JPH0846570A - Optical terminal and optical network - Google Patents

Abstract

PURPOSE:To provide a subcarrier multiplex optical multiaccess network where the working of an entire system is never stopped even when an optical terminal has a fault or an optical fiber transmission line is disconnected. CONSTITUTION:At an optical terminal 103, the signal light 112 of a working system and the signal light 124 of a stand-by system are converted into the high frequency signals 153 and 163 by the light receivers 133 and 143 repectively. Then a carrier signal 43 is multiplexed by the multiplexers 173 and 183 and then inputted to the light transmitters 193 and 203 which output the signal light 113 and 123. Thus the analog optical relaying is performed at each optical terminal in both working and stand-by systems. Therefore the working of an entire system is never stopped even when an optical terminal has a fault or an optical fiber transmission line is disconnected.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an optical information transmission network.

[0002]

2. Description of the Related Art Conventionally, a subcarrier relay point multiplex system has been studied as one of the systems for transmitting information signals from a plurality of points through an optical fiber network. In this system, N (N is a positive integer) optical terminals are serially inserted into an optical fiber transmission line terminated by a center terminal. Each optical terminal once converts the signal light sent from the preceding optical terminal into an electric signal, frequency-multiplexes the carrier signal (subcarrier signal) from the information source with this electric signal, and converts this into a signal light again. It is converted and output to the optical terminal in the subsequent stage. The carrier wave signals from the respective information sources have different frequencies. The signal light is finally input to the center terminal and converted into a high frequency signal by the optical receiver. Carrier waves from each information source are frequency-multiplexed with this high-frequency signal. Therefore, the center terminal can receive the information signal from any optical terminal by taking out any of these carriers and demodulating it by the tuner.

By using this subcarrier relay point multiplex system, it is possible to realize an optical multi-access network which is low in cost, capable of long-distance transmission and has high flexibility, and is applicable to, for example, a surveillance information transmission system. Is expected. The subcarrier relay point multiplex system is described in detail, for example, in documents such as "Proposal of optical multiaccess using subcarrier relay point multiplex system" by Tomon et al., IEICE Technical Report OCS93-99 (1993). It is written.

[0004]

In the subcarrier relay point multiplex system as described above, a large number of optical terminals are inserted in series in the optical fiber transmission line. Therefore, if any one of these optical terminals fails or the optical fiber transmission line is broken, the entire system stops. Therefore, an object of the present invention is to provide a highly reliable optical network in which the entire system does not stop even if an optical terminal fails or the optical fiber transmission line is broken.

[0005]

The optical terminal of the first invention comprises:
First and second optical receivers for respectively receiving the first and second signal lights input to the optical terminal, a carrier signal and first and second optical signals output from the first and second optical receivers. A first and a second for respectively multiplexing the two high frequency signals
And a first multiplexer for modulating the intensities of the first and second signal lights output from the optical terminal by the first and second high-frequency signals output from the first and second multiplexers, respectively. It is characterized by having first and second optical transmitters.

In the optical network of the second invention, N (N is a natural number) optical terminals are cascade-connected to the first and second loop optical fiber transmission lines, and the first and second loop optical fibers are connected. In an optical fiber network with a double loop configuration in which the fiber transmission line is terminated by a center terminal, an information source for outputting carrier signals having different frequencies is connected to each optical terminal, and the k-th (k is a natural number of N or less). ) Optical terminal receives the first signal light transmitted from the (k-1) th optical terminal through the first loop-shaped optical fiber transmission line by the first optical receiver, and the first optical receiver receives the first signal light. The first high-frequency signal output from the receiver and the carrier signal from the information source are multiplexed and input to the first optical transmitter, whereby the kth optical terminal transmits to the k + 1th optical terminal. Intensity of the first signal light Tone, and receives the second signal light transmitted from the k + 1 th light terminal by the second loop-shaped optical fiber transmission line by a second optical receiver,
The second high frequency signal output from the second optical receiver and the carrier signal from the information source are multiplexed and input to the second optical transmitter, whereby the k-th optical terminal outputs k- It is characterized in that the second signal light transmitted to the first optical terminal is intensity-modulated.

An optical terminal of a third invention is the optical terminal of the first invention, wherein pilot signals are detected from the first and second high frequency signals output from the first and second optical receivers, respectively. It has first and second signal detectors and a pilot signal generator, and when the pilot signal is not detected by the first signal detector, the pilot signal output from the pilot signal generator is used as the first signal. A pilot signal output from the pilot signal generator is input to the second optical transmitter when no pilot signal is detected by the second signal detector. To do.

An optical terminal of a fourth invention is the optical terminal of the third invention, wherein the first and second pilot signals are:
It is characterized in that it is modulated with a different terminal identification signal for each optical terminal.

An optical terminal of a fifth invention is the optical terminal of the third invention, characterized in that the frequencies of the first and second pilot signals are different for each optical terminal.

An optical terminal of a sixth invention is the optical terminal of the first invention, which is a filter for removing a pilot signal from the first and second high-frequency signals output from the first and second optical receivers. A pilot signal generator, the first signal after the pilot signal is removed by the filter
And a pilot signal output from the pilot signal generator is newly multiplexed on the second high frequency signal.

An optical terminal of a seventh invention is the optical network of the second invention, wherein the center terminal is the first and second loop optical fiber transmission lines sent by the first and second loop-shaped optical fiber transmission paths. First and second optical receivers for respectively receiving signal light, and a carrier wave for receiving carrier wave signals included in the first and second high frequency signals output from the first and second optical receivers, respectively. It has a signal receiver and a switch for inputting one of the first and second high frequency signals to the carrier signal receiver.

An optical terminal of an eighth invention is the optical network of the second invention, wherein the center terminal is the first and second loop optical fiber transmission lines sent by the first and second loop optical fiber transmission paths. First and second optical receivers for respectively receiving signal light, and a carrier wave for receiving carrier wave signals included in the first and second high frequency signals output from the first and second optical receivers, respectively. A switch for inputting to the carrier wave signal receiver any one of a signal receiver, the first high frequency signal, the second high frequency signal, and a signal in which the first and second high frequency signals are multiplexed. It is characterized by having.

An optical terminal of a ninth invention is the optical terminal of the first invention, wherein a first loopback path for guiding the first high-frequency signal to the second optical receiver and the second high-frequency signal are provided. A second loopback path for guiding a signal to the first optical transmitter is provided, and the first signal light is intensity-modulated by either the first or second high-frequency signal, and the second signal is transmitted. The signal light is intensity-modulated by either the second or first high-frequency signal.

An optical terminal according to a tenth aspect of the present invention is the optical terminal according to the first aspect of the present invention, wherein the first and second optical signals detect the pilot signals contained in the first and second high frequency signals, respectively.
Pilot signal detector, a first changeover switch for inputting the first high-frequency signal to either one of the first or second optical transmitter, and the second high-frequency signal for the second or second A second changeover switch for inputting to either one of the first optical transmitters, and when the first pilot signal detector does not detect a pilot signal, the second high-frequency signal is the first optical transmission signal. The second changeover switch so that the first high frequency signal is input to the second optical transmitter when the pilot signal is not detected by the second pilot signal detector. It is characterized in that the first changeover switch is changed over.

The optical terminal of the eleventh invention is the optical terminal of the ninth invention, characterized in that it has a filter for removing the carrier signal in the first and second loopback paths.

The optical network according to the twelfth invention is the optical network according to the second invention, wherein the L-th and M-th optical terminals (L and M) of the respective optical terminals due to the occurrence of a failure.
Is a natural number that satisfies L <M), and the loopback is performed with an i-th optical terminal (i is a natural number that satisfies i <L)
The carrier signal is input to the second optical transmitter, and the carrier signal is input to the first optical transmitter at the j-th optical terminal (j is a natural number satisfying j> M). To do.

An optical terminal according to a thirteenth aspect of the present invention is the optical terminal according to the first aspect of the present invention, wherein the second optical terminal output from the second optical receiver is used.
A second signal detector for detecting a pilot signal or a carrier signal included in the high frequency signal of the above, and when the second signal detector does not detect the pilot signal or the carrier signal, the second optical transmitter is The second optical transmitter is stopped, and the second optical transmitter is operated when the pilot signal or the carrier signal is detected by the second signal detector.

An optical terminal according to a fourteenth invention is the optical terminal according to the first invention, wherein the first optical signal output from the first optical receiver is used.
A first signal detector for detecting a pilot signal or a carrier signal included in the high frequency signal of the above, and when the pilot signal or the carrier signal is not detected by the first signal detector, the second optical receiver and It is characterized in that the second optical transmitter is operated.

[0019]

In the first and second aspects of the invention, the two transmission systems, the working system and the standby system, transmit signals in opposite directions by the double-loop optical fiber network, so that the optical terminal is broken or the optical fiber transmission is performed. Even if the road is broken, the whole system does not stop.

In the third invention, each optical terminal has a pilot signal generator, and when the pilot signal from the preceding optical terminal is interrupted due to a transmission path failure or the like, it is output from this pilot signal generator. The pilot signal is transmitted to the subsequent optical terminal. The optical terminal in the latter stage can perform automatic gain control and the like using this pilot signal.

In the fourth aspect of the invention, the pilot signal output from the pilot signal generator of each optical terminal is modulated by the terminal identification signal unique to that optical terminal. As a result, similar to the third aspect, even if a transmission path failure or the like occurs, automatic gain control using the pilot signal becomes possible, and at the same time, it is possible to know where the failure has occurred in the optical terminal and the center terminal in the subsequent stage.

In the fifth aspect of the invention, the frequency of the pilot signal output from the pilot signal generator of each optical terminal is different for each optical terminal. As a result, similar to the fourth aspect of the invention, it becomes possible to perform automatic gain control at the time of a transmission line failure and confirm the location of the failure.

In the sixth invention, each optical terminal regenerates and relays only the pilot signal. That is, after performing automatic gain control or the like by the pilot signal from the optical terminal at the preceding stage, this pilot signal is once removed by a filter, and the pilot signal output from the pilot signal generator of each optical terminal is newly multiplexed. As a result, similar to the third aspect of the invention, automatic gain control using a pilot signal becomes possible even if a transmission path failure or the like occurs.

In the center terminal of the seventh invention, each carrier signal receiver has an input changeover switch, and either one of the received signals of the active system and the standby system is inputted to the carrier signal receiver. This allows the center terminal to receive the carrier signal from each optical terminal even if the optical terminal fails or the optical fiber transmission line is broken.

In the center terminal of the eighth aspect of the invention, either the active system, the standby system, or the sum of the active system and the standby system is input to the carrier signal receiver. This allows the center terminal to receive the carrier signal from each optical terminal even when a failure occurs, as in the seventh aspect.

In the ninth aspect of the invention, so-called loopback is performed at the optical terminals before and after the location of the fault, where signals are returned from the active system to the standby system and from the standby system to the active system.

In the tenth aspect of the invention, each optical terminal detects the pilot signal or carrier signal of the active system and the standby system, and controls the loopback changeover switch by this. With this, even if there is no instruction from the center terminal, each optical terminal can automatically perform loopback when a failure occurs.

In the eleventh aspect of the invention, each optical terminal is provided with a filter for removing a carrier signal on the loopback path. Therefore, even if the carrier signal of each optical terminal is transmitted by both the working system and the protection system, the carrier signals of the working system and the protection system do not interfere with each other during the loopback.

In the twelfth aspect of the invention, when loopback is performed, the carrier signal is transmitted by the transmission system which is closer to the center terminal in the working system and the protection system. As a result, the number of times the carrier signal is photoelectrically converted is reduced, and the deterioration of the transmission quality during loopback can be reduced.

In the thirteenth aspect of the invention, when the pilot signal or the carrier signal is not received by the standby system of each optical terminal, the transmission light source of the standby system is turned off to prolong the life of the standby system and lower the optical terminal. Aim to reduce power consumption. When a failure occurs, the transmission signal of the standby system of each optical terminal can be automatically turned on by transmitting the pilot signal of the standby system from the center terminal.

In the fourteenth aspect of the invention, normally, all the spare systems of each optical terminal are turned off, and the life and power consumption are reduced. However, if the pilot signal or carrier signal is no longer received in the active system due to a failure, etc.,
The standby system is automatically turned on, and the instruction from the center terminal can be received using the standby system.

[0032]

The present invention will be described below with reference to the drawings.

FIG. 1 shows the overall configuration of an optical network according to the first embodiment of the present invention. In FIG. 1, optical terminals 100-1
04 and the center terminal 500 are the optical fiber transmission lines 10,
They are connected in a loop by 20. The signal light is transmitted clockwise by the optical fiber transmission line 10 and counterclockwise by the optical fiber transmission line 20. Optical terminal 10
Information sources 30 to 34 are connected to 0 to 104, respectively, and carrier signals 40 to 44 modulated by the information signals are output from the information sources 30 to 34. The carrier signals 40 to 44 are input to the optical terminals 100 to 104,
The center terminal 500 through the optical fiber transmission lines 10 and 20.
Be transmitted to.

The configurations of the optical terminal 103 and the center terminal 500 in FIG. 1 are shown in FIGS. 2 and 3, respectively. Figure 2
In the optical terminal 103, the signal lights 112 and 124 sent from the optical terminals 102 and 104 by the optical fiber transmission lines 10 and 20 are transmitted to the optical receivers 133 and 143 as shown in FIG.
Are converted into high frequency signals 153 and 163. Further, by the multiplexers 173 and 183, the high frequency signals 153 and 1
63 and the carrier wave signal 43 are multiplexed, and the optical transmitters 193, 2
It is input to 03. The signal lights 113 and 123 are output from the optical transmitters 193 and 203, and are transmitted to the optical terminals 104 and 102. The information sources 30 to 34 of the present embodiment are video cameras, and the carrier signals 40 to 44 are arranged at frequency intervals of 40 MHz from 1090 MHz to 1250 MHz, and each is FM-modulated by a video signal.

In the center terminal 500, as shown in FIG. 3, the signal lights 114 and 1 sent from the optical terminals 104 and 100 through the optical fiber transmission lines 10 and 20, respectively.
20 receives the high frequency signal 5 by the optical receivers 510 and 520.
Converted to 30,540. This high frequency signal 530,5
Carrier signals 40 to 44 are frequency-multiplexed on 40. The tuner 560 to 564 has a changeover switch 55.
0 to 554 input one of the high frequency signals 530 and 540, and select carrier signals 40 to 44 respectively.
The information signals 50 to 54 are demodulated and output. In a normal state, the high frequency signal 530 of the working system is the tuners 560-5.
64 is input.

According to this embodiment, the optical fiber transmission line 1
Even if a failure occurs in 0, 20 or the optical terminals 100 to 104, the center terminal 500 can obtain the status signals 50 to 54 because the optical network has the double loop configuration. That is, for example, the optical fiber transmission lines 10 and 2
When 0 is disconnected between the optical terminals 101 and 102, the carrier signals 40 and 41 drop out from the high frequency signal 530, and the tuners 560 and 561 cannot receive. In this case, by switching the changeover switches 550 and 551, the high frequency signal 540 in which the carrier wave signals 40 and 41 are frequency-multiplexed is input to the tuners 560 and 561. In this way, the center terminal can obtain signals from all the information sources even if the optical fiber transmission line is broken.

The configurations of the optical terminal and the center terminal in the second embodiment of the present invention are shown in FIGS. The overall configuration of the optical network of this embodiment is the same as that of the first embodiment (FIG. 1). The center terminal 500 of FIG. 5 has pilot signal generators 570 and 580, and the optical transmitter 6
The signal lights 630 and 640 output from the optical fiber transmission lines 10 and 20 from the 10, 620 are pilot signals 650 and 6 respectively.
Modulated by 60. Pilot signal 6 of this embodiment
The frequency of 50,660 was 700 MHz.

In the optical terminal 103 of FIG. 4, the optical receiver 1
High frequency signals 153, 163 output from 33, 143
Contains the pilot signals 650 and 660, and the intensities of the pilot signals 650 and 660 are detected by the signal detectors 213 and 223. The automatic gain control circuits 233, 243 use the signal detectors 213, 223.
Of the variable gain amplifiers 253 and 263, the gains of the variable gain amplifiers 253 and 263 are adjusted so that the intensities of the pilot signals 650 and 660 become predetermined values. As a result, for example, even if the intensity of the signal light 112 input to the optical terminal 103 changes, the high frequency signal 1
The strength of 53 is kept constant. The signal detector 21
If no pilot signals 650, 660 are detected at 3, 223, the automatic gain control circuits 233, 243 minimize the gain of the variable gain amplifiers 253, 263. As a result, for example, when the pilot signal generator 570 of the center terminal 500 fails and the signal detector 213 does not detect the pilot signal 650, the high frequency signal 153 is greatly amplified and the input level of the optical transmitter 193 becomes excessive. Can be avoided.

Further, the optical terminal 103 uses the pilot signal 29.
Pilot signal generator 273,2 for generating 3,303
83. However, in the normal state, power is not supplied to the pilot signal generators 273 and 283, and the pilot signals 293 and 303 are not input to the transmission light sources 193 and 203. Now, for example, when the optical fiber transmission line 10 is disconnected between the optical terminals 102 and 103, and the pilot signal 650 is no longer detected by the signal detector 213,
Power is supplied to the pilot signal generator 273, and the output pilot signal 293 is multiplexed with the high frequency signal 153 and the carrier signal 43 by the multiplexer 173 and input to the optical transmitter 193. Even if a failure occurs in the optical fiber transmission line and the pilot signal from the center terminal is interrupted in this way, the pilot signal is regenerated at the optical terminal immediately after the failure occurrence point, and the subsequent optical terminal uses this. Automatic gain control can be performed.

The structure of the optical terminal of the third embodiment of the present invention is shown in FIG. The overall configuration of the optical network and the configuration of the center terminal of this embodiment are the same as those of the first embodiment (FIGS. 1 and 3). In this embodiment, the high-frequency signals 153 and 163 output from the optical receivers 133 and 143 are kept constant in intensity by the signal detectors 213 and 223, the automatic gain control circuits 233 and 243, and the variable gain amplifiers 253 and 263. Then, it is input to the filters 313 and 323. The filters 313 and 323 remove only the pilot signal from the high frequency signals 153 and 163. In this embodiment, a high pass filter with a cutoff frequency of 900 MHz was used. High frequency signal 153 after passing through the filter 313
Are multiplexed by the multiplexer 173 with the carrier signal 43 and the pilot signal 293 output from the pilot signal generator 273. Similarly, the high frequency signal 163 after passing through the filter 323 is transmitted by the multiplexer 183 to the carrier signal 4
3 and the pilot signal 303 output from the pilot signal generator 283. In this way, in this embodiment, since the pilot signal is regenerated and relayed at each optical terminal, each optical terminal can send the pilot signal to the subsequent optical terminal even if the optical fiber transmission line is broken.

In the fourth embodiment of the present invention, the configuration of each optical terminal is similar to that of the second embodiment, but the pilot signal output from the pilot signal generator of each optical terminal is unique to each optical terminal. It is modulated by the terminal identification signal. As shown in FIG. 7, the center terminal 500 includes an optical receiver 510,
Signal detectors 670 and 680 are provided for detecting pilot signals included in high frequency signals 530 and 540 output from 520 and discriminating terminal identification signals superimposed on the pilot signals. The input signals of the tuners 560 to 564 are collectively switched by the switches 690 and 700.

The signal detector 670 normally detects the pilot signal 650 transmitted from the center terminal 500. In this case, switch 690 is on and switch 700 is
Is turned off, and the active system, that is, the high frequency signal 530 is supplied to the tuners 560 to 564. However, when a failure occurs in the working system, for example, when the optical fiber transmission line 10 is broken between the optical terminals 102 and 103, the signal detector 67
At 0, the pilot signal 29 transmitted from the optical terminal 103
3 is detected. In this case, the center terminal 500 issues an alarm for the occurrence of a failure in the active system, turns off the switch 690, turns on the switch 700, and supplies the high-frequency signal 540 to the tuners 560 to 564 to switch to the standby system.

Further, when a failure occurs in the standby system, for example, the optical fiber transmission line 20 between the optical terminals 102 and 103.
If it is also cut off, the pilot signal detector 680
The pilot signal 302 transmitted from the optical terminal 102 is detected. In this case, the center terminal 500 issues an alarm that the standby system has also failed, and the switch 690,
Both 700 are turned on, and both the active system and the standby system, that is, the high frequency signals 530 and 540 are combined, and the tuner 56
0 to 564. As a result, the center terminal can receive the information signal from each optical terminal even when one or both of the double-loop optical fiber transmission lines are disconnected. Moreover, the number of switches required in the center terminal can be significantly reduced as compared with the second embodiment.

Further, as a modification of the present embodiment, there is a system in which the frequency of the pilot signal output from the pilot signal generator of each optical terminal is changed for each optical terminal. In this case, the signal detectors 670 and 680 of the center terminal 500 are
By detecting the frequency of the pilot signal, the presence / absence of a fault and the fault occurrence point can be determined.

In the fifth embodiment of the present invention, so-called loopback is performed in which the signal is returned at the optical terminal when a failure occurs. FIG. 8 shows the configuration of the optical terminal of this embodiment, and FIG. 9 shows the operation of each optical terminal during loopback. Optical terminal 10 of FIG.
3, the high frequency signal 153 of the active system is input to either the transmission light source 193 of the active system or the multiplexer 183 of the standby system by the changeover switch 333. Similarly, the high frequency signal 163 of the standby system is transmitted to the changeover switch 343.
Is input to either the standby transmission light source 203 or the active multiplexer 173. The carrier signal 43 is multiplexed only in the active system via the multiplexer 173.

The above-mentioned changeover switch 333 is connected to the transmission light source 193 of the working system when the pilot signal is detected by the signal detector 223 of the protection system, and the signal detector 223 is connected.
If the pilot signal is not detected at, it is connected to the multiplexer 183 of the standby system. Similarly, the changeover switch 343
Is connected to the transmission light source 203 of the standby system when the pilot signal is detected by the signal detector 213 of the active system, and is connected to the multiplexer 173 of the active system when the pilot signal is not detected by the signal detector 213. It Under normal conditions,
Since the pilot signal is detected by both of the signal detectors 213 and 223, the changeover switch 333 is operated by the transmission light source 193.
In addition, the changeover switch 343 is connected to the transmission light source 203. In this case, loopback is not performed and the carrier signal 4
3 is transmitted by the optical fiber transmission line 10 of the working system.

FIG. 9 shows the operation of each optical terminal when the optical fiber transmission lines 10 and 20 are cut off between the optical terminals 102 and 103, for example. In the optical terminal 102, since the pilot signal of the standby system is lost, the changeover switch 332 is switched to the multiplexer 182 of the standby system. by this,
The carrier signals 40 to 42 and the pilot signal 650 which have passed through the working optical fiber transmission line 10 are looped back by the optical terminal 102 and transmitted to the center terminal 500 through the standby optical fiber transmission line 20. Further, in the optical terminal 103, the pilot signal of the working system is cut off, so the changeover switch 343 is switched to the multiplexer 172 of the working system. As a result, the pilot signal 660 that has passed through the optical fiber transmission line 20 of the standby system is looped back at the optical terminal 103, and is multiplexed with the carrier signals 43 and 44 on the way, while passing through the optical fiber transmission line 10 of the active system to the center. It is transmitted to the terminal 500.

In the optical terminal 101, the pilot signal of the backup system is cut off at the moment when the optical fiber transmission lines 10 and 20 are cut off, so that loopback is performed here. However, the loopback is performed in the optical terminal 102 and the pilot signal is transmitted through the optical fiber transmission line 20 of the standby system, so that the loopback of the optical terminal 101 is immediately released. Similarly, in the optical terminal 104, the optical fiber transmission line 10,
The loopback is performed at the moment when 20 is cut off, but when the loopback is performed by the optical terminal 103, the loopback of the optical terminal 104 is released. As described above, according to this embodiment, when a failure occurs in the optical fiber transmission line, each optical node can automatically perform loopback even if there is no instruction from the center terminal.

In the sixth embodiment of the present invention, similar to the fifth embodiment, loopback is performed when a failure occurs. At this time, each optical terminal switches the input location of the carrier wave signal to make the loopback. Prevent deterioration of transmission quality.

The configuration of the optical terminal in this embodiment is shown in FIG. In the optical terminal 103 of FIG. 9, the carrier signal 43 is
The changeover switch 63 inputs the signal to either the current-system multiplexer 173 or the standby-system multiplexer 183. In addition, the pilot signal 65 output from the center terminal 500
0 and 660 are each modulated by an identification signal, and the signal detector 223 can identify whether the pilot signal sent by the standby system is the active system or the standby system. The pilot signal 660 of the standby system is detected by the signal detector 223.
Is detected, the changeover switch 63 is connected to the transmission light source 193 of the active system. On the contrary, when the signal detector 223 detects the pilot signal 650 of the working system or no pilot signal at all, the changeover switch 63 is connected to the multiplexer 183 of the standby system. The changeover switch 333 for loopback is used.
The operation of 353 is the same as that of the fifth embodiment.

In the normal state, the pilot signal 660 of the standby system is detected by the signal detector 223, so that the carrier signal 43 is input to the multiplexer 173 of the active system. Now, the optical fiber transmission line 1 is provided between the optical terminal 104 and the center terminal 500.
If 0 and 20 are cut off, the optical terminal 104 loops back as in the fifth embodiment. At this time, the signal detector 223 of the optical terminal 103 detects the pilot signal 650 of the working system, and the changeover switch 63 is connected to the multiplexer 183 of the standby system. In the fifth embodiment,
When the loopback is performed in the optical terminal 104, the carrier signal 43 returns to the optical terminal 103 via the optical terminal 104 once, and then is transmitted to the center terminal 500 via the optical fiber transmission line 20 of the standby system. It will be. However, in the present embodiment, the carrier signal 43 is transmitted from the optical terminal 103 directly through the optical fiber transmission line 20 of the standby system to the center terminal 500.
Be transmitted to. For this reason, this embodiment has less accumulation of distortion and noise than the fifth embodiment.

The seventh embodiment of the present invention is to prevent the deterioration of the transmission quality at the time of loopback by inserting a filter in the loopback path.

The structure of the optical terminal of this embodiment is shown in FIG.
The optical terminal 103 of FIG. 11 is the optical terminal of the fifth embodiment (FIG. 8).
Although the configuration is almost the same as that of the first embodiment, filters 353 and 363 are inserted between the active system changeover switch 333 and the standby system multiplexer 183 and between the standby system changeover switch 343 and the active system multiplexer 173. It The filters 353 and 363 in this embodiment are low-pass filters having a cutoff frequency of 900 MHz, and the pilot signals 650 and 660 having a frequency of 700 MHz pass through as they are, but the frequency of 10
The 90 MHz to 1250 MHz carrier signals 40 to 44 are removed. Further, the carrier wave signal 43 is generated by the multiplexers 173, 18
Input to both 3 The operations of the changeover switches 333 and 343 in the normal state and when a failure occurs are the same as in the fifth embodiment.

Now, assume that the optical fiber transmission lines 10 and 20 are cut off between the optical terminals 103 and 104. In this case, in the optical terminal 103, since the pilot signal of the protection system is lost,
The changeover switch 333 is switched to the multiplexer 183 of the standby system, and the high frequency signal 153 of the active system is looped back. At this time, the carrier signals 40 to 43 of the high frequency signal 153 are removed by the filter 353, and only the pilot signal 650 is input to the standby system. The pilot signal 650 is multiplexed with the carrier signal 43 by the multiplexer 183, and is transmitted as the high frequency signal 163 to the center terminal 500 through the optical fiber transmission line 20 of the standby system.

As described above, according to the present embodiment, the carrier signal is multiplexed into both the active system and the standby system, but the carrier signal multiplexed into the system distant from the center terminal at the time of loopback is generated. Removed by filter. That is, since the carrier signal is transmitted by the system that is closer to the center terminal among the working system and the standby system, the transmission quality does not deteriorate even during loopback. Further, in the case of the present embodiment, it is not necessary to discriminate whether the pilot signal is of the active system or the standby system and switch the input position of the carrier signal accordingly, as in the sixth embodiment.

In the eighth embodiment of the present invention, the transmission light source of the spare system of each optical terminal is normally turned off to extend the useful life of the spare system and reduce the power consumption of each optical terminal.

The configuration of the center terminal of this embodiment is the fourth in FIG.
Is the same as the embodiment described above. However, the pilot signals 650 and 660 of the working system and the protection system are modulated by the optical terminal control signal. In addition, the standby pilot signal generator 580 is not normally supplied with power, and the pilot signal 6
60 is off. The structure of the optical terminal is the same as that of the seventh embodiment shown in FIG. However, the signal detector 21
The optical terminal control signal is output from the optical terminals 3 and 223, and the changeover switches 333 and 343 are controlled by the optical terminal control signal. Normally, the changeover switch 333 is connected to the transmission light source 193 of the active system, and the changeover switch 3
Reference numeral 43 is connected to the transmission light source 203 of the standby system.
The standby system transmission light source 203 is supplied with power only when a pilot signal is detected by the active system pilot signal detector 213. Therefore, since the pilot signal 650 is not normally output from the center terminal 500, the transmission light source 203 is not powered and the signal light 123 is not output.

Now, it is assumed that the working optical fiber transmission line 10 is disconnected between the optical terminals 103 and 104. In this case, the active signal detector 670 of the center terminal 500 does not detect the pilot signal 650. In this case, the standby pilot signal generator 580 is supplied with power, and the pilot signal 660 is transmitted to each optical terminal through the optical fiber transmission line 20. As a result, the standby transmission light sources of the optical terminals are sequentially turned on, and the carrier signals 40 to 44 are transmitted to the center terminal 500 through the optical fiber transmission line 20.

Further, assuming that the spare optical fiber transmission line 20 is also disconnected between the optical terminals 103 and 104, even if a certain time elapses after the spare pilot signal generator 580 is turned on, the pilot signal is detected by the signal detector 680. 660 is not detected. In this case, an instruction is sent to perform loopback in order from the optical terminal farther from the center terminal. That is,
The center terminal 500 first sends an optical terminal control signal by using the working system so that the changeover switch 334 of the optical terminal 104 is switched to the multiplexer 184 of the standby system. After that, when the pilot signal is not detected by the signal detector 680 even after a fixed time elapses, the changeover switch 333 of the optical terminal 103.
Is sent to the multiplexer 183 of the standby system. This operation is performed until the signal detector 680 detects a pilot signal. At the same time, the center terminal 500 sends an optical terminal control signal using the standby system so as to switch the changeover switch 340 of the optical terminal 100 to the multiplexer 170 of the active system. After that, when the pilot signal is not detected by the signal detector 670 even after a certain period of time, the optical terminal control signal is sent so as to switch the changeover switch 341 of the optical terminal 101 to the multiplexer 171 of the active system. This operation is repeated until the signal detector 670 detects a pilot signal.

In the ninth embodiment of the present invention, all of the spare system including the transmission light source and the optical receiver are normally turned off. Therefore, as in the eighth embodiment, the service life of the spare system is extended. And the power consumption of optical terminals is being reduced.

The configuration of the center terminal of this embodiment is the fourth in FIG.
The configuration of the optical terminal is the same as that of the seventh embodiment of FIG. 11. However, the standby system for each optical terminal and the center terminal, including the transmission light source and the optical receiver, is normally off. The protection system for each of the optical terminals and the center terminal is automatically turned on when the pilot signal for the working system is lost.

Now, when the optical fiber transmission lines 10 and 20 are broken between the optical terminals 102 and 103, the optical terminals 103 and 10
4 and the center terminal 500, the pilot signal of the active system is cut off, so that the standby system is automatically turned on. The standby system of the optical terminals 100 to 102 is the center terminal 500.
Is turned on by an optical terminal control signal transmitted from the working system. After that, loopback is performed by the same procedure as in the eighth embodiment.

[0063]

As described above, according to the present invention, a highly reliable optical multi-access network can be realized.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an overall configuration of a first embodiment of the present invention.

FIG. 2 is a diagram for explaining the configuration of the optical terminal according to the first embodiment of the present invention.

FIG. 3 is a diagram for explaining the configuration of the center terminal according to the first embodiment of this invention.

FIG. 4 is a diagram for explaining a configuration of an optical terminal according to a second embodiment of the present invention.

FIG. 5 is a diagram for explaining a configuration of a center terminal according to a second embodiment of the present invention.

FIG. 6 is a diagram for explaining the configuration of an optical terminal according to a third embodiment of the present invention.

FIG. 7 is a diagram for explaining a configuration of a center terminal according to a fourth embodiment of the present invention.

FIG. 8 is a diagram for explaining a configuration of an optical terminal according to a fifth exemplary embodiment of the present invention.

FIG. 9 is a diagram for explaining the operation of each optical terminal during loopback according to the fifth embodiment of the present invention.

FIG. 10 is a diagram for explaining the configuration of the optical terminal according to the sixth embodiment of the present invention.

FIG. 11 is a diagram for explaining the configuration of the optical terminal according to the seventh embodiment of the present invention.

[Explanation of symbols]

10, 20 Optical fiber transmission line 30-34 Information source 40-44 Carrier wave signal 50-54 Information signal 60-64 Changeover switch 100-104 Optical terminal 110-114, 120-124 Signal light 130-134, 140-144 Optical reception High-frequency signal 170-174, 180-184 Multiplexer 190-194,200-204 Optical transmitter 210-214, 220-224 Signal detector 230-234, 240-244 Automatic gain control Circuit 250-254, 260-264 Variable gain amplifier 270-274, 280-284 Pilot signal generator 290-294, 300-304 Pilot signal 310-314, 320-324 Filter 330-334, 340-344 Changeover switch 350- 354,360 64 filter 500 center terminal 510,520 optical receiver 530,540 high frequency signal 550-554 changeover switch 560-564 tuner 570,580 pilot signal generator 610,620 optical transmitter 630,640 signal light 650,660 pilot signal 670, 680 signal detector 690,700 switch

Claims (14)

[Claims] 1. A first and a second optical receiver for respectively receiving a first and a second signal light inputted to an optical terminal, and a carrier signal and an output from the first and the second optical receiver. The first and second multiplexers for respectively multiplexing the first and second high-frequency signals, and the optical signals by the first and second high-frequency signals output from the first and second multiplexers, respectively. An optical terminal having first and second optical transmitters for respectively modulating the intensities of first and second signal lights output from the terminal. 2. N (N is a natural number) optical terminals are cascade-connected to the first and second loop-shaped optical fiber transmission lines, and the first and second loop-shaped optical fiber transmission lines are connected by a center terminal. In an optical fiber network having a terminated double loop configuration, an information source for outputting carrier signals having different frequencies is connected to each optical terminal, and the k-th optical terminal (k is a natural number of N or less) is A first optical receiver receives the first signal light transmitted from the (k-1) th optical terminal via the first loop-shaped optical fiber transmission line, and outputs the first optical signal output from the first optical receiver. 1 high-frequency signal and the carrier signal from the information source are multiplexed and input to the first optical transmitter, whereby the first signal light transmitted from the k-th optical terminal to the k + 1-th optical terminal is generated. Intensity modulated, the second loop light The second signal light transmitted from the (k + 1) th optical terminal through the fiber transmission line is received by the second optical receiver, and the second high-frequency signal output from the second optical receiver and the information source. It is possible to combine the carrier wave signal from the optical signal from the optical signal into the second optical transmitter and to intensity-modulate the second signal light transmitted from the kth optical terminal to the (k-1) th optical terminal. Characteristic optical network. 3. A first and second signal detector for detecting a pilot signal from the first and second high-frequency signals output from the first and second optical receivers, and a pilot signal generator, respectively. If the pilot signal is not detected by the first signal detector, the pilot signal output from the pilot signal generator is input to the first optical transmitter, and the pilot signal is output by the second signal detector. 2. The optical terminal according to claim 1, wherein a pilot signal output from the pilot signal generator is input to the second optical transmitter when no signal is detected. 4. The first and second pilot signals are:
The optical terminal according to claim 3, wherein the optical terminal is modulated with a terminal identification signal different for each optical terminal. 5. The optical terminal according to claim 3, wherein the frequencies of the first and second pilot signals are different for each optical terminal. 6. A filter for removing a pilot signal from the first and second high-frequency signals output from the first and second optical receivers, and a pilot signal generator, wherein the pilot signal is removed by the filter. First after being done
The optical terminal according to claim 1, wherein the pilot signal output from the pilot signal generator is newly multiplexed with the second high frequency signal. 7. The center terminal includes first and second optical receivers for receiving the first and second signal lights sent by the first and second loop optical fiber transmission lines, respectively. A carrier signal receiver for receiving a carrier signal contained in the first and second high frequency signals output from the first and second optical receivers, and the first and second
2. An optical network having a switch for inputting one of the high frequency signals of 1. to the carrier signal receiver. 8. The center terminal includes first and second optical receivers for respectively receiving first and second signal lights sent by the first and second loop optical fiber transmission lines. A carrier signal receiver for receiving a carrier signal included in the first and second high frequency signals output from the first and second optical receivers, and the first high frequency signal or the second high frequency signal. An optical network having a switch for inputting a high frequency signal or one of the signals obtained by multiplexing the first and second high frequency signals to the carrier signal receiver. 9. A first loopback path for guiding the first high frequency signal to the second optical receiver, and a second loopback for guiding the second high frequency signal to the first optical transmitter. A path, the first signal light is intensity-modulated by either the first or second high-frequency signal, and the second signal light is either one of the second or first high-frequency signal. The optical terminal according to claim 1, wherein the optical terminal is intensity-modulated. 10. A first and a second detecting a pilot signal included in the first and second high frequency signals, respectively.
Pilot signal detector, a first changeover switch for inputting the first high-frequency signal to either one of the first or second optical transmitter, and the second high-frequency signal for the second or second A second changeover switch for inputting to either one of the first optical transmitters, and when the first pilot signal detector does not detect a pilot signal, the second high-frequency signal is the first optical transmission signal. The second changeover switch so that the first high frequency signal is input to the second optical transmitter when the pilot signal is not detected by the second pilot signal detector. The optical terminal according to claim 1, wherein the first changeover switch is changed over. 11. The optical terminal according to claim 9, further comprising a filter for removing the carrier signal in the first and second loopback paths. 12. L among the optical terminals when a failure occurs
When the loopback is performed at the th and M-th optical terminals (L and M are natural numbers satisfying L <M), the carrier signal is transmitted at the i-th optical terminal (i is a natural number satisfying i <L). The signal is input to the second optical transmitter and the j-th optical terminal (j is
The optical network according to claim 2, wherein the carrier signal is input to the first optical transmitter with a natural number satisfying j> M. 13. A second optical signal output from the second optical receiver.
A second signal detector for detecting a pilot signal or a carrier wave signal included in the high frequency signal, and when the pilot signal or the carrier wave signal is not detected by the second signal detector, the second optical transmitter is used. 2. The optical terminal according to claim 1, wherein the second optical transmitter is stopped and the second optical transmitter is operated when a pilot signal or a carrier signal is detected by the second signal detector. 14. A first optical signal output from the first optical receiver.
A first signal detector for detecting a pilot signal or a carrier signal included in the high frequency signal of the above, and when the pilot signal or the carrier signal is not detected by the first signal detector, the second optical receiver and The optical terminal according to claim 1, wherein the second optical transmitter is operated.