JP2009017497A - Method of switching communication path, and control unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of switching communication path capable of excluding the influence on service, accompanying the interference relocating work. <P>SOLUTION: An optical path difference between a branching line 5 and a detour line 11 is measured. Based on the measured result, the amount of delay in a delay unit 20 is controlled to set the optical path length of the branching line 5 equal to that of the detour line 11. In this state, the signal light of the branching line 5 is gradually shifted to the detour line 11, and the branching line 5 is exchanged for a change-over destination line 5', while the signal light detours to the detour line 11 completely; and a light path difference between the detour line 11 and the change-over destination line 5' is measured similarly. Based on the measurement result, the amount of delay in the delay unit 20 is controlled gradually to be within the range of error time of the error hour permitted by a frame turnaround following function, so that the optical path length in both the lines 11, 5' is set identical. Finally, the signal light of the detour line 11 is restored to the change-over destination line 5' and the switching of a signal path is completed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for switching a path of signal light in an optical communication system applied to, for example, an optical access network.

  The fiber to the home (FTTH) service that connects the network operator's office (station) and the user's home with optical fiber is spreading. In FTTH, a so-called PON (Passive Optical Network) type network configuration in which an optical splitter is provided outside a station building and an optical fiber is branched is generally used (see, for example, Patent Document 1).

  The line configuration of the PON is such that one optical fiber is branched into a plurality of lines at a station building, and each of the plurality of optical fibers is further branched into a plurality of lines outdoors. Thereby, it is possible to consolidate a plurality of external transmission termination devices in one in-house transmission device, thereby reducing the equipment cost of the transmission device and sharing the optical line equipment. For this reason, the cost of the entire communication facility can be greatly reduced, and it has begun to be widely used in access networks and the like.

  By the way, there are often cases where the optical fiber line route is forced to change due to public works such as widening of roads, bridge replacement, new construction or repair of electricity or water supply, and the like. Hereinafter, such a construction forcing a change in the route of the off-site optical line equipment is referred to as troubled relocation work. In the PON system, a plurality of external transmission termination devices are aggregated in one in-house transmission device. Therefore, it is required to stop a lot of traffic at the same time when troublesome relocation work is carried out. The impact on is immeasurable.

In order to reduce this effect as much as possible, there are currently only countermeasures such as distributing the construction time and implementing route switching work during low traffic hours, such as from midnight to early morning. It will be significantly disturbed. In particular, in the case where trouble relocation work is performed in an underground trunk section or an imaginary wiring section, the impact on the user is most serious. In such a case, it is inevitable that the work at night will be prolonged as well as the work time will be dispersed.
JP-A-8-102710

As described above, the branch type asynchronous optical communication system represented by PON has the merit that the equipment cost can be greatly reduced, but it has a great influence on the user due to the troubled relocation work, and some measures are desired. . Since it is impossible to obtain a consensus from many users regarding the service stop period (time period), it is necessary to perform switching work in a time period in which the traffic volume decreases, for example, from midnight to early morning. As described above, there is a problem that the troublesome relocation work cannot be implemented with a planability even though the work directly affects the service.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a communication path switching method and a control device capable of eliminating the influence on the service associated with the troubled transfer work.

  In order to achieve the above object, according to one aspect of the present invention, a transmission device that transmits signal light, a termination device that terminates an optical fiber that transmits the signal light, and communication between the transmission device and the termination device Is a communication path switching method used in an optical communication system having a management function for managing the timing of the transmission based on a measurement value of a frame round-trip time between the transmission apparatus and the termination apparatus, and is connected to a variable delay device Connecting a detour path to the switching source line to form a closed path, a first measurement step of measuring an optical path difference between the switching source line and the detour path on the closed path, and the first measurement A first correction step for controlling a delay amount of the variable delay device from a result obtained in the step to correct an optical path difference between the switching source line and the detour path; and the switching after completion of the first correction step. A detour step of detouring the signal light of the line to the detour path, an exchange step of replacing the switching source line with a switch destination fiber, and measuring an optical path difference on the closed path between the switch destination fiber and the detour path From the second measurement step and the result obtained in the second measurement step, the delay amount of the variable delay device is gradually controlled within the error time range of the communication time allowed by the management function, and the switching destination fiber And a second correction step of correcting an optical path difference with the detour path, and a recovery step of restoring the signal light of the detour path to the switching destination fiber after the completion of the second correction step. A route switching method is provided.

  By taking such means, the signal light of the switching source line is temporarily transferred to the detour path. Then, after the switching source line is replaced with the switching destination fiber, the optical path difference between the detour path and the switching destination fiber is measured. According to the result, the delay amount of the delay device is controlled and gradually changed until the optical path difference becomes zero. In that process, by gradually changing the error time range of the communication time allowed by the timing management function, transmission data loss and transmission logical link mismatch due to differences in optical path lengths are avoided by upper layer processing. be able to. Moreover, the above process can be executed in-service. Therefore, it is possible to eliminate the influence on the service associated with the relocation work.

  According to the present invention, it is possible to provide a communication path switching method and a control device capable of eliminating the influence on the service associated with the trouble relocation work.

[First Embodiment]
FIG. 1 is a system diagram showing an embodiment of an optical communication system according to the present invention. In this embodiment, a branching asynchronous communication system called a GE-PON system in which a typical Giga Ethernet (registered trademark) is applied to a PON system as an asynchronous communication method is taken as an example.

  In FIG. 1, the signal light transmitted from the branch line transmission device 1 is branched into, for example, four branch lines 5 (5 a to 5 d) by a branch unit (splitter) 3. These are further branched into a plurality of core wires by branch portions 6a to 6d. For example, the branch section 6a is branched into seven systems, and the fiber cores 7 are terminated by branch line terminating devices 9-1 to 9-7, respectively, and drawn into the user's house. As a result, a PON in which the transmission device 1 is under the control of the termination devices 9-1 to 9-7 is formed. The fiber core 7 is provided with a test light blocking filter 8 for preventing test light for optical fiber testing from entering the terminal devices 9-1 to 9-7. As a result, an in-service test can be performed.

  The branch line 5 is the target of the construction. The method described in this embodiment is carried out in response to a request for public works, for example. In this embodiment, a switching destination line 5 ′ (5a ′ to 5d ′) is prepared for each of the branch lines 5a to 5d, and a switching route is individually formed with the switching points 10a and 10b as boundaries. Since this route switching takes work time, the traffic is detoured to the detour route 11 during that time.

  The detour line 11 has terminals at both ends thereof. The upstream side is a single terminal 11a, and the downstream side is a single terminal 11b. Test light insertion couplers 4a to 4d are connected to the branch lines 5a to 5d on the upstream side of the switching point 10a, respectively. The test light insertion couplers 4a to 4d are preferably connected in advance to the branch lines 5a to 5d when the system is installed, that is, before the service is started. Among these, the variable bending loss device 21 is attached to the downstream side of the test light insertion coupler 4a on the branch line 5a to be constructed.

  The test light insertion coupler 4 a includes a test light insertion port 12 and a power monitor port 13. Among these, the test light generated by the optical pulse tester 17 is incident on the test light insertion port 12. A signal light blocking filter 16 for preventing signal light from entering the optical pulse tester 17 is provided in the optical waveguide between the test light insertion port 12 and the optical pulse tester 17. Further, a test light blocking filter 2 for preventing the test light from entering the transmission device 1 is provided between the branching unit 3 and the transmission device 1.

  The power monitor port 13 is connected to the one terminal 11 a of the detour line 11 via the wavelength tunable filter 19 and the delay device 20. As a result, the signal light 23 and the test light flowing through the branch line 5 a can also flow through the detour path 11. In order to distinguish the signal light flowing through the detour path 11 from the signal light 23, reference numeral 24 is attached. One terminal 11 b of the detour line 11 is connected to the compensation signal insertion port 14 and the monitor port 15 of the branching unit 6 a via the coupler 22. As a result, another closed route passing through the detour route 11 is formed.

  The branching unit 6a is a 2-input N-output (2 × N) optical branching unit (N is the number of branches). Of the N output terminals, for example, the oldest number is the monitor port 15 for extracting the signal light 23, and one of the two input terminals is the compensation signal insertion port 14. A compensation signal 25 in which a difference in transmission time due to a difference in optical path between the bypass line 11 and the branch line 5 a is compensated for the signal light 24 is incident on the compensation signal insertion port 14.

  The optical pulse tester 17 is an apparatus such as an OTDR (Optical Time Domain Reflectometer) for individually measuring the lengths of the branch line 5a, the detour line 11, and the switching destination line 5a ′. The signal light blocking filter 16 transmits the test light from the optical pulse tester 17 and blocks the signal light guided to the test light insertion port 12 via the test light insertion coupler 4a.

  The wavelength tunable filter 19 has a characteristic capable of changing its transmission band continuously and freely. That is, the wavelength tunable filter 19 can move its transmission band in accordance with the control of the control unit 18, and transmits or blocks the signal light 23 that bypasses the power monitor port 13. Furthermore, the wavelength tunable filter 19 also has a characteristic that the test light from the optical pulse tester 17 is always transmitted.

  In general, the wavelength of the test light is longer than that of the signal light so that the bending loss of the optical fiber can be sensitively detected. In order to satisfy the above characteristics, it can be realized by either a Long Wave Pass Filter (LWPF) or a Band Pass Filter (BPF) that can change the transmission wavelength band. As examples of this type of wavelength tunable filter, those using a dielectric multilayer filter as an etalon and those using FBG (Fiber Bragg Grating) are generally used. In addition, it can be realized by using an optical prism or a diffraction grating.

  The delay device 20 is an optical delay device whose amount of delay can be varied, and for example, an extended optical fiber can be used. That is, a plurality of types of lines corresponding to the delay amount may be prepared, and these may be switched and connected to the detour line 11. At this time, since the signal light 23 needs to be transferred from the branch line 5 to the detour path 11 and then from the detour path 11 to the switching destination line 5 ′, the length of the extension optical fiber is changed. A four-port optical circulator is installed so that the signal light can be changed, and an extension optical fiber having a reflector at one end is connected to reflect and delay the signal light 23. Since the delay optical fiber having a different length can be replaced by such a configuration, an arbitrary delay amount can be created.

Apart from this, FSO (Free Space Optics) using optical space communication can also be used as the delay device 20. That is, a part of the detour path 11 can be replaced with optical wireless communication (FSO), and a delay can be given to the signal light by utilizing a difference in propagation speed between the optical fiber and the space. In addition, the signal light 24 detoured to the monitor port 13 side is optical / electrically converted, the time corresponding to the delay amount is stopped by the delay amount time by the signal accumulator, and the electric / optical conversion is performed again to the detour line 11. It may be sent out.
The variable bending loss device 21 is a variable optical attenuator that can freely adjust the amount of loss to the signal light 23 under the control of the control unit 18. For example, the magnitude of radiation loss due to bending can be adjusted by creating a bend in the branch line 5a and freely controlling the bend diameter. The variable bending loss device 21 has the characteristics of transmitting and blocking the signal light 23, and also has the same characteristics for the test light from the optical pulse tester 17.

  Here, the test wavelength is longer than the wavelength of the signal light. Since the radiation loss due to bending can be detected more sensitively with light having a longer wavelength, it is convenient as monitoring light, and the loss amount of the signal light 23 may be controlled in accordance with this (test) light loss change. For example, if 1.31 micrometers is used for the wavelength of the signal light 23 and 1.65 micrometers is used for the wavelength of the test light, the loss for bending changes approximately three times larger with the test light of 1.65 μm. The loss of the signal light 23 is controlled in consideration of the ratio. Usually, a bending curvature of 5 to 10 mm is used, and a loss of 0 to 40 dB is obtained at this time.

  The control unit 18 controls the transmission band of the wavelength tunable filter 19, the delay amount of the delay device 20, and the loss amount of the variable bending loss device 21 based on the optical path difference obtained by the optical pulse tester 17. In addition, the control unit 18 controls the power level of the signal light while monitoring the power level of the test light when the signal light is transferred from the branch line 5 to the detour line 11 (or the switching destination line 5 ′).

  In FIG. 1, the power monitor port 13 of the test light insertion coupler 4 a installed in the branch line 5 is used as means for extracting the signal light 23 to the detour line 11. Further, one of the fiber cores 7 is used as the monitor port 15 for the signal light 23, and the branching unit 6 a is used as means for returning the signal light 24 (compensation signal 25) after delay compensation from the detour path 11 to the branch line 5. I have to.

  In the above configuration, it is meaningless if the signal is interrupted when the traffic is detoured to the detour line 11 and when the traffic is restored to the switching route. In addition, no matter how the signals are reconnected without interruption, if a transmission data loss or a transmission logical link mismatch occurs, it still becomes a serious problem. The point of the present invention is how to prevent it. In this embodiment, this problem is solved by utilizing the frame round-trip time tracking function provided in many GE-PON systems. The following describes the round-trip time tracking function.

  The round-trip time tracking function refers to each branch path termination device in order to avoid collision of uplink signals transmitted on the uplink from the branch path termination devices 9-1 to 9-7 thereunder to the transmission apparatus 1. This is a so-called communication timing management function that measures the communication time required for communication to 9-1 to 9-7 and assigns the communication time to each of the devices. In this function, the transmission apparatus 1 measures frame round trip time (RTT: Round Trip Time) at intervals of several hundred milliseconds for all the terminal apparatuses 9-1 to 9-7, and based on the result. The terminal devices 9-1 to 9-7 are notified of the communication transmission time and the communication amount. The terminal devices 9-1 to 9-7 transmit to the transmission device 1 according to the notified communication transmission time and communication time. This management function is always executed in many GE-PON systems in order to immediately respond to changes in line conditions such as line deviation and addition of termination devices. Hereinafter, this type of management function is referred to as a frame round-trip time tracking function. Next, the route switching procedure and transmission time in the above configuration will be described.

2 and 3 are diagrams schematically showing a change in transmission time accompanying line switching and its correction. Here, it is assumed that the branch line 5 is bypassed to the switching destination line 5 ′. Note that the same type of cable as the branch line 5 is usually used as the switching destination line 5 '.
FIG. 2 shows a case where the switching destination line 5 ′ is longer than the branch line 5. If the transmission time is proportional to the line length, the relationship of the transmission time is: detour line 11 <branch line 5 <switch destination line 5 ′. The transmission time of the branch line 5 is T0, the transmission time of the detour line 11 is T1, and the transmission time of the switching destination line 5 ′ is T2. These can be measured using an optical pulse tester 17.

  First, the control unit 18 changes the delay amount of the delay unit 20 so that the transmission time of the detour line 11 is equal to the transmission time of the branch line 5. (Steps (1) to (2)). That is, T0 = T1 + ΔT1. In this state, the traffic on the branch line 5 is gradually transferred to the detour line 11. Next, the delay amount of the delay device 20 is further increased, and the transmission time of the detour line 11 is made equal to the transmission time of the switching destination line 5 '(step (3)). That is, T2 = T1 + ΔT1 + ΔT2.

  In this embodiment, signal logical link mismatch is prevented by utilizing the frame round-trip time tracking function provided in the GE-PON system. In other words, ΔT2 is compensated by changing (about ten or more nanoseconds) within the error time range of the communication time allowed by the frame round-trip time tracking function. By doing so, the transmission time of the signal before switching before and after switching will eventually be extended by ΔT2, but the signal is transferred without causing any contradiction in the logical link by the frame round-trip time tracking function. Is possible.

  FIG. 3 shows a case where the switching destination line 5 ′ is shorter than the branch line 5. The relationship of the transmission time is: detour path 11 <switching destination line 5 ′ <branch line 5. First, the control unit 18 changes the delay amount of the delay device 20 to T0 = T1 + ΔT1 (steps (1) to (2)). In this state, the traffic on the branch line 5 is gradually transferred to the detour line 11. Next, the delay amount of the delay unit 20 is shortened by ΔT2, and the transmission time of the detour line 11 is made equal to the transmission time of the switching destination line 5 ′ (step (3)). The reduction in the delay amount of ΔT2 is compensated by gradually changing and compensating within the error time range of the communication time allowed by the frame round-trip time tracking function, so that the signal does not contradict the logical link as in the case of FIG. Can be transferred.

  FIG. 4 is a diagram for explaining a method of correcting the optical path difference using the delay device 20. FIG. 4 shows an OTDR waveform as a result of performing the optical pulse test by OTDR on the closed optical path described in the explanation of FIG. The test light is incident from the test light insertion coupler 4a. In FIG. 4, reference numeral 37 denotes Fresnel reflected light from the branching section 3, the branch line 5, and the detour path 11, reference numeral 40 denotes Fresnel reflected light near the branching section 6 a, and reference numeral 41 denotes the test light blocking filter 8. Reflected light.

  Since the branch line 5a and the return light from the detour line 11 are superimposed on the front side from the branch unit 6a to the optical pulse tester 17, it is possible to specify the far end 11b of the detour line 11 in the state of FIG. Can not. However, at the stage where the detour line 11 is delayed by controlling the delay unit 20, the reflection position of the far end 11b changes in the OTDR waveform and is specified as Fresnel reflected light (reference numeral 38) at the position where the line length is the longest. it can.

  Further, since the optical path is closed, the test pulse light itself returns to the optical pulse tester 17, and this test pulse return light 39 indicates the true intermediate position of the closed optical path. Therefore, the control unit 18 measures the optical path difference ΔL between the Fresnel reflected light 38 in the vicinity of the branching unit 6 a and the test pulse return light 39 via the detour path 11. Then, considering that the OTDR waveform is converted to a one-way conversion, the delay amount 20 is instructed to the delay device 20 and a correction of 2ΔL is given to the detour line 11. As a result, the line length of the branch line 5a and the detour line 11 coincide with each other. If the length of the line connecting the branching portion 6a and the far end 11b of the detour path 11 is negligible, the optical path difference between the Fresnel reflected light 38 from the far end 11b of the detour path 11 and the test pulse return light 39 is expressed by ΔL. It is also good.

  FIG. 5 is a flowchart showing the procedure for switching the path of the signal light in this embodiment. This procedure will be described with reference to FIGS. As shown in FIG. 6, the detour line 11 is connected to the branch line 5 a (branch line 5) where the trouble transfer has occurred so as to include the switching points (10 a and 10 b) so that the signal light 23 can be detoured. A closed optical path is created between the test light inserting coupler 4a and the branching portion 6a. In this state, the switching destination line 5 'is not yet connected. At this time, the control unit 18 sets the wavelength tunable filter 19 so as to transmit the test light from the optical pulse tester 17 and to block the signal light 23 bypassed to the power monitor port 13.

  In the state of FIG. 6, the control unit 18 performs an optical pulse test on the closed optical path by the procedure described in the description of FIG. 4, and measures the optical path difference ΔL (step S1 in FIG. 5). If ΔL takes a negative value (step S2), the detour path 11 is shortened so that the optical path difference takes a positive value (step S4). As described above, the control unit 18 measures the optical path difference ΔL between the branch line 5 a and the detour path 11, and gives the delay amount corresponding to 2ΔL to the delay unit 20, so that the optical path difference between the branch line 5 a and the detour path 11 is increased. Correction is made so as to be 0 (step S3).

  Next, the control unit 18 gradually increases the loss of the variable bending loss device 21 as shown in FIG. 7 while keeping the line lengths of the branch line 5a and the detour line 11 to be the same length, while changing the wavelength of the wavelength variable filter 19 Is gradually changed so that the signal light 23 is transmitted (step S5 in FIG. 5). When this procedure is completed, the signal light 23 that has passed through the branch line 5 a is moved to the detour line 11. That is, the transfer of the signal light 23 (reference numeral 24 in the detour path 11) to the detour path 11 is completed. At this time, the test light of the optical pulse tester 17 is in the transmission band of the wavelength tunable filter 19 but is subject to the loss of the variable bending loss device 21, so that the test pulse return light 39 shown in FIG. 4 is also attenuated. The amount of interruption of the signal light 23 can be estimated from this attenuation amount. Since the test pulse regression light 39 is a return light, the level when it is input to the optical pulse tester 17 is sufficiently strong and can cover the range of the magnitude of the loss generated by the variable bending loss device 21. .

  Next, as shown in FIG. 8, with the signal light 24 passing through the detour path 11, a part of the branch line 5a is replaced with a switching destination line 5a 'at the switching points (10a and 10b) (FIG. 5). Step S6). In this state, the control unit 18 measures the optical path difference between the path including the switching destination line 5a ′ and the detour path 11 by the optical pulse tester 17 (step S7 in FIG. 5), and obtains ΔL. By doubling this, the control unit 18 instructs the delay unit 20 to specify a delay amount 2ΔL, and corrects the optical path difference so that the transmission time of the detour line 11 matches the transmission time of the path including the switching destination line 5a ′ ( Step S8).

  Next, the control unit 18 gradually changes the characteristics of the wavelength tunable filter 19 so as to block the signal light 23 while gradually reducing the loss of the variable bending loss device 21 (step S9). When this procedure is completed, the signal light 24 that has passed through the detour line 11 is returned to the original path. That is, the return of the signal light 23 to the branch line 5a is completed. Finally, as shown in FIG. 9, the detour path 11 and the variable bending loss device 21 are removed, and the signal light path switching is completed.

  In all the above procedures, the frame reciprocation time tracking function is functioning simultaneously. In order to use this function, in the procedure of step S8, the time is gradually changed within the range of the error time of the communication time allowed by the frame round-trip time tracking function. Further, in steps S3 and S8, an optical pulse test is also performed.

  As described above, in this embodiment, an optical path difference (change in transmission time) caused by a change in the route of signal light is automatically compensated using the frame round-trip time tracking function. As a result, it is possible to transfer the signal light to another path without causing inconsistency or mismatch of the logical link, and it is possible to carry out trouble relocation work without interrupting the service. As a result, it is not necessary to obtain consent from a large number of users, and trouble relocation work can be implemented systematically.

  FIG. 10 is a diagram for explaining path switching of existing signal light for comparison. This figure is for explaining the switching of overhead lines in a general GE-PON system, and shows how an optical fiber is branched at a station 35 and further branched by a branching device 6 near a user's house via a cable pulling point 36. Show. In FIG. 10, the system is branched into eight systems at the most downstream side, but if the route of one branch line 5 is switched due to the troubled transfer work, the service to all downstream users is stopped. The signal light reaches the user's home via the trunk section A (underground), the wiring section B (aerial), and the cable withdrawal section C (aerial), but when trouble relocation work occurs in the trunk section A and the wiring section B , The impact on the user becomes the most serious.

  On the other hand, in this embodiment, the bypass path 11 for bypassing the signal light of the branch line 5 is connected to form a closed path, and the optical path difference between the branch line 5 and the bypass path 11 is measured. Based on the result, the delay amount of the delay device 20 provided in the detour line 11 is controlled, and the optical path lengths of both lines 5 and 11 are made the same. In this state, the signal light of the branch line 5 is gradually transferred to the detour line 11. The branch line 5 is exchanged for the switching destination line 5 ′ in a state where the signal light is completely diverted to the bypass path 11, and similarly, the optical path difference between the bypass path 11 and the switching destination line 5 ′ is measured. Up to this point, the signal light has continuously reached the branching section 6a without interruption.

  Next, if the optical path difference between the detour line 11 and the switching destination line 5 ′ is known, the delay amount of the delay device 20 is controlled again so that the optical path lengths of both lines 11 and 5 ′ are the same. At this time, the delay amount of the delay unit 20 is gradually changed within the range of the error time of the communication time allowed by the frame round-trip time tracking function provided in the GE-PON system. By doing so, the influence on the logical link due to the change in the optical path length can be eliminated, and the optical path lengths of both lines 11 and 5 'can be made the same without adversely affecting the transmission quality. Finally, the signal light of the detour line 11 is restored to the switching destination line 5 ′, and the switching of the signal path is completed. Even in the process so far, the signal light continuously reaches the branching section 6a without interruption.

  Through the two-stage route change as described above, normal communication is maintained throughout the route switching work, and it is possible to perform systematic trouble relocation work without affecting service to many users. Become. Therefore, improvement of service and reduction of construction cost in the branch type asynchronous optical communication system can be expected. That is, according to this embodiment, it is possible to provide a communication path switching method and a control device that can eliminate the influence on the service associated with the trouble relocation work.

[Second Embodiment]
FIG. 11 is a system diagram showing a second embodiment of the optical communication system according to the present invention. In FIG. 11, parts that are the same as those in FIG. 1 are given the same reference numerals, and only different parts will be described here.
In the second embodiment, instead of the optical pulse tester 17 of FIG. 1, the optical path difference of each line is obtained in-service by optical fiber ring interference. That is, the coherent light generated by the DFB laser diode (DFB-LD) 27 enters the closed path from the test light insertion port 12 via the interference optical coupler 26. Then, the return light is re-entered into the interference optical coupler 26, and the interference light is observed with the optical oscilloscope 28, whereby the optical path difference is obtained. A vibrator 29 is provided on the path from the branching section 6a to the detour line 11.

  Also in FIG. 11, the power monitor port 13 of the test light insertion force plastic 4 a installed on the branch line 5 is used as means for extracting the signal light 23 to the detour path 11. Further, one of the fiber cores 7 is used as the monitor port 15 for the signal light 23, and the branching unit 6 a is used as means for returning the signal light 24 (compensation signal 25) after delay compensation from the detour line 11 to the branch line 5.

  FIG. 12 is a flowchart showing a procedure for switching the path of signal light in the second embodiment of the present invention. This procedure will be described with reference to FIGS. As shown in FIG. 13, the detour line 11 is connected so as to include the switching points (10a and 10b) so that the signal light 23 can be detoured with respect to the branch line 5a (branch line 5) in which trouble relocation occurs. A closed optical path is created between the test light inserting coupler 4a and the branching portion 6a. In this state, the switching destination line 5 'is not yet connected. At this time, the control unit 18 sets the wavelength tunable filter 19 in a state in which the test light from the DFB-LD 27 is transmitted and the signal light 23 bypassed to the power monitor port 13 is blocked.

  In the state of FIG. 13, the closed path including the branch line 5a and the detour line 11 becomes a fiber ring interferometer. Further, a vibrator 29 is installed in the vicinity of the monitor port 15 of the branching section 6a, and vibration is applied to the closed path (vibration), and the interference of the test light is observed with the optical oscilloscope 28 (step S21 in FIG. 12).

  If the excited position deviates from the middle point of the ring, a phase difference occurs between the right-hand test light and the left-hand test light of the ring in the optical path from the vibration position to the optical oscilloscope 28, and the interference optical coupler 26 The interference light intensity fluctuates at. On the other hand, if the excited position is the middle point of the ring, the fluctuation of the interference light intensity is minimized, and the optical oscilloscope 28 can hardly detect it. Due to the characteristics of the fiber ring interferometer, an intermediate point of the closed path can be detected.

Therefore, the control unit 18 corrects the optical path length of the detour path 11 by controlling the delay unit 20 so that the fluctuation of the interference light intensity is minimized, so that the lengths of the branch line 5a and the detour path 11 are matched (step). (S22, S23, S24 loop).
Next, the control unit 18 gradually increases the loss of the variable bending loss device 21 as shown in FIG. 14 while keeping the line lengths of the branch line 5a and the detour line 11 at the same length, while changing the wavelength of the wavelength tunable filter 19. Are gradually changed so that the signal light 23 is transmitted (step S25). When this procedure is completed, the signal light 23 that has passed through the branch line 5 a is moved to the detour line 11. That is, the transfer of the signal light 23 (reference numeral 24 in the detour path 11) to the detour path 11 is completed. At this time, the test light of the DFB-LD 27 is also in the transmission band, and the test is continuously performed.

  Next, as shown in FIG. 15, with the signal light 24 passing through the detour path 11, a part of the branch line 5a is replaced with the switching destination line 5a 'at the switching points (10a and 10b) (step S26). ). In this state, since the fiber ring interferometer is formed by the detour path 11 and the switching destination line 5a ′, the control unit 18 determines the optical path difference between the switching destination line 5a ′ and the detour path 11 in the same manner as in step S21. Measurement is performed (step S27).

  Next, the control unit 18 monitors the interference light intensity (step S28), and changes the delay amount of the delay device 20 until the interference light intensity does not change. Also in this step, the delay amount is gradually changed within the range of the error time of the communication time allowed by the frame round-trip time tracking function. If the interference light intensity does not change, the transmission times of the switching destination line 5a ′ and the detour line 11 coincide (No in step S28).

  Next, the control unit 18 gradually changes the characteristics of the wavelength tunable filter 19 so as to block the signal light 23 while gradually reducing the loss of the variable bending loss device 21 (step S31). When this procedure is completed, the signal light 24 that has passed through the detour line 11 is returned to the original path. That is, the return of the signal light 23 to the switching destination line 5a ′ is completed. Finally, as shown in FIG. 15, the detour path 11 and the variable bending loss device 21 are removed, and the path switching of the signal light is completed.

  As described above, in the second embodiment, the optical path difference is measured by an optical fiber ring interferometer instead of using the optical pulse tester 17 of the first embodiment. Even in this case, the optical path difference can be compensated similarly to the first embodiment, and the signal light can be transferred to another path without causing a logical link inconsistency or mismatch. That is, according to this embodiment as well, it is possible to provide a communication path switching method and a control device that can eliminate the influence on the service associated with the troubled transfer work.

  The present invention is not limited to the above embodiment. For example, if there is an unused branch line 5, this can be used as a detour line. This is obvious because the same signal light is transmitted to the branch line 5 downstream from the branch part 3. In this way, there is no need to connect the detour line 11, and effects such as simplified work can be obtained.

  Furthermore, the present invention is not limited to the above-described embodiments as they are, 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 components 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 system diagram showing an embodiment of an optical communication system according to the present invention. The figure which shows typically the change of the transmission time accompanying line switching, and its correction | amendment. The figure which shows typically the change of the transmission time accompanying line switching, and its correction | amendment. The figure for demonstrating the method of correct | amending an optical path difference using the delay device. The flowchart which shows the switching procedure of the path | route of the signal light in embodiment of this invention. The figure which shows the initial state in the switching procedure of FIG. The figure which shows the next state of FIG. The figure which shows the next state of FIG. The figure which shows the next state of FIG. The figure for demonstrating per path switching of the existing signal light for a comparison. The system figure which shows 2nd Embodiment of the optical communication system in connection with this invention. The flowchart which shows the switching procedure of the path | route of the signal light in 2nd Embodiment of this invention. The figure which shows the initial state in the switching procedure of FIG. The figure which shows the next state of FIG. The figure which shows the next state of FIG. The figure which shows the next state of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Transmission apparatus, 2 ... Test light cutoff filter, 3 ... Branch part (splitter), 4a-4d ... Test light insertion coupler, 5 (5a-5d) ... Branch line, 5 '(5a'-5d') ... switching destination line, 6a to 6d ... branching section, 7 ... fiber core wire, 8 ... test light blocking filter, 9-1 to 9-7 ... termination device, 10a, 10b ... switching point, 11 ... detour path, 11a , 11b ... one terminal, 12 ... test light insertion port, 13 ... power monitor port, 14 ... compensation signal insertion port, 15 ... monitor port, 16 ... signal light cutoff filter, 17 ... optical pulse tester, 18 ... Control unit, 19 ... tunable wavelength filter, 20 ... delay device, 21 ... variable bending loss device, 22 ... coupler, 23 ... signal light, 24 ... signal light flowing through detour path 11, 25 ... compensation signal, 26 ... interference light Coupler, 27 ... DFB laser diode (DFB-LD), 28 ... optical oscilloscope, 29 ... vibrator, 34 ... reflected light from the test light blocking filter 8, 37 ... Fresnel reflected light from the branching section 3, the branch line 5, and the detour path 11, 38 ... Fresnel reflected light from the far end 11b of the detour path 11, 39 ... Test pulse return light, 40 ... Fresnel reflected light near the branching section 6a, 41 ... Reflected light from the test light blocking filter 8

Claims (7)

A transmission device that transmits signal light, a termination device that terminates the optical fiber that transmits the signal light, and a frame round-trip time between the transmission device and the termination device for communication timing between the transmission device and the termination device A communication path switching method used in an optical communication system having a management function to manage based on the measured value of
A connection step of connecting a bypass path connected to the variable delay device to the switching source line to form a closed path;
A first measurement step of measuring an optical path difference on the closed path between the switching source line and the bypass path;
A first correction step of controlling a delay amount of the variable delay device from the result obtained in the first measurement step to correct an optical path difference between the switching source line and the bypass path;
A detour step of detouring the signal light of the switching source line to the detour path after completion of the first correction step;
An exchange step of exchanging the switching source line with a switching destination fiber;
A second measurement step of measuring an optical path difference on the closed path between the switching destination fiber and the bypass path;
From the result obtained in the second measurement step, a delay amount of the variable delay device is compensated within an error range allowed by the management function, and an optical path difference between the switching destination fiber and the bypass path is corrected. 2 correction steps;
A communication path switching method comprising: a restoration step of restoring the signal light of the bypass path to the switching destination fiber after completion of the second correction step. Connecting a tunable filter to the bypass path;
A variable loss device is attached to the switching source line,
2. The communication according to claim 1, wherein the bypassing step is a step of adjusting a transmission band of the wavelength tunable filter to a wavelength of the signal light and increasing a loss of the variable loss device with respect to the wavelength light. Route switching method. Connecting a tunable filter to the bypass path;
A variable loss device is attached to the switching source line,
2. The communication path according to claim 1, wherein the restoration step is a step of removing a transmission band of the wavelength tunable filter from a wavelength of the signal light and reducing a loss of the variable loss device with respect to the wavelength light. Switching method. An optical coupler that is also connected to the detour path is connected in advance to the switching source line,
At least one of the first measurement step and the second measurement step is performed by calculating the optical path difference by an optical pulse test method performed by entering test light through the optical coupler to the switching source line and the bypass path. The communication path switching method according to claim 1, wherein the communication path switching method is a measuring step. An optical coupler that is also connected to the detour path is connected in advance to the switching source line,
At least one of the first and second measurement steps includes the step of entering the test light into the optical coupler and observing the interference with the return light returning through the closed path by fiber ring interferometry. The communication path switching method according to claim 1, wherein the step of measuring the communication path is performed. The optical communication system is a form in which an optical fiber extending from the transmission device is branched into a plurality of branch lines, and each branch line is further branched into a plurality of core wires,
2. The communication path switching method according to claim 1, wherein when there is an unused branch line among the plurality of branch lines, the unused branch line is used as the detour path. A transmission device that transmits signal light, a termination device that terminates the optical fiber that transmits the signal light, and a frame round-trip time between the transmission device and the termination device for communication timing between the transmission device and the termination device A control device for carrying out a communication path switching method used in an optical communication system having a management function to manage based on the measured value of
A first measurement process for measuring an optical path difference between the switching source line and the bypass path on a closed path formed by connecting a bypass path connected to the variable delay device to the switching source line;
A first correction process for controlling a delay amount of the variable delay device from a result obtained in the first measurement process to correct an optical path difference between the switching source line and the bypass path;
A detour process for detouring the signal light of the switching source line to the detour path after the completion of the first correction process;
After the switching source line is replaced with a switching destination fiber, a second measurement is performed to measure an optical path difference on the closed path between the switching destination fiber and the detour path in a state where the signal light is detoured to the detour path. Processing,
From the result obtained in the second measurement process, a delay amount of the variable delay device is compensated within an error range allowed by the management function to correct an optical path difference between the switching destination fiber and the detour path. 2 correction processing;
And a restoration process for restoring the signal light of the detour path to the switching destination fiber after the completion of the second correction process.

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