is folded at the end of the optical fiber (termination filter 22 portion) as shown in FIG. A waveform like this appears. That is, an OTDR waveform equivalent to that obtained by measuring the received light intensity by inputting a light pulse from the opposite end of the optical fiber to be measured, that is, the termination filter 22 side, is obtained.

  Here, if the transmission loss of the optical fiber 5 and the connector connection point 20 is Lf, and the reflection loss of the FBG type optical filter is Lrl, the difference of the transmission loss Lf in the section A, the reflection of the FBG type optical filter in the termination filter 22 A step corresponding to the loss Lrl is made, and thereafter, a difference corresponding to the transmission loss Lf is made in the section B.

  Since the reflection of the FBG type optical filter is about −1 dB, the level difference due to the reflection at the termination filter 22 that is the FBG type optical filter is as small as about 1 dB. As the termination filter 22, not only the FBG type optical filter but also any other optical filter, for example, a dielectric multilayer film type optical filter, can be used as long as it reflects an optical pulse serving as test light with high efficiency and has a small reflection loss. Etc. can also be used.

  A method of analyzing the optical characteristics of the optical line will be described using the waveform A and the waveform B shown in FIG. 1 without the influence of Fresnel reflection at the connector connection point 20, that is, without an unmeasurable interval. 2 shows an OTDR waveform around the Fresnel reflection at the connector connection point 20 and its tailing in the waveform A (FIG. 2A), and the Fresnel reflection at the connector connection point 20 in the waveform B and the periphery of the tailing. It is the graph which showed the OTDR waveform (FIG.8 (b)) of this in association with the position in an optical fiber.

  In the waveform A of FIG. 2A, a section (first section) in which the received light intensity of the backscattered light cannot be measured accurately due to Fresnel reflection at the connector connection point 20 and its tail is a section where the backscattered light cannot be measured. This is defined as section X. The waveform B in FIG. 2B is an OTDR waveform equivalent to that measured by inputting an optical pulse from the termination filter 22 side, so that the waveform B corresponding to the section X that cannot be measured in the waveform A is obtained. The light receiving intensity of the backscattered light in the section X (second section) is accurately measured.

  Therefore, it is possible to regard the received light intensity of the backscattered light in the above-mentioned section in the waveform B as the received light intensity of the backscattered light in the section X in which the waveform A cannot be measured, and by analyzing the waveform B, Using OTDR from one end, it is possible to measure the optical characteristics of the optical line without an unmeasurable interval.

  Further, the measurement data of the waveform B is extracted, and the measurement data is converted (conversion means) so as to match the received light intensity of the backscattered light in the section X where the waveform A cannot be measured. By replacing the measurement data of the section X, as shown in FIG. 3, it is possible to acquire an OTDR waveform without an unmeasurable section. In the case of FIG. 3, in order to leave the information on the amount of reflection of Fresnel reflection at the connector connection point 20, the waveform of the Fresnel reflection portion is the waveform A (means for leaving part of the measurement data).

  Hereinafter, a procedure for replacing the waveform in the non-measurable section with respect to the entire OTDR waveform will be described. In the OTDR waveform shown in FIG. 4, Fresnel reflection A (within waveform A) and Fresnel reflection B (within waveform B) appear at symmetrical distances around the Fresnel reflection of the termination filter 22. Fresnel reflection A and Fresnel reflection B at symmetrical distances correspond to waveforms when the same connector connection point 20 is measured from the incident end side and from the termination filter 22 side, respectively.

  Here, since the Fresnel reflection A and the Fresnel reflection B are in symmetrical positions, the waveform of the tailing portion of the Fresnel reflection A (that is, the unmeasurable section on the right side of the reflection A) is backscattered immediately before the Fresnel reflection B. Replace with the light level (i.e., the left section of reflection B). This result is represented by the replaced waveform W1 in the figure.

  Next, the backscattered light level of the replaced waveform W1 is corrected by DL corresponding to the line loss. This result is represented by a waveform W2 whose level is corrected in the drawing. Next, the level-corrected waveform W2 is inverted to match the measurement direction. This result is represented by a waveform W3 whose level is inverted in the figure. By replacing the waveform W3 obtained as a result of the above conversion with that of the same section in the waveform A, an OTDR waveform of the connector connection point that eliminates the non-measurable section due to Fresnel reflection is obtained.

  An example of a specific method for converting OTDR measurement data will be described below with reference to FIGS. 4, 5, and 6. First, as shown in FIG. 4, when the number of data measurement points of the OTDR waveform consisting of the waveform A and the waveform B is 2N + 1, the data measurement points are numbered 0 to N-1 as waveform A, and the data measurement points are Waveform B is from N + 1 to 2N.

  Since the data measurement points at symmetrical distances in the waveform A and the waveform B with respect to the data measurement point N at the reflection point in the termination filter 22 are the numbers Ni and N + i, respectively, the numbers Ni and N + i The measurement data P (N−i) and P (N + i) in the number can be replaced as the measurement data at the same point in the optical fiber. Here, i is an integer of 1 to N.

<Determining the section to be replaced>
First, a section to be replaced in the waveform A is determined (Step 1 in FIG. 6). Here, a section X that cannot be measured due to Fresnel reflection is a section to be replaced. Assuming that the start point and end point of the data measurement points of the section X in the waveform A that cannot be measured are the NK number and the NL number (K and L are positive integers, K> L), the section X These data measurement points can be expressed as N−j (j is an integer and L ≦ j ≦ K).

  The data measurement point in the waveform B corresponding to the data measurement point N−j in the section X is the number N + j, and the section in the waveform B corresponding to the section X in the waveform A is a set of the data measurement points N + j. It becomes.

<Waveform replacement>
When the measurement data of the reflection amount at the data measurement point x is P (x), the measurement data at the data measurement point Nj in the section X of the waveform A can be expressed as P (Nj). Therefore, in the waveform obtained by replacing the measurement data in the section X of the waveform A with the measurement data in the corresponding section in the waveform B (“replaced waveform W1” in FIG. 4), P (N−j) is changed to P (N + j). It will be replaced. As shown in step 2 in FIG. 6, when the replaced measurement data is P1 (N−j), it can be expressed as P1 (N−j) = P (N + j) (where L ≦ j ≦ K).

<Correction of waveform>
Next, the “replaced waveform W1”, which is a set of measurement data of the replaced waveform B, is corrected so as to coincide with the Rayleigh backscattered light level in the waveform A (step 3 in FIG. 6). This correction method will be described with reference to FIG.

  The joint of “replaced waveform W1” to waveform A is the end point of section X in waveform A where measurement is impossible. Assuming that the loss difference between the data measurement point N−L as the joint and the data measurement point N + L in the waveform B corresponding to this connection is DL, the data P1 (replacement of the measurement data P (N + j) in the waveform B) By adding the loss difference DL to N−j), it is possible to correct the backscattered light level in the waveform A.

  Therefore, when “level corrected waveform W2” obtained by correcting the backscattered light level of “replaced waveform W1” is P2 (N−j), P2 (N−j) = P1 (N−j) + DL. Where L ≦ j ≦ K. The loss difference DL can also be obtained by using numerical values obtained from the approximate straight line of the backscattered light level in the waveform A and the waveform B.

<Invert waveform>
Next, the level of the Rayleigh backscattered light is inverted for the “level corrected waveform W2” so as to correspond to the measurement direction (step 4 in FIG. 6). This level inversion method will be described with reference to FIG.

  Here, the data measurement point that becomes the contact point between the level-corrected waveform W2 and the Rayleigh backscattered light level of the waveform A is the NL number. Therefore, in the level-corrected waveform P2 (Nj) of the waveform W2, Rayleigh backscattering is performed by inverting the backscattered light level up and down with reference to P2 (NL) corresponding to the NL data measurement point. The inclination of the light level can be corrected so as to correspond to the OTDR waveform in the measurement direction measured from the incident end side.

  Therefore, a waveform (level-inverted waveform W3) obtained by vertically inverting the backscattered light level with P2 (N−j) of the level-corrected waveform W2 as a reference is set to P3 (N−j). ), P3 (Nj) = P2 (Nj) + 2 × (P2 (NL) −P2 (Nj)), that is, P3 (N−j) = 2 × P2 (N−L) −P2 (N−j ).

<Waveform replacement>
Replacing P (Nj) of the waveform of data measurement point Nj in waveform A with P3 (Nj) of waveform W3 obtained by level inversion obtained by the above-described procedure (step 5 in FIG. 6). Thus, an OTDR waveform without an unmeasurable interval as shown in FIG. 4 can be obtained.

  Here, as shown in FIG. 3, when the measurement information of the Fresnel reflection level in the OTDR waveform is held, the waveform of the Fresnel reflection portion needs to be the waveform A. Therefore, the data measurement points NK to OTDR pulse width (pw + 1 in terms of the number of data measurement points), that is, data measurement points NK to NK + pw are replaced. By using the measurement data P (NK) to P (N−K + pw) without using the data P3 (N−j), an OTDR waveform as shown in FIG. 7 is obtained. Note that the number of data measurement points pw varies depending on the OTDR pulse width.

  As described above, by performing the above-described waveform processing on all Fresnel reflections in the section of the waveform A, that is, the section from the incident end to the termination filter 22, over the entire length of the optical line (optical fiber 5). Thus, an OTDR waveform without an unmeasurable interval can be obtained.

<Method of determining the length of an unmeasurable section>
Next, a method for determining the section length of the section X where the Rayleigh backscattered light cannot be measured in the waveform A will be described. In JIS-C6185, a section where the difference between the waveform due to Fresnel reflection and the approximate straight line of the backscattered light located behind it is 0.1 dB or more is defined as a dead zone and spatial resolution.

  Therefore, as shown in FIG. 8, the difference between the approximate curve of the backscattered light located behind the Fresnel reflection (the right side of the reflection in the drawing) and the trailing waveform of the Fresnel reflection is a certain threshold value (for example, JIS- In C6185, a section of 0.1 dB) or more can be defined as a section in which the Rayleigh backscattered light level cannot be measured. This section also includes a Fresnel reflection waveform (width is equal to OTDR pulse width) at a connector or the like.

A method of determining the section length of the section X incapable of measurement based on the response characteristics of the OTDR light receiving device in the present embodiment will be described with reference to FIG. When the response characteristic of the OTDR light receiving device is approximated as a first-order low-pass filter, the temporal change Pref (t) of the fringe reflection tailing at the connector connection point 20 is considered to be the impulse response of the light receiving device. Accordingly, when t = 0 when the optical pulse having the pulse width τ [S] completely passes through the connector connection point 20, it can be expressed by the following equation (1).

  Here, δ [dB] is the height δ [dB] of Fresnel reflection in the OTDR waveform, and is the height of reflection from the Rayleigh backscattered light level immediately before Fresnel reflection. BW is the band of the OTDR light receiving device (high-band cutoff frequency, that is, a frequency that is 3 dB down in the frequency characteristics), and ρ [dB] is the difference in the Rayleigh backscattered light level before and after Fresnel reflection.

  In order to simplify the model, the Rayleigh scattering coefficients of the optical fibers around the connector connection point 20 are the same, and the Rayleigh backscattered light level behind the reflection at the connector connection point 20 is also constant.

Next, a section in which the difference between the Rayleigh backscattered light level located behind the Fresnel reflection and the trailing waveform of the Fresnel reflection is equal to or greater than a certain threshold Th [dB] is defined as an unmeasurable section. In this case, the distance corresponding to the time t satisfying the following expressions (2) and (3) is a non-measurable section.

When the above formulas (2) and (3) are converted, the following formula (4) is obtained.

In consideration of the definition of t, the time obtained by converting the time obtained by adding the pulse width τ of OTDR to the above equation (4) into the distance is the actual unmeasurable interval Lref [m]. Therefore, if the speed of light in vacuum is c and the refractive index of the core of the optical fiber is n, the unmeasurable interval Lref is expressed by the following equation (5).

  As a result, the band BW of the OTDR light receiving device, the height δ of the Fresnel reflection at the connector connection point 20, the difference ρ of the Rayleigh backscattered light level before and after the Fresnel reflection (that is, the connection loss at the connector connection point 20), and the OTDR The unmeasurable interval Lref can be defined by the optical pulse width τ. In addition, by approximating the response characteristics of the OTDR light receiving device with a higher-order filter, it becomes possible to define the measurement impossible section more accurately.

It is a figure which shows 0 TDR waveform of the optical line which installed the FBG type | mold termination filter in the termination | terminus. It is a figure which shows the OTDR waveform of each area of the optical line which installed the FBG type | mold termination filter in the termination | terminus. It is a figure which shows the OTDR waveform which performed the waveform processing which concerns on embodiment, and was the OTDR waveform which eliminated the measurement impossible area, and left the information of the amount of reflections of Fresnel reflection. It is a figure explaining the analysis method using the backscattered light of a reflected pulse. It is a figure explaining the inversion method of the backscattered light level of a reflected pulse. It is a flowchart explaining the analysis method using the backscattered light of a reflected pulse. It is a figure explaining the method of hold | maintaining the measurement information of Fresnel reflection and performing a waveform process. It is a figure explaining the definition method of an unmeasurable area. It is a figure explaining the method to calculate an unmeasurable area from the response characteristic of the light receiving device of OTDR. It is a schematic block diagram of the conventional optical line test monitoring system. It is a schematic block diagram of the optical coupler module installed in an optical termination. It is a figure which shows the transmission loss spectrum of a dielectric multilayer filter and a FBG filter. It is a figure which shows the OTDR waveform of the optical line which installed the optical connector in the termination | terminus. It is a figure which shows the OTDR waveform at the time of setting a mask.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Communication equipment building 2 Transmission equipment 3 User building 4 Transmission equipment 5 Optical fiber 6 Equipment management center 7 Database 8 Operation terminal 9 Communication network 10 Optical coupler 11 Optical filter 12 Optical coupler module 13 Termination filter 14 Optical termination 15 Optical test equipment 16 Core selection device (FS)
17 FTES
18 Optical Measuring Device 19 Test Control Device A to D Port 20 Connector Connection Point 21 Terminal Optical Connector 22 Termination Filter

Claims (17)

In the optical line characteristic analysis method for analyzing the optical characteristics in the optical line from one end of the optical line to the test light reflecting means provided in the optical line by the test light incident from the one end,
Before the test light reflected by the test light reflecting means returns to the one end, the backscattered light and Fresnel reflection measurement data generated by the test light and reflected by the test light reflecting means are used. do it,
An optical line characteristic analysis method, comprising: analyzing an optical characteristic of the optical line. In the optical line characteristic analysis method for analyzing the optical characteristics in the optical line from one end of the optical line to the test light reflecting means provided in the optical line by the test light incident from the one end,
First measurement data of backscattered light and Fresnel reflection generated before the incident test light reaches the test light reflecting means,
Second measurement data of backscattered light and Fresnel reflection generated by the test light and reflected by the test light reflecting means until the test light reflected by the test light reflecting means returns to the one end. To convert,
An optical line characteristic analysis method, comprising: analyzing an optical characteristic of the optical line. In the optical line characteristic analysis method according to claim 2,
The conversion of the first measurement data using the second measurement data is as follows:
A first section located behind the Fresnel reflection in the first measurement data,
In the second measurement data, the conversion is performed by replacing with a second section located in front of the Fresnel reflection measured at a distance symmetrical to the first section with the measurement data in the test light reflecting means as the center. Analysis method of optical line characteristics. In the optical line characteristic analysis method according to claim 3,
The transformation for replacing the first interval with the second interval is:
The measurement data of the second section is replaced with the measurement data of the first section, the level correction of the measurement data of the second section, and the inversion corresponding to the measurement direction of the measurement data of the second section. An optical line characteristic analysis method characterized by: In the method for analyzing optical line characteristics according to claim 3 or 4,
The first section is a dead zone that is located behind the Fresnel reflection and incapable of measuring backscattered light. In the analysis method of the optical line characteristic in any one of Claims 3 thru | or 5,
The first section is a section calculated based on a function consisting of the pulse width of the test light, the light intensity of the backscattered light before and after the Fresnel reflection, the intensity of the Fresnel reflection, and the response characteristic of the light receiving unit of the optical test means. An optical line characteristic analysis method characterized by the above. In the analysis method of the optical line characteristic in any one of Claims 2 thru | or 6,
A method of analyzing optical line characteristics, wherein a part of measurement data of Fresnel reflection in the first measurement data is left. In the optical line test monitoring system for analyzing the optical characteristics of the optical line from one end of the optical line to the test light reflecting means provided in the optical line by analyzing the test light incident from the one end, and monitoring the optical line,
Means for entering test light from one end of the optical line;
First measurement data of backscattered light and Fresnel reflection generated before the incident test light reaches the test light reflecting means;
Second measurement data of backscattered light and Fresnel reflection generated by the test light and reflected by the test light reflecting means until the test light reflected by the test light reflecting means returns to the one end. Means for measuring
Means for converting the first measurement data by using the second measurement data. In the optical line test monitoring system according to claim 8,
The means for converting the first measurement data includes:
A first section located behind the Fresnel reflection in the first measurement data,
The second measurement data is a means for replacing the second measurement data with a second section located in front of the Fresnel reflection measured at a distance symmetrical to the first section with the measurement data in the test light reflecting means as the center. Optical line test monitoring system. In the optical line test monitoring system according to claim 9,
The means for replacing the first section with the second section is:
A means for replacing the measurement data of the second section with the measurement data of the first section, a level correction means for the measurement data of the second section, and an inversion means corresponding to the measurement direction of the measurement data of the second section; An optical line test monitoring system comprising: In the optical line test monitoring system according to claim 9 or 10,
The optical section test and monitoring system, wherein the first section is a dead zone located behind the Fresnel reflection and incapable of measuring backscattered light. In the optical line test monitoring system according to any one of claims 9 to 11,
The first section is a section calculated based on a function consisting of the pulse width of the test light, the light intensity of the backscattered light before and after the Fresnel reflection, the intensity of the Fresnel reflection, and the response characteristic of the light receiving unit of the optical test means. An optical line test monitoring system characterized by that. In the optical line test monitoring system according to any one of claims 8 to 12,
The optical line test and monitoring system further comprises means for leaving a part of measurement data of Fresnel reflection in the first measurement data. Inserting an optical coupling / branching means for inputting / outputting test light in the vicinity of one transmission device of the optical line whose both ends are connected to the transmission device,
A test light reflecting means that transmits the communication light and reflects the test light is inserted immediately before the other transmission device,
The test light from the optical test means for measuring the optical characteristics consisting of the distance and light intensity of the optical line is incident on the optical line through the optical coupling / branching means,
Backscattered light and Fresnel reflected light intensity generated by the test light until reaching the test light reflecting means, and the test light reflected by the test light reflecting means, and further reflected by the test light reflecting means The light intensity of the backscattered light and the Fresnel reflection is measured by the light test means,
In the measurement data measured by the optical test means, the first section located behind the Fresnel reflection is positioned in front of the Fresnel reflection measured at a symmetrical distance with the measurement data in the test light reflection means as the center. By replacing the measurement data of two sections and analyzing the backscattering level,
An optical line characteristic analysis method, comprising: analyzing an optical characteristic composed of a distance and light intensity of the optical line without an unmeasurable interval. In the analysis method of the optical line characteristic of Claim 14,
The first section is a section calculated based on a function consisting of the pulse width of the test light, the light intensity of the backscattered light before and after the Fresnel reflection, the intensity of the Fresnel reflection, and the response characteristic of the light receiving unit of the optical test means. An optical line characteristic analysis method characterized by the above. Optical coupling / branching means for inserting and outputting test light, both ends of which are inserted in the vicinity of one transmission device of an optical line connected to the transmission device,
A test light reflecting means that is inserted immediately before the other transmission device and transmits the communication light and reflects the test light;
In an optical line test monitoring system having an optical test means for measuring optical characteristics consisting of a distance and light intensity of the optical line,
The test light from the optical test means is incident on the optical line via the optical coupling / branching means,
Backscattered light and Fresnel reflected light intensity generated by the test light until reaching the test light reflecting means, and the test light reflected by the test light reflecting means, and further reflected by the test light reflecting means The light intensity of the backscattered light and the Fresnel reflection is measured by the light test means,
In the measurement data measured by the optical test means, the first section located behind the Fresnel reflection is positioned in front of the Fresnel reflection measured at a symmetrical distance with the measurement data in the test light reflection means as the center. By replacing the measurement data of two sections and analyzing the backscattering level,
An optical line test / monitoring system, wherein the optical line is monitored by analyzing optical characteristics including the distance and the light intensity of the optical line without an unmeasurable interval. The optical line test and monitoring system according to claim 16,
The first section is a section calculated based on a function consisting of the pulse width of the test light, the light intensity of the backscattered light before and after the Fresnel reflection, the intensity of the Fresnel reflection, and the response characteristic of the light receiving unit of the optical test means. An optical line test monitoring system characterized by that.

Images