JP2014022852A - Ring-type passive optical network - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a passive optical network that is able to continue communication even at the time of the occurrence of a fault.SOLUTION: There is a fault detection optical transmission path 17a which extends clockwise relative to a ring-type optical transmission path 11 and a fault detection optical transmission path 17b which extends anti-clockwise along the ring. The fault detection optical transmission path 17a is folded back at the position of a closure 12b-2 and extends anti-clockwise along the ring. Also, the fault detection optical transmission path 17b is folded back at the position of the closure 12b-2 and extends clockwise along the ring. In addition, optical couplers 170 are inserted into the fault detection optical transmission paths 17a, 17b at the position of each closure 12b and the fault detection optical transmission paths 17a, 17b branch off branches 171a-c. A fault place of the optical transmission path 11 can be detected by receiving or not receiving signals from the fault detection optical transmission paths 17a, 17b and branches 171a-c, and on the basis of that the transmission path is switched and communication can be continued even if a fault occurs on the optical transmission path 11.

Description

  The present invention relates to a ring-type passive optical network capable of communication by switching a transmission path even when a failure occurs in the optical transmission path.

  Network configurations (network topologies) that connect nodes (communication terminals, center devices, etc.) include ring-type, star-type, tree-type, mesh-type, and bus-type configurations. There is also. A star-type network configuration is used in FTTH (Fiber to the Home) in which the center device and the optical line terminator at each subscriber's house are connected by an optical fiber. A star-type network using an optical fiber can be constructed using only an optical coupler which is a passive element without using an active element, and is easy to maintain and save power. In addition, a network using optical fibers composed only of passive elements is called PON (Passive Optical Network))

  On the other hand, the ring type network has a double transmission path, so the optical transmission line is broken, or the optical attenuation is excessive due to the cord being caught or extremely bent, causing problems such as communication failure. Even so, communication can be maintained by switching the transmission path. Therefore, it is desirable to adopt a ring-type network configuration also in FTTH.

  Patent Document 1 describes a ring-type passive optical network (PON). The ring-type PON of Patent Document 1 constitutes a ring-type passive optical network by connecting a plurality of optical network unit (ONT) and a plurality of optical network units (ONUs). In normal times, as a line-type network configuration starting from the OLT, a signal is transmitted / received from one of the two terminals of the OLT, and each ONU other than the terminal transmits / receives a signal at the two terminals. Send and receive signals at one terminal. When a disconnection or the like is caused by a failure, the optical switch is switched so that signals are transmitted and received at both of the two terminals of the OLT. That is, the ring-type PON disclosed in Patent Document 1 can maintain communication even if a failure occurs by switching the transmission path to a line type during normal operation and a two-branch line type during failure.

JP 2009-77364 A

  Patent Document 1 does not specifically describe how a failure occurrence is detected and the optical switch of the OLT is switched, but whether the failure occurrence is normally performed in the upstream communication from each ONU to the OLT. It is suggested that the judgment is based on no. Therefore, it cannot be applied to a communication system that performs only downlink communication from the OLT to each ONU (for example, a broadcast distribution service in a CATV system). That is, the ring-type PON disclosed in Patent Document 1 has low versatility and is not suitable for a CATV system network.

  In addition, the conventional PON has a limited communication distance and can only communicate up to 10 km or 20 km. Therefore, the ring-type PON described in Patent Document 1 cannot be applied to a PON system communication having a large scale such that the circumference of the ring exceeds 20 km, for example.

  Accordingly, an object of the present invention is to realize a ring-type passive optical network that is highly versatile and can automatically switch communication paths and maintain communication even when a failure occurs in an optical transmission line. Another object is to realize a ring-type passive optical network that can be applied even when the scale of the ring is large.

  The invention according to claim 1 is a ring-type passive optical network configured by a center device and a ring-type optical transmission path connected to the center device, and maintaining communication by switching the transmission path when the optical transmission path fails. , The input end is connected to the center device, extends clockwise along the ring shape of the optical transmission line, is folded at a predetermined position and extends in the reverse direction along the ring shape, and the output end is connected to the center device. The first failure detection optical transmission line and the input terminal connected to the center device, extending counterclockwise along the ring shape of the optical transmission line, and folded back at a predetermined position or beyond A second fault detection optical transmission line extending in the opposite direction along the shape and having an output end connected to the center device, a section extending clockwise of the first fault detection optical transmission line, and a second Obstacle An optical branching device inserted at predetermined intervals in a section extending in a counterclockwise direction of the detection optical transmission line, and branched by each optical branching unit, and a first failure detection optical transmission line and a ring shape along the ring shape A branch line extending in the opposite direction to the extending direction of the second failure detection optical transmission line and connected to the center device, the center device including the first failure detection optical transmission line, and the second A transmitter that transmits a signal to the failure detection optical transmission line, a first failure detection optical transmission line, a second failure detection optical transmission line, and a receiver that receives each signal from each branch line; A ring-type passive optical network comprising switching means for detecting a faulty part of an optical transmission path depending on whether or not each signal is received by a receiver and switching the transmission path according to the faulty part.

  According to a second aspect of the present invention, there is provided a ring-type passive optical network comprising a center device and a ring-type optical transmission line connected to the center device, and maintaining communication by switching the transmission path when a failure occurs in the optical transmission line. , The input end is connected to the center device, extends clockwise along the ring shape of the optical transmission line, is folded at a predetermined position and extends in the reverse direction along the ring shape, and the output end is connected to the center device. The first failure detection optical transmission line and the input terminal connected to the center device, extending counterclockwise along the ring shape of the optical transmission line, and folded back at a predetermined position or beyond A second fault detection optical transmission line extending in the opposite direction along the shape and having an output end connected to the center device, a section extending clockwise of the first fault detection optical transmission line, and a second Obstacle Inserted at predetermined intervals into sections extending in the counterclockwise direction of the detection optical transmission line, and sections extending in the reverse direction of the first optical path for detection of faults, respectively, And a section extending in the opposite direction of the second failure detection optical transmission line, is inserted corresponding to the optical demultiplexer at predetermined intervals, and the light demultiplexed by the corresponding optical demultiplexer is multiplexed. An optical multiplexer, and the center device wavelength-multiplexes a signal for each demultiplexing wavelength of each optical demultiplexer to produce a first failure detection optical transmission line and a second failure detection optical transmission line A transmitter for transmitting to the receiver, and a receiver for receiving the signals from the first failure detection optical transmission line and the second failure detection optical transmission line separately for each separation wavelength of the optical demultiplexer; The fault location of the optical transmission line is detected based on the presence / absence of reception of each signal for each separation wavelength of the optical demultiplexer. A ring-shaped passive optical network characterized by having a a switching means for switching the transmission path in accordance with the.

  According to a third aspect of the present invention, there is provided a ring-type passive optical network comprising a center device and a ring-type optical transmission line connected to the center device, and maintaining communication by switching the transmission path when a failure occurs in the optical transmission line. , The input end is connected to the center device, extends clockwise along the ring shape of the optical transmission line, is folded at a predetermined position and extends in the reverse direction along the ring shape, and the output end is connected to the center device. The first failure detection optical transmission line and the input terminal connected to the center device, extending counterclockwise along the ring shape of the optical transmission line, and folded back at a predetermined position or beyond A second fault detection optical transmission line extending in the opposite direction along the shape and having an output end connected to the center device, a section extending clockwise of the first fault detection optical transmission line, and a second Obstacle An optical branching device inserted at predetermined intervals in a section extending in the counterclockwise direction of the detection optical transmission path, a section extending in the reverse direction of the first optical path for detection of fault, and a second fault detection An optical coupler that is inserted in a section extending in the reverse direction of the optical transmission line for each predetermined interval corresponding to the optical branching device and couples the light branched by the corresponding optical branching device, The apparatus transmits a pulse signal to the first failure detection optical transmission line and the second failure detection optical transmission line, the first failure detection optical transmission line, and the second failure detection transmission. A receiver that receives a pulse signal from the optical transmission line, and a switching unit that detects a faulty part of the optical transmission line based on the number of pulses of the received pulse signal and switches the transmission path according to the faulty part. A characteristic ring-type passive optical network That.

  According to a fourth aspect of the present invention, there is provided a ring-type passive optical network comprising a center device and a ring-type optical transmission line connected to the center device, wherein the communication is maintained by switching the transmission path when a failure occurs in the optical transmission line. , The input end is connected to the center device, the first failure detection optical transmission line extending clockwise to a predetermined position along the ring shape of the optical transmission line, and the input end connected to the center device, A second fault detection optical transmission line extending to a predetermined position counterclockwise along the ring shape of the transmission path, and the center device transmits the pulse signal to the first fault detection optical transmission line, And a pulse signal that is transmitted back to the second failure detection optical transmission line and reflected and returned at the end of the first failure detection optical transmission line and the second failure detection optical transmission line. Distance to fault on transmission line And OTDR measuring the a ring-shaped passive optical network characterized by having a a switching means for switching the transmission path in response to the failure point.

  The invention according to claim 5 is the invention according to claim 1 to claim 4, wherein only one of the first failure detection optical transmission line and the second failure detection optical transmission line is provided. The ring is stretched to make one round.

  The invention according to claim 6 is the invention according to claims 1 to 5, wherein the ring-type optical transmission line has 2 input ports and N output ports (N is an integer of 1 or more). A plurality of optical couplers to which the optical line terminator is connected, a first optical transmission line that is connected to one of the input ports of each optical coupler and extends clockwise along the ring shape, and each 2 × N optical coupler And a second optical transmission line that extends counterclockwise along the ring shape.

  The invention according to claim 7 is the invention according to claims 1 to 6, wherein the ring type optical transmission line has a short-circuit optical transmission line connected so as to divide the inside of the ring, and the center device , A third fault detection optical transmission line that extends along the short-circuit optical transmission path and connects to the center apparatus again, and the transmitter of the center apparatus has a third fault detection optical transmission path The center device receiver receives the signal from the third failure detection optical transmission line, and the switching means of the center device receives the signal from the third failure detection optical transmission line. The ring-type passive optical network is characterized in that a fault location in a short-circuit optical transmission path is detected from the presence or absence of the fault and the transmission path is switched in accordance with the fault location.

  The invention according to claim 8 is the invention according to claim 7, wherein the third failure detection optical transmission line is branched from the first failure detection optical transmission line or the second failure detection optical transmission line. It is characterized by being.

  According to a ninth aspect of the present invention, there is provided a ring-type passive optical network according to the first to seventh aspects of the present invention, and a video optical line terminating device connected to the center apparatus via the ring-type passive optical network. A CATV system characterized by comprising:

  According to the present invention, in a ring-type passive optical network, it is possible to detect the presence or absence of a failure in the optical transmission line and control the signal transmission path by the optical transmission line on the center device side. In addition, the transmission path can be switched to perform normal communication. In particular, the present invention can be applied even to a system (for example, a video distribution service of a CATV system) that performs only downlink communication from the center device to each optical line termination device, and becomes a highly versatile passive optical network. ing.

1 is a diagram illustrating a configuration of a CATV system according to a first embodiment. The figure shown about the structure of the optical transmission line 11. FIG. The figure shown about the structure of the center apparatus. The figure shown about the structure of the optical transmission path 17 for a fault detection. The figure shown about other structures of the center apparatus. The figure which showed the structure of the center apparatus 200 of the CATV system of Example 2. FIG. The figure shown about the structure of the optical transmission line 217 for a fault detection. The figure which showed the structure of the center apparatus 300 of the CATV system of Example 3. FIG. The figure shown about the structure of the optical transmission path 317 for a fault detection. The figure which showed the structure of the center apparatus 400 of the CATV system of Example 4. FIG. The figure shown about the structure of the optical transmission line 417 for a fault detection. FIG. 10 is a diagram illustrating a configuration of an optical transmission line 511 according to a fifth embodiment. FIG. 10 is a diagram illustrating a configuration of an optical transmission line 511 according to a fifth embodiment. The figure shown about the structure of the optical transmission path 517 for a fault detection. The figure which showed the structure of the center apparatus 500 of the CATV system of Example 5. FIG. The figure which showed the modification of the structure of the center apparatus. The figure which showed the other structure in the subscriber house. The figure shown about the other structure of the optical transmission line 217 for a fault detection. The figure which showed the other structure of the optical transmission line 517 for a fault detection. The figure which showed the other structure of the center apparatus.

  Hereinafter, specific examples of the present invention will be described with reference to the drawings. However, the present invention is not limited to the examples.

  FIG. 1 is a diagram illustrating a configuration of a CATV system according to the first embodiment. The CATV system according to the first embodiment is an FTTH system in which the center device 10 to the optical line terminator 15 arranged in each subscriber's house is connected by an optical transmission line, and the network configuration is a combination of a ring type and a star type. It is a thing. As shown in FIG. 1, the center device 10 is connected to a closure 12 a inserted in a ring-type optical transmission line 11 through an optical transmission line 18. Four other closures 12b are inserted in the optical transmission line 11. Hereinafter, the four closures 12b are referred to as 12b-1, 12b-2, 12b-3, and 12b-4 in order from the closure 12a in the clockwise direction. Two optical transmission lines 13a and 13b are branched from the optical transmission line 11 by the closure 12b and distributed in a star shape to 64 by a 2 × 64 optical coupler 16 and arranged in each subscriber home 14 ( V-ONU) 15. The optical line terminator 15 is connected to a TV receiver (not shown). Active elements are not used in either the ring type network or the star type network, and the network configuration of the CATV system according to the first embodiment is a passive type configured by only passive elements. That is, the network of the CATV system according to the first embodiment is a PON having a network configuration in which a ring type and a star type are combined, in which a trunk portion is a ring type and a branch line portion is a star type.

  The optical transmission line 11 is a single multi-core optical fiber cable. In addition, a plurality of single-core or multi-core optical fiber cables may be used. The core wire of the optical transmission line 11 is arranged as shown in FIG. That is, for each section from the center device 10 to each closure 12b, and for each closure 12b, two core wires are laid in the clockwise direction along the ring of the optical transmission path 11 and the core wire 11b counterclockwise. Has been. If only the core wires 11a and 11b corresponding to the closure 12b-1 are shown, the result is as shown in FIG. In the case of the first embodiment, since four closures 12b are arranged, the optical transmission line 18 from the center device 10 to the closure 12a has a total of eight cores and the optical transmission line 11 has a total of four cores. Is done. One of the two cores 11a and 11b is a core used during normal communication, and the other is a backup core used when communication cannot be performed due to a failure in the optical transmission line 11. Which of the two cores 11a and 11b is used for backup is arbitrary. For example, the counter-clockwise core is always determined for backup, or the longer one of the two cores 11a, 11b from the center device 10 to the closure 12b is determined for backup. The failure is, for example, when the optical transmission line 11 is disconnected or when the optical attenuation becomes excessive due to the optical fiber core being caught or extremely bent, and communication is impossible.

  As shown in FIG. 3, the center device 10 is connected to the transmitter 100 that transmits a video signal that is an optical signal, the optical amplifier 101 that amplifies the video signal, and the optical amplifier 101 that is connected to the transmitter 100. An optical coupler 102 that distributes four video signals, four optical switches 103 connected to the optical coupler 102, and a control device 104 that controls the optical switch 103 are included. The optical switch 103 is selectively connected to one of the two core wires 11a and 11b. Which one is connected is controlled by the control device 104 and is controlled according to the presence or absence of a failure in the optical transmission line 11 and the location of the failure. The center device 10 is used for detecting a fault location in the optical transmission line 11, and includes a transmitter 110 that transmits a fault detection signal and five receivers 120 to 124 that receive the fault detection signal. doing.

  The closure 12a branches the core wire of the optical transmission line 18 into a core wire extending clockwise along the ring of the optical transmission line 11 and a core wire extending counterclockwise. The closure 12b takes out one core wire 11a corresponding to the closure 12b out of the core wires of the optical transmission line 11 extending in the clockwise direction, and out of the core wires of the optical transmission path 11 extending in the counterclockwise direction One core wire 11b corresponding to the closure 12b is taken out and branched. The two extracted cores 11 a and b are two optical transmission lines 13 a and b connected to the optical coupler 16.

  The 2 × 64 optical coupler 16 can be configured such that the first stage is a 2 × n optical coupler and a plurality of 1 × n optical couplers are connected to the subsequent stage. A structure in which 32 optical couplers are connected can be used. A part of the plurality of optical couplers constituting the optical coupler 16 or the entire optical coupler 16 may be housed in the closure 12b. For example, of the 2 × 64 optical couplers 16, the first stage 2 × 2 optical coupler may be integrated in the closure 12 b and the remaining optical couplers constituting the optical coupler 16 may be connected to the closure 12 b. .

  Further, the number of branches by the optical coupler 16 is not limited to 64, and may be an arbitrary integer of 1 or more. However, the number of branches is preferably a power of 2 because of symmetry and ease of configuration. For example, by changing the number of branches of the optical coupler 16 according to the number of households in each area, the optical network in the CATV system of the first embodiment can be made more efficient.

  In the optical transmission line 11 according to the first embodiment, the number of the optical couplers 16 connected to the closure 12b is one with the number of the cores 11a, b up to one closure 12b being one. A plurality of optical couplers 16 connected to one closure 12b may be provided with a plurality of b. In this case, for example, as shown in FIG. 5A, a two-branch optical coupler 105 is provided in front of the optical switch 103 and another optical switch 103 is provided, so that the number of the cores 11a and 11b is two. It can be. Further, for example, as shown in FIG. 5B, by providing optical couplers 105a and 105b for branching the core wires 11a and 11b at the subsequent stage of the optical switch 103, the two core wires 11a and 11b are provided. be able to. Two optical couplers 16 can be connected to each closure 12b.

  Further, the CATV system of the first embodiment has a failure detection optical transmission line 17 connected to the center apparatus 10 as shown in FIGS. The failure detection optical transmission line 17 is divided into a failure detection optical transmission line 17a (corresponding to the first failure detection optical transmission line of the present invention) and a failure detection optical transmission line 17b (second of the present invention) by the optical coupler 111. (Corresponding to a fault detection optical transmission line). The failure detection optical transmission line 17 a extends clockwise along the ring of the optical transmission line 11. The failure detection optical transmission line 17 b extends counterclockwise along the ring of the optical transmission line 11. The fault-detecting optical transmission paths 17 a and 17 b may be the core of the optical transmission path 11, or may be the core of another optical fiber cable provided separately from the optical transmission path 11.

  The failure detection optical transmission line 17a is connected to the transmitter 110 of the center apparatus 10 and extends to the closure 12a. Then, it extends clockwise along the ring of the optical transmission line 11, turns back clockwise from the closure 12 a at the position of the second closure 12 b-2, and rotates counterclockwise along the ring of the optical transmission line 11. It extends and extends to the center device 10 from the position of the closure 12a. In a section extending clockwise in the failure detection optical transmission line 17a, an optical coupler 170 is inserted and branched at the position of the first closure 12b-1 clockwise from the closure 12a. The branch line 171a extends counterclockwise along the ring of the optical transmission line 11, and extends from the position of the closure 12a to the center device 10.

  The failure detection optical transmission line 17b is connected to the transmitter 110 of the center apparatus 10 and extends to the closure 12a. Then, it extends clockwise along the ring of the optical transmission line 11, turns back counterclockwise from the closure 12 a at the position of the third closure 12 b-2, and rotates clockwise along the ring of the optical transmission line 11. It extends and extends to the center device 10 from the position of the closure 12a. The return position of the failure detection optical transmission line 17a and the return position of the failure detection optical transmission line 17b are coincident with each other, which is one round of the ring. However, the folding positions do not necessarily coincide with each other. If the ring covers one week, the fault detection optical transmission path 17a and the fault detection optical transmission path 17b may be folded back so as to cross over. It doesn't matter. In the section extending in the counterclockwise direction of the failure detection optical transmission line 17b, the optical coupler 170 is placed at the position of the first and second closures 12b-4 and 12b-3 counterclockwise from the closure 12a. The branched branch lines 171 b and 171 c are inserted and branched in a clockwise direction along the ring of the optical transmission line 11, and extend from the position of the closure 12 a to the center device 10.

  Note that two transmitters 110 may be provided and the failure detection optical transmission lines 17a and 17b may be connected to each other.

  The failure detection optical transmission line 17a extending from the closure 12a to the center apparatus 10 and its branch line 171a, and the failure detection optical transmission line 17b extending from the closure 12a to the center apparatus 10 and its two branch lines 171b, c are: These are connected to the receivers 120 to 124 of the center apparatus 10 respectively. In addition, the receivers 120 to 124 are connected to the control device 104 and detect the presence / absence of reception of signals in the receivers 120 to 124.

  Here, when signals are transmitted to the failure detection optical transmission lines 17 a and 17 b by the transmitter 110 of the center apparatus 10, the presence or absence of signals received by the receivers 120 to 124 is the presence or absence of a failure in the optical transmission line 11. , And corresponding to the fault location.

  The correspondence is specifically described as follows. For example, if a failure occurs in the optical transmission line 11 in any part of the section from the closure 12a to the closure 12b-1 in the clockwise direction, the failure occurs in the section to the closure 12b-1. A failure also occurs in the detection optical transmission line 17a. Therefore, both the failure detection optical transmission line 17a and the signal from the branch line 171a are not received. Further, for example, when a failure occurs in the optical transmission line 11 in any part of the section from the closure 12b-1 to the closure 12b-2 in the clockwise direction, the optical transmission path for failure detection In 17a, no fault occurs in the section up to the closure 12b-1, but a fault occurs in the section up to the closure 12b-2. Therefore, only the signal from the branch line 171a among the signals from the failure detection optical transmission line 17a and the branch line 171a is received. When there is no failure in the optical transmission line 11 in the section from the closure 12a to the closure 12b-2 in the clockwise direction, both the failure detection optical transmission line 17a and the signal from the branch line 171 are received.

The failure of the optical transmission line 11 between the other closures 12b can be considered in the same manner as in the above example. The correspondence between the presence / absence of signal reception and the failure part of the optical transmission line 11 is summarized as follows. .
(1) When all the five signals from the failure detection optical transmission lines 17a and 17b and the branch lines 171a to 171c are received, no failure has occurred in the optical transmission line 11.
(2) When signals from the failure detection optical transmission line 17a and its branch line 171a are not received, a failure has occurred in the optical transmission line 11 in the section from the closure 12a to the closure 12b-1.
(3) When the signal from the failure detection optical transmission line 17a is not received but the signal from the branch line 171a is received, the optical transmission line in the section from the closure 12b-1 to the closure 12b-2 in the clockwise direction 11 has failed.
(4) When signals from the failure detection optical transmission line 17b and its branch lines 171b, c are not received, a failure occurs in the optical transmission line 11 in the section from the closure 12a to the closure 12b-4 counterclockwise. ing.
(5) When signals from the failure detection optical transmission line 17b and its branch line 171b are not received, a failure occurs in the optical transmission line 11 in the section from the closure 12b-4 to the closure 12b-3 counterclockwise. ing.
(6) When a signal from the failure detection optical transmission line 17b is not received, a failure has occurred in the optical transmission line 11 in the section from the closure 12b-3 to the closure 12b-2 counterclockwise.

  Thus, by detecting the presence or absence of reception of each signal from the failure detection optical transmission line 17 by the receivers 120 to 124, it is possible to detect the presence or absence of a failure in the optical transmission line 11 and the location of the failure. .

  In the first embodiment, the transmitter 110 that transmits the failure detection signal is provided separately from the transmitter 100 that transmits the video signal. However, the transmitter 110 is not provided, and the video output from the transmitter 100 is provided. The signal is used as a failure detection signal, the video signal is sent to the failure detection optical transmission line 17, and the presence or absence of the failure and the location of the failure are detected based on whether or not the video signals are received by the receivers 120 to 124. It may be.

  Next, an operation when a failure occurs in the optical transmission line 11 of the CATV system according to the first embodiment will be described.

  When a failure occurs in the optical transmission line 11, the failure location of the optical transmission line 11 is detected by the failure detection optical transmission line 17. In the center device 10, the control device 104 controls the optical switch 103 for the optical switch 103 corresponding to the portion where communication is disabled in the section from the center device 10 to the closures 12 b-1 to 12 b-4 due to a failure. Of the cores 11a and 11b of the optical transmission line 11, the core used for normal operation is switched to the backup core. As a result, a transmission path is formed so as to avoid a faulty part of the optical transmission path 11, and communication can be maintained.

  As a specific example, a case where a failure occurs in the optical transmission line 11 between the closure 12b-1 and the closure 12b-2 will be described. Of the cores 11a and 11b up to the respective closures 12b, the clockwise core 11a is used for the closures 12b-1 and 12b, and the counterclockwise heart for the closures 12b-3 and 4 is used. It is assumed that the line 11b is used during normal operation. In this case, since there is no failure in the optical transmission line 11 from the closure 12a to the closure 12b-1 in the clockwise direction, the signal is normally transmitted. Therefore, for the optical switch 103 corresponding to the closure 12b-1, switching of the connected core wire is not performed. No signal is transmitted to the closure 12b-2 in the clockwise direction due to the failure of the optical transmission line 11. Since the signal is transmitted counterclockwise up to the closure 12b-3, the signal is normally transmitted. Therefore, the optical switch 103 corresponding to the closure 12b-2 is controlled to switch to the core wire 11b that transmits the signal counterclockwise. Then, since there is no failure of the optical transmission line 11 from the closure 12a to the closure 12b-2 in the counterclockwise direction, the signal is normally transmitted. In this way, by switching the transmission path by the optical switch 103 according to the failure location of the optical transmission path 11, it is possible to normally transmit signals to the respective closures 12b-1 to 12b-4.

  When recovering from the failure, it is detected by the failure detection optical transmission line 17 that there is no failure in the optical transmission line 11, and based on this, the control device 104 controls the optical switch 103, whereby normal transmission is performed. You can automatically return to the route.

  As described above, in the CATV system according to the first embodiment, even if the ring-type optical transmission line 11 becomes incapable of communication due to a failure, the failure point is detected by the failure detection optical transmission line 17, and the center device 10 becomes the failure point. Since the transmission path is switched based on this, the video distribution service to each subscriber can be automatically continued.

  In the CATV system of the second embodiment, the fault detection optical transmission line 17 and the center apparatus 10 in the CATV system of the first embodiment are replaced with a fault detection optical transmission path 217 and a center apparatus 200 described below, respectively. It is. Other configurations are the same as those of the center apparatus 10 of the CATV system of the first embodiment.

  As illustrated in FIG. 6, the center apparatus 200 replaces the transmitter 110, the optical coupler 111, and the receivers 120 to 124 of the center apparatus 10 of the first embodiment with a transmitter 210, optical couplers 211 and 218, and a receiver 222. It is a configuration. Other configurations are the same as those of the center apparatus 10 of the first embodiment. The transmitter 221 wavelength-multiplexes and transmits five signals having different wavelengths (wavelengths λ1, λ2,... Λ5). For example, a CWDM (Coarse Wavelength Division Multiplex) apparatus is used. The receiver 222 separates the wavelength-multiplexed signal into five signals having different wavelengths, and receives each signal.

  As shown in FIGS. 6 and 7, the failure detection optical transmission line 217 is connected to the transmitter 210 of the center apparatus 10 and is branched into two by the wavelength division device 211 into the failure detection optical transmission lines 217 a and 217 b. The wavelength division device 211 outputs signals of wavelengths λ1 and λ2 to the failure detection optical transmission line 217a and signals of wavelengths λ3 to λ5 to the failure detection optical transmission line 217b. Two transmitters 210 may be provided and connected to the failure detection optical transmission lines 217a and 217b, respectively.

  As shown in FIG. 7, the failure detection optical transmission line 217a extends from the optical coupler 223 to the closure 12a, extends clockwise along the ring of the optical transmission line 11, and is turned back at the position of the closure 12b-2. . Further, it extends counterclockwise along the ring of the optical transmission line 11 and extends to the center device 200 from the position of the closure 12a. WDM filters 270a-1 and 270b-1 are inserted into the positions of the closure 12b-1 in the section extending in the clockwise direction and the section extending in the counterclockwise direction of the failure detection optical transmission line 217a, respectively. Yes. The WDM filters 270a-1 and 270b-1 multiplex and demultiplex the signal of wavelength λ1, and the signal of wavelength λ1 demultiplexed by the WDM filter 270a-1 is input to the WDM filter 270b-1. The WDM filter 270a-1 and the WDM filter 270b-1 are connected so as to be waved.

  As shown in FIG. 7, the failure detection optical transmission line 217b extends from the optical coupler 223 to the closure 12a, extends counterclockwise along the ring of the optical transmission line 11, and is folded back at the position of the closure 12b-2. Yes. Further, it extends clockwise along the ring of the optical transmission line 11 and extends to the center device 200 from the position of the closure 12a. WDM filters 270a-3 and 270b-3 are inserted into the positions of the closure 12b-3, respectively, in the section extending clockwise and the counterclockwise section of the failure detection optical transmission line 217b. Yes. The WDM filters 270a-3 and 270b-3 multiplex / demultiplex the signal of wavelength λ3. The signal of wavelength λ3 demultiplexed by the WDM filter 270a-3 is input to the WDM filter 270b-3 and combined. The WDM filter 270a-3 and the WDM filter 270b-3 are connected so as to be waved. Similarly, WDM filters 270a-4 and 270b-4 are inserted into the sections extending in the clockwise direction and the sections extending in the counterclockwise direction, respectively, at the positions of the closures 12b-4. The WDM filters 270a-4 and 270b-4 multiplex and demultiplex the signal of wavelength λ4. The signal of wavelength λ4 demultiplexed by the WDM filter 270a-4 is input to the WDM filter 270b-4 and combined. The WDM filter 270a-4 and the WDM filter 270b-4 are connected so as to be waved.

  The failure detection optical transmission lines 217 a and 217 b extending from the closure 12 a are connected to the optical coupler 218 of the center device 10, and the output side of the optical coupler 218 is connected to the receiver 222 of the center device 10. Signals from the failure detection optical transmission lines 217a and 217b are combined by the optical coupler 218, and then input to the receiver 222 of the center apparatus 10 to detect the presence / absence of reception for each wavelength. The receiver 222 is connected to the control device 104. Note that two receivers 222 may be provided to receive signals from the failure detection optical transmission lines 217a and 217b, respectively.

  Here, when signals of wavelengths λ1 to λ5 are transmitted to the failure detection optical transmission paths 217a and 217b by the transmitter 210 of the center apparatus 200, the presence / absence of signals of each wavelength received by the receiver 222 is determined by the optical transmission. It corresponds to the presence or absence of a failure on the road 11 and the location of the failure. For example, when a failure has occurred in the section of the optical transmission line 11 from the closure 12b-1 to the closure 12b-2, no fault has occurred in the section from the closure 12b-1 to the failure detection optical transmission line 217a. No failure has occurred, and the signal of wavelength λ1 is transmitted through the failure detection optical transmission line 217a via the WDM filters 270a-1 and 270b-1, and is received by the receiver 222. On the other hand, since the failure detection optical transmission line 217a in the section between the closure 12b-1 and the closure 12b-2 has a failure, the signal of the wavelength λ2 transmitted through the WDM filter 270a-1 extends counterclockwise. The fault detection optical transmission line 217 a is not transmitted and is not received by the receiver 222. Therefore, when the signal of wavelength λ2 is not received, it is possible to detect that a failure has occurred between the closure 12b-1 and the closure 12b-2 of the optical transmission line 11.

  Thus, the presence / absence of the signal of each wavelength received differs according to the fault location. Therefore, conversely, the presence or absence of a failure in the optical transmission line 11 and the location of the failure can be detected by detecting the presence or absence of reception of each signal from the failure detection optical transmission line 217 by the receiver 222.

  As described above, in the CATV system according to the second embodiment, as in the first embodiment, even when a failure occurs in the ring-type optical transmission path 11, the communication path can be switched to a communication path according to the failure location. The video distribution service to the user can be continued.

  Further, in the failure detection optical transmission line 17 of the first embodiment, the number of the cores of the failure detection optical transmission line 17 increases as the number of the closures 12b increases, but the failure detection optical transmission line 217 of the second embodiment increases. Then, even if the number of closures 12b increases, the number of cores of the failure detection optical transmission line 217 does not change. Therefore, when constructing a large-scale ring-type passive optical network, it is more advantageous than the failure detection optical transmission line 17 of the first embodiment.

  In the CATV system according to the third embodiment, the failure detection optical transmission line 17 and the center apparatus 10 in the CATV system according to the first embodiment are replaced with a failure detection optical transmission line 317 and a center apparatus 300 described below. . Other configurations are the same as those of the CATV system of the first embodiment.

  As shown in FIG. 8, the center apparatus 300 has a configuration in which the transmitter 110 and the receivers 120 to 124 of the center apparatus 10 of the first embodiment are replaced with a transmitter 310 and receivers 320a and 320b. Other configurations are the same as those of the center apparatus 10 of the CATV system of the first embodiment. The transmitter 310 transmits a pulse signal, and the receivers 320a and 320b receive the pulse signal and measure the number of pulses.

  As shown in FIGS. 8 and 9, the failure detection optical transmission path 317 is connected to the transmitter 310 of the center apparatus 300 and is branched into two by the optical coupler 111 into the failure detection optical transmission paths 317 a and 317 b.

  As shown in FIG. 9, the failure detection optical transmission path 317a extends from the optical coupler 111 to the closure 12a, extends clockwise along the ring of the optical transmission path 11, and is turned back at the position of the closure 12b-2. . Further, it extends counterclockwise along the ring of the optical transmission line 11 and extends to the center device 300 from the position of the closure 12a. Optical couplers 370a-1 and 370b-1 are inserted into the positions of the closure 12b-1, respectively, in a section extending clockwise and a counterclockwise section of the failure detection optical transmission line 317a. Yes. One of the two output ends of the optical coupler 370a-1 is connected to one of the two input ends of 370b-1.

  As shown in FIG. 9, the failure detection optical transmission line 317b extends in the opposite direction to the failure detection optical transmission line 317a and is turned back. That is, it extends from the optical coupler 111 to the closure 12a, extends counterclockwise along the ring of the optical transmission path 11, and is folded back at the position of the closure 12b-2. Further, it extends clockwise along the ring of the optical transmission line 11 and extends to the center device 300 from the position of the closure 12a. An optical coupler 370a-3 and 370b-3 are inserted into the position of the closure 12b-3, respectively, in a section extending in the counterclockwise direction of the optical transmission path 317b for detecting a fault and a section extending in the clockwise direction. Yes. One of the two output ends of the optical coupler 370a-3 is connected to one of the two input ends of 370b-3. Similarly, the optical couplers 370a-4 and 370b-4 are inserted into the sections extending in the counterclockwise direction and the section extending in the clockwise direction, respectively, at the position of the closure 12b-4. One of the two output ends of the optical coupler 370a-4 is connected to one of the two input ends of 370b-4.

  The failure detection optical transmission lines 317a and 317b extending from the closure 12a are connected to the receivers 320a and 320b, respectively. Signals from the failure detection optical transmission lines 317a and 317b are input to the receivers 320a and 320b, and the number of pulses of the signal is detected.

  The pulse signals transmitted through the failure detection optical transmission lines 317a and 317b are divided at the positions of the respective closures 12b, and then combined again and received by the receivers 320a and 320b. Therefore, the received signal is a signal including a plurality of pulses due to a pulse delay corresponding to the position of each closure 12b. The number of received signal pulses increases or decreases according to the presence or absence of a failure in the optical transmission path and the location of the failure.

  For example, when a failure occurs in the section of the optical transmission line 11 from the closure 12b-3 to the closure 12b-2, no trouble occurs in the section from the closure 12b-3, so the failure detection optical transmission line 317b is also used. No failure has occurred, and the pulse signal is transmitted through the failure detection optical transmission line 317b via the optical couplers 370a-4 and 370b-4, and also via the optical couplers 370a-3 and 370b-3. It transmits through the failure detection optical transmission line 317b and is received by the receiver 320b. At this time, a delay occurs in the pulse signal passing through the optical couplers 370a-3 and 370b-3 due to the difference between the two path lengths, so the number of pulses of the received pulse signal is two. On the other hand, since the failure detection optical transmission line 317b in the section between the closure 12b-3 and the closure 12b-2 has a failure, the pulse signal branched by the optical coupler 370a-3 and directed to the closure 12b-2 is The failure detection optical transmission line 317a extending in the clockwise direction is not transmitted and is not received by the receiver 320. Therefore, the number of pulses of the pulse signal received by the receiver 320b is two. From this, it is possible to detect that a failure has occurred between the closure 12b-3 and the closure 12b-2 of the optical transmission line 11. This is because the number of pulses of the pulse signal received by the receiver 320b is two only when a failure occurs between the closure 12b-3 and the closure 12b-2.

  As described above, the number of received signal pulses differs depending on the presence or absence of a failure in the optical transmission line 11 and the location of the failure. Therefore, conversely, by detecting the number of pulses of each signal from the failure detection optical transmission line 317 by the receiver 322, it is possible to detect the presence or absence of the failure in the optical transmission line 11 and the location of the failure. Note that the signals of the failure detection optical transmission lines 317a and 317b may be combined by an optical coupler or the like, and the signal may be received by one receiver. In this case, if the distances are equal, the pulses may overlap and become indistinguishable. However, such a possibility is very low and there is no problem even if it is not considered.

  As described above, in the CATV system according to the third embodiment, as in the first embodiment, even when a failure occurs in the ring-type optical transmission path 11, the communication path can be switched to a communication path according to the failure location. The video distribution service for subscribers can be continued.

  Further, the failure detection optical transmission line 317 according to the third embodiment is advantageous in the case of constructing a large-scale ring-type passive optical network without restriction on the number of the closures 12b.

  In the CATV system according to the fourth embodiment, the failure detection optical transmission line 17 and the center apparatus 10 in the CATV system according to the first embodiment are replaced with a failure detection optical transmission line 417 and a center apparatus 400 described below. . Other configurations are the same as those of the CATV system of the first embodiment.

  As shown in FIG. 10, the center device 400 has a configuration in which the transmitter 110, the optical coupler 111, and the receivers 120 to 124 of the center device 10 of the first embodiment are replaced with OTDRs (optical time domain reflectometers) 420a and 420b. is there. Other configurations are the same as those of the center apparatus 10 of the first embodiment. The OTDRs 420a and 420b are devices that measure the time required for a pulse to be incident on an optical fiber, reflected at the end of the optical fiber, and returned, thereby measuring the distance to the fault location on the optical fiber. The OTDRs 420 a and b are connected to the control device 104.

  As shown in FIGS. 10 and 11, the failure detection optical transmission line 417 is configured with two optical transmission lines 417 a and b for failure detection, and is connected to the OTDRs 420 a and b of the center device 400, respectively. ing.

  The failure detection optical transmission line 417a extends from the center device 400 to the closure 12a, and extends clockwise along the ring of the optical transmission line 11 to the closure 12b-2.

  The failure detection optical transmission line 417b extends from the center device 400 to the closure 12a, and extends counterclockwise along the ring of the optical transmission line 11 to the closure 12b-2.

  Since the failure detection optical transmission paths 417a and 417b extend along the ring-shaped optical transmission path 11 as described above, the failure location of the failure detection optical transmission paths 417a and 417b is the same as that of the optical transmission path 11. It can be estimated as a fault location. Therefore, the fault location of the optical transmission line 11 can be measured by measuring the fault location of the fault detection optical transmission paths 417a and 417 using the OTDR 420a and b.

  As described above, in the CATV system according to the fourth embodiment, similarly to the CATV system according to the first embodiment, even when a failure occurs in the ring-type optical transmission path 11, it is possible to switch to a transmission path capable of communication according to the failure location. The video distribution service to each subscriber can be continued.

  Further, according to the failure detection optical transmission line 417 of the fourth embodiment, the number of cores of the failure detection optical transmission line 417 does not change even if the number of the closures 12b is increased. This is advantageous when building a network.

  The CATV system according to the fifth embodiment includes an optical transmission path 11, a failure detection optical transmission path 17, and a center apparatus 10 that are part of the CATV system according to the first embodiment. The optical transmission line 517 and the center device 500 are replaced. Other configurations are the same as those of the CATV system of the first embodiment.

  As shown in FIG. 12, the optical transmission line 511 is a ring type optical transmission line 511A similar to the optical transmission line 11 in which the closures 12a and b-1 to b-4 are inserted, the closure 12b-1 and the closure 12b. -4 and a short-circuit optical transmission line 511B. By this short-circuit optical transmission line 511B, a ring-type optical transmission line smaller than the ring formed by the optical transmission line 511A connected to the center device 10 is formed.

  The optical transmission line 511 is a single multi-fiber optical fiber cable, and the core wire is arranged as shown in FIG. That is, the section from the center device 10 to each closure 12b, the closures 12b-1 and 12b-4 are along a small ring by the short-circuit optical transmission path 511B, and the optical transmission paths 511A are the closures 12b-2 and 12-3. Two core wires are laid along the large ring by the core wire 511a clockwise and the core wire 511b counterclockwise. One of the two cores 511a and 511b is a core used for normal communication, and the other is a backup core used when communication cannot be performed due to a failure in the optical transmission line 511.

  In this ring-type optical transmission line 511, by providing a short-circuiting optical transmission line 511B so as to divide the ring to form a small ring, a part of the distance between the cores 511a and 511b reaching each closure 12b is reduced. The communication distance can be shortened and the communication distance can be shortened. Specifically, the core wire 511b leading to the closure 12b-1 and the core wire 511a reaching the closure 12b-4 are shorter than when the short-circuit optical transmission line 511B is not provided (see FIG. 2A). ing.

  The closure 12b may be inserted into the short-circuit optical transmission line 511B. The optical transmission line 511 has only one short-circuit optical transmission line 511B, but a plurality of optical transmission lines 511B may be provided.

  As shown in FIG. 14, the failure detection optical transmission path 517 is an optical coupler 170 inserted in the position of the closure 12b-1 of the failure detection optical transmission path 17a in the failure detection optical transmission path 17 of the first embodiment. Is replaced with a three-branch optical coupler 570 to increase the branch line 571. The branch line 571 is extended from the closure 12b-1 to the closure 12b-4 along the short-circuit optical transmission line 511B, and the position of the closure 12b-4 And then extended from the closure 12b-4 toward the closure 12b-1, further extended counterclockwise along the ring from the closure 12b-1 to the closure 12a, and extended from the closure 12a to the center device 10. It is a configuration. Other configurations are the same as those of the failure detection optical transmission line 17.

  The branch line 571 may be extended along the short-circuit optical transmission line 511B. For example, the branch line 571 may be extended along the short-circuit optical transmission line 511B and then not folded at the position of the closure 12b-4. You may make it extend | stretch from 12b-4 to the closure 12a.

  In addition, the failure detection optical transmission line 17a of the first embodiment is not further branched at the position of the closure 12b-1, but the failure detection optical transmission lines 217a, 317a, and 417a of the second to fourth embodiments are used. It is good also as a structure branched and extended to the optical transmission path 511B for a short circuit. Further, the failure detection optical transmission lines 17b, 217b, 317b, and 417b extending in the counterclockwise direction are branched instead of the failure detection optical transmission lines 17a, 217a, 317a, and 417a extending in the clockwise direction. It is good also as a structure extended to the optical transmission line 511B.

  As shown in FIG. 15, the center device 500 is obtained by further adding a receiver 520 to the receivers 120 to 124 of the center device 10, and the other configuration is the same as that of the center device 10. A branch line 571 extending from the closure 12 a is connected to the receiver 520, and the receiver 520 receives a signal from the branch line 571.

  By providing the branch line 571 extended along the short-circuit optical transmission line 511B in this manner, it is possible to detect the presence or absence of a failure in the short-circuit optical transmission line 511B based on whether or not a signal is received from the branch line 571. it can. Therefore, even when the short-circuit optical transmission path 511B fails, the failure can be detected and the transmission path can be switched, and the video distribution service can be continued.

  Instead of branching out the failure detection optical transmission lines 17a, b, a failure detection optical transmission line 17c extending to the short-circuiting optical transmission line 511B is provided separately from the failure detection optical transmission lines 17a, b. Also good. An example is shown in FIGS. As shown in FIG. 20, the optical coupler 111 in the center device 10 of the first embodiment is branched to the failure detection optical transmission lines 17a to 17c instead of the three-branch optical coupler 511. Further, a receiver 125 for receiving a signal from the failure detection optical transmission line 17c is added. As shown in FIG. 19, the failure detection optical transmission line 17 c extends from the center device 10 to the closure 12 a and extends clockwise along the ring of the optical transmission line 11 to the closure 12 b-1. And it is extended | stretched along the optical transmission path 511B for short circuit from the closure 12b-1, and it is return | folded and extended to the closure 12b-1 in the position of the closure 12b-4. Furthermore, it extends between the closures 12a counterclockwise along the ring from the closure 12b-1 and extends to the center device 10. As described above, when the failure detection optical transmission line 17c is separately provided, the failure detection optical transmission lines 17a and 17b are branched and extended along the short-circuit optical transmission line 511B. Since the failure of the short-circuit optical transmission path 511B can be detected and the transmission path can be switched accordingly, the video distribution service can be continued.

  As described above, in the CATV system of the fifth embodiment, the optical transmission path 511 is provided with the short-circuit optical transmission path 511B that divides the ring, and the communication distance is shortened. Therefore, when the ring diameter of the optical transmission path 511 is large, That is, it is effective when the optical transmission line 511 is laid in a wide area.

  In the first to fifth embodiments, the CATV system that provides only the downlink communication using the V-ONU and provides the video distribution service is shown, but the present invention is not limited to this. For example, in addition to the video distribution service using V-ONU, it is also possible to realize a CATV system that operates a GE-PON bidirectional communication service or the like, and only a GE-PON bidirectional communication service. It is also possible to realize a CATV system that operates the system. As a method for realizing this, for example, there is a method for realizing it by laying an optical transmission line used for the GE-PON system separately from the optical transmission line used for the video distribution service. In this case, the number of the optical transmission lines 11 shown in the embodiment may be doubled. In addition, there is a method that enables the two services to be compatible using the same optical transmission line by wavelength multiplexing. For example, as shown in FIG. 16, a WDM 601 is inserted between the optical amplifier 101 and the optical coupler 102 of the center apparatus 10, and a transceiver 610 that transmits and receives GE-PON communication signals is connected to the WDM 601. . Also, as shown in FIG. 17, a WDM 620 is provided at the subscriber's home 14, the optical line terminator 15 that receives the video distribution service signal in the WDM 620, and the optical line terminator (the GE-PON system communication signal) D-ONU) 630 is connected. According to such a configuration, the video distribution service signal from the transmitter 100 and the GE-PON system signal from the transmitter / receiver 610 can be wavelength-multiplexed by the WDM 601 and transmitted through a single optical transmission line. Both video distribution service and GE-PON communication can be operated. The ring-type passive optical network of the present invention can be applied not only to the CATV system shown in the first to fifth embodiments but also to other systems. That is, the ring-type passive optical network of the present invention is highly versatile.

  Further, in the CATV systems of the first to fifth embodiments, a network configuration in which a ring type and a star type are combined is used, but other network configurations may be used as long as at least a ring type network is provided. . For example, a network configuration using only a ring type, a network configuration combining a ring type and a ring type, a network configuration combining a ring type and other types of topology, such as a ring type and a tree type, a ring type and a line type, etc. Can be used.

  In the CATV systems of Examples 1 to 5, two rings that extend clockwise and counterclockwise are prepared as failure detection optical transmission lines. However, either one of the rings is extended to make one round. Also good. As an example, in the case of the second embodiment, FIG. 18 shows that only the fault detection optical transmission line 217 is extended clockwise along the ring (the fault detection optical transmission line 217a). Shows the configuration of a circle. However, WDM filters 270a-2 and 270b-2 for multiplexing and demultiplexing the signal of wavelength λ2 are further inserted at the position of the closure 12b-2. The fault-detecting optical transmission line 217 that has made a round to the closure 12a may be folded back and extended in the reverse direction as shown in FIG. 18 (a), or the WDM filter 270b-4 as shown in FIG. 18 (b). You may extend to the center apparatus 10 as it is, without providing. Even in such a configuration, it is possible to detect the presence / absence of a failure in the optical transmission path 11 and the location of the failure as in the failure detection optical transmission path 217 of the second embodiment. Further, in the case of such a configuration, the number of cores of the failure detection optical transmission line between the closure 12a and the center apparatus 10 can be reduced.

  The configuration of the ring-type optical transmission line 11 is not limited to that shown in the first to fifth embodiments, and any conventionally known ring-type optical transmission line 11 can be used. For example, the ring-type optical transmission line 11 described in Patent Document 1 may be used.

  The present invention can be applied to a CATV system and the like, and can perform broadcasting, Internet service, telephone service, and the like.

10, 200, 300, 400, 500: Center devices 11, 13a, 13b, 18: Optical transmission lines 12a, b: Closures 14: Subscriber premises 15: Optical line terminators 16, 102: Optical couplers 17, 217, 317 417, 517: optical transmission lines for failure detection 100, 110, 210, 310, 410: transmitter 101: optical amplifier 103: optical switch 104: control devices 120 to 124, 222, 320, 520: receiver

Claims (9)

In a ring-type passive optical network that is configured by a center device and a ring-type optical transmission line connected to the center device, and maintains communication by switching the transmission path when a failure occurs in the optical transmission line,
An input end is connected to the center device, extends clockwise along the ring shape of the optical transmission line, turns back at a predetermined position, extends in the reverse direction along the ring shape, and outputs to the center device. A first fault detection optical transmission line to which
An input end is connected to the center device, extends counterclockwise along the ring shape of the optical transmission line, and is folded back at the predetermined position or a position exceeding the predetermined position and extended in the reverse direction along the ring shape. A second failure detection optical transmission line whose output end is connected to the center device;
Optical branching units inserted at predetermined intervals in a section extending clockwise in the first failure detection optical transmission line and in a section extending counterclockwise in the second failure detection optical transmission line, ,
Branched by each of the optical splitters, and extends in the reverse direction with respect to the extending direction of the first failure detection optical transmission line and the second failure detection optical transmission line along the ring shape to the center device A branch line to be connected;
Have
The center device is
A transmitter for transmitting a signal to the first failure detection optical transmission line and the second failure detection optical transmission line;
A receiver for receiving each signal from the first failure detection optical transmission line, the second failure detection optical transmission line, and the branch lines;
A switching means for detecting a fault location in the optical transmission path depending on whether or not each signal is received by the receiver, and switching the transmission path according to the fault location,
Having
A ring-type passive optical network. In a ring-type passive optical network that is configured by a center device and a ring-type optical transmission line connected to the center device, and maintains communication by switching the transmission path when a failure occurs in the optical transmission line,
An input end is connected to the center device, extends clockwise along the ring shape of the optical transmission line, turns back at a predetermined position, extends in the reverse direction along the ring shape, and outputs to the center device. A first fault detection optical transmission line to which
An input end is connected to the center device, extends counterclockwise along the ring shape of the optical transmission line, and is folded back at the predetermined position or a position exceeding the predetermined position and extended in the reverse direction along the ring shape. A second failure detection optical transmission line whose output end is connected to the center device;
Inserted into the section extending in the clockwise direction of the first fault detection optical transmission line and the section extending in the counterclockwise direction of the second fault detection optical transmission path at predetermined intervals, respectively. With different optical demultiplexers,
Corresponding to the optical demultiplexer at each predetermined interval in a section extending in the reverse direction of the first fault detection optical transmission line and a section extending in the reverse direction of the second fault detection optical transmission path And an optical multiplexer that multiplexes the light demultiplexed by the corresponding optical demultiplexer, and
Have
The center device is
A transmitter that wavelength-multiplexes a signal for each separation wavelength of each of the optical demultiplexers and transmits the multiplexed signal to the first failure detection optical transmission line and the second failure detection optical transmission line;
A receiver for receiving a signal from the first optical path for detecting a fault and a signal from the second optical path for detecting a fault separately for each separated wavelength of the optical demultiplexer;
Switching means for detecting a fault location of the optical transmission path according to the presence or absence of reception of each signal for each separation wavelength of the optical demultiplexer, and switching the transmission path according to the fault location;
Having
A ring-type passive optical network. In a ring-type passive optical network that is configured by a center device and a ring-type optical transmission line connected to the center device, and maintains communication by switching the transmission path when a failure occurs in the optical transmission line,
An input end is connected to the center device, extends clockwise along the ring shape of the optical transmission line, turns back at a predetermined position, extends in the reverse direction along the ring shape, and outputs to the center device. A first fault detection optical transmission line to which
An input end is connected to the center device, extends counterclockwise along the ring shape of the optical transmission line, and is folded back at the predetermined position or a position exceeding the predetermined position and extended in the reverse direction along the ring shape. A second failure detection optical transmission line whose output end is connected to the center device;
Optical branching units inserted at predetermined intervals in a section extending clockwise in the first failure detection optical transmission line and in a section extending counterclockwise in the second failure detection optical transmission line, ,
A section extending in the reverse direction of the first fault detection optical transmission line and a section extending in the reverse direction of the second fault detection optical transmission path correspond to the optical branching unit at each predetermined interval. An optical coupler that couples the light branched by the corresponding optical splitter, and
Have
The center device is
A transmitter for transmitting a pulse signal to the first failure detection optical transmission line and the second failure detection optical transmission line;
A receiver for receiving a pulse signal from the first failure detection optical transmission line and the second failure detection optical transmission line;
A switching means for detecting a fault location in the optical transmission path according to the number of pulses of the received pulse signal and switching the transmission path according to the fault location;
Having
A ring-type passive optical network. In a ring-type passive optical network that is configured by a center device and a ring-type optical transmission line connected to the center device, and maintains communication by switching the transmission path when a failure occurs in the optical transmission line,
A first fault detection optical transmission line that has an input end connected to the center device and extends clockwise to a predetermined position along the ring shape of the optical transmission line;
A second fault-detecting optical transmission line that has an input end connected to the center device and extends to the predetermined position counterclockwise along the ring shape of the optical transmission line;
Have
The center device is
A pulse signal is transmitted to the first failure detection optical transmission line and the second failure detection optical transmission line, and the first failure detection optical transmission line and the second failure detection optical transmission are transmitted. An OTDR that receives the pulse signal reflected back at the end of the path and measures the distance to the fault location in the optical transmission path;
Switching means for switching the transmission path according to the fault location;
Having
A ring-type passive optical network.   2. The apparatus according to claim 1, wherein only one of the first failure detection optical transmission line and the second failure detection optical transmission line is provided, and one of the first failure detection optical transmission line is extended to go around the ring. The ring-type passive optical network according to claim 4. The ring-type optical transmission line is
A plurality of optical couplers in which the input port is 2, the output port is N (N is an integer of 1 or more), and an optical line terminator is connected to each output port;
A first optical transmission line connected to one of the input ports of each of the optical couplers and extending clockwise along a ring shape;
A second optical transmission line connected to the other input port of each of the 2 × N optical couplers and extending counterclockwise along the ring shape;
The ring-type passive optical network according to claim 1, wherein the ring-type passive optical network is provided. The ring-shaped optical transmission line has a short-circuit optical transmission line connected so as to divide the inside of the ring,
A third fault detection optical transmission line connected to the center apparatus, extending along the short-circuit optical transmission line and connected to the center apparatus again;
The transmitter of the center device transmits a signal to the third failure detection optical transmission line,
The receiver of the center device receives a signal from the third failure detection optical transmission line,
The switching means of the center device detects a fault location of the short-circuit optical transmission path from the presence or absence of reception of a signal from the third fault detection optical transmission path, and sets a transmission path according to the fault location. Switch,
The ring-type passive optical network according to claim 1, wherein the ring-type passive optical network is provided.   8. The third failure detection optical transmission line is obtained by branching the first failure detection optical transmission line or the second failure detection optical transmission line. The described ring-type passive optical network. A ring-type passive optical network according to any one of claims 1 to 8,
An optical line terminating device for video connected to the center device via the ring-type passive optical network;
A CATV system characterized by comprising:

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