JP2912164B2 - Optical terminal and optical network - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. 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 multiplexing method has been studied as one of the methods for transmitting information signals from a plurality of locations through an optical fiber network. In this system, N (N is a positive integer) optical terminals are inserted in series in 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 electric signal with a carrier signal (subcarrier signal) from an information source, and converts this into signal light again. The signal is converted and output to the subsequent optical terminal. Note that carrier signals from each information source have different frequencies. The signal light is finally input to the center terminal and is converted into a high-frequency signal by the optical receiver. A carrier wave from each information source is frequency-multiplexed on this high-frequency signal. Therefore, the center terminal can receive an information signal from an arbitrary optical terminal by taking out and demodulating an arbitrary carrier among these carriers by the tuner.

[0003] By using the subcarrier relay point multiplexing system, a low cost, long distance transmission and highly flexible optical multi-access network can be realized. For example, application to a monitoring information transmission system or the like is possible. Expected. The subcarrier relay point multiplexing method is described in detail in, for example, literature such as "Proposal of optical multi-access using subcarrier relay point multiplexing method" by Domon et al. It is noted.

[0004]

In the above-described subcarrier relay point multiplexing system, a large number of optical terminals are inserted in series in an optical fiber transmission line. Therefore, if even one of these optical terminals breaks down or the optical fiber transmission line breaks, 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 an optical fiber transmission line is disconnected.

[0005]

An optical terminal according to a first aspect of the present invention comprises:
First and second optical receivers for receiving first and second input signal lights input to an optical terminal, respectively, and a first and a second optical receiver output from the first and second optical receivers; the first and second multiplexer for multiplexing the second high-frequency signals, respectively, first and second high-frequency signal output from the first and second multiplexer is input 1 And
And a second optical transmitter, the first and second optical transmitters
The intensity of the first and second output signal lights output from the detector is
Modulated by the first and second high frequency signals respectively
That is output from the first and second optical receivers.
A pilot signal from each of the first and second high-frequency signals
First and second signal detectors for detecting and detecting the signal;
Automatic control to control the strength of the high-frequency signal in response to the output of the
A gain control circuit and a pilot signal generator.
No pilot signal is detected by the signal detector
Is the pilot output from the pilot signal generator.
A signal is input to a first optical transmitter and said second signal detector
If no pilot signal is detected at
The pilot signal output from the
2 is input to the optical transmitter .

A second invention relates to an optical terminal according to the first invention.
In this case, the pilot signal is different for each optical terminal.
It is characterized by being modulated by another signal.

A third invention is an optical terminal according to the first invention.
Therefore, the frequency of the pilot signal differs for each optical terminal.
It is characterized by the following.

[0008] A fourth invention relates to an optical terminal according to the first invention.
The first and second optical receivers output the first
And removing the pilot signal from the second high frequency signal
A filter and a pilot signal generator, wherein the filter
First and second after the pilot signal is removed by
2 output from the pilot signal generator.
The new pilot signal is newly multiplexed.
You.

An optical terminal according to a fifth aspect of the present invention is configured such that
Receiving first and second input signal lights, respectively.
And a second optical receiver, a carrier signal and the first and second optical receivers.
First and second high-frequency waves output from a second optical receiver
First and second multiplexers for respectively multiplexing the signal and the signal;
The first and second signals output from the first and second multiplexers
And second optical transmitters to which two high-frequency signals are input
Output from the first and second optical transmitters.
The first and second output signal light intensities are equal to the first and second output signal lights.
2 are respectively modulated by the high-frequency signals of
A first loop bar for guiding a high-frequency signal to the second optical transmitter;
Transmission path and the second high-frequency signal to the first optical transmission
A second loopback path leading to the vessel, wherein the first output
The force signal light is one of the first and second high frequency signals.
On the other hand, the intensity of the second output signal light is modulated.
Intensity modulation on either the second or first high frequency signal
It is characterized by being performed.

An optical terminal according to a sixth aspect of the present invention comprises the first and second optical terminals.
2. A filter for removing the carrier signal in the loopback path 2
It is characterized by having a filter .

[0011]

[0012]

[0013]

[0014]

[0015]

[0016]

[0017]

[0018]

[0019]

In the optical terminal and the optical network according to the present invention, since the two transmission systems , the working system and the protection system, transmit signals in mutually opposite directions through the double-loop optical fiber network, the optical terminal may fail or the optical fiber may fail. Even if the transmission line is disconnected, the entire system does not stop.

In the first aspect , each optical terminal has a pilot signal generator, and when the pilot signal from the preceding optical terminal is interrupted due to a transmission line failure or the like, the pilot signal is output from the pilot signal generator. The pilot signal is transmitted to the subsequent optical terminal. The optical terminal at the subsequent stage can perform automatic gain control and the like using the pilot signal.

In the second invention , the pilot signal output from the pilot signal generator of each optical terminal is modulated by a terminal identification signal unique to the optical terminal. As a result, automatic gain control using a pilot signal becomes possible even when a transmission line failure or the like occurs as in the first invention , and at the same time, the optical terminal and the center terminal at the subsequent stage can know where the failure has occurred.

In the third invention , the frequency of the pilot signal output from the pilot signal generator of each optical terminal differs for each optical terminal. Thus, similar to the second aspect, automatic gain control at the time of a transmission line failure and confirmation of a failure occurrence location can be performed.

In the fourth invention , each optical terminal reproduces and relays only the pilot signal. That is, after performing automatic gain control or the like using a pilot signal from the optical terminal at the preceding stage, the 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. Thus, as in the first aspect, automatic gain control using a pilot signal can be performed even if a transmission path failure or the like occurs.

In the fifth invention, the light before and after the location where the failure occurs is described.
At the terminal, switch from the active system to the standby system and from the standby system to the active system.
The return of the signal, so-called loopback, is performed.

In the sixth invention, a loop is provided at each optical terminal.
A filter is installed in the back path to remove the carrier signal.
Have been. For this reason, the carrier signal of each optical terminal is
Even if it is transmitted in both the standby system, the current
The carrier signals of the service system and the standby system do not interfere with each other.

[0026]

[0027]

[0028]

[0029]

[0030]

[0031]

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 shows the overall configuration of an optical network according to a first embodiment of the present invention. In FIG. 1, the optical terminals 100-1
04 and the center terminal 500 are the optical fiber transmission lines 10,
20 are connected in a loop. 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 the information sources 30 to 34 output carrier signals 40 to 44 modulated by information signals. The carrier signals 40 to 44 are input to the optical terminals 100 to 104,
Center terminal 500 through optical fiber transmission lines 10 and 20
Is transmitted to

FIGS. 2 and 3 show the configurations of the optical terminal 103 and the center terminal 500 in FIG. 1, respectively. FIG.
In the optical terminal 103, the signal lights 112 and 124 transmitted from the optical terminals 102 and 104 via 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, the high frequency signals 153 and 1 are output from the multiplexers 173 and 183.
63 and the carrier signal 43 are multiplexed to form an optical transmitter 193, 2
03 is input. The signal lights 113 and 123 are output from the optical transmitters 193 and 203 and transmitted to the optical terminals 104 and 102. The information sources 30 to 34 of this embodiment are video cameras, and the carrier signals 40 to 44 are arranged at a frequency interval of 40 MHz from 1090 MHz to 1250 MHz, and are FM-modulated by video signals, respectively.

In the center terminal 500, as shown in FIG. 3, the signal lights 114, 1 transmitted from the optical terminals 104, 100 via the optical fiber transmission lines 10, 20, respectively.
20 is a high-frequency signal 5 by the optical receivers 510 and 520.
30,540. These high-frequency signals 530 and 5
In 40, carrier signals 40 to 44 are frequency-multiplexed. The tuners 560 to 564 include a changeover switch 55
Either of the high-frequency signals 530 and 540 is input by 0 to 554, and the carrier signals 40 to 44 are selected /
Demodulated, and information signals 50 to 54 are output. In a normal state, the high-frequency signal 530 of the working system is output from the tuners 560 to 5.
64.

According to this embodiment, the optical fiber transmission line 1
Even when a failure occurs at 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 a double loop configuration. That is, for example, the optical fiber transmission lines 10 and 2
If 0 is disconnected between the optical terminals 101 and 102, the carrier signals 40 and 41 drop out of the high-frequency signal 530, so that 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 signals 40 and 41 are frequency-multiplexed is input to the tuners 560 and 561. Thus, even if the optical fiber transmission line is broken, the center terminal can obtain signals from all information sources.

FIGS. 4 and 5 show the configurations of the optical terminal and the center terminal in the second embodiment of the present invention. Note that 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 620 to the optical fiber transmission lines 10 and 20 are pilot signals 650 and 6.
Modulated by 60. Pilot signal 6 of this embodiment
The frequency of 50,660 was 700 MHz.

In the optical terminal 103 shown in FIG.
High frequency signals 153, 163 output from 33, 143
Includes the pilot signals 650 and 660, and the strengths of the pilot signals 650 and 660 are detected by the signal detectors 213 and 223. The automatic gain control circuits 233 and 243 are provided with the signal detectors 213 and 223, respectively.
, The gains of the variable gain amplifiers 253 and 263 are adjusted so that the strengths of the pilot signals 650 and 660 become predetermined values. Thus, 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. Note that the signal detector 21
If no pilot signal 650 or 660 is detected at 3,223, the automatic gain control circuits 233,243 minimize the gains of the variable gain amplifiers 253,263. As a result, for example, when pilot signal generator 570 of center terminal 500 fails and pilot signal 650 is not detected by signal detector 213, high-frequency signal 153 is greatly amplified and the input level of optical transmitter 193 becomes excessive. Can be avoided.

Further, the optical terminal 103 transmits the pilot signal 29
3,303 for generating pilot signal generators 273,2
83. However, in a normal state, power is not supplied to pilot signal generators 273 and 283, and pilot signals 293 and 303 are not input to transmission light sources 193 and 203. Now, for example, if 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,
The 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 is input to the optical transmitter 193. Thus, even if a failure occurs in the optical fiber transmission line and the pilot signal from the center terminal is interrupted, the pilot signal is generated again at the optical terminal immediately after the failure point, and the subsequent optical terminal uses this. To perform automatic gain control.

FIG. 6 shows the configuration of an optical terminal according to the third embodiment of the present invention. The overall configuration of the optical network and the configuration of the center terminal according to the present embodiment are the same as those of the first embodiment (FIGS. 1 and 3). In the present embodiment, the high-frequency signals 153 and 163 output from the optical receivers 133 and 143 have their intensities fixed by the signal detectors 213 and 223, the automatic gain control circuits 233 and 243, and the variable gain amplifiers 253 and 263. After that, they are 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 having a cutoff frequency of 900 MHz is used. High frequency signal 153 after passing through filter 313
Are combined with the carrier signal 43 and the pilot signal 293 output from the pilot signal generator 273 by the multiplexer 173. Similarly, the high-frequency signal 163 after passing through the filter 323 is converted by the multiplexer 183 into the carrier signal 4.
3 and the pilot signal 303 output from the pilot signal generator 283. As described above, in this embodiment, since the pilot signal is regenerated and relayed at each optical terminal, each optical terminal can transmit the pilot signal to the subsequent optical terminal even if the optical fiber transmission line is disconnected.

In the fourth embodiment of the present invention, the configuration of each optical terminal is the same as 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. 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 for detecting pilot signals included in high-frequency signals 530 and 540 output from 520 and determining terminal identification signals superimposed on the pilot signals are provided. The input signals of the tuners 560 to 564 are collectively switched by the switches 690 and 700.

Normally, signal detector 670 detects pilot signal 650 transmitted from center terminal 500. In this case, the switch 690 is on and the switch 700
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 disconnected between the optical terminals 102 and 103, the signal detector 67
0 indicates the pilot signal 29 transmitted from the optical terminal 103
3 is detected. In this case, the center terminal 500 issues an alarm indicating that a failure has occurred in the active system, turns off the switch 690, turns on the switch 700, and switches to the standby system by supplying the high-frequency signal 540 to the tuners 560 to 564.

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

Further, as a modified example of this embodiment, there is a method of changing the frequency of the pilot signal output from the pilot signal generator of each optical terminal for each optical terminal. In this case, the signal detectors 670 and 680 of the center terminal 500
By detecting the frequency of the pilot signal, it is possible to determine the presence or absence of a failure and the location of the failure.

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

When the pilot signal is detected by the standby signal detector 223, the changeover switch 333 is connected to the active transmission light source 193, and the signal detector 223 is turned on.
If the pilot signal is not detected in step (1), the signal is connected to the standby multiplexer 183. Similarly, the changeover switch 343
Is connected to the backup transmission light source 203 when the pilot signal is detected by the working signal detector 213, and is connected to the working multiplexer 173 when the pilot signal is not detected by the signal detector 213. You. Under normal conditions,
Since the pilot signal is detected by both the signal detectors 213 and 223, the changeover switch 333 is set to the transmission light source 193.
The changeover switch 343 is connected to the transmission light source 203. In this case, no loopback is performed and the carrier signal 4
3 is transmitted by the working optical fiber transmission line 10.

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

In the optical terminal 101, at the moment when the optical fiber transmission lines 10 and 20 are cut off, the pilot signal of the standby system is interrupted. However, since the loopback is performed in the optical terminal 102 and the pilot signal is transmitted through the protection optical fiber transmission line 20, 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 optical terminal 103 performs the loopback, the loopback of the optical terminal 104 is released. As described above, according to the present embodiment, when a failure occurs in the optical fiber transmission line, each optical node can automatically perform loopback without an instruction from the center terminal.

In the sixth embodiment of the present invention, loopback is performed at the time of occurrence of a failure, as in the fifth embodiment. At this time, the input location of the carrier signal is switched at each optical terminal, thereby achieving loopback. To prevent transmission quality from deteriorating.

FIG. 9 shows the configuration of the optical terminal in this embodiment. In the optical terminal 103 of FIG. 9, the carrier signal 43 is
The signal is input to one of the working multiplexer 173 and the standby multiplexer 183 by the changeover switch 63. Also, pilot signal 65 output from center terminal 500
0 and 660 are modulated by the identification signals, respectively, and the signal detector 223 can identify whether the pilot signal transmitted in 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 working transmission light source 193. Conversely, if the active pilot signal 650 is detected by the signal detector 223 or if no pilot signal is detected, the changeover switch 63 is connected to the standby multiplexer 183. The changeover switches 333 and 333 for loopback
The operation of 353 is the same as that of the fifth embodiment.

In the normal state, since the pilot signal 660 of the protection system is detected by the signal detector 223, the carrier signal 43 is input to the multiplexer 173 of the working system. Now, the optical fiber transmission line 1 between the optical terminal 104 and the center terminal 500
Assuming that 0 and 20 have expired, loopback is performed at the optical terminal 104 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 protection 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 once through the optical terminal 104, and then is transmitted to the center terminal 500 through the protection optical fiber transmission line 20. Will be. However, in this embodiment, the carrier signal 43 is directly transmitted from the optical terminal 103 through the optical fiber transmission line 20 of the protection system to the center terminal 500.
Is transmitted to Therefore, the present embodiment has less accumulation of distortion and noise than the fifth embodiment.

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

FIG. 11 shows the configuration of the optical terminal of this embodiment.
The optical terminal 103 of FIG. 11 is the optical terminal of the fifth embodiment (FIG. 8).
However, filters 353 and 363 are inserted between the switch 333 of the active system and the multiplexer 183 of the standby system and between the switch 343 of the standby system and the multiplexer 173 of the active system. You. The filters 353 and 363 in this embodiment are low-pass filters having a cut-off frequency of 900 MHz, and the pilot signals 650 and 660 having a frequency of 700 MHz pass through as they are.
The 90 MHz to 1250 MHz carrier signals 40 to 44 are removed. The carrier wave signal 43 is supplied to the multiplexers 173, 18
3 is input to both. 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, it is assumed that the optical fiber transmission lines 10 and 20 have been cut between the optical terminals 103 and 104. In this case, in the optical terminal 103, since the pilot signal of the standby system is interrupted,
The changeover switch 333 is switched to the standby multiplexer 183, and the active high-frequency signal 153 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 transmitted as the high-frequency signal 163 to the center terminal 500 through the optical fiber transmission line 20 of the protection system.

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

In the eighth embodiment of the present invention, the transmission light source of the standby system of each optical terminal is normally turned off, the service life of the standby system is extended, and the power consumption of each optical terminal is reduced.

The configuration of the center terminal of this embodiment is similar to that of the fourth embodiment shown in FIG.
This is the same as the embodiment. However, the pilot signals 650 and 660 of the working system and the protection system are modulated by the optical terminal control signal. The standby pilot signal generator 580 is not normally supplied with power,
60 is off. The configuration 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 3, 223, and the changeover switches 333, 343 are controlled by this optical terminal control signal. Normally, the changeover switch 333 is connected to the active transmission light source 193, and the changeover switch 3
Reference numeral 43 is connected to the backup transmission light source 203.
The backup transmission light source 203 is supplied with power only when a pilot signal is detected by the working pilot signal detector 213. Therefore, the pilot signal 650 is not output from the center terminal 500 during normal times, so that 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 pilot signal 650 is no longer detected by the working signal detector 670 of the center terminal 500. 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 backup transmission light sources of the respective 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, if the protection optical fiber transmission line 20 is also cut between the optical terminals 103 and 104, the pilot signal generator 580 of the protection system is turned on and the pilot signal is detected by the signal detector 680 even after a certain period of time. 660 is not detected. In this case, a command to perform loopback is sent in order from the optical terminal farther from the center terminal. That is,
The center terminal 500 first sends an optical terminal control signal using the working system so that the changeover switch 334 of the optical terminal 104 is switched to the standby multiplexer 184. Thereafter, if a pilot signal is not detected by the signal detector 680 even after a certain period of time, the changeover switch 333 of the optical terminal 103
Is transmitted to the multiplexer 183 of the standby system. This operation is performed until the pilot signal is detected by the signal detector 680. At the same time, the center terminal 500 sends an optical terminal control signal using the backup system so that the changeover switch 340 of the optical terminal 100 is switched to the working multiplexer 170. Thereafter, if a pilot signal is not detected by the signal detector 670 even after a certain period of time, an optical terminal control signal is sent so that the changeover switch 341 of the optical terminal 101 is switched to the working multiplexer 171. This operation is performed until a pilot signal is detected by the signal detector 670.

In the ninth embodiment of the present invention, the standby system including the transmission light source and the optical receiver is normally off at all times, and the service life of the standby system is extended as in the eighth embodiment. The power consumption of optical terminals has been reduced.

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

Now, when the optical fiber transmission lines 10 and 20 are cut between the optical terminals 102 and 103,
4, and the center terminal 500 automatically turns on the standby system because the active pilot signal is interrupted. 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 active system. Thereafter, loopback is performed in 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 the drawings]

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

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

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

FIG. 4 is a diagram illustrating 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 illustrating a configuration of an optical terminal according to a third embodiment of the present invention.

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

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

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

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

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

[Explanation of symbols]

10,20 Optical fiber transmission line 30-34 Information source 40-44 Carrier 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 150-154, 160-164 High-frequency signal 170-174, 180-184 Combiner 190-194, 200-204 Optical transmitter 210-214, 220-224 Signal detector 230-234, 240-244 Automatic gain control Circuit 250 to 254, 260 to 264 Variable gain amplifier 270 to 274, 280 to 284 Pilot signal generator 290 to 294, 300 to 304 Pilot signal 310 to 314, 320 to 324 Filter 330 to 334, 340 to 344 Changeover switch 350 to 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

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁶ , DB name) H04B 10/00-10/28 H04L 11/00-11/00 340 H04B 1/74

Claims (5)

(57) [Claims] 1. A first and second optical receiver for receiving first and second input signal lights input to an optical terminal, respectively, a carrier signal and an output from the first and second optical receivers. First and second multiplexers for multiplexing the obtained first and second high-frequency signals, respectively, and first and second high-frequency signals output from the first and second multiplexers. First and second optical transmitters to be input, and the first and second output signal lights output from the first and second optical transmitters have the intensities of the first and second optical transmitters. First and second signal detectors, each of which is modulated by a high-frequency signal and detects a pilot signal from the first and second high-frequency signals output from the first and second optical receivers, respectively; Gain control that controls the strength of the high-frequency signal in response to the output of the And a pilot signal generator. When 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 an optical terminal for inputting a pilot signal output from the pilot signal generator to the second optical transmitter when the pilot signal is not detected by the second signal detector. 2. The system according to claim 1, wherein the pilot signal is modulated with a terminal identification signal different for each optical terminal.
An optical terminal as described. 3. The optical terminal according to claim 1, wherein the frequency of the pilot signal is different for each optical terminal. 4. 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 filter removes the pilot signal. The first after
2. The optical terminal according to claim 1, wherein a pilot signal output from the pilot signal generator is newly multiplexed with a second high-frequency signal. 5. A first and second optical receiver for respectively receiving first and second input signal lights input to an optical terminal, a carrier signal and an output from said first and second optical receivers. First and second multiplexers for multiplexing the obtained first and second high-frequency signals, respectively, and first and second high-frequency signals output from the first and second multiplexers. First and second optical transmitters to be input, and the first and second output signal lights output from the first and second optical transmitters have the intensities of the first and second optical transmitters. A first loopback path for guiding the first high-frequency signal output from the first multiplexer to the second optical transmitter, respectively modulated by a high-frequency signal, and an output from the second multiplexer. A second loop-back path for guiding the extracted second high-frequency signal to the first optical transmitter. ,
Providing the carrier signal on the first and second loopback paths;
No. has a filter for removing said first output signal light is intensity modulated with one of the first or second high-frequency signal, the second output signal light and the second or the first An optical terminal characterized in that one of high-frequency signals is intensity-modulated.