JP4504789B2 - Optical communication system and optical test apparatus - Google Patents

Description

  The present invention relates to an optical communication system and an optical test apparatus used in the optical communication system. In particular, the present invention relates to a technique for testing and monitoring the state of a branched optical line in which an intra-station device and a plurality of subscriber terminals are connected via an optical splitter.

  In the optical communication system, there are a single star (SS) configuration, a passive double star (PDS) configuration, and the like as the form of the optical line connecting the intra-station device and the subscriber terminal. The SS configuration is a form in which one intra-station device and one subscriber terminal are connected by one optical fiber. The PDS configuration is a form in which a branching optical line is formed by an optical splitter provided in the station. As a method for testing such an optical line, a so-called OTDR test method is known in which pulse light is transmitted from a station and reflected light is measured.

  In order to operate the optical communication system soundly, it is indispensable to test the optical line and check the transmission state of the optical signal. This type of test is called a light test. In recent years, a PDS configuration has attracted attention because of a demand for reduction in system installation cost, and among these, a configuration in which an optical branch point is provided near the user's home has become mainstream. A test method for such an optical line is disclosed in Non-Patent Document 1, for example. The existing optical test method will be described below.

  FIG. 11 is a diagram for explaining an example of an existing optical test method. In the system of FIG. 11, the trunk optical fiber 2 drawn from the in-office device 1 is branched to the terminal side optical fibers 4-1 to 4-4 by the optical splitter 3 to form a branched optical line. The terminal side optical fibers 4-1 to 4-4 are connected to the subscriber terminals 5-1 to 5-4, respectively. An optical coupler 9 is inserted between the intra-station device 1 and the trunk optical fiber 2, and the pulsed test light from the optical pulse tester 40 is turned on / off by the optical switch 8, and sent from the optical coupler 9 to the terminal side. Is done.

  At the time of the test, backscattered light or reflected light generated with respect to the test light in each optical fiber is guided to the optical pulse tester 40 through the optical coupler 9 and the optical switch 8, and its intensity spectrum is measured. . Optical filters 6-1 to 6-4 that transmit signal light and block test light are provided at the incident ends of the subscriber terminals 5-1 to 5-4, respectively, and the test light reflects backward. . As the optical filters 6-1 to 6-4, for example, a filter in which a fiber Bragg grating (FBG) is written in an optical fiber core can be used. In the following description, the direction from the intra-station device 1 to each of the subscriber terminals 5-1 to 5-4 is referred to as the downstream side, and the opposite direction is referred to as the upstream side.

  FIG. 12 is a diagram illustrating a configuration example of the optical pulse test apparatus 40. In FIG. 12, the output light of the semiconductor laser 51 is pulse-modulated by an optical modulator 54 to generate pulsed test light. This test light is output from the optical coupler 52 and is incident on the branched optical line via the optical switch 8 and the optical coupler 9 of FIG. A part of this incident light returns by backscattering or reflection in each optical fiber of FIG. 11, and is detected by the light receiving element 53 of FIG. 12 via the optical coupler 9, the optical switch 8, and the optical coupler 52.

  FIG. 13 is a diagram illustrating an example of a waveform measured by the optical pulse test apparatus 40. Since the optical filters 6-1 to 6-4 strongly reflect the test light, a large peak is observed corresponding to the position. Since the intensity of the reflected light is stronger than the backscattering that occurs in the optical fibers 2 and 4, the reflection from each of the optical filters 6-1 to 6-4 can be confirmed from the position of the reflected light peak. It can be used for identifying the terminal side optical fibers 4-1 to 4-4. Incidentally, the distance resolution of the optical pulse test device 40 is about 30 m from a 35 dB Fresnel reflection point with a pulse width of 20 nsec.

  However, in order to identify the terminal side optical fibers 4-1 to 4-4 by the time width of the reflected light peak as described above, it is necessary to individually change the lengths of the terminal side optical fibers 4-1 to 4-4. is there. That is, since the position identification shorter than the reflection distance resolution is impossible in the above method, it is necessary to make the lengths of the terminal side optical fibers 4-1 to 4-4 different from each other by at least about 30 m. There is a problem that the construction work of the cable becomes complicated.

  For example, in FIG. 11, assuming that the line length from the optical splitter 3 to the optical filter 6-1 is substantially equal to the line length from the optical filter 6-4, the two optical filters 6-1 and 6 in the optical pulse test apparatus 40 are used. -4 reflections overlap. That is, when the difference in the positions of the plurality of optical filters is smaller than the time width of the reflected light peak, the positions of the plurality of optical filters are observed only as one peak position. Therefore, even if one of the two terminal side optical fibers 4-1 and 4-4 breaks down and the reflected light disappears, a reflected light peak from the remaining optical fiber exists, so that the occurrence of the failure cannot be detected. . Furthermore, in order to identify the line where reflection or loss has occurred by using this method, it is necessary to register and manage the fact every time the state of each line (length, presence or absence of filter, etc.) is changed. become. Next, other existing optical test methods will be described. The following method is disclosed in Non-Patent Document 2, for example.

  FIG. 14 is a diagram for explaining another example of the existing optical test method. The system of FIG. 14 replaces the optical splitter 3 with an Arrayed Waveguide Grating (AWG) type optical splitter 3 'in the system of FIG. 11, and replaces the optical filters 6-1 to 6-4 with the optical filters 6-1' to 6-4 '. Further, the optical pulse test device 40 is replaced with a variable wavelength variable optical pulse test device 40 '. The variable optical pulse test apparatus 40 ′ switches the output light wavelength stepwise from, for example, λ1 to λ4. These pulsed lights are distributed and output by the optical splitter 3 'according to the wavelength, and reach the optical filters 6-1' to 6-4 'via the terminal side optical fibers 4-1 to 4-4, respectively. Reflected. For example, when test light having a wavelength λ1 is transmitted from the variable optical pulse test apparatus 40 ', the test light is distributed only to the optical fiber 4-1 by the optical splitter 3', so the line condition of the optical fiber 4-1 is monitored. can do. By switching the test light wavelength, the line states of all the optical fibers 4-1 to 4-4 can be monitored.

  However, optical components such as AWG are expensive, and there is a problem that if the temperature change in the installation environment is large, the transmission wavelength drifts, so that correction is required. Of course, the wavelength-tunable optical pulse test apparatus is expensive in itself, and is problematic because it conflicts with the purpose of the PDS configuration that requires economic efficiency.

In addition, in any of the above methods, when Fresnel reflection occurs at the connection point of the optical line, a dead zone (interval that cannot be measured) that exceeds the width of the measured pulse light occurs due to the tailing of the reflection. There is also a problem that the loss of light cannot be determined.
Other related techniques are disclosed in Non-Patent Document 3 below. This document shows the relationship between the refractive index n of an optical fiber and the GeO2 addition concentration w.
I. Sankawa, et.al. "Fault loation technique for in-service branched optical fiber networks", IEEE Photon. Technol. Letter, vol. 2, No. 10, Oct, 1990 K. Tanaka, et.al. "Measuring the individual attenuation distribution of passive branched optical networks", IEEE Photon.Technol.Letter, vol8, No.7, July, 1996 Y. Koyamada et.al., "Simulating and designing Brillouin gain spectrum in single-mode fibers", JLT, Vol. 22 No. 2, February 2004

As described above, the existing optical test technology has a problem that the system arrangement and information management are troublesome, or expensive optical parts are required, so that the system itself is expensive.
The present invention has been made for the above-mentioned circumstances, and the object thereof is to enable inexpensive detection of the position of a failure occurring in an optical line having a PDS configuration regardless of the line length difference from the inside of the station. It is an object to provide an optical communication system and an optical test apparatus capable of efficiently carrying out the above-mentioned at low cost.

In order to achieve the above object, according to one aspect of the present invention, in an optical communication system comprising an intra-station device and an optical branching device that branches a trunk optical fiber extended from the intra-station device into a plurality of branch optical fibers. An optical test device having a light source for generating test light and entering the test light into the trunk optical fiber, wherein at least one of the plurality of branch optical fibers is connected to an end remote from the in-station device. An optical discriminating unit that excites Brillouin scattered light with respect to the test light at an inherent frequency shift different from that of the connected branch optical fiber, and the optical test apparatus arrives via the optical splitter and the trunk optical fiber and observation means for observing the Brillouin scattered light, based on the frequency of the observed Brillouin scattered light, identified individually identify the branch optical fiber with the optical identification unit And the plurality of branch optical fibers are single mode fibers, and the optical identification unit is connected to each branch optical fiber and has a unique refractive index distribution for each branch optical fiber. An optical communication system is provided in which the relative refractive index of the core and the clad in the rare earth-doped optical fiber is equal to that of the single mode fiber.

  By taking such means, Brillouin scattered light having a different frequency shift is excited for each branch optical fiber, and this Brillouin scattered light returns to the optical test apparatus. Therefore, by monitoring the frequency of the Brillouin scattered light, the branch line optical fibers (that is, the terminal side optical fibers) can be individually distinguished. Furthermore, the state of each terminal-side optical fiber can be detected by monitoring the presence or absence of Brillouin scattered light. Therefore, it is not necessary to change or manage the length of the terminal side optical fiber, and it is possible to efficiently perform an optical test by reducing labor. Further, since expensive optical components such as an optical filter and a multi-wavelength compatible optical splitter are not required, the system cost can be easily reduced.

  ADVANTAGE OF THE INVENTION According to this invention, the optical communication system and optical test apparatus which can implement an optical test efficiently at low cost can be provided.

[First Embodiment]
FIG. 1 is a block diagram showing a first embodiment of an optical communication system according to the present invention. In FIG. 1, parts that are the same as those in FIG. 11 are given the same reference numerals, and only different parts will be described here. The system shown in FIG. 1 has a PDS type topology similar to that shown in FIG. 11 except that the optical pulse test apparatus 40 is replaced with the optical test apparatus 7. In-service monitoring is performed in accordance with a command from the in-station device 1 by inserting an optical coupler 9 into the trunk optical fiber 2 on the station side and connecting the measuring device 7 to the optical coupler 9 via the optical switch 8. Can do. In in-service monitoring, test light is sent from the test apparatus 7 to the trunk optical fiber 2 via the optical switch 8 and the optical coupler 9, and the return light from the PDS type optical path passes through the optical coupler 9 and the optical switch 8. And received by the test apparatus 7.

  Further, in FIG. 1, the optical filters 6-1 to 6-4 in FIG. 11 are excluded, and the optical identification markers 10-1 to 10-1 are respectively attached to part of the terminal side optical fibers 4-1 to 4-4 on the subscriber terminal side. 10-4 is formed. The optical identification markers 10-1 to 10-4 are optical fiber members connected (fused) to the respective terminal side optical fibers 4-1 to 4-4, and each have an inherent refractive index distribution. Preferably, the optical identification markers 10-1 to 10-4 are rare-earth doped optical fibers doped with GeO2 or the like in the core. By varying the GeO2 addition concentration, the characteristics of the light identification markers 10-1 to 10-4 can be changed regardless of the length.

  That is, the test light having the optical frequency ν0 incident on the trunk optical fiber 2 interacts with sound waves (phonons) in the optical fiber in the route from the subscriber terminals 5-1 to 5-4. Due to this interaction, a part of the test light is scattered, and its frequency is shifted according to the acoustic velocity of the optical fiber that is the propagation medium, and Brillouin scattered light is generated.

  By changing the refractive index distribution of the optical fiber in such a configuration, the frequency of the Brillouin scattered light can be uniquely set. In this embodiment, the refractive index distribution of each path from the in-station device 1 to each of the subscriber terminals 5-1 to 5-4 is changed by making the refractive index distributions of the optical identification markers 10-1 to 10-4 different. I try to change it.

  FIG. 2 is a functional block diagram showing an embodiment of the optical test apparatus 7 of FIG. In FIG. 2, a test light source 21 continuously generates and outputs test light having an optical frequency ν0. This test light is partially branched at the mouth by the optical coupler 25-1, and local light and probe light are generated. Among these, the probe light is output from the optical coupler 25-2 through the optical fiber and is incident on the trunk optical fiber 2 (FIG. 1).

  The local light is incident on the observation unit 20 that observes the Brillouin scattered light coming through the optical splitter 3 and the trunk optical fiber 2. That is, the Brillouin scattered light generated in FIG. 1 is similarly incident on the observation unit 20 via the optical coupler 25-2. The local light (frequency ν0) and the Brillouin scattered light (frequency ν0 ± νB) are combined by the optical coupler 25-3 and converted from the light receiving element 23 such as a photodiode (PD) into an electric signal including the beat signal νB. . This electric signal is amplified by the amplifier 22 and then input to the spectrum analyzer 30. The electric signal is heterodyne detected by the spectrum analyzer 30. That is, the electric signal is mixed by the mixer 27 with the local signal of the local oscillator (LO) 29 that generates a frequency signal close to νB, and converted into a baseband signal. An unnecessary wave component is removed from the baseband signal by a low-pass filter (LPF) 28, and thereby a beat component based on Brillouin scattered light having a Brillouin frequency shift νB is extracted. This beat component is digitally converted by the A / D converter 31 and given to the control unit 50.

  In order to reduce polarization fluctuation that is likely to occur in heterodyne detection, it is convenient that the local light is incident on the optical coupler 25-3 after passing through the polarization scrambler 24. By combining the Brillouin backscattered light ν0 ± νB and the local light ν0 and performing heterodyne detection, the light receiving element 23 detects the Brillouin scattered light as a beat signal having a frequency νB.

  The control unit 50 includes an identification processing unit 50a, a detection processing unit 50b, and a discrimination processing unit 50c as processing functions according to the present embodiment. The identification processing unit 50a identifies each of the terminal-side optical fibers 4-1 to 4-4 based on the observed frequency of the Brillouin scattered light. The detection processing unit 50b individually detects the states of the identified terminal-side optical fibers 4-1 to 4-4 based on the Brillouin scattered light. The determination processing unit 50c determines the position of the failure in each of the terminal side optical fibers 4-1 to 4-4 based on the center frequency of the sideband of the beat component and its intensity. Next, the operation of the above configuration will be described in detail.

  FIG. 3 is a schematic diagram showing Brillouin backscattered light from the light identification markers 10-1 to 10-4. The four terminal-side optical fibers 4-1 to 4-4 on the downstream side from the optical splitter 3 are measured, and each of the terminal-side optical fibers 4-1 to 4-4 is an optical fiber portion having a common characteristic. And optical identification markers 10-1 to 10-4 having individual characteristics. When the test light ν0 is incident on the branched optical line having this configuration, (ν0 ± νb) Brillouin scattered light is generated in the optical fiber portion. On the other hand, in the light identification markers 10-1 to 10-4, Brillouin scattered light having frequencies (ν0 ± ν1) to (ν0 ± ν4) is individually generated. The Brillouin shift amounts of the respective light identification markers 10-1 to 10-4 are expressed as ν1, ν2, ν3, and ν4, respectively. Therefore, the frequency of the beat signal detected by the optical test apparatus 7 is expressed as νB = ± (νb + ν1 + ν2 + ν3 + ν4).

For example, if the frequency shift amount of Brillouin scattered light when the wavelength λ = 1.55 μm is Δν, Δν is the refractive index of the optical fiber, the acoustic velocity in the longitudinal direction of the fiber is VL, and the test light wavelength λ is the parameter. It is represented by Formula (1).

The refractive index n and VL are determined by the following formulas (2) and (3) based on the GeO 2 addition concentration w [wt%]. Equations (2) and (3) can be derived from Non-Patent Document 3, for example.

  Thus, the Brillouin scattering shift frequency generated by the plurality of light identification markers 10-1 to 10-4 can be measured as a beat signal. When the Brillouin frequency shift generated in each optical fiber on the downstream side from the optical splitter 3 is calculated using the equations (1) to (3), the following values are obtained.

  That is, the GeO 2 addition concentration w of the terminal side optical fibers 4-1 to 4-4 and the optical identification markers 10-1 to 10-4 is set to (3.0), (7.3), (11.6), ( 15.8), (19.9) [wt%], when the test wavelength is 1.55 μm, the refractive index n is (1.462), (1.469), (1.475), ( 1.481) and (1.487). Further, the Brillouin shift amount Δν is (10.97), (10.67), (10.37), (10.07), (9.77) [GHz].

  FIG. 4 is a diagram showing a spectrum of Brillouin backscattered light. When these Brillouin backscattered light is measured in the optical test apparatus 7 (FIG. 1), identification signals having different wavelengths are obtained for the respective optical identification markers 10-1 to 10-4 as shown in FIG. If the optical fiber of the system of FIG. 1 is a single mode fiber, the relative refractive index of the core and the clad should be made equal to that of the single mode fiber by adjusting the GeO 2 addition concentration of each of the optical identification markers 10-1 to 10-4. For example, connection loss due to a difference in mode field diameter can be suppressed. The concentration of GeO2 added to the clad hardly affects the Brillouin shift amount.

  When the temperature changes in the range of -20 to 75 ° C due to environmental fluctuations, the Brillouin frequency fluctuates on the order of about 100 MHz. In order to identify adjacent Brillouin scattered lights having frequency shifts, the respective spectra need to be sufficiently separated.

  Since the frequency band of Brillouin scattered light is about 50 MHz, if the center frequency of the Brillouin frequency shift from the light identification markers 10-1 to 10-4 is maintained at about 0.3 GHz as described above, the light identification marker The Brillouin frequency shift due to 10-1 to 10-4 can be observed with a margin.

  Note that the Brillouin shift frequency of the optical fiber fluctuates not only by temperature change but also by application of tensile strain. By actively utilizing this fact and controlling the tension and temperature, the optical identification markers 10-1 to 10-4 can be given a Brillouin frequency shift. In this case, the core concentration of the light identification markers 10-1 to 10-4 may be constant.

  5 and 6 are schematic diagrams showing beat signal frequencies ν1 to ν4 obtained by heterodyne detection in the optical test apparatus 7 (FIG. 1). FIG. 5 shows a case where none of the terminal side optical fibers 4-1 to 4-4 has any obstacles. In this case, all beat signal frequencies ν1 to ν4 are observed at different spectral positions. FIG. 6 shows a case where a failure that causes excessive loss occurs in the terminal-side optical fiber 4-2. 6 corresponds to a state in which the optical identification marker 10-2 (and the subscriber terminal 5-2) is not connected as shown in FIG. In this case, the beat signal ν2 is attenuated and observed as shown by the broken line in FIG.

  As shown in these drawings, according to the present embodiment, when a failure occurs in any of the terminal side optical fibers 4-1 to 4-4, the beat signals by the corresponding optical identification markers 10-1 to 10-4 are displayed. Attenuates or disappears. Which terminal side optical fiber has failed can be uniquely identified by the beat signal frequency. Therefore, even if the line lengths of the terminal side optical fibers 4-1 to 4-4 are the same, it becomes possible to specify the terminal side optical fiber in which the failure has occurred.

  Accordingly, the terminal side optical fibers 4-1 to 4-4 on the downstream side from the optical splitter 3 can be identified for each line regardless of the line length difference. In the present embodiment, the excited Brillouin frequency is uniquely determined by the characteristics of the light identification markers 10-1 to 10-4. Therefore, the test light may have a single wavelength, and a multi-wavelength light source is unnecessary, and the apparatus cost can be reduced.

  Further, the main optical fiber 2 is frequency-separated and identified by sufficiently separating the Brillouin shift wavelength of the main optical fiber 2 from the Brillouin shift wavelengths from the plurality of terminal side optical fibers 4-1 to 4-4. It is also possible to do. Further, since the Brillouin scattered light can be separated from the Fresnel reflection or Rayleigh scattered light on the frequency axis, according to the present embodiment, there is an advantage that a dead zone due to reflection does not occur in the measurement of the Brillouin light power over time.

  In summary, in the present embodiment, the optical identification markers 10-1 to 10-4 having different Brillouin shift frequencies are formed in the terminal side optical fibers 4-1 to 4-4, respectively. Then, test light having a single wavelength is incident on the trunk optical fiber 2, and the reflected light from the downstream side of the optical splitter 3 is heterodyne detected to extract a beat component. Then, by observing the Brillouin shift frequency and its intensity spectrum indicated by each beat component, each of the terminal side optical fibers 4-1 to 4-4 is specified, and the presence or absence of a fault is detected.

  Since it did in this way, each information of the optical fiber located downstream from the optical splitter 3 can be obtained by using the Brillouin wavelength shift amount change as a parameter. That is, by detecting the Brillouin scattered light from the optical identification markers 10-1 to 10-4 in the vicinity of each subscriber terminal, the terminal side optical fibers 4-1 to 4-4 are individually identified, and the occurrence of a failure is detected. can do. This makes it possible to streamline operations such as branching optical fiber monitoring tests. From these facts, according to the present embodiment, it is possible to provide an optical communication system and an optical test apparatus capable of performing an optical test efficiently and at low cost.

[Second Embodiment]
In the first embodiment, a technique has been disclosed in which a terminal-side optical fiber in which a failure has occurred can be identified in the station. In addition to this, the second embodiment discloses a technique that makes it possible to specify the position where a failure has occurred, that is, the length from the optical test apparatus 7 to the location of the failure.
FIG. 8 is a schematic diagram showing, for example, the beat signal frequency of FIG. 5 enlarged with respect to the frequency axis. The light identification marker 10-i is distinguished by the suffix i (i = 1 to n). That is, FIG. 8 shows a spectrum obtained by enlarging the beat signal νi of the Brillouin scattered light and the local light returning from the light identification marker 10-i with respect to the frequency axis and measuring the intensity modulation of the optical power. As shown in FIG. 8, there is a side band of νi ± fi with respect to the extracted beat signal.

If the optical path length between the test light source 21 (FIG. 2) and the light identification marker 10-i is Li1, and the lengths of the light identification markers 10-1 to 10-4 are Li2, respectively, the Brillouin from the light identification marker 10-i. The center frequency fi of the sideband of the beat signal of the scattered light is expressed by the following equation (4).

  In Expression (4), v represents the speed of light in the optical fiber. When Li1 is 5 km, a sideband can be observed if a resolution of about 20 kHz from the center wavelength can be achieved. That is, the sideband can be observed with sufficient accuracy by the spectrum analyzer 30. As the accuracy of the distance L, for example, in a 5 km line, a distance difference of 1 m can be read as a frequency difference of 2 Hz.

FIG. 9 is a diagram illustrating a line state when the optical fiber identification unit 10-1 is disconnected halfway. The terminal side optical fibers 4-2 to 4-4 are not shown because they are in a healthy state. It is assumed that a disconnection failure of the optical fiber identification unit 10-1 occurs at a position Lf [km] from the subscriber terminal 5-1. At this time, the center frequency f1 ′ of the sideband is shifted as shown in FIG. 10 and the following equation (5).

The power P of the sideband signal at this time is given by the following equation (1) when the spectrum curve is a function I (f) of frequency and the resolution of the spectrum analyzer including this sideband is a constant B as shown in FIG. 6) It is expressed by 2.

This can be explained for the following reason. That is, when a failure occurs in the light identification markers 10-1 to 10-4, the return light on the downstream side from the failure disappears, so P is proportional to the length of the light identification marker (L i 2−Lf) / L i. The power spectrum is narrowed by a factor of 2, thereby narrowing the power spectrum. By observing the change of the center frequency f i ′ of the sideband, the change of the spectrum width, and the change of the power spectrum, the line length from the test light source 21 to the fault position can be detected with high accuracy. That is, according to the second embodiment, it is possible to detect a position where a failure has occurred. Furthermore, by applying this fact, according to the present embodiment, it is possible to accurately measure the line length information of the terminal side optical fibers 4-1 to 4-4.

The present invention is not limited to the above embodiment. For example, the test light is not limited to continuous light but may be pulsed. The wavelength of the test light is not always unique. For example, the wavelength may be switched to a plurality of wavelengths, and an appropriate test light wavelength may be used according to system requirements. It will be apparent that the Brillouin shift for each light identification marker has a unique value even when the test light wavelength is switched.
Further, the number of branches in the optical splitter 3 is not limited to four. By appropriately setting the Brillouin shift wavelength interval for any number of branches, it is possible to individually test the state on the terminal side from the optical splitter 3 even in a PDS configuration with a large number of branches. Further, the entire downstream side from the optical splitter 3 may be used as a light identification marker. That is, the optical identification markers 10-1 to 10-4 are not formed only on a part of the terminal side optical fibers 4-1 to 4-4, but reach from the optical splitter 3 to the subscriber terminals 5-1 to 5-4. All of the paths may be the optical identification markers 10-1 to 10-4. Since the optical identification markers 10-1 to 10-4 are also optical fibers and have an optical signal transmission function, such a configuration is sufficiently possible.

  Furthermore, 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. In addition, 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, constituent elements over different embodiments may be appropriately combined.

1 is a block diagram showing a first embodiment of an optical communication system according to the present invention. The functional block diagram which shows one Embodiment of the optical test apparatus 7 of FIG. The schematic diagram which shows the Brillouin backscattered light from the optical identification markers 10-1 to 10-4. The figure which shows the spectrum of Brillouin backscattered light. The schematic diagram which shows beat signal frequency (nu) 1- (nu) 4 obtained by the heterodyne detection of the optical test apparatus 7. FIG. The schematic diagram which shows beat signal frequency (nu) 1- (nu) 4 obtained by the heterodyne detection of the optical test apparatus 7. FIG. The schematic diagram which shows the state in which the optical identification marker 10-2 (and subscriber terminal 5-2) is not connected. The schematic diagram which expands and shows the separated beat signal frequency with respect to the frequency axis. The figure which shows the state in which the optical fiber identification part 10-1 was disconnected on the way. The figure which shows the state which the spectrum of the sideband of the Brillouin scattered light shifted. The figure for demonstrating about an example of the existing optical test method. The figure which shows the example of 1 structure of the optical pulse test apparatus. The figure which shows an example of the waveform measured by the optical pulse test apparatus. The figure for demonstrating the other example of the existing optical test method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Station apparatus, 2 ... Trunk optical fiber, 3 ... Optical splitter, 4 (4-1 to 4-4) ... Terminal side optical fiber, 5 (5-1 to 5-4) ... Subscriber terminal, 6 (6 -1 to 6-4) ... optical filter, 7 ... optical test device, 8 ... optical switch, 9 ... optical coupler, 10 (10-1 to 10-4) ... optical identification marker, 20 ... observation section, 21 ... test Light source, 22 ... amplifier, 23 ... light receiving element, 24 ... polarization scrambler, 25 (25-1 to 25-3) ... optical coupler, 27 ... mixer, 28 ... low pass filter, 29 ... local oscillator, 30 ... spectrum analyzer , 40... Optical pulse test device, 40 ′. Wavelength tunable optical pulse test device, 50... Control unit, 50 a ... identification processing unit, 50 b ... detection processing unit, 50 c ... discrimination processing unit, 51 ... semiconductor laser, 52 ... optical coupler 53. Light receiving element

Claims (13)

In an optical communication system comprising an intra-station device and an optical branching device for branching a trunk optical fiber extended from the intra-station device into a plurality of branch optical fibers,
An optical test apparatus having a light source for generating test light and entering the test light into the trunk optical fiber;
At least one of the plurality of branch optical fibers is
An optical identification unit that is connected to an end far from the in-station device and excites Brillouin scattered light with respect to the test light at a unique frequency shift different from the connected branch optical fiber ;
The optical test apparatus
Observation means for observing Brillouin scattered light coming through the optical splitter and the trunk optical fiber;
Identification means for individually identifying the branch optical fiber provided with the light identification unit based on the frequency of the observed Brillouin scattered light,
The plurality of branch optical fibers are single mode fibers;
The optical identification unit is a rare earth-doped optical fiber that is connected to each branch optical fiber and has a specific refractive index distribution for each branch optical fiber,
An optical communication system, wherein a relative refractive index of a core and a clad in the rare earth-doped optical fiber is equal to that of the single mode fiber. The optical test apparatus
2. The optical communication system according to claim 1, further comprising detection means for individually detecting presence / absence of the light identification unit in the identified branch optical fiber based on the Brillouin scattered light. The optical test apparatus
2. The optical communication system according to claim 1, further comprising detection means for detecting presence / absence of a failure in each of the identified branch optical fibers based on an intensity spectrum of Brillouin scattered light at each frequency. The optical test apparatus
Branching means for partially branching test light generated by the light source to generate local light;
A multiplexing means for multiplexing the reflected light and the local light coming through the optical splitter and the trunk optical fiber;
A light receiving element that converts the light combined by the multiplexing means into an electrical signal,
The observation means includes
Detection means for extracting the beat component by heterodyne detection of the electrical signal;
The optical communication system according to claim 1, further comprising: a spectrum analyzer that measures frequency vs. intensity characteristics of the extracted beat component. The optical test apparatus
And a discriminating unit that discriminates a position of a fault in each of the plurality of optical discriminating units based on a change in a center frequency of a sideband of the beat component and a power spectrum of the sideband. The optical communication system according to claim 4. 2. The optical communication system according to claim 1, wherein the rare earth-doped optical fiber is a GeO 2 -doped optical fiber having a different GeO 2 -doped concentration for each branch optical fiber. 2. The optical communication system according to claim 1, wherein the rare earth-doped optical fiber is temperature-controlled at a specific temperature for each branch optical fiber. 2. The optical communication system according to claim 1, wherein the rare earth-doped optical fiber is applied with a tensile strain specific to each branch optical fiber. In an optical test apparatus used for an optical communication system comprising an intra-station device and an optical branching device for branching a trunk optical fiber extended from the intra-station device into a plurality of branch optical fibers,
A light source for generating test light incident on the trunk optical fiber;
Observation means for observing Brillouin scattered light that is excited by the test light in the optical identification unit connected to each of the branch optical fibers and arrives via the optical splitter and the trunk optical fiber;
Identification means for identifying each of the plurality of branch optical fibers based on the frequency of the observed Brillouin scattered light,
The plurality of branch optical fibers are single mode fibers;
The optical identification unit is a rare earth-doped optical fiber that is connected to each branch optical fiber and has a specific refractive index distribution for each branch optical fiber,
An optical test apparatus characterized in that a relative refractive index of a core and a clad in the rare earth-doped optical fiber is equal to a relative refractive index of the single mode fiber. The optical test apparatus according to claim 9, further comprising detection means for individually detecting presence / absence of the light identification unit in the identified branch optical fiber based on the Brillouin scattered light. The optical test apparatus
The optical test apparatus according to claim 9, further comprising detection means for detecting presence / absence of a failure in each of the identified branch optical fibers based on an intensity spectrum of Brillouin scattered light at each frequency. Further, branching means for partially branching test light generated by the light source to generate local light,
A multiplexing means for multiplexing the reflected light and the local light coming through the optical splitter and the trunk optical fiber;
A light receiving element that converts the light combined by the multiplexing means into an electrical signal,
The observation means includes
Detection means for extracting the beat component by heterodyne detection of the electrical signal;
The optical test apparatus according to claim 9, further comprising: a spectrum analyzer that measures frequency vs. intensity characteristics of the extracted beat component. And a discriminating unit that discriminates a position of a fault in each of the plurality of optical discriminating units based on a change in a center frequency of a sideband of the beat component and a power spectrum of the sideband. The optical test apparatus according to claim 12.

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