JP5875944B2 - PON transmission line redundancy system - Google Patents

Description

  The present invention relates to redundancy of an access optical fiber communication network. More specifically, the present invention relates to a PON (Passive Optical Network) transmission path redundancy scheme in which a part of transmission paths are shared by a plurality of users.

  As an access optical fiber communication network, a PON that shares a part of a transmission path among a plurality of users is widely used as a general Internet connection line for homes. In general, an internet connection line for home use is cost-intensive, and therefore, transmission lines and ONUs are generally not made redundant. For this reason, when a line abnormality such as disconnection or breakage of a transmission line occurs due to a disaster or an unexpected accident on a line shared by a plurality of users (also referred to as a trunk line in the specification, hereinafter referred to as a trunk line) Since all users who share this trunk line (all ONUs under their control) cannot communicate with each other, the influence of a network failure is large, which becomes a big problem. On the other hand, in the electric power business, it is considered that a more reliable communication line is required in some cases, so that PON fault tolerance technology becomes important.

  When a normal optical communication service is not possible due to an optical line failure, the carrier identifies the faulty part and repairs the faulty part immediately or replaces the section of the optical cable that has been cut or damaged with another optical cable. Need to be laid again. In particular, when the main line is damaged, it must be promptly restored to cause inconvenience to all users sharing the main line. However, for re-laying the trunk line, a construction vehicle such as a unic car, an engineer having a technology capable of laying an optical cable, and the like are required. That is, since it takes various times to complete the repair work, it is difficult to instantaneously restore the optical communication service. Therefore, it is desired to increase the reliability by making the optical transmission line (optical line), particularly the trunk line redundant.

  Therefore, a PON transmission line redundancy scheme that uses an adjacent trunk line as a detour line has been proposed. As shown in FIG. 10, this PON transmission line redundancy system is configured to connect the drop cable branch closures 104 and 104 ′ of the two trunk lines 103 and 103 ′ to the side of the trunk line where the failure occurs when a failure occurs in the trunk line. By connecting the drop cable branch closure in series after the trunk drop closure on the trunk line where no failure has occurred, the ONU device on the trunk side where the failure has occurred is connected to the drop cable on the trunk line where the failure has not occurred. By connecting as one of a plurality of output lines of the main branch closure, a redundant configuration of an optical communication line that protects the trunk lines of each other is constructed. For example, as shown in FIG. 10, the drop cable branch closure 104 is provided with an optical switch 105 in the upper stage of the optical splitter 106, and includes a light reception monitoring unit 107 using one of the output terminals of the optical splitter 106. The optical switch 105 is controlled by detecting the downstream signal of the trunk line branched from the splitter 106. On the other hand, the default side terminal of the optical switch 105 is connected to one of the output terminals of the optical splitter 106 ′ of the drop cable branch closure 104 ′ connected to another trunk line by a bypass optical fiber 109. In the figure, reference numeral 101 denotes an OLT in the concentrator, 102 denotes an optical splitter, 108 denotes a drop cable, and 110 denotes an ONU.

  Therefore, according to this PON transmission line redundancy system, when a line abnormality occurs on the trunk line 103, the light reception monitoring unit 107 of the drop cable branch closure 104 detects the downstream signal after being branched by the optical splitter 106. Then, the abnormality of the received light power is detected, and the optical switch 105 is switched from the state shown in FIG. 11A to the state shown in FIG. 11B, thereby changing the upper line connection destination from the main line 103 to another main line (standby main line) 103 ′ ( (See FIG. 10). As a result, the drop cable branch closure 104 is reconnected as one of the output lines after the drop cable branch closure 104 ′ of the other trunk line 103 ′ connected to the same OLT 101. Therefore, each ONU device 110 in which a communication failure has occurred includes a drop cable branch closure 104 (optical splitter 106 → optical switch 105 → bypass optical fiber 109), drop cable branch closure 104 ′ (optical splitter 106 ′ → Signal transmission / reception with the OLT device 101 can be performed via the optical switch 105 ′) and another trunk line 103 ′, and automatic recovery can be performed.

  Similarly, when a line abnormality occurs on the trunk line 103 ′, the light reception monitoring unit 107 ′ of the drop cable branch closure 104 ′ detects an abnormality of the light reception power and switches the optical switch 105 ′ to connect the upper line. The destination is changed from the trunk line 103 ′ to another trunk line (backup trunk line) 103. As a result, the drop cable branch closure 104 ′ is reconnected to the subsequent stage of the drop cable branch closure 104. Therefore, each ONU device 110 ′ in which a communication failure has occurred includes a drop cable branch closure 104 ′ (optical splitter 106 ′ → optical switch 105 ′ → bypass optical fiber 109 ′), drop cable branch closure 104 (optical Signals can be transmitted / received to / from the OLT apparatus 101 via the spare trunk line 103 via the splitter 106 → the optical switch 105), and can be automatically restored.

JP 2011-193263 A

  However, in the redundant configuration described in Patent Document 1, even if the restoration of the line is completed and the optical signal reaches the closure, it cannot be detected by the optical power monitor in the subsequent stage of the optical switch (FIG. 12A). )reference). Therefore, in order to return the transmission line to the original state, an operator must perform an operation of opening the closures one by one and manually switching the optical switch as shown in FIG. This requires not only an aerial work vehicle, but also delivery of work to the police and labor costs. In addition, since it cannot be easily switched by hand, a circuit for manually switching after recovery from a failure is required, and the circuit becomes complicated.

  Of course, if the optical switch is not restored so that the connection destination of the upper line is returned to the original trunk line immediately after the failure is recovered, it does not cause any trouble. In that case, which line passes through which closure. It is necessary to manage separately whether or not. Analyzing the signal packet does not tell which closure it has passed through, so it is quite difficult to detect the path. Therefore, if the data on the administrator side and the actual route are inconsistent, the disconnection position and the range of the line disconnection will be confused unlike the data when a failure occurs in the future.

  In the redundancy system described in Patent Document 1, the optical power monitors 107 and 107 ′ are connected to one of the output terminals of the optical splitters 106 and 106 ′, and the default terminals of the optical switches 105 and 105 ′ are connected. Since the bypass cables 109 and 109 'thus connected are connected to one of the output terminals of the optical splitters 106 and 106' of the other drop cable branch closures 104 and 104 ', the output terminals of the optical splitters 106 and 106' There is a problem that the number of lead-in lines (drop cables) 108 and 108 ′ to the ONUs 110 and 110 ′ must be reduced rather than the number. That is, the number of connection of the drop cables 108 and 108 'is two less for each drop cable branch closure 104 and 104'. In general drop cable branch closures 104 and 104 ′, eight drop cables 108 and 108 ′ are connectable by optical splitters 106 and 106 ′. A 25% drop cable reduction will be forced. Originally, an optical fiber branched by a drop cable branch closure is an important infrastructure for increasing profits as lead-in wires (drop cables) 108, 108 'to the ONUs 110, 110', and it is desirable to reduce the number thereof. Absent.

On the other hand, when a failure occurs in the trunk line, the ONU connected to the trunk line on which the failure has occurred is connected to the trunk line on which the failure has not occurred via the two drop cable branch closures. Therefore, a drop cable branch closure between the ONU on the side where the failure has occurred on the trunk line and the ONU originally connected to the trunk line on which the failure has not occurred, that is, before and after the failure of the trunk line occurs. By connecting as one of the plurality of output lines, there is a problem that the light intensity reaching the ONU is extremely different. For example, according to FIG. 13 showing the change in light intensity before and after the failure, in the redundancy system described in Patent Document 1, assuming that the light output intensity from the OLT 101 is 100, first, the 4-branch optical splitter 102 in the master station 1 / 4 of 25. Since the transmission loss of the optical switch 105 is small, if it is ignored, it is further reduced to 1/8 by the eight-branch optical splitter 106, and eventually the ONU 110 receives light having an intensity of 3.125. When this is a failure, as shown in FIG. 13B, since it passes through the 8-branch optical splitter twice (106 → 106 ′), the ONU 110 on the trunk line 103 side where the failure has occurred is 0.39 (before the failure occurs). Only 12.48%) of light will reach. That is, there is a problem in that a large change in transmission loss that cannot be ignored before and after the main line failure occurs. In addition, when multiple faults occur and the switch to the drop cable branch closure of another trunk line occurs in a cascade manner, it passes through the optical splitter each time. Since the transmission loss coefficient (transmission loss coefficient = (1 / a) ⁿ , where a is the number of branches of the optical splitter and n is the number of cascade stages), the transmission loss is suddenly increased to cause signal degradation. It is a redundant configuration that cannot cope with multiple failures. For example, when the number of cascade stages is 2, the light intensity of 3.125 that has reached the ONU at the normal time deteriorates to 0.0488 (about 1.56% before the occurrence of the failure), which is two orders of magnitude smaller.

  In addition, the light intensity required for the optical power monitors 107 and 107 ′ is sufficient to be one-hundredth of the power of the input light and does not require the light intensity required for optical communication. Even if an optical power monitor is connected to the output terminal, most of the power is wasted.

  An object of the present invention is to provide a PON transmission line redundancy system that is simple and can efficiently use the performance of the OLT, can cope with multiple failures, and does not cause communication interruption even in the event of a power failure. It is another object of the present invention to provide a PON transmission line redundancy system that can be applied to a network that requires high reliability such as that for electric utilities. Furthermore, an object of the present invention is to provide a PON transmission line redundancy system that can be configured redundantly without reducing the number of lines drawn into the ONU.

  In order to achieve this object, the PON transmission path redundancy system according to claim 1 is an optical system in which a plurality of drop cables connected to a slave station (ONU) are connected by branching a trunk line connected to the master station (OLT). A transmission path changeover switch module is disposed above the splitter, and the transmission path changeover switch module includes a first optical coupler connected to the trunk line, and a non-self-holding optical switch connected to the first optical coupler. , An optical power monitor that controls a non-self-holding optical switch by detecting a downstream signal from the main line branched from the first optical coupler, and a second optical coupler connected to the non-self-holding optical switch. A bypass optical fiber for bypassing one of the branch ports of the second optical coupler of another trunk transmission line switch module connected to the same OLT as the default side port of the non-self-holding optical switch. When the main power down signal is detected by the optical power monitor, the connection state of the non-self-holding optical switch is held on the non-default side, and when the fault occurs and the main signal down signal cannot be detected, The holding type optical switch is switched to the default side to change the ONU connection destination trunk line connected to the faulty trunk line to another trunk line that is not faulty. Is detected by an optical power monitor, the non-self-holding optical switch is automatically returned to the original state, and the upper line connection destination is returned to the original trunk before the occurrence of the failure.

  Further, in the PON transmission line redundancy system according to claim 1 according to the invention of claim 2, the default of the non-self-holding type optical switch of each transmission path changeover switch module provided on the trunk line branched from the same OLT The side port and the branch port of the second optical coupler of the other transmission line changeover switch module are cascade-connected by a bypass optical fiber.

  The invention according to claim 3 is the PON transmission line redundancy system according to claim 1, wherein the transmission line changeover switch modules of adjacent trunk lines installed in geographically close locations are connected by a bypass optical fiber, The adjacent trunk line is used as a detour route.

  According to a fourth aspect of the present invention, in the PON transmission line redundancy system according to the first aspect, a transmission line that reaches a branch closure for a drop cable by dividing a plurality of trunk lines connected to the same OLT into separate multi-core cables. And drop cable branch closures connected to the same OLT are installed in geographically close locations, and the bypass optical fiber connecting the transmission line changeover switch modules is installed between adjacent ONUs. It is characterized by being.

  According to the PON transmission line redundancy system according to claim 1, a non-self-holding type optical switch is used as a switch for switching the upper line connection destination, and an optical power monitor is provided in the preceding stage. When a failure occurs in the trunk line up to the previous section, it automatically bypasses the failed trunk line, and when the trunk line fault is removed and restored, the upper line connection destination is automatically changed to the original trunk line before the failure occurred. Since it can be restored, the communication is not interrupted and the light intensity is restored to the original at the same time as the failure is restored. In addition, it is not necessary for the worker to open the closures one by one and manually switch the optical switch. At the same time, there is no need to send work to an aerial work vehicle or police for the work of switching based on the optical switch, and labor costs. In addition, even when a power failure occurs, the non-self-holding optical switch automatically switches to the default side and the line is maintained, so communication such as communication lines for power distribution automation, etc., where communication is required to restore power May also be available.

  In addition, the ONU can be connected using all the optical fibers branched by the optical splitter of the drop closure for the drop cable as drop lines (drop cables). Obstacles can be applied. Thereby, bandwidth resources can be effectively used. In addition, OLT and ONU do not require any new functions, can be used as they are, and the distance between connection closures is shorter than the length of the main line, making it less expensive than duplicating the main line It can be suppressed.

  In this redundant system, the switching control signal of the optical switch is obtained at the closure part, so remote control or the like is unnecessary, and a control line for that purpose is not required. Further, since a non-self-holding optical switch is used, For generation, the output of the photodiode is simply amplified by the transistor in the optical power monitor. In this redundant system, the non-self-holding optical switch may have a low operating speed and can be selected with lower power consumption. In addition, by selecting an optical switch having a small wavelength dependency, there is a possibility that the present invention can be applied to a case where an optical splitter is replaced with an AWG in the future to form a WDM-PON.

  In addition, the PON transmission line redundancy system of the present invention includes a drop cable branch closure connected to a trunk line on which a failure has occurred and a trunk line on which no failure has occurred when a failure occurs on the trunk line. Since the drop cable branch closure is connected in parallel to the trunk line in which no failure has occurred, the light intensity reaching the ONU changes drastically before and after the failure of the trunk line ( It will not deteriorate. For example, as shown in FIG. 9 showing the change in the light intensity before and after the failure, assuming that the light output intensity from the OLT 1 is 100, first, it becomes 1/4 of 25 in the 4-branch optical splitter 2 in the master station. Since the transmission loss caused by branching the signal to the optical power monitor 6 by the first optical coupler 5 and the transmission loss at the optical switch are small and neglected, the second optical coupler 8 having two branches further reduces the 12.2. Then, it is further reduced to 1/8 by the 8-branch optical splitter 10 and eventually the ONU 12 reaches 1.56 light intensity. When this is a failure, since it passes through the second optical coupler 8 of two branches twice, 0.78 (50% before the failure) of light reaches the ONU 12 on the trunk line where the failure has occurred. That is, it is possible to suppress a change in transmission loss so that the signal strength is reduced by half before and after the main line failure, and a signal strength twice that of the redundancy method described in Patent Document 1 can be obtained.

  As described above, according to the PON transmission line redundancy system of the present invention, it is simple, can efficiently use the performance of the OLT, can cope with multiple failures, and does not cause communication interruption even in the event of a power failure. It is possible to build fault tolerance that can be applied to networks that require high reliability.

  According to the second aspect of the present invention, the trunk line transmission line changeover switch modules connected to the same OLT are connected to each other by cascade connection, so that the upper line connection destination is multiplexed to cope with multiple failures. it can. In addition, the drop closure for the main drop cable on the failed side and the branch closure for the drop drop on the main trunk that has not failed are connected in parallel to the trunk that has not failed. Even if switching to a branch closure for a drop cable of another trunk line occurs, the light is only halved every time it passes through the second optical coupler. It can handle multiple failures without optical signal degradation and transmission loss. For example, even if the number of cascade stages is 2, the light intensity of 1.56 that has reached the ONU at normal time can only deteriorate to 0.39 (about 25% before the failure) of 1/4, This is the same as the light intensity reaching the ONU in the case of the cascade stage number 1 in the case of the redundancy method described in Patent Document 1.

  The invention according to claim 3 is the PON transmission line redundancy system according to claim 1, wherein the transmission line changeover switch modules of adjacent trunk lines installed in geographically close locations are connected by a bypass optical fiber, Since the adjacent trunk line is used as a detour line, the construction work of the bypass optical fiber is not required to be relatively large over a relatively short distance, and the labor and cost of the construction can be reduced.

  According to the fourth aspect of the present invention, fault tolerance is provided in the section from the OLT to the final closure even in a transmission line using a multi-core cable.

It is explanatory drawing which shows the basic composition of the PON transmission line redundancy system of this invention. It is explanatory drawing which shows one Embodiment of a transmission-line changeover switch module. It is a basic block diagram of the PON transmission line redundancy system of this invention which shows the state of cascade connection. It is a basic composition figure showing one embodiment of a PON transmission line redundancy system of the present invention using a multi-core cable. It is a basic block diagram which shows one Embodiment of the connection structure in the urban area of the PON transmission line redundancy system of this invention using a multi-core cable. It is a schematic structure figure of a transmission line changeover switch module. It is a figure explaining the operation | movement condition of the transmission path changeover switch module at the time of a failure, (A) is the moment of failure occurrence, (B) shows the switching state of the non-self-holding type switch when a failure occurrence is detected. It is a figure explaining the operation | movement condition of the transmission path changeover switch module after failure recovery, (A) is the moment of failure recovery, (B) shows the switching state of the non-self-holding type switch when failure recovery is detected. It is a figure which shows the change of the loss of the optical signal before and after failure occurrence, (A) shows before failure occurrence, (B) shows after failure occurrence. It is explanatory drawing which shows the basic composition of the conventional PON transmission line redundancy system. FIGS. 10A and 10B are diagrams for explaining the operation status of the transmission line changeover switch module when a failure occurs in the PON transmission line redundancy system of FIG. 10, where FIG. 10A is the moment of failure occurrence, and FIG. Indicates the switch switching status. FIGS. 10A and 10B are diagrams for explaining the operation status of the transmission path changeover switch module after the failure recovery of the PON transmission path redundancy method of FIG. 10, where FIG. 10A is the moment of failure recovery, and FIG. Indicates the switch switching status. It is a figure which shows the change of the loss of the optical signal before and after failure occurrence of the PON transmission line redundancy system of FIG. 10, (A) shows before failure occurrence, (B) shows after failure occurrence.

  Hereinafter, the configuration of the present invention will be described in detail based on embodiments shown in the drawings.

  In the PON transmission line, it is necessary to make the trunk line redundant because the influence at the time of disconnection is larger than the branch line. Here, since the PON transmission line is usually branched once by the optical splitter in the concentrating station, the fibers connected to the same OLT are often laid on a relatively close path. Therefore, line costs can be further reduced if adjacent trunk lines can be used as backup lines. In general, the common part of the transmission line is relatively long, while the distance between adjacent drop cable branch closures (optical splitters) is short, so it is necessary to connect the closures rather than duplicating the trunk line for a redundant configuration. The total fiber length is considered to be shorter.

  Therefore, in the PON transmission line redundancy system of the present invention, a transmission line changeover switch module is arranged immediately before an outdoor optical splitter, and adjacent modules are connected by a bypass optical fiber, and a failure occurs in the connecting trunk line. In this case, the subordinate ONUs are configured to be connected in parallel to the adjacent trunk line together with the ONUs subordinate to the adjacent trunk line by switching the signal path using a non-self-holding optical switch.

  Specifically, as shown in FIG. 1 and FIG. 2, the PON transmission path redundancy system of the present embodiment has a plurality of trunk lines connected to the master station (OLT) branched to the slave station (ONU) 12. The transmission line changeover switch module 4 is disposed above the optical splitter 10 to which the drop cable 11 is connected, and the transmission line changeover switch module is connected between the plurality of trunk lines 3, 3 ′,... Connected to the same OLT 1. 4 and 4 ′ are connected to each other by bypass optical fibers 9 and 9 ′, so that the adjacent trunk lines 3 and 3 ′ are used as a detour line.

Here, the transmission path changeover switch module 4 includes a first optical coupler 5 connected to the trunk line 3, a non-self-holding optical switch 7 connected to the first optical coupler 5, and a first optical coupler 5. And an optical power monitor 6 for detecting the downstream signal of the trunk line 3 branched from the optical line 7 and controlling the non-self-holding optical switch 7, and a second optical coupler 8 connected to the non-self-holding optical switch 7. And a drop cable branch closure (for example, a box indicated by reference numeral 18 in FIGS. 6 to 9, a box indicated by reference numerals 18 _A1 and 18 _{A2 and} 18 _B1 and 18 _B2 in FIGS. 4 and 5). The second light of the transmission path changeover switch module 4 ′ connected to the default side port B of the non-self-holding optical switch 7 of the transmission path changeover switch module 4 and the other trunk line 3 ′ branched from the same OLT 1. A bypass optical fiber 9 is connected to one of the branch ports of the coupler 8 ′. In other words, when the non-self-holding optical switch 7 is switched to the default side port B, the transmission line changeover switch 4 on the main line 3 side where the failure has occurred via the bypass optical fiber 9 connected to the default side port B. And the transmission line changeover switch 4 ′ on the trunk line 3 ′ on which no failure has occurred are connected in parallel to the trunk line on which no failure has occurred, so that a redundant configuration using the adjacent trunk line as a detour line is obtained. . In the case of this embodiment, the transmission path changeover switch module 4 includes, for example, as shown in FIG. 2, first and second two 1 × 2 optical couplers 5 and 8 and one single 1 × 2 non-self-holding. A type optical switch 7 is disposed, and a power source 13 is connected for the operation of the optical power monitor 6. Since the power supply 13 normally uses a power pole with a power cable laid when laying a transmission line, it is easy to branch off the power cable. In this embodiment, the transmission path changeover switch module 4 is incorporated in the drop cable branch closure, but is not particularly limited to this, and in some cases, a housing different from the drop cable branch closure. You may make it arrange | position in the body and arrange | position in the front | former stage of the branch closure for drop cables.

  The non-self-holding optical switch 7 has a characteristic that the connection state of the switch returns to a specific (default) state when the power is cut off. The non-self-holding optical switch 7 always needs to apply a voltage to the optical switch in the normal (non-accident / failure) state, but automatically returns to the default state when the power is turned off (bypassing to the adjacent trunk line). ), And the power supply (and optical signal) is restored again to automatically return to the normal state, which simplifies operation. In the present embodiment, the switching operation of the non-self-holding optical switch 7 is controlled using the current generated by the optical power monitor 6. For example, as shown in FIG. 6, power supply to the non-self-holding optical switch 7 is performed by amplifying the output of the optical power monitor 6 with an amplifier 14. That is, when the optical power monitor 6 can receive the downstream optical signal from the OLT 1 and power is supplied to the non-self-holding optical switch 7, the ports A and C are connected (non-default state), and the power or When the optical input from the OLT 1 is lost, it automatically returns to the default state (connection between B and C).

  The optical power monitor 6 normally uses a photodiode as a light receiving element, and generates a weak current when receiving light. This is amplified by a simple electric circuit such as the operational amplifier 14 and added to a current or voltage exceeding the threshold required by the non-self-holding optical switch 7, so that the switch bar of the non-self-holding optical switch 7 is in the default state. (The state on the left side in FIG. 2: B port) can be switched to the non-default state (the state on the right side in FIG. 2: connection between A and C). To supply power to the non-self-holding optical switch 7, it is only necessary to amplify the output of the optical power monitor 6, and when the optical input from the power source 13 or the OLT 1 is lost (power is cut off), the non-self-holding switch 7 automatically returns to the default state (connection between B and C). Further, when the optical input from the power supply 13 and the OLT 1 is restored, the ports A and C are automatically connected, so that a reset operation or the like is unnecessary. Here, the power interruption is a concept including both the case where the optical signal (downstream signal) received by the optical power monitor 6 is interrupted or the power source 13 for operating the amplifier 14 is cut off. Even if the downstream signal is not interrupted, if the power supply fails, the default state is switched. For example, if a power pole laying a transmission line collapses and the power cable is disconnected, the optical cable will be damaged a little, and in some cases, it is assumed that it will be damaged greatly. It is reasonable to force it to bypass.

  As shown in FIG. 2, the drop cable branch closures (transmission path switching switch modules 4, 4 ′) are connected to each other by default port B of the non-self-holding optical switch 7 of one trunk line 3 and the other trunk line 3. By connecting the branch port of the second optical coupler 8 ′ of the “transmission path changeover switch module 4” with the bypass optical fiber 9, two adjacent trunk lines 3 and 3 ′ are mutually protected. However, in some cases, as shown in FIG. 3, all drop cable branch closures (transmission path switching switches) provided on the trunk lines 3,..., 3 ′ ″ branched from the same OLT 1 The modules 4,..., 4 ′ ″) may be cascaded. In the case of cascade connection, a loop can be configured by connecting the closures at both ends. In the case of cascade connection, the ONUs under each of the failed trunk lines switch the upper line connection destination until they are connected to the connection destination trunk line that does not cause a failure, so that it is possible to cope with multiple failures. Here, it is preferable to connect the transmission line changeover switch modules of adjacent trunk lines installed in geographically close locations with a bypass optical fiber and use the adjacent trunk line as a bypass path. In this case, the total length of the optical fiber required for trunk redundancy can be reduced.

  According to the PON transmission path redundancy system configured as described above, when a downstream signal of a connection destination trunk line is detected, a failure occurs in the connection destination trunk line 3 as shown in FIG. 7A, for example. In a normal state that is not, the connection state of the non-self-holding optical switch 7 is held on the non-default side. That is, when the optical power monitor 6 can receive the downstream optical signal from the OLT 1 and the power is supplied, the non-self-holding optical switch 7 is connected to the ports A and C. However, when a downstream signal cannot be detected, such as when a failure occurs in the connecting trunk 3, the optical signal is interrupted by the optical power monitor 6 in front of the non-self-holding optical switch 7 as shown in FIG. Therefore, the control voltage from the optical power monitor 6 decreases or disappears, and the switching control of the non-self-holding optical switch 7 is automatically performed. The non-self-holding optical switch 7 is in a state where the ports B and C are connected (default). That is, as shown in FIG. 9 (B), the non-self-holding optical switch 7 is switched to the default state, and another transmission line change-over switch connected to the other trunk line 3 ′ via the bypass optical fiber 9 The connection destination trunk line of the ONU 12 connected to the optical splitter via the second optical coupler 8 'of the module 4' is changed to another trunk line 3 '. In addition, the PON transmission line redundancy system of the present invention uses the transmission line changeover switch module 4 (drop cable branch closure) on the main line side where the failure has occurred and the transmission line changeover switch module 4 on the main line side where no trouble has occurred. By connecting in parallel with '(branch closure for drop cable) and the trunk line 3 where no failure has occurred, the ONU 12 on the side of the trunk line 3 where the failure has occurred also has 50% light intensity before the failure. A downstream optical signal arrives. For this reason, the communication line is not lost even in the event of a power failure.

  Further, when the main line failure is removed and restored, as shown in FIG. 8A, the main line down signal reaches the non-self-holding optical switch 7 of the drop cable branch closure. An optical signal / downstream signal is detected by the optical power monitor 6 in the preceding stage of the optical switch 7. Then, as shown in FIG. 8B, the control voltage from the optical power monitor 6 is applied, and the non-self-holding optical switch is automatically switched from the port B to A, and the original state (connection between AC is connected). Return to. As a result, the upper line connection destination is automatically returned to the original trunk line before the failure occurred. At the same time, the ONU 12 connected to the main line after the failure is restored to the light intensity (1.56) before the occurrence of the failure, as shown in FIG.

FIG. 4 shows an example of an embodiment of a redundant configuration in a transmission line using a multi-core cable. Note that the configurations of the OLT and the transmission path connected to the OLT in this embodiment are distinguished by alphabets and numbers attached to the reference numerals in the drawing. Generally, multi-core cables 15 and 16 are used for laying optical fiber transmission lines. In this case, a multi-core cable 15 generally lays a relatively long distance (up to several kilometers) from the concentrating station, and the multi-core cable 15 is further branched into a plurality of multi-core cables 16 by a cable branch closure 17 on the way. Thereafter, the drop cables are branched into a plurality of drop cables at the branch closures 18 _A1 and 18 _{A2 and} 18 _B1 and 18 _B2 .

Usually, the concentrator station has a plurality of OLTs (or a plurality of optical interfaces in one OLT) 1 _A and 1 _B , and a plurality of multi-core cables are also connected, so one stage of each OLT 1 _A and 1 _B The branch lines 3 _A1 and 3 _B1 , 3 _A2 and 3 _B2 are accommodated in separate multi-core cables 15 at the branch of the eye. In FIG. 4, for the sake of simplicity, two branches are used, and 3 _A1 and 3 _B1 , 3 _A2 and 3 _B2 are combined into a cable. Thereafter, the drop cable branch closures 18 _A1 and 18 _{A2 and} 18 _B1 and 18 _B2 are laid through the cable branch closure 17 and connected to the same OLT 1 _A or 1 _B. 18 _A1 and 18 _A2 or 18 _B1 and 18 _B2 are installed in geographically close places. Specifically, for example, the drop cable branch closures 18 _A1 and 18 _{A2 of the} trunk lines 3 _A1 and 3 _A2 connected to the OLT 1A and the drop cables branch of the trunk lines 3 _B1 and 3 _B2 connected to the OLT 1 _B are used. The closures 18 _B1 and 18 _B2 are installed close to each other. The bypass optical fibers 9 _A and 9 _B connecting the transmission path changeover switch modules 4 _A1 and 4 _{A2 and} 4 _B1 and 4 _B2 pass through between the adjacent ONUs 12 _A1 and 12 _{A2 and} 12 _B1 and 12 _B2. Laid. By connecting in this way, fault tolerance is provided in the sections from OLT _1A , _1B to final closures 18 _A1 , 18 _{A2 and} 18 _B1 , 18 _B2 .

  PON transmission lines are often laid out in a grid pattern in urban areas. In this case, if the PON transmission path redundancy system of the present invention is used, the closures can be connected as shown in FIG. 5, for example.

  The above-described embodiment is an example of a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the scope of the present invention. For example, if the increase in transmission loss due to the insertion of a non-self-holding optical switch or optical coupler becomes so large that it cannot be ignored, measures such as increasing the light source output of the OLT or using an optical amplifier are required. Sometimes.

1,1 _A , 1 _B OLT
2 optical splitters 3, 3 ', _3A1 , _3B1 , _3A2 , _3B2 trunk lines 4, 4', _4A1 , _4B1 , _4A2 , _4B2 transmission line changeover switch module
5, 5 ′ first optical coupler 6, 6 ′ optical power monitor 7, 7 ′ non-self-holding optical switch 8, 8 ′ second optical coupler 9, 9 ′, 9 ″, 9 ′ ″, 9 _A , 9 _B , bypass optical fiber 10, 10 ′, 10 ″, 10 ′ ″ optical splitter to which a plurality of drop cables are connected

Claims (4)

A transmission path changeover switch module is arranged above the optical splitter to which a plurality of drop cables connected to the slave station (ONU) are branched by branching the main line connected to the master station (OLT),
The transmission path switch module is
A first optical coupler connected to the main line; a non-self-holding optical switch connected to the first optical coupler; and a down signal on the main line branched from the first optical coupler, An optical power monitor for controlling the non-self-holding optical switch; and a second optical coupler connected to the non-self-holding optical switch;
The second optical coupler of the transmission path changeover switch module of another trunk line connected to the same OLT as the default side (connection destination when drive power is not applied) of the non-self-holding optical switch Connect one of the branch ports with a bypass optical fiber,
When the downstream signal of the trunk line is detected by the optical power monitor, a switching control signal is given to the non-self-holding optical switch to keep the connection state on the non-default side, and a failure occurs and the trunk line downlink signal is detected. When the power supply is lost, the non-self-holding optical switch is switched to the default side, and the connection destination trunk line of the ONU connected to the trunk line where the failure has occurred On the other hand, when the failure is recovered, the non-self-holding optical switch is automatically returned to the original non-default side by detecting the downstream signal of the main line by the optical power monitor, and the upper line connection A PON transmission line redundancy system characterized in that the destination is returned to the original trunk line before the failure occurred.   A default-side port of the non-self-holding optical switch of each of the transmission line changeover switch modules provided on the main line branched from the same OLT, and a second optical coupler of the transmission line changeover switch module of another main line. 2. The PON transmission line redundancy system according to claim 1, wherein the branch port is cascade-connected by a bypass optical fiber.   2. The PON transmission line redundancy according to claim 1, wherein said transmission line changeover switch modules of adjacent trunk lines installed in geographically close locations are connected by said bypass optical fiber, and the adjacent trunk line is used as a bypass line. method.   Dividing multiple trunks connected to the same OLT into separate multi-core cables and laying a transmission line to the drop cable branch closure, and the drop cable branch closures connected to the same OLT are geographically close to each other 2. The PON transmission line redundancy system according to claim 1, wherein the bypass optical fiber connecting the transmission line changeover switch modules is laid between adjacent ONUs.

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