JP4160939B2 - Optical line fault search method - Google Patents

Description

  The present invention relates to an optical path fault search method for searching for an optical path fault in an optical communication network in which a transmission device of a communication station and an optical terminal at each user's house are connected via an optical splitter via an optical path.

  An optical communication network as a PON (Passive Optical Network) that connects a communication station and each user's home with an optical line such as an optical branching unit and an optical fiber is configured as shown in FIG. For example, the downstream optical signal a having a wavelength of 1.55 μm output from the transmission apparatus 2 installed in the communication station 1 of the communication carrier is a basic ray composed of the optical filter 3, the optical coupler 4, and the optical fiber. For example, the light enters the optical branching device 6 attached to a utility pole installed near the user's home via the path 5.

  The downstream optical signal a from the transmission device 2 incident on the optical branching device 6 is branched into four downstream optical signals a, which are respectively transmitted to the user's home via branched optical lines 7a, 7b, 7c, and 7d made of optical fibers or the like. It is incident on 8a, 8b, 8c, 8d. The downstream optical signal a incident on each of the user homes 8a to 8d is incident on the optical terminals 10a, 10b, 10c, and 10d via the optical filter 9. The optical terminals 10a to 10d convert the incident downstream optical signal a into an electrical signal c and send it to each information terminal 11a, 11b, 11c, 11d such as a PC.

  The electric signal c addressed to the communication station 1 output from the information terminals 11a to 11d of the user homes 8a to 8d is converted into an upstream optical signal b having a wavelength of 1.31 μm in the optical terminals 10a to 10d. The upstream optical signal b output from the optical terminals 10a to 10d is incident on the optical branching device 6 through the optical filter 9 and its own branched optical lines 7a, 7b, 7c, and 7d.

  The optical branching unit 6 multiplexes the upstream optical signals b incident from the branched optical lines 7 a, 7 b, 7 c, and 7 d and sends them to the communication station 1 via the trunk optical line 5. Each upstream optical signal b having a wavelength of 1.31 μm input into the communication station 1 enters the transmission device 2 via the optical coupler 4 and the optical filter 3.

  In the optical communication network having such a configuration, the optical line composed of the trunk optical line 5 and the branched optical lines 7a to 7d that connect the transmission device 2 of the communication station 1 and the optical terminals 10 of the user homes 8a to 8d is normal. It is necessary to carry out confirmation inspection at regular intervals even after the operation of this optical communication network. When a communication abnormality occurs, it is necessary to investigate the abnormality occurrence location.

  In the optical communication network having such a configuration, the transmission device 2 of the communication station 1 and the information terminals 11a to 11d of the user homes 8a to 8d use the downstream optical signal a and the upstream optical signal b to perform normal data. Non-Patent Document 1 proposes a method for searching for an optical line fault in an operating state in which transmission is performed.

According to this proposal, an optical pulse tester (OTDR) 12 is connected to the optical coupler 4 provided in the communication station 1 when searching for a failure in the optical line. Then, an optical pulse d is sent from the optical pulse tester 12 to the trunk optical line 5 through the optical coupler 4. The wavelength λ _S of the optical pulse d is set to 1.65 μm, which is longer than the wavelength 1.55 μm of the downstream optical signal a used for the data transmission and the wavelength 1.31 μm of the upstream optical signal b.

  The optical filter 3 provided in the communication station 1 absorbs a wavelength component of 1.65 μm from the light incident from the trunk optical line 5 and does not enter the transmission device 2. Further, the optical filter 9 provided in each of the user homes 8a to 8d reflects a wavelength component of 1.65 μm out of the light incident from the branched optical lines 7a to 7d and does not enter the optical terminals 10a to 10d. . Further, in the optical pulse tester 12, an optical filter 13 that incorporates only a wavelength component of 1.65 μm out of the light incident from the optical coupler 4 is incorporated.

  The optical pulse d output from the optical pulse tester 12 to the trunk optical line 5 via the optical coupler 4 is branched into four by the optical branching unit 6, and each user home 8a is passed through the branched optical lines 7a to 7d. Reflected by the optical filter 9 to 8d and propagated in the reverse direction through the branched optical lines 7a to 7d as Fresnel reflected light.

  The light pulse tester 12 receives the back scattered light of the light pulse d and the return light e consisting of each Fresnel reflected light. The optical pulse tester 12 displays and outputs the time change of the light intensity of the return light e, that is, the characteristic of the distance change from the communication station 1 as the return light characteristic A shown in FIG.

In this return light characteristic A, the light intensity becomes discontinuous at the position of the optical branching device 6 on the horizontal axis of the distance L, and at the positions of the optical filters 9 at the preceding stage of the optical terminals 10a to 10d of the user homes 8a to 8d, respectively. A Fresnel reflection waveform 14 is generated. Since the line length L ₀ of the basic optical line 5 and the line lengths L ₁ , L ₂ , L ₃ , L ₄ of the branched optical lines 7 a to 7 d are known, the corresponding line lengths L ₁ , L ₂ , L ₃ , When the Fresnel reflection waveform 14 corresponding to the L ₄ position does not occur, the optical pulse d has not reached the corresponding optical terminals 10a to 10d, so it is determined that an abnormality such as cutting has occurred in the corresponding branched optical lines 7a to 7d. it can.

However, the following problem to be solved still exists in the failure search method for searching for a failure in an optical line by the above-described method.
That is, when the line lengths L ₁ , L ₂ , L ₃ , and L _{4 of the} branched optical lines 7a, 7b, 7c, and 7d from the optical branching unit 6 to the user homes 8a, 8b, 8c, and 8d are approximated There is. In such a case, although depending on the time (distance) resolution of the optical pulse tester 12, as shown in FIG. 9, the Fresnel corresponding to each branched optical line 7a, 7b, 7c, 7d in the return light characteristic A The reflected waveform 14 is displayed partially overlapping.

  As a result, even if an abnormality such as disconnection occurs in some of the branched optical lines 7a to 7d among the branched optical lines 7a to 7d corresponding to the Fresnel reflection waveform 14 displayed in an overlapping manner, this abnormality is not detected. The branch optical lines 7a to 7d that are generated cannot be specified.

  The present invention has been made in view of such circumstances, and even if the line length of each branch optical line from the optical branching device to the optical terminal of each user's home is approximate, A light beam that can be easily searched from the communication station side for the failure of the branch optical line laid between the optical terminal at the home and the optical branching unit without affecting the data transmission between the communication station and the user's home. An object of the present invention is to provide a road obstacle search method.

In the present invention, a transmission apparatus of a communication station and an optical branching unit are connected by a trunk optical line, and the optical branching unit and the optical terminals of a plurality of user homes are wavelengths of optical signals for data transmission provided in the user homes. Each optical line failure from the transmission device to the optical terminal in each user's house is connected to the communication station through an optical filter that reflects the optical pulse for testing at a longer wavelength. This is a method for searching for a failure in an optical line, which is searched by an optical pulse tester provided on the side.

In the optical line fault searching method of the present invention, each of one or a plurality of Fresnel reflection waveforms from the optical filter obtained when the optical pulse for testing is made incident on the main optical line from the optical pulse tester. The peak value is read as each reference peak value. Next, an optical pulse was incident on the main optical line from the optical pulse tester in a state where the position on the optical splitter side of the optical filter in one branch optical line to be measured was bent among the multiple optical paths. Each peak value of one or more Fresnel reflection waveforms from the optical filter that is sometimes obtained is read as each test peak value.
Then, when all the test peak values have not decreased by a predetermined value or more with respect to the corresponding reference peak values, it is determined that the branch optical line to be measured is abnormal.

  When one test peak value is lower than the corresponding reference peak value by a predetermined value or more, the branch optical line to be measured is determined to be normal, and all the test peak values correspond to the respective reference peaks. When the value is not lower than the predetermined value, the branch optical line to be measured is determined to be abnormal.

  In the optical line fault search method configured as described above, one branch optical line to be measured among a plurality of branch optical lines is bent. For example, if a branched optical line made of an optical fiber is bent, the transmission loss of light in the branched optical line increases.

  Therefore, when the branch optical line to be measured is normal, the optical pulse that is output from the optical pulse tester and reaches the optical terminal at the user's home in the reference state before bending is bent at the user's home when the branch optical line is bent. It does not reach the optical terminal. As a result, Fresnel reflection does not occur in the optical terminal that was generated in the reference state. Therefore, each peak value of one Fresnel reflection waveform in the return light characteristic in the optical pulse tester is lower than that in the reference state. Therefore, it can be determined that the branch optical line to be measured is conductive and normal.

On the contrary, if the branch optical line to be measured is abnormal, the optical pulse output from the optical pulse tester does not reach the optical terminal at the user's house even in the reference state before bending, Even if it is bent, Fresnel reflection does not occur at the optical terminal. Therefore, the peak values of all Fresnel reflection waveforms in the return light characteristic in the optical pulse tester do not change compared to the reference state. Therefore, it is possible to determine that the branch optical line to be measured is in an abnormal state or in a loss state and is abnormal.
Furthermore, the wavelength of the optical pulse is set longer than the wavelength of the light used for data transmission on the optical line. FIG. 3 shows the wavelength dependence characteristics of the transmission loss of light transmitted through the optical fiber when the optical fiber constituting the branch optical line is bent with the same radius of curvature R, for example. The transmission loss is small at the wavelength of 1.55 μm and the wavelength of 1.31 μm used for normal data transmission, but the transmission loss is large at the wavelength of 1.65 μm of the optical pulse. Therefore, by bending each branch optical line, it is possible to selectively attenuate only the optical pulse for fault search largely and largely without affecting normal data transmission.

  Moreover, another invention cancels the bent state in the branch optical line determined to be abnormal in addition to the optical line fault searching method of the invention described above, and the bent position in the branch optical line determined to be abnormal. Abnormal test of the peak value of the reflected waveform from the branch optical line that was determined to be abnormal when the optical pulse was incident on the main optical line with the optical splitter side position bent again Read as peak value.

  When the abnormal test peak value is lower than a predetermined value with respect to the reference peak value corresponding to the branch optical line determined to be abnormal, the abnormal position of the corresponding branch optical line is determined to be the user's home side from the bent position again. When the abnormal test peak value is not lower than the corresponding reference peak value by a predetermined value or more, the abnormal position of the branch optical line is determined to be the optical branching side from the bent position again.

  That is, as a result of carrying out the above-described search method of the invention, it was possible to determine a branched optical line in which an abnormality occurred. However, in this state, it is unclear at which position (region) in the corresponding branch optical line the abnormality has occurred.

  Therefore, when an optical pulse is incident from the optical pulse tester to the branching optical line where the abnormality has occurred, a reflected wave is generated at the abnormality occurrence position and propagates to the optical pulse tester side, and is determined to be abnormal. The bending position in the branched optical line is moved from the previous bending position to the optical branching unit, and the optical pulse is again incident on the main optical line from the optical pulse tester.

  In this case, when the abnormality occurrence position of the corresponding branch optical line is located on the user's home side from the bent position again, the abnormality test peak value is lower than a predetermined value with respect to the previously measured reference peak value. . On the contrary, when the abnormality occurrence position of the branch optical line is located on the optical branching side from the bent position again, the abnormality test peak value does not decrease by a predetermined value or more with respect to the reference peak value. In this way, it can be determined at which position (region) in the branch optical line the abnormality has occurred.

Furthermore, the wavelength of the optical pulse is set to 1.65 μm, which is longer than the wavelength of light used for data transmission on the optical line.

  In another invention, in the optical line fault searching method of the invention described above, the radius of curvature in a state where the branch optical line is bent is 1.0 cm or more in a state where the branch optical line is wound once. It is set to 5 cm or less.

  FIG. 4 shows the bend radius dependence characteristics of the optical transmission loss at each wavelength of light transmitted through the optical fiber. As can be understood from this characteristic, the transmission loss at the wavelength of 1.55 μm and the wavelength of 1.31 μm used for normal data transmission can be suppressed as much as possible, and the transmission loss of the optical pulse at the wavelength of 1.65 μm is a certain value or more ( 1 to 5 dB) The bend radius (curvature radius) that can be secured is 1.0 cm or more and 1.5 cm or less in a state where the branch optical line is wound once.

  In another invention, in the optical line fault search method of the invention described above, the branch optical line is bent by housing the branch optical line in a groove of a bending jig having a groove with a predetermined radius of curvature. I have to.

  In this way, since the branching optical line is bent using the bending jig, the branching optical line is always bent with a constant radius of curvature, the loss due to bending can be controlled to be constant, and the fault search accuracy of the optical line can be improved. .

In the optical line fault searching method of the present invention, one branch optical line to be measured is bent, and the peak values of the Fresnel reflection waveforms in the return light characteristics before and after the bending are compared.
Therefore, even if the line length of each branch optical line from the optical branching unit to the optical terminal at each user's home is approximate, it is laid between the optical terminal at each user's home to the optical branching unit. It is possible to quickly find a failure of the branched optical line from the communication station side without affecting the data transmission between the communication station and the user's home.

  FIG. 1 is a schematic diagram showing a schematic configuration of an optical communication network to which an optical line fault searching method according to an embodiment of the present invention is applied. The same parts as those of the conventional optical communication network shown in FIG.

  The downstream optical signal a having a wavelength of 1.55 μm output from the transmission device 2 installed in the communication station 1 is split through the optical filter 3, the optical coupler 4, and the basic optical line 5 such as an optical fiber. Incident on the vessel 6. The downstream optical signal a from the transmission device 2 incident on the optical branching device 6 is branched into four downstream optical signals a, and the user's home 8a is passed through branched optical lines 7a, 7b, 7c, 7d such as optical fibers, respectively. , 8b, 8c, and 8d. The downstream optical signal a incident on each of the user homes 8a to 8d is incident on the optical terminals 10a, 10b, 10c, and 10d via the optical filter 9, respectively. The optical terminals 10a, 10b, 10c, and 10d convert the incoming downstream optical signal a into an electrical signal c and send it to information terminals 11a, 11b, 11c, and 11d such as PCs.

  The electric signal c addressed to the communication station 1 output from the information terminals 11a to 11d of the user homes 8a to 8d is converted into an upstream optical signal b having a wavelength of 1.31 μm in the optical terminals 10a to 10d. The upstream optical signal b output from the optical terminals 10a to 10d is incident on the optical branching device 6 through the optical filter 9 and its own branched optical lines 7a, 7b, 7c, and 7d, respectively.

  The optical branching unit 6 multiplexes the upstream optical signals b incident from the branched optical lines 7 a, 7 b, 7 c, and 7 d and sends them to the communication station 1 via the trunk optical line 5. Each upstream optical signal b having a wavelength of 1.31 μm input into the communication station 1 enters the transmission device 2 via the optical coupler 4 and the optical filter 3.

  In such an optical communication network, when searching for an optical line failure, an optical pulse tester (OTDR) 20 is connected to the optical coupler 4 provided in the communication station 1.

In the optical pulse tester 20, the optical pulse d output from the semiconductor laser (LD) 21 passes through the optical coupler 22 in the optical pulse tester 20 and the optical coupler 4 in the communication station 1, and the basic optical line 5. Is output. Note that the pulse width and pulse period of the optical pulse d output from the semiconductor laser (LD) 21 are controlled by a pulse signal applied from the pulse generation circuit 23. The wavelength λ _S of the optical pulse d is set to 1.65 μm, which is longer than the wavelength 1.55 μm of the downstream optical signal a used for data transmission and the wavelength 1.31 μm of the upstream optical signal b, in the operation unit 24. Is done.

  The optical filter 3 provided in the communication station 1 absorbs a wavelength component of 1.65 μm in the light incident from the trunk optical line 5 and does not enter the transmission apparatus 2. Further, the optical filter 9 provided in each of the user homes 8a to 8d reflects a wavelength component of 1.65 μm out of the light incident from the branched optical lines 7a to 7d and does not enter the optical terminals 10a to 10d. .

  The optical pulse d output to the trunk optical line 5 is branched by the optical branching unit 6 and is passed through the branched optical lines 7a to 7d by the optical filters 9 of the user homes 8a to 8d which are the far ends of the branched optical lines. The light is reflected and propagated in the reverse direction through the branched optical lines 7a to 7d as Fresnel reflected light. The light pulse tester 20 is supplied with the back scattered light of the light pulse d and the return light e made up of each Fresnel reflected light through the optical coupler 4.

  The return light e input to the optical pulse tester 20 enters the optical filter 13 via the optical coupler 22. The optical filter 13 absorbs the wavelength 1.55 μm component of the downstream optical signal a used for data transmission and the wavelength 1.31 μm component of the upstream optical signal b in the return light e incident from the optical coupler 22. Only the wavelength component of 1.65 μm of the optical pulse d is allowed to pass and enter the light receiver 25.

  The light receiver 25 converts the return light e from which the 1.55 μm wavelength component and the 1.31 μm wavelength component are removed into a return light g of an electrical signal. The return light g converted into an electric signal is amplified by the amplifier 25, then converted into a digital return light g by the A / D converter 27, and input to the processing unit 28 made of, for example, a computer. The processing unit 28 displays and outputs on the display unit 29 the time variation of the light intensity of the input digital return light g, that is, the characteristic of the distance change from the communication station 1 as the return light characteristic A shown in FIG.

  In the return light characteristic A shown in FIG. 5 (a), the light intensity becomes discontinuous at the position of the optical branching device 6, and the optical filters in the preceding stage of the optical terminals 10a, 10b, 10c, and 10d of the user homes 8a to 8d. A Fresnel reflection waveform 14 is generated at each of the nine positions.

FIGS. 5B and 5C show the distance axis (time axis) in the return light characteristic A shown in FIG. 5A when the operator operates the operation unit 24 in the optical pulse tester 20. It is an enlarged view in which a portion where the Fresnel reflection waveform 14 is enlarged is displayed. In FIG. 5B, the line lengths L ₁ , L ₂ , L ₃ , L _{4 of the} branched optical lines 7a, 7b, 7c, 7d from the optical branching device 6 to the user homes 8a, 8b, 8c, 8d. Since they are separated from each other by the time (distance) resolution of the optical pulse tester 20, the Fresnel reflection waveform 14 for each branch optical line 7a, 7b, 7c, 7d is separated and displayed.

However, in FIG. 5C, the time (distance) resolution of the optical pulse tester 20 is between the line lengths L ₁ , L ₂ , L ₃ and L _{4 of the} branched optical lines 7a, 7b, 7c and 7d. Since they are not separated from each other, the Fresnel reflection waveform 14 for each branch optical line 7a, 7b, 7c, 7d is not displayed separately, but only two Fresnel reflection waveforms 14 are displayed, for example.

  FIG. 2A is an enlarged perspective view showing a main part of a bending jig 30 for bending the branched optical lines 7a, 7b, 7c, and 7d made of optical fibers by the failure searching method of this embodiment. A groove 31 having a constant radius of curvature R is formed on the upper surface of the bending jig 30. On both sides of the groove 31, a pair of support members (not shown) for guiding the optical fiber into the groove 31 of the bending jig 30 are attached.

  Then, by accommodating the branched optical lines 7a to 7d made of optical fibers in the groove 31, the branched optical lines 7a to 7d are bent at a constant radius of curvature R as shown in FIG. Is possible. In the fault search method of this embodiment, the radius of curvature R is set to 1.0 cm to 1.5 cm in a state where each branch optical line 7a to 7d made of an optical fiber is wound once (360 °). . In addition, the transmission loss of the light in the optical fiber resulting from a bending changes according to the curvature radius R and the optical fiber length (bending circumference) of a bending state.

  Thus, by bending each of the branched optical lines 7a to 7d, the transmission loss of light in each of the branched optical lines 7a to 7d increases.

  FIG. 3 is a diagram showing the wavelength dependence characteristics of the transmission loss of light transmitted through the optical fiber when bent at the same radius of curvature R. According to this wavelength-dependent characteristic, transmission loss increases rapidly as the wavelength of light increases. For example, the transmission loss is small at the wavelength 1.55 μm of the downstream optical signal a and the wavelength 1.31 μm of the upstream optical signal b used for normal data transmission, but the transmission loss is not present at the wavelength 1.65 μm of the optical pulse d. large.

  FIG. 4 shows an optical fiber having optical transmission loss at a wavelength of 1.55 μm of downstream optical signal a, a wavelength of 1.31 μm of upstream optical signal b, and a wavelength of 1.65 μm of optical pulse d used for normal data transmission. The bending radius dependence characteristics are shown. As can be understood from this characteristic, the transmission loss at the wavelength of 1.55 μm and the wavelength of 1.31 μm used for normal data transmission can be suppressed as much as possible, and the transmission loss of the optical pulse d at the wavelength of 1.65 μm is a certain value or more. The bend radius (curvature radius) that can be secured (1 to 5 dB) is 1.0 cm or more and 1.5 cm or less in a state where the branched optical line is wound once.

  In general, when the length of the optical fiber connecting the optical communication devices is excessive, the optical fiber is wound in an annular shape. The radius of curvature at the time of winding is 2 cm or more, and the transmission loss of light caused by bending Is prevented from occurring.

  Therefore, by bending each of the branched optical lines 7a to 7d using the bending jig 30, only the optical pulse d for fault search can be selectively attenuated with little influence on normal data transmission. It becomes possible.

  In addition to bending the optical line, the optical pulse d for fault search may be attenuated by crushing the optical line to some extent or applying stress.

  Then, using the optical pulse tester 20 and the bending jig 30 configured as described above, the operator follows the procedure shown in FIG. 6 from the transmission device 2 of the communication station 1 in the optical communication network to each of the user homes 8a to 8a. The failure of each optical line from the 8d optical terminals 10a to 10d is searched. Specifically, a failure is searched for in the branched optical lines 7a, 7b, 7c, and 7d from the optical branching device 6 to the optical terminals 10a to 10d of the user homes 8a to 8d.

First, the operation unit 24 of the optical pulse tester 20 is operated to set the wavelength λ _S of the optical pulse d to 1.65 μm (S1). Next, in a reference state in which the branched optical lines 7a to 7d are not bent by the bending jig 30, the optical pulse d is output, the return light e is measured, and the return light characteristic A shown in FIG. Further, the enlargement characteristic shown in FIG. 5B or FIG. 5C is obtained (S2). Each peak value of each Fresnel reflection waveform 14 in this expansion characteristic is read as reference peak values P ₁ , P ₂ ,..., P _n (S3).

Next, the number N that identifies the branch optical lines 7a to 7d to be measured is initialized (N = 1) (S4). Then, the optical fibers of the Nth branch optical lines 7a to 7d are bent using the bending jig 30 shown in FIG. 2A (S5). In this state, the operation unit 24 of the optical pulse tester 20 is operated to output the optical pulse d, and the return light e is measured to obtain the return light characteristic A shown in FIG. The enlargement characteristic shown in FIG. 5D, FIG. 5E, or FIG. 5F is obtained (S6). Each peak value of each Fresnel reflection waveform 14 in this expansion characteristic is read as test peak values Q ₁ , Q ₂ ,..., Q _n (S7).

Each reference peak value _{P 1, P 2, ...,} P n and each test peak value Q _1, Q _2, ..., it is compared with Q _n (S8). Then, as shown in FIG. 5 (d) or FIG. 5 (e), the respective test peak value Q _1, Q _2, ..., one test peak to Q ₁ of the _{Q n, Q 2, ...,} Q n Is lower than a predetermined value with respect to the corresponding reference peak values P ₁ , P ₂ ,..., P _n (S9), it is determined that the branch optical line to be measured is normal (S10).

Lowering Further, as shown in FIG. 5 (f), the whole of the test the peak value Q _1, Q _2, ..., each reference peak Q _n corresponding values P _1, P _2, ..., a predetermined or more with respect to P _n If it has not been changed and there is no change (S9), it is determined that the branch optical line to be measured is abnormal (S11).

  Since the inspection (measurement) for the presence or absence of an abnormality (failure) such as disconnection with respect to the N-th branch optical lines 7a to 7d has been completed, the N-th branch optical lines 7a to 7d are attached. The bending jig 30 is removed.

Then, the number N of the branch optical lines 7a to 7d to be measured is updated (N = N + 1) (S12). When it is confirmed that the updated number N does not exceed the number N _E (= 4) of the branched optical lines 7a to 7d (S13). Returning to S5, the bending jig 30 is attached to the N-th branched optical lines 7a to 7d to be measured after the update, and then bent. Then, inspection (measurement) for the presence or absence of abnormality (failure) such as disconnection of the corresponding branched optical lines 7a to 7d is started.

In S13, when the updated number N exceeds the number N _E (= 4) of the branched optical lines 7a to 7d, each of the optical branching units 6 in the optical communication network to the optical terminals 10 of the respective user homes 8a to 8d. The search for faults in the branched optical lines 7a, 7b, 7c, 7d is terminated.

  Next, when, for example, one branch optical line 7a to 7d in which an abnormality has occurred is specified in the procedure shown in FIG. 6, the approximate position (region) of the abnormality in the branch optical line 7a to 7d in which the abnormality has occurred is determined. The grasping procedure will be described with reference to FIG.

  In this method, for example, when an abnormality has occurred due to the cutting of the optical fiber, if the optical pulse d is incident on the branched optical lines 7a to 7d where the abnormality has occurred from the optical pulse tester 20, the abnormality occurs at the position where the abnormality has occurred. A reflected wave is generated and propagates to the optical branching device 6 side, and this reflected wave enters the optical pulse tester 20 as return light e. If the corresponding branched optical lines 7a to 7d are bent halfway, The fact that the reflected wave caused by the abnormality does not reach the optical pulse tester 20 is utilized.

  Specifically, the previously bent state in the branched optical lines 7 a to 7 d is released, and the optical pulse d is incident on the trunk optical line 5 from the optical pulse tester 20. The optical pulse d is reflected at the abnormal position of the branched optical lines 7a to 7d determined to be abnormal, propagates to the optical branching device 6 side, and this reflected wave enters the optical pulse tester 20 as return light e. The optical pulse tester 20 reads the peak value of the reflected waveform of the return light e as an abnormal reference peak value.

  In the method of this embodiment, in order to obtain the abnormality reference peak value necessary for grasping the approximate position (region) of the abnormality in the branched optical lines 7a to 7d where the abnormality has occurred, the previously bent state is used. The optical pulse d is again incident on the trunk optical line 5 under the same conditions, and the reference peak value is measured again. First, in order to identify the branched optical lines 7a to 7d in which an abnormality has occurred, measurement is performed first. The obtained reference peak value can be reused as the abnormal reference peak value.

  Next, the optical pulse d is incident on the trunk optical line 5 from the optical pulse tester 20 in a state where the position on the optical branching device 6 side is bent again from the bent position in the branched optical lines 7a to 7d determined to be abnormal. . Then, the optical pulse tester 20 reads the peak value of the reflected waveform of the return light e from the branched optical lines 7a to 7d determined to be abnormal as the abnormal test peak value.

  Then, when the abnormal test peak value is lower than the predetermined value with respect to the abnormal reference peak value, it can be considered that the optical pulse d cannot reach the abnormal position due to bending. Therefore, in this case, the abnormal positions of the corresponding branched optical lines 7a to 7d are determined to be on the user homes 8a to 8d side from the bent position.

Conversely, when the abnormal test peak value has not decreased by a predetermined value or more with respect to the abnormal reference peak value, it can be considered that the optical pulse d has reached the abnormal position. Therefore, in this case, the abnormal position of the corresponding branched optical lines 7a to 7d is determined to be the optical branching device 6 side from the bent position again.
Thus, the approximate abnormal position (region) in the branched optical lines 7a to 7d can be easily grasped.

  In the optical line fault search method configured as described above, a measurement target is selected from the plurality of branched optical lines 7a, 7b, 7c, and 7d that connect the optical branching device 6 and the user homes 8a, 8b, 8c, and 8d. One of the branched optical lines 7a, 7b, 7c, 7d is bent with a constant radius of curvature R using a bending jig 30.

  Therefore, when the branched optical lines 7a, 7b, 7c, and 7d made of, for example, one optical fiber to be measured are normal, as shown in FIGS. 5 (d) and 5 (e), the light is in the reference state before bending. When the optical pulse d output from the pulse tester 20 and reaches the optical filter 9 of the optical terminals 10a to 10d of the corresponding user homes 8a to 8d bends the branched optical lines 7a to 7d, the optical terminals of the corresponding user homes 8a to 8d. It does not reach the optical filters 9 of 10a to 10d. As a result, Fresnel reflection does not occur in the optical filter 9 of the optical terminal 10 that has occurred in the reference state.

  Therefore, the test peak value Q of one Fresnel reflection waveform 14 in the return light characteristic A in the optical pulse tester 20 is lower than the reference peak value P of the corresponding Fresnel reflection waveform 14 in the reference state. Therefore, it is possible to determine that the branch optical lines 7a to 7d to be measured are conductive and normal.

  On the contrary, when the branch optical lines 7a to 7d to be measured are abnormal, the optical filter 9 of the optical terminals 10a to 10d of the corresponding user homes 8a to 8d is output from the optical pulse tester 20 even in the reference state before bending. Therefore, even if the branch optical lines 7a to 7d to be measured are bent, the Fresnel reflection does not occur in the optical filter 9 of the optical terminals 10a to 10d.

  Therefore, as shown in FIG. 5 (f), each test peak value Q of all Fresnel reflection waveforms 14 in the return light characteristic A in the optical pulse tester 20 corresponds to each of the corresponding Fresnel reflection waveforms 14 in the reference state. There is no change compared to the reference peak value P. Therefore, it is possible to determine that the branch optical lines 7a to 7d to be measured are in an abnormal state or in a loss state and are abnormal.

Thus, for example, the line lengths L ₁ , L ₂ , L ₃ , and L _{4 of the} branched optical lines 7a, 7b, 7c, and 7d from the optical branching device 6 to the optical terminals 10 of the user homes 8a to 8d are approximate. Even if the Fresnel reflection waveforms 14 corresponding to the branched optical lines 7a, 7b, 7c, and 7d in the return light characteristic A are displayed partially overlapping as shown in FIG. Faults in the optical lines 7a, 7b, 7c, and 7d can be reliably searched with the optical pulse tester 20 provided on the communication station 1 side.

Further, the wavelength λ _S of the optical pulse d output from the optical pulse tester 20 is longer than the wavelength 1.55 μm of the downstream optical signal a used for data transmission and the wavelength 1.31 μm of the upstream optical signal b. It is set to 65 μm.

  Further, in the communication station 1, an optical filter 3 that absorbs a wavelength component of 1.65 μm from the light incident from the trunk optical line 5 and does not enter the transmission apparatus 2 is provided. Further, an optical filter 9 that reflects a wavelength component of 1.65 μm out of the light incident from the branched optical lines 7a, 7b, 7c, and 7d and does not enter the optical terminals 10a to 10d in the user homes 8a to 8d. Is provided. Further, the optical pulse tester 20 absorbs the wavelength 1.55 μm component of the downstream optical signal “a” and the wavelength 1.31 μm component of the upstream optical signal “b” used for data transmission. An optical filter 13 that allows only the wavelength component of 65 μm to pass through and enters the light receiver 25 is incorporated.

  Therefore, the optical pulse tester in which the failure of each branch optical line 7a, 7b, 7c, 7d is provided on the communication station 1 side without affecting the data transmission between the communication station 1 and the user homes 8a, 8b, 8c, 8d. 20 can be searched reliably.

  Moreover, the rough abnormal position (area | region) in branch optical path 7a-7d can be grasped | ascertained easily.

1 is a schematic diagram showing a schematic configuration of an optical communication network to which an optical line failure searching method according to an embodiment of the present invention is applied. The figure which shows the bending jig used with the fault search method of the optical line concerning the embodiment, and its usage method The figure which shows the wavelength dependence characteristic of the transmission loss of the light transmitted in the optical fiber at the time of bending with the same curvature radius R The figure which shows the bend radius dependence characteristic of the optical transmission loss of each wavelength of the light which is transmitted inside the optical fiber The figure for demonstrating the fault search principle in the fault search method of the optical line of the embodiment Flowchart showing a fault search operation procedure in the optical fiber fault search method of the embodiment Schematic diagram showing the schematic configuration of a general optical communication network The figure which shows the return light characteristic which is measured with the conventional optical fiber obstacle search method Similarly, the figure which shows the return light characteristic which is measured with the conventional optical fiber obstacle search method

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Communication station, 2 ... Transmission apparatus, 3, 9, 13 ... Optical filter, 4, 22 ... Optical coupler, 5 ... Trunk optical line, 6 ... Optical branching device, 7a, 7b, 7c, 7d ... Branch optical line, 8a, 8b, 8c, 8d ... user home, 10a, 10b, 10c, 10d ... optical terminal, 11a, 11b, 11c, 11d ... information terminal, 12, 20 ... optical pulse tester, 14 ... Fresnel reflection waveform, 21 ... Semiconductor laser (LD), 23 ... Pulse generation circuit, 24 ... Operation unit, 25 ... Light receiving unit, 26 ... Amplification unit, 27 ... A / D conversion unit, 28 ... Processing unit, 29 ... Display unit, 30 ... Bending jig 31 ... groove

Claims (5)

The transmission device of the communication station and the optical branching unit are connected by a trunk optical line, and the optical branching unit and the optical terminals of a plurality of user homes have a wavelength longer than the wavelength of the optical signal for data transmission provided in the user home. A failure of each optical line from the transmission device to the optical terminal at each user's house in the optical communication network connected by the branched optical line via the optical filter that reflects the test optical pulse is transmitted to the communication station side. A method for searching for an obstacle in an optical line to search with an optical pulse tester provided,
Read each peak value of one or a plurality of Fresnel reflection waveforms from the optical filter obtained when the optical pulse for testing is incident on the main optical line from the optical pulse tester as each reference peak value,
The optical pulse is incident on the main optical line from the optical pulse tester in a state where the optical filter side of the optical filter in the one of the plurality of optical paths is bent. Reading each peak value of one or a plurality of Fresnel reflection waveforms from the optical filter obtained as a test peak value,
When one test peak value is lower than a predetermined value relative to the corresponding reference peak value, the branch optical line to be measured is determined to be normal,
A method for searching for a fault in an optical line, characterized in that when all the test peak values have not decreased by a predetermined value or more with respect to each corresponding reference peak value, the branch optical line to be measured is determined to be abnormal. The optical pulse tester in a state in which the bent state in the branch optical line determined to be abnormal is released and the position on the optical branching unit side is bent again from the bent position in the branch optical line determined to be abnormal. The peak value of the reflected waveform from the branched optical line determined as the abnormality obtained when the optical pulse is incident on the main optical line is read as an abnormal test peak value.
When the abnormal test peak value is lower than a predetermined value with respect to the reference peak value corresponding to the branch optical line determined to be abnormal, the abnormal position of the corresponding branch optical line is determined to be the user's home side from the bent position again. And
The abnormal position of the branch optical line is determined to be closer to the optical splitter than the bent position when the abnormal test peak value is not lower than a predetermined value with respect to the corresponding reference peak value. The method for searching for an obstacle in an optical line according to 1.   3. The optical line fault search method according to claim 2, wherein the wavelength of the optical pulse is 1.65 [mu] m.   4. The optical fiber fault search according to claim 3, wherein a radius of curvature in a state where the branched optical line is bent is 1.0 cm or more and 1.5 cm or less in a state where the branched optical line is wound once. Method. 3. The optical line fault search method according to claim 1, wherein the branch optical line is bent by housing the branch optical line in the groove of a bending jig having a groove with a predetermined curvature radius.

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