JPH07131420A - Optical amplifying and repeating system - Google Patents

Abstract

PURPOSE:To provide the optical amplifying and repeating system which detects a fault point on a transmission line without adding a special circuit to an optical amplifying repeater provided on the transmission line. CONSTITUTION:A transmission part 11 of a terminal station constituting the optical amplifying and repeating system is provided with an oscillator 15 whose output signal frequency is periodically changed from f1 to f2, and the monitor signal is superposed on a transmission signal and they are outputted as an optical signal, and the change with time of the level of the monitor signal is monitored by a fault point detection circuit 17 provided in a reception part 13. The level of the monitor signal monitored by the fault point detection circuit 17 is reduced from a frequency fD when the frequency of the monitor signal in the optical signal placed at the fault point is defined to fD at the time of the occurrence of the fault in the transmission line, and an arbitrary point in the transmission line is allowed to correspond to the frequency of the monitor signal, and therefore, the fault point detection circuit 17 specifies the fault point on the transmission line in accordance with the frequency fD from which the level is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplification repeater system used in, for example, an optical submarine communication system, and more particularly, to a transmission line fault point without adding a special function to the optical amplification repeater. The present invention relates to an optical amplification repeater system capable of performing orientation.

[0002]

2. Description of the Related Art An optical communication system is usually composed of a pair of terminal stations and two transmission lines provided between the terminal stations, and each transmission line amplifies an attenuated optical signal. A repeater is provided. In such an optical communication system, in order to avoid service deterioration due to communication failure, a mechanism for quickly identifying a failure point on the transmission path, such as a failed repeater or a damaged or broken optical fiber, is provided. ing. First, a fault location technique used in a conventional optical communication system will be described by taking an optical submarine communication system that is currently in practical use as an example.

FIG. 3 shows an outline of an optical submarine repeater used in an optical submarine communication system. Optical submarine repeater amplifies the optical signal transmitted from the terminal station connected to the optical fiber 21 ₁ side, and the relay circuit 27 ₁ to output to the terminal station connected to the optical fiber 21 ₂ side, reverse It is composed of a relay circuit 27 ₂ for amplifying an optical signal propagating to the. Relay circuit 27
Reference numeral ₁ denotes an optical / electrical conversion element 22 for converting an optical signal input from the optical fiber 21 ₁ into an electric signal, and a waveform shaping / identification circuit 2 for equalizing amplification, shaping and identification of the signal waveform.
3, an electric / optical conversion element 24 for converting the output signal into an optical signal, an optical switching circuit 25 for switching the output path of the optical signal, and a monitoring circuit 26 for monitoring and controlling the state of each circuit. It is configured.

The optical signal input from the optical fiber 21 ₁ is amplified by the optical / electrical conversion element 22, the waveform shaping / identification circuit 23, and the electric / optical conversion element 24 during the service (online state), and optical switching is performed. It is output to the optical fiber 21 ₂ via the circuit 25. In this state, a command signal of a specific code or a specific frequency is transmitted from the terminal station, and when the command signal is identified by the waveform shaping / identifying circuit 23, the monitoring circuit 26 starts an operation for fault point evaluation. To do. There are various functions of the monitoring circuit 26, such as an optical loopback function, a status notification function of notifying the terminal station of the bias current of the electric / optical conversion element, and a switching function to the standby circuit. Of these, the optical loopback function is used to search for and locate faults by forming a loopback connection for returning the optical signal input from one terminal station to that terminal station. is there.

The loopback connection is formed by the monitoring circuit 26 switching the optical switching circuit 25. This switching, optical signal input from the optical fiber 21 _1, come to be outputted to the optical fiber 21 _3, The optical fiber 21 ₃ is connected to the relay circuit 27 ₂ inside the optical-electrical transducer element As a result, a folded connection is formed in which the optical signal from the optical fiber 21 ₁ is output to the optical fiber 21 ₄ .

[0006] With reference to Fig. 4, a search for a fault point and an operation for locating the fault using the optical loopback function will be briefly described. A fault point is searched and located on one of the terminal stations. For example, when the terminal station 29 ₁ is used, the terminal station 29 ₁ to each of the repeaters 2 is used.
8 is instructed to execute the return connection in order, and it is confirmed whether the optical signal can be accurately transmitted through the formed return connection. As a result of such processing, for example, when the loop-back connection 30 ₁ is formed, the transmitted optical signal is normally looped back, and when the loop-back connection 30 ₂ is not formed, normal reception cannot be performed. , Repeater 28 ₁
It can be determined that the optical fiber is installed between the optical fiber and the optical fiber installed between ₂ and 28 ₂ .

[0007] As a technique for detecting a location of a fault point by making a loopback connection by remote control as described above,
Various forms have been proposed, for example, in Japanese Patent Publication No. 3-40985, each repeater causes an optical signal to be returned to its own device based on a specific frequency component in the optical signal. A system for determining whether it is a connection formation command is disclosed.

Further, each repeater is provided with a function of monitoring its state, and when an abnormality occurs, the abnormality is detected by using a monitoring line provided separately from a transmission line for transmitting information. There is also a system that notifies the terminal. Such a system is disclosed in, for example, Japanese Patent Laid-Open No. 3-46830.

[0009]

In the conventional optical communication system described above, a circuit for detecting a fault is provided in the repeater, and a fault point is searched for and located by using this circuit. It is relatively easy to add a circuit for detecting a failure in a so-called 3R repeater in which an optical signal is converted into an electric signal and thereafter, equalization amplification, identification reproduction, and retiming are performed. However, in a repeater using an optical amplifier that directly amplifies an optical signal, there is no need to convert the optical signal into an electric signal at all. Therefore, the system using the optical amplification repeater, without adding a special circuit to each repeater,
It is desirable to be able to search and locate fault points.

Therefore, it is an object of the present invention to provide an optical amplification repeater system capable of detecting a fault point without adding a special circuit to the optical amplification repeater.

[0011]

According to the present invention, (a) a supervisory signal output means for outputting as a supervisory signal a signal whose frequency periodically changes from a first frequency to a second frequency, and a supervisory signal output means. Superimposing means for superimposing the monitoring signal output by the superimposing means on the transmission signal, and a transmission section provided with an electrical / optical converting means for converting the signal superimposed by the superimposing means into an optical signal, (b)
A transmission line composed of an optical fiber and an optical amplification repeater for propagating the optical signal output from the transmission unit, and (c) an optical / electrical conversion means for converting the optical signal received through the transmission line into an electric signal, When a level detection unit that extracts a monitoring signal from the electric signal output by the optical-electrical conversion unit and detects the level of the monitoring signal and a time change of the level of the monitoring signal detected by the level detection unit and the level changes And a receiving unit provided with specifying means for specifying a failure point in the transmission path based on the frequency of the monitoring signal and the frequency changing cycle of the monitoring signal output means.

That is, in the optical amplification repeater system according to the present invention, the transmitting unit transmits the optical signal on which the supervisory signal whose frequency changes periodically and superimposes it, and the receiving unit which receives the optical signal through the transmission line is The time change of the level of the supervisory signal component contained in the optical signal is monitored, and the fault point is identified based on the frequency of the supervisory signal when the level changes. When the frequency of the supervisory signal in the optical signal located at the fault point is f _D when the fault occurs in the transmission line, the level of the supervisory signal observed in the receiving unit is lowered from the frequency f _D. Become. Further, since any point in the transmission line is associated with the frequency of the supervisory signal, it is possible to identify the faulty point on the transmission line from the frequency f _D at which the level drop occurs. It is desirable that the frequency change cycle of the supervisory signal output by the supervisory signal output means is made to coincide with the time required for the optical signal to propagate between the transmitter and the receiver.

[0013]

EXAMPLES The present invention will be described in detail below with reference to examples.

FIG. 1 shows the configuration of an optical amplification repeater system according to an embodiment of the present invention. The optical amplification repeater system includes a transmission unit 11, an optical amplification repeater 12, a transmission line formed by an optical fiber, and a reception unit 13. The transmission unit 11 is provided with an electric / optical conversion element 14 for converting an electric signal into an optical signal and an oscillator 15, and a transmission signal 31 which is an information signal to be transmitted is a monitoring signal output from the oscillator 15. Are superposed on each other and then converted into an optical signal by the electro-optical conversion element 14. The optical amplification repeater 12 is a device that amplifies an optical signal using an optical fiber amplifier. The receiver 13 includes an electric / optical conversion element 16 for converting an optical signal input through the transmission line into an electric signal, and a level of a supervisory signal component in the converted electric signal to evaluate the level on the transmission line. A fault point detection circuit 17 for detecting the position of the fault point is provided.

The fault detecting operation in this optical amplification repeater system will be described below.

First, the operation of the oscillator 15 will be described.
The oscillator 15 is a so-called variable frequency oscillator, and here, the frequency f _SV of the output monitoring signal is the frequency f ₁
From the frequency f ₂ (f ₁ <f ₂ ) to the frequency f _{2 so} that the cycle T of the change coincides with the time required for the optical signal to reach the receiver 13 from the transmitter 11. Is configured. The level and frequency band of the supervisory signal are set so as not to adversely affect the transmission signal. The supervisory signal output from the oscillator 15 is transmitted by the transmitter 1
After being superposed on the transmission signal in 1, the electric / optical conversion element 14 converts the optical signal into an optical signal.

The optical signal output from the electrical / optical conversion element 14 propagates through the transmission path provided with the optical amplification repeater 12 at time T, and is input to the reception unit 13. The optical signal input to the receiver 13 is converted into an electric signal by the optical / electrical conversion element 16. Fault point detection circuit 17 to which the electric signal is input
Is a kind of spectrum analyzer, and this circuit
The signal level of f ₁ to f ₂ which is the frequency range of the supervisory signal in the signal is measured, and the fault point on the transmission path is specified based on the measurement result. The principle of the fault point identification operation in the fault point detection circuit will be described below.

FIG. 2 shows the difference between the frequency and level characteristics measured in the fault point detection circuit depending on the presence or absence of a fault. In the figure, the frequency / level characteristics shown by the solid line are the characteristics (measurement results) when there is no failure in the transmission line, and the ones shown by the broken line are the characteristics immediately after the failure has occurred in the transmission line. . It can be easily understood that the frequency / level characteristic of the supervisory signal measured by the fault point detection circuit 17 becomes flat when no fault occurs on the transmission path.

The reason why the characteristic shown by the broken line is obtained when a failure occurs in the transmission line is as follows. That is, when a failure occurs, the optical signal propagating in the transmission path on the transmission side from the failure point is attenuated according to the degree of the failure when passing through the failure point. For this reason, when the frequency of the supervisory signal in the optical signal located at the fault point is f _D at the time of occurrence of the fault, the level of the supervisory signal input to the receiving unit 13 decreases from the frequency f _D. Therefore, the frequency / level characteristic measured in the fault point detection circuit 17 becomes as shown by the broken line in FIG. 2 immediately after the fault occurs. On the other hand, any point in the transmission line
Since the frequency is correlated with the frequency of the supervisory signal, the fault point on the transmission line can be identified from the frequency f _D at which the level drop occurs.

For the purpose of obtaining the relationship between the position of the faulty point on the transmission line and the frequency, the change cycle of the oscillation frequency of the oscillator coincides with the time until the optical signal sent from the transmitter reaches the receiver. However, it is also possible to set the time to be larger than this time and to take the difference into consideration so as to identify the failure point.

[0021]

As described above, according to the present invention, a fault point can be located only by adding a function only to a terminal portion, so that it is not necessary to add a special function to the repeater, and the optical amplification repeater system The configuration can be simple.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an optical amplification repeater system according to an embodiment of the present invention.

FIG. 2 is a frequency / level characteristic diagram for explaining a fault point detection operation in the optical amplification repeater system of the embodiment.

FIG. 3 is a block diagram showing a configuration of a conventional optical submarine repeater.

FIG. 4 is an explanatory diagram showing an outline of a fault point detection method in a conventional optical submarine repeater system.

[Explanation of symbols]

 11 Transmitter 12 Optical amplification repeater 13 Receiver 14 Electro-optical conversion element 15 Oscillator 16 22 Optical-electrical conversion element 17 Fault detection circuit 21 Optical fiber 23 Waveform shaping / identification circuit 25 Optical switching circuit 26 Monitoring circuit 27 Relay circuit 28 Repeater 29 Terminal station 30 Return connection 31 Transmission signal

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H04B 10/16

Claims (2)

[Claims] 1. A supervisory signal output means for outputting, as a supervisory signal, a signal whose frequency periodically changes from a first frequency to a second frequency, and a supervisory signal output by the supervisory signal output means is superimposed on a transmission signal. A superposing means, a transmitting section having an electric / optical converting means for converting the signal superposed by the superposing means into an optical signal, an optical fiber for propagating the optical signal output by the transmitting section, and an optical amplification relay. A transmission line composed of a device, an optical / electrical conversion unit that converts an optical signal received through the transmission line into an electric signal, and the monitoring signal is extracted from the electric signal output by the optical / electrical conversion unit. Level detecting means for detecting a level, monitoring the time change of the level of the monitor signal detected by the level detecting means, and the frequency of the monitor signal when the level changes and the monitor signal output means Optical amplification relay system characterized by comprising a receiving unit having a specific means for a particular point of failure in the transmission path based on the period of change in the definitive frequency. 2. The light according to claim 1, wherein the period in which the frequency of the monitor signal output means changes is matched with the time required for the optical signal to propagate from the transmitter to the receiver. Amplification relay system.