JP2015152399A - Fiber optic characteristic analysis apparatus and fiber optic characteristic analysis method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fiber optic characteristic analysis apparatus with improved detection sensitivity.SOLUTION: In testing loss distribution of a target fiber optic 20, test optical pulses with a wavelength shorter than a cutoff wavelength are used, and the pulses are incident on the target fiber optic 20 in either a reference mode LP01 or a higher mode LP11. When the test optical pulses propagate through the target fiber optic 20, back scattering light is generated at each position, and its optical strengths in the reference mode LP01 and the higher mode LP11 are separated by a mode multiplexer/demultiplexer 14. The separated back scattering light strength in each mode is received at optical receivers 15, 17, and each output voltage at the optical receivers 15, 17 is analyzed. Thereby, individual loss distribution of the target fiber optic 20 in the reference mode and the higher mode is obtained.

Description

  The present invention relates to a technique for detecting optical fiber characteristics (for example, the position of a bend, the position of a connector, or the presence or absence of a connection point by fusion).

  In an optical communication system, an optical fiber as a transmission medium is tested by various methods. For example, by detecting backscattered light or Fresnel reflected light of Rayleigh scattered light derived from light propagating in the optical fiber, transmission loss distribution in the longitudinal direction of the optical fiber and return loss at the connection point can be obtained. . Based on the result, it is possible to specify the loss due to bending, the position of the connector connection point, the reflection point, and the like. An optical fiber characteristic analysis device (optical fiber line distribution measurement device) using such a principle is known. The optical fiber characteristic analysis device can be used to detect an abnormality such as a breakage or failure of the optical fiber and specify the position thereof.

  As optical fiber characteristic analyzers, OTDR (Optical Time Domain Reflectometer) and OFDR (Optical Frequency Domain Reflectometer) are famous. The OTDR acquires distribution data based on the round trip time of the pulsed test light. OFDR uses the frequency-modulated test light to analyze the modulation frequency and acquire position information.

  By the way, the detection sensitivity of the optical fiber characteristic analyzer is limited. That is, it is not possible to detect an abnormality that has an effect lower than the detection sensitivity. For example, a bending point with a large bending radius, a normally fused connection point, or a connection point with an APC (Angled Physical Contact) polished connector that suppresses the return loss has only a slight loss (reflection). It is only generated. In other words, the loss and reflection that occur in these places are smaller than the detection sensitivity of the existing optical fiber characteristic analyzers, so it is difficult to detect anomalies.

  By the way, it is known that the bending loss of an optical fiber is larger in a higher-order mode than in a fundamental mode. Non-Patent Document 1 discloses a core contrast technique using a higher-order mode. Further, as disclosed in Non-Patent Document 2, it is known that the connector loss of an optical fiber including a higher-order mode increases.

  However, existing optical fiber characteristic analyzers generally use test light having a wavelength longer than the cutoff wavelength of the fiber under test (FUT) in order to propagate the test light in a single mode. is there. For example, if the optical fiber under test is a general single mode fiber, basic modes such as a 1.31 μm band, a 1.49 μm band, a 1.55 μm band, and a 1.65 μm band are employed as test light. The optical fiber characteristic analyzer detects and analyzes the fundamental mode of the return light generated in the optical fiber under test.

  Non-Patent Document 3 discloses an optical fiber line test by OTDR using test light having a wavelength band shorter than the cutoff wavelength of a single mode fiber. However, the technique of Non-Patent Document 3 aims to reduce the influence on communication by test light by using a wavelength outside the light receiving band of the transmission apparatus, and does not aim at improving the accuracy of OTDR.

Mabuchi, Shinzo Ayukawa, Shinichi Aozuma, Yuji Higashi, “Concentration Control Technique for Low Bending Loss Optical Fiber Using Higher Order Mode of Visible Light”, OFT 2012-43, p. 55-60, Optical Fiber Application Study Group, 2012, October Masatoshi Kawase, Mitsutoshi Tachida, Junji Hira, Kazuhiro Serizawa, “Improvement of reproducibility of multimode optical fiber connector loss measurement by excitation mode control”, OFT 2005-88, pp. 15-18, Optical Fiber Application Study Group, 2006, March Yoko Yoshida et al., "A Proposal for Determining Failure of Optical Splitter Using 0.65μm Band OTDR", 2004 IEICE General Conference, B-13-33, pp. 581

As described above, since the detection sensitivity of the existing optical fiber characteristic analyzer is limited, it is not possible to detect an anomaly that has an effect smaller than this sensitivity. It is desired to further improve the detection sensitivity of the optical fiber characteristic analyzer.
The present invention has been made in view of the above circumstances, and an object thereof is to provide an optical fiber characteristic analyzing apparatus and an optical fiber characteristic analyzing method with improved detection sensitivity.

  The optical fiber characteristic analyzer according to the present invention has the following configuration.

  (1) The optical fiber characteristic analyzing apparatus analyzes the intensity distribution with respect to the distance of the return light from the optical fiber under test into which the light is incident. The optical fiber characteristic analyzer includes a generation unit that generates a test optical pulse having a wavelength shorter than the cutoff wavelength of the optical fiber under test, an incident unit that inputs the generated test optical pulse into the optical fiber under test, A separation unit that receives the return light of the test light pulse and separates and outputs the backscattered light in the fundamental mode and the backscattered light in the higher-order mode from the return light, and the rear of the higher-order mode output from the separation unit A high-order mode light-receiving unit that generates a higher-order mode signal by optical / electrical conversion of scattered light, and a signal processing unit that analyzes the higher-order mode signal and obtains an intensity distribution of the back-scattered light in the higher-order mode To do.

  Therefore, according to (1), a higher-order mode component is extracted on the light receiving side, and an intensity distribution based on higher-order mode backscattered light can be obtained. As a result, the optical fiber characteristics can be detected with higher sensitivity than when the fundamental mode is used.

  (2) In (1), the optical fiber characteristic analyzer further includes a basic mode light receiving unit that generates a basic mode signal by optical / electrically converting backscattered light of the basic mode output from the separation unit. The signal processing unit analyzes the fundamental mode signal and acquires the intensity distribution of the backscattered light in the fundamental mode.

  Therefore, according to (2), it is possible to obtain an intensity distribution based on the backscattered light in the fundamental mode.

  (3) In (1), the optical fiber characteristic analyzing apparatus includes a mode multiplexer / demultiplexer including first, second, and third ports, and the mode multiplexer / demultiplexer is incident on the first port. The test light pulse incident on the optical fiber under test in the fundamental mode from the third port, and the test optical pulse incident on the second port incident on the optical fiber under test in the higher order mode from the third port; The backscattered light in the fundamental mode included in the return light incident on the third port is output from the first port in the fundamental mode, and the backscattered in the higher order mode included in the return light incident on the third port. Light is output from the second port in the basic mode.

  Therefore, according to (3), the fundamental mode and the higher order mode can be separated and received by the mode multiplexer / demultiplexer.

  (4) In the optical fiber characteristic analyzing apparatus, in (3), an optical switch unit that selectively enters the test light pulse generated by the generation unit into either the first port or the second port. It is characterized by comprising.

  Therefore, according to (4), it becomes possible to make the test light pulse of either the fundamental mode or the higher order mode enter the optical fiber under test.

  (5) In the optical fiber characteristic analyzer, the signal processing unit in (1) is characterized in that the bending position of the optical fiber under test is specified based on the intensity distribution of the backscattered light in the higher order mode.

  Therefore, according to (5), the bending position of the optical fiber under test can be specified.

  (6) In the optical fiber characteristic analyzer, in (1), the signal processing unit specifies the position of the connection point by the connector of the optical fiber under test based on the intensity distribution of the backscattered light in the higher order mode. And

  Therefore, according to (6), the position of the connection point by the connector of the optical fiber to be tested can be specified.

  (7) In the optical fiber characteristic analyzer, in (1), the signal processing unit specifies the position of the connection point by fusion of the optical fibers to be tested based on the intensity distribution of the backscattered light in the higher order mode. Features.

  Therefore, according to (7), the position of the connection point by fusion of the optical fiber under test can be specified.

  (8) The optical fiber characteristic analysis method is a method of analyzing the intensity distribution with respect to the distance of return light from the optical fiber under test into which light is incident. The optical fiber characteristic analysis method generates a test optical pulse having a wavelength shorter than the cut-off wavelength of the optical fiber under test, enters the generated optical test light pulse into the optical fiber under test, and determines the fundamental mode from the return light of the optical test pulse. The back-scattered light and the higher-order mode back-scattered light are separated and output, and the higher-order mode signal is generated by optical / electrical conversion of the output higher-order mode back-scattered light. The intensity distribution of the high-order mode backscattered light is obtained by analysis.

  Therefore, according to (8), since the intensity distribution based on the backscattered light in the higher order mode can be obtained, it becomes possible to detect the optical fiber characteristics with higher sensitivity than in the case where the fundamental mode is used.

  According to the present invention, it is possible to extract a higher-order mode component contained in backscattered light and analyze the optical fiber characteristics using this. Accordingly, it is possible to provide an optical fiber characteristic analyzing apparatus and an optical fiber characteristic analyzing method with improved detection sensitivity.

FIG. 1 is a functional block diagram illustrating an example of an optical fiber characteristic analyzing apparatus according to an embodiment. FIG. 2 is a functional block diagram illustrating another example of the optical fiber characteristic analyzer according to the embodiment. FIG. 3 is a diagram for explaining the operation of the mode multiplexer / demultiplexer 14. FIG. 4 is a diagram for explaining the backscattered light generated in the optical fiber under test that has entered a test light pulse having a wavelength shorter than the cutoff wavelength. FIG. 5 is a functional block diagram showing an example of an optical fiber characteristic analyzer capable of measuring the bending loss in the optical fiber 20 to be tested. FIG. 6 is a diagram showing the backscattered light intensity distribution obtained by the optical fiber characteristic analyzing apparatus according to the embodiment in comparison with the intensity distribution by the existing OTDR. FIG. 7 is a graph in which the analysis result of the bending loss with respect to the bending radius R of the measured fiber is plotted for each propagation mode. FIG. 8 is a graph showing an example of a measurement result by an existing OTDR for a non-test optical fiber having a connection point by an APC connector. FIG. 9 is a graph illustrating an example of a result of measurement performed by the optical fiber characteristic analyzer according to the embodiment under the same conditions as the graph of FIG. FIG. 10 is a graph illustrating an example of a result of measurement performed by the optical fiber characteristic analyzer according to the embodiment under the same conditions as the graph of FIG.

  Embodiments of the present invention will be described with reference to the drawings. The embodiment described below is an example of the present invention, and the present invention is not limited to the following embodiment.

  FIG. 1 is a functional block diagram illustrating an example of an optical fiber characteristic analyzing apparatus according to an embodiment. FIG. 1 shows an example of an apparatus capable of injecting basic mode test light into an optical fiber under test. The optical fiber characteristic analyzer shown in FIG. 1 calculates the characteristic of the optical fiber under test 20 by analyzing the intensity distribution with respect to the distance of the return light from the optical fiber under test based on the principle of OTDR.

  In FIG. 1, continuous light output from a light source 11 is pulsed by an optical pulse generator 12. The optical pulse generator 12 is an acousto-optic modulator including an acousto-optic switch configured to drive an acousto-optic element, for example. The test light pulse generated by the optical pulse generator 12 is incident on the Port 1 of the mode multiplexer / demultiplexer 14 via the optical circulator 13. The test light pulse is incident on the optical fiber under test 20 from the port 3 of the mode multiplexer / demultiplexer 14 in the fundamental mode LP01. In the embodiment, the basic mode is expressed as LP01, and the higher order mode is expressed as LP11 to distinguish them.

  In the embodiment, the wavelength of continuous light output from the light source 11 is set to a wavelength at which a higher-order mode can propagate in the optical fiber 20 to be tested. That is, by setting the oscillation wavelength of the light source 11 to a wavelength shorter than the cutoff wavelength of the optical fiber 20 to be tested, the wavelength of the test light pulse is made shorter than the cutoff wavelength of the optical fiber 20 to be tested.

  The backscattered light of the test light pulse generated in the optical fiber 20 to be tested reenters the mode multiplexer / demultiplexer 14 from Port 3. The mode multiplexer / demultiplexer 14 intensity-separates the fundamental mode component LP01 and the higher-order mode component LP11 included in the return light incident from the Port 3. That is, the fundamental mode LP01 of backscattered light is output from Port1, and the higher-order mode LP11 is output from Port2.

  As described above, when the return light including the backscattered light in the fundamental mode and the backscattered light in the higher-order mode is incident from the Port 3 to the mode multiplexer / demultiplexer 14, the light intensity of each mode in the mode multiplexer / demultiplexer 14. Are separated. The basic mode LP01 included in the return light reaches the optical receiver 15 via the optical circulator 13 and is converted into digital data by an A / D (analog / digital) converter 16 after optical / electrical conversion. The high-order mode LP11 reaches the optical receiver 17 from the Port 2 of the mode multiplexer / demultiplexer 14 and is converted into digital data by the A / D converter 18 after optical / electrical conversion.

  Digital data derived from the basic mode (basic mode signal) and digital data derived from the higher order mode (higher order mode signal) are input to the arithmetic processing unit 19. The arithmetic processing unit 19 analyzes the higher order mode signal and acquires the intensity distribution of the backscattered light in the higher order mode. Further, the arithmetic processing unit 19 analyzes the fundamental mode signal and acquires the intensity distribution of the backscattered light in the fundamental mode.

  That is, the arithmetic processing unit 19 performs arithmetic processing on the voltage value of the backscattered light corresponding to each mode to obtain an intensity distribution (synonymous with loss distribution) with respect to the distance. With such a configuration, the loss characteristics in the optical fiber 20 under test can be measured separately for the fundamental mode and the higher-order mode.

  FIG. 2 is a functional block diagram illustrating another example of the optical fiber characteristic analyzer according to the embodiment. FIG. 2 shows an example of an apparatus capable of injecting test light of a higher order mode into the optical fiber under test. The configuration in FIG. 2 corresponds to a configuration in which Port 1 and Port 2 of the mode multiplexer / demultiplexer 14 of the apparatus shown in FIG. 1 are interchanged. According to such a configuration, the fundamental mode test light pulse is incident on the Port 2 of the mode multiplexer / demultiplexer 14. This test light pulse is converted into a higher-order mode and is incident on the optical fiber 20 to be tested from Port 3.

  That is, the mode multiplexer / demultiplexer 14 can selectively enter the test optical pulse of either the fundamental mode or the higher order mode into the optical fiber 20 to be tested. By providing an optical switch (not shown), Port 1 and Port 2 can be optically interchanged, and the same apparatus can be switched to the configuration shown in FIGS.

  The bending loss and connection loss of the test light pulse in the higher mode are larger than the loss of the test light pulse in the fundamental mode. Therefore, by selecting a higher-order mode as the test light pulse, a greater loss can be obtained at the bent portion or the connection portion in the optical fiber to be tested, so that highly sensitive measurement is possible. However, while higher-sensitivity measurement is possible, a greater loss occurs at the bent portion and the connection portion, so that the intensity of backscattered light returning to the device may be lower than the detection sensitivity of the device. In such a case, the basic mode is selected as the test light pulse. Therefore, it is necessary to use different modes of the test light pulse depending on the loss value of the applied line. A configuration using an optical switch is convenient for such an application.

  FIG. 3 is a diagram for explaining the operation of the mode multiplexer / demultiplexer 14. As shown in FIG. 3, the fundamental mode light incident from the Port 1 of the mode multiplexer / demultiplexer 14 is emitted from the Port 3 while remaining in the fundamental mode. The fundamental mode light incident from Port 2 is converted to a higher-order mode and emitted from Port 3. The fundamental mode light incident from Port 3 is emitted from Port 1 while remaining in the fundamental mode. Higher-order mode light incident on Port 3 is converted to a fundamental mode and emitted from Port 2.

  FIG. 4 is a diagram for explaining the backscattered light generated in the optical fiber 20 under test that has been irradiated with a test light pulse having a wavelength shorter than the cutoff wavelength. When the test light pulse propagates through the optical fiber 20 under test, Rayleigh scattering occurs at various locations of the optical fiber 20 under test. A part of this Rayleigh scattering is coupled to the fundamental mode and higher order mode propagating in the direction of the incident end, and thereby the fundamental mode and higher order mode of the backscattered light are generated.

  FIG. 5 is a functional block diagram showing an example of an optical fiber characteristic analyzer capable of measuring the bending loss in the optical fiber 20 to be tested. Based on the configuration shown in FIG. 1, it is assumed that the total length of the optical fiber 20 to be tested is about 1 km, and a bend with a radius R is applied to a position about 500 m from the end point. In the measurement system of FIG. 5, a test light pulse having a wavelength of 1050 nm was incident in the fundamental mode. The spatial resolution was 5 m. If the optical fiber 20 under test is bent by one turn with a radius of 15 mm, a measurement result as shown in FIG. 6 can be obtained.

  FIG. 6 shows the backscattered light intensity distribution obtained by the measurement system shown in FIG. FIG. 6A shows the backscattered light intensity distribution in the fundamental mode. FIG. 6B shows the backscattered light intensity distribution in the higher order mode. FIG. 6C shows a backscattered light intensity distribution at a wavelength of 1650 nm measured using an existing OTDR for comparison.

  The horizontal axis of each graph in FIGS. 6A to 6C indicates the distance at which backscattered light is generated in the optical fiber 20 to be tested. The vertical axis represents the backscattered light intensity in each mode. Comparing FIG. 6A and FIG. 6B, it can be seen that the loss in the vicinity of the bending portion with respect to the backscattered light intensity is larger in the higher-order mode than in the fundamental mode.

  FIG. 7 is a graph in which the analysis result of the bending loss with respect to the bending radius R of the measured fiber is plotted for each propagation mode. FIG. 7 shows that the test light with a wavelength of 1050 nm changes more sensitively in the higher order mode than in the fundamental mode. Even when compared with the result of OTDR measurement using the test light of the fundamental mode of 1650 nm, it can be seen that the bending loss is higher in the higher-order mode than in the fundamental mode. From the above results, it can be seen that by measuring the loss distribution characteristic of the higher-order mode, it is possible to detect with high sensitivity a bend that cannot be detected by normal OTDR measurement.

  In general, when a test light pulse is incident on the measured fiber in the fundamental mode, it propagates in the fundamental mode up to the position where the scattering occurs, and the higher-order mode until it returns from the position where the backscattered light in the higher order mode occurs to the incident end. Propagate in mode. Therefore, the change in the backscattered light intensity in the higher order mode means the average of the loss of the fundamental mode light propagating through the optical fiber under test and the loss of the higher order mode light. This is also reflected in the graph of FIG.

  FIG. 8 is a graph showing an example of a measurement result by an existing OTDR for a non-test optical fiber having a connection point by an APC polished connector. Two optical fibers of the same standard of about 0.45 km were connected by an APC polished connector to form a 0.9 km optical fiber to be measured, and a loss distribution of backscattered light with respect to the optical fiber to be measured was obtained.

  9 and 10 are graphs showing examples of measurement results for the non-test optical fiber under the same conditions as in FIG. 8 by the optical fiber characteristic analyzer according to the embodiment. FIG. 9 shows the measurement result of the fundamental mode LP01 component of the backscattered light. FIG. 10 shows the measurement result of the higher-order mode LP11 component of the backscattered light.

  From the graphs of FIGS. 8 and 9, it can be seen that the connection position of the APC connector that should be present at 0.45 km cannot be clearly confirmed. In contrast, the graph of FIG. 10 shows that a loss of 0.4 dB can be observed in the vicinity of 0.45 km. That is, it can be seen that the measurement method of the embodiment using the higher-order mode LP11 component realizes higher detection sensitivity than the existing technology.

  As described above, in this embodiment, in the loss distribution test of the optical fiber 20 under test, a test optical pulse having a wavelength shorter than the cutoff wavelength is used, and this is applied in either the fundamental mode LP01 or the higher-order mode LP11. The light enters the test optical fiber 20. The mode multiplexer / demultiplexer 14 separates the light intensities of the fundamental mode LP01 and the higher-order mode LP11 of backscattered light generated at various points when the test light pulse propagates through the optical fiber 20 to be tested. The separated backscattered light intensity of each mode is individually received by the optical receivers 15 and 17, and the output voltages of the optical receivers 15 and 17 are analyzed, so that the fundamental mode in the optical fiber 20 to be tested and Individual loss distributions of higher order modes are required.

  Therefore, according to the embodiment, based on the loss distribution characteristic of the higher-order mode, it is possible to detect the bend (and its position) that cannot be detected from the loss distribution characteristic of the fundamental mode with high sensitivity. It is also possible to specify the connection point and its position by fusion, and the connection point and its position by APC polishing connector connection.

  That is, in the embodiment, the bending loss of the optical fiber is larger in the higher order mode (LP11) than the fundamental mode (LP01), and the connector loss of the optical fiber is larger in LP11 than in LP01. By focusing on the above and analyzing the LP11 component of the backscattered light, it is possible to obtain a more highly sensitive backscattered light intensity distribution.

  Furthermore, according to the embodiment, it is possible to individually measure the loss distribution characteristics of each mode without mixing the characteristics of a plurality of propagation modes in the optical fiber 20 under test.

  For example, when OTDR measurement is performed on a single mode fiber (SMF) at a wavelength shorter than the cutoff wavelength, since there are a plurality of propagation modes, the transmission speed in the optical fiber to be measured differs, and transmission characteristics such as transmission loss and bending loss. Will be mixed between modes. Therefore, it is difficult to accurately detect abnormal points such as optical fiber transmission loss measurement and bending loss from the OTDR waveform, and it is difficult to obtain individual characteristics of each propagation mode.

  On the other hand, according to the embodiment, since the fundamental mode and the higher order mode are separated by the mode multiplexer / demultiplexer 14, the loss distribution characteristics of each mode can be individually measured.

  Accordingly, it is possible to provide an optical fiber characteristic analyzing apparatus and an optical fiber characteristic analyzing method with improved detection sensitivity.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Moreover, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

  DESCRIPTION OF SYMBOLS 11 ... Light source, 12 ... Optical pulse generator, 13 ... Optical circulator, 14 ... Mode multiplexer / demultiplexer, 15 ... Optical receiver, 16 ... A / D converter, 17 ... Optical receiver, 18 ... A / D conversion 19 ... arithmetic processing unit, 20 ... optical fiber under test

Claims (8)

In an optical fiber characteristic analyzer that analyzes the intensity distribution with respect to the distance of the return light from the optical fiber under test that is incident with light,
A generator for generating a test light pulse having a wavelength shorter than the cutoff wavelength of the optical fiber under test;
An incident portion for injecting the generated test light pulse into the optical fiber under test;
A separation unit that receives the return light of the incident test light pulse and separates and outputs the backscattered light of the fundamental mode and the backscattered light of the higher-order mode from the returned light;
A higher-order mode light-receiving unit that generates a higher-order mode signal by optical / electrically converting the higher-order mode backscattered light output from the separation unit;
An optical fiber characteristic analyzing apparatus comprising: a signal processing unit that analyzes the high-order mode signal and acquires an intensity distribution of the backscattered light in the high-order mode. And a fundamental mode light receiving unit that generates a fundamental mode signal by optical / electrically converting backscattered light of the fundamental mode output from the separation unit,
2. The optical fiber characteristic analyzing apparatus according to claim 1, wherein the signal processing unit analyzes the fundamental mode signal to acquire an intensity distribution of backscattered light in the fundamental mode. Comprising a mode multiplexer / demultiplexer comprising first, second and third ports;
The mode multiplexer / demultiplexer is
The test light pulse incident on the first port is incident on the optical fiber under test in the fundamental mode from the third port;
The test light pulse incident on the second port is incident on the optical fiber under test in a higher order mode from the third port;
Outputting backscattered light of the fundamental mode included in the return light incident on the third port from the first port in the fundamental mode;
2. The optical fiber characteristic according to claim 1, wherein the high-order mode backscattered light included in the return light incident on the third port is output from the second port in a fundamental mode. 3. Analysis device.   The optical switch unit according to claim 3, further comprising an optical switch unit that selectively makes the test light pulse generated by the generation unit incident on either the first port or the second port. The optical fiber characteristic analysis apparatus described.   2. The optical fiber characteristic analysis apparatus according to claim 1, wherein the signal processing unit specifies a bending position of the optical fiber under test based on an intensity distribution of the backscattered light in the higher-order mode.   2. The optical fiber characteristic according to claim 1, wherein the signal processing unit specifies a position of a connection point by a connector of the optical fiber under test based on an intensity distribution of backscattered light in the higher-order mode. Analysis device.   2. The optical fiber according to claim 1, wherein the signal processing unit specifies a position of a connection point by fusion of the optical fiber under test based on an intensity distribution of backscattered light in the higher-order mode. Characteristic analysis device. In the optical fiber characteristic analysis method for analyzing the intensity distribution with respect to the distance of the return light from the optical fiber under test where light is incident,
Generating a test light pulse having a wavelength shorter than the cutoff wavelength of the optical fiber under test;
The generated test light pulse is incident on the optical fiber under test,
Separately output the backscattered light of the fundamental mode and the backscattered light of the higher order mode from the return light of the test light pulse,
A high-order mode signal is generated by optical / electrical conversion of the output backscattered light of the higher-order mode,
An optical fiber characteristic analysis method characterized in that the higher-order mode signal is analyzed to obtain an intensity distribution of the backscattered light in the higher-order mode.

Images