JPH10229366A - Method for monitoring in-service of optical amplification relay transmission line - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a loss change position by measuring a reception level of a back- scattered light, corresponding to an elapsed time after transmission of an monitoring optical pulse, so as to locate a content of an abnormal loss and its produced position on an optical amplification relay transmission line. SOLUTION: A monitoring optical pulse, sent from an optical transmission section 1, is combined with an optical communication signal by a combiner 2, and the combined signal is sent to an optical amplification relay transmission line which is a monitor object. An optical repeater 4, incorporating an optical fiber amplifier 3, is placed in the optical amplification relay transmission line to compensate a loss received by the optical signal at each relay block. A back-scattered light generated in the optical amplification relay transmission line by the monitoring optical pulse is led to an opposite line. The back-scattered light and the optical communication signal propagated through the opposite line have different wavelength bands, so that they are separated by an optical filter 7. The separated back-scattered light is given to an optical reception section 6, where the strength of the back-scattered light is measured. Thus, the position of the transmission line at which a loss abnormality is in existence is located, based on an elapsed time after the monitoring optical pulse is transmitted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an in-service monitoring method for monitoring the state of an optical amplification repeater transmission line in which an optical fiber amplifier is inserted during operation.

[0002]

2. Description of the Related Art As a technique for in-service monitoring of the state of an optical amplification repeater transmission line, a method of superimposing a monitoring signal on an optical communication signal has been proposed (Technical Digest of Conferen).
ce onOptical Fiber Communication, OFC'94, San Jos
e, USA, vol. 4, ThR3, pp. 256-257, 1994). The outline is shown in FIG.

An optical communication signal is intensity-modulated by a modulator 8 by a monitor signal. Thus, the monitoring signal is superimposed on the optical communication signal and propagates through the optical amplification relay transmission line. Each of the repeaters 4 incorporating the optical fiber amplifiers 3 on the optical amplification repeater transmission line is provided with an optical loopback 9 for returning a part of the optical communication signal to the opposite line, and the optical communication signal on which the monitoring signal is superimposed. Is returned on the opposite line.

[0004] At the receiving end of the opposite line, there is a separator 10 for separating the optical communication signal and the supervisory signal, and the supervisory signal receiver 11 measures the intensity of the returned supervisory signal. By comparing the measured intensity of the returned monitor signal with the value in the initial state, it is possible to detect a loss change in the transmission path. In addition, since it is possible to identify which repeater has returned the monitoring signal from the elapsed time from the transmission of the monitoring signal, it is possible to detect a loss change in each relay section. Further, by reducing the intensity modulation index of the modulator 8 so as not to affect the transmission characteristics of the optical communication signal, in-service monitoring becomes possible.

[0005]

By the way, the conventional in-service monitoring method shown in FIG. 5 performs an in-service monitoring of an optical amplification relay transmission line by utilizing the transparency of an optical signal of an optical amplifier. It is a method. However, what can be detected by this conventional method is a total loss change in each relay section, and detailed information indicating at which position in each relay section a loss change has not been obtained.

An object of the present invention is to provide an in-service monitoring method of an optical amplification repeater transmission line capable of detecting a position where a loss change has occurred.

[0007]

At present, the OTDR technique is widely used as a technique for detecting a failure point in an optical transmission line. This is because the optical pulse for exploration is input to the optical fiber under test, the backscattered light generated by this optical pulse, propagated in the opposite direction and returned is received, and the intensity is measured as the time from the transmission of the optical pulse. By performing the measurement in accordance with the progress, the loss abnormality of the optical fiber can be detected with high distance resolution.

The in-service monitoring method of the optical amplification repeater transmission line according to the present invention uses the OTDR technology to
The first feature is that a loss change of the optical amplification repeater transmission line is detected including position information. Further, in the present invention,
The second feature is that the pulse width of the monitoring optical pulse that is wavelength-multiplexed with the optical communication signal and propagated through the optical amplification relay transmission line is sufficiently shorter than the transient response time of the optical fiber amplifier. Therefore, even if the monitoring optical pulse passes, the gain of the optical fiber amplifier does not change, and even if the monitoring optical pulse is multiplexed with the optical communication signal and propagated through the amplification relay transmission line at the same time, the optical communication signal Does not affect transmission characteristics. Further, since the wavelength of the monitoring optical pulse is different from that of the optical communication signal, the monitoring optical pulse and the optical communication signal can be easily separated. As described above, according to the present invention, it is possible to detect a change in loss of the amplification relay transmission line in-service including the position information.

[0009]

FIG. 1 shows a system configuration to which an in-service monitoring method of the present invention is applied. In the figure,
The monitoring optical pulse transmitted from the optical transmitter 1 is transmitted to the multiplexer 2
Multiplexed with the optical communication signal, and sent out to the optical amplification relay transmission line to be monitored. An optical repeater 4 having a built-in optical fiber amplifier 3 is arranged in this optical amplification relay transmission line.
The loss received by the optical signal in each relay section is compensated. Each optical repeater 4 is provided with an optical path 5 connecting between the opposing lines, and the backscattered light generated in the optical amplification relay transmission line by the monitoring light pulse is guided to the opposing lines. The backscattered light and the optical communication signal that have propagated through the opposite line are separated by the optical filter 7 because they have different wavelengths. The separated backscattered light is input to the light receiving unit 6 and its intensity is measured.

FIG. 2 shows an example of measuring the backscattered light intensity with respect to the lapse of time after the transmission of the monitoring light pulse. In this measurement example, a change in transmission line loss is observed at point A. The time until the backscattered light generated at the point A returns to the light receiving unit 6 after transmitting the monitoring light pulse is the time for the optical communication signal to reciprocate between the transmitting end and the point A. Therefore, it is possible to specify the position of the transmission line having the loss abnormality from the elapsed time after the transmission of the monitoring light pulse.

FIG. 3 shows a time change of the input light intensity of the optical fiber amplifier. The portion where the light intensity rises is the portion where the monitoring optical pulse is multiplexed with the optical communication signal. Fig. 4 shows the relationship between the gain of the optical fiber amplifier and the input light intensity.
Shown in Normally, the operating point of the optical fiber amplifier (the point at which the gain matches the loss in the relay section) is set as shown in FIG. The input light intensity at the operating point is Ps. At the point where the monitoring optical pulse is multiplexed with the optical communication signal, the intensity of the optical signal input to the optical fiber amplifier becomes larger than Ps, as shown in FIG. Therefore, the gain of the optical fiber amplifier is smaller than the loss in the repeater section, and the loss of the optical signal received in the repeater section transmission line is not compensated by the optical fiber amplifier. Thus, in general, the optical communication signal in the portion where the monitoring optical pulse is multiplexed has a low intensity at the receiving end, the signal-to-noise ratio decreases, and the transmission characteristics of the optical communication signal deteriorate.

However, the transient response of the optical fiber amplifier is very slow, and its response time is about 1 msec. Also,
In the present invention, the pulse width of the monitoring light pulse is set to be sufficiently shorter than the transient response time, for example, 10 μsec. Therefore, when an optical pulse shorter than such a transient response time passes, the gain of the optical fiber amplifier does not change following the passage of the optical pulse, and the gain maintains the value of the relay section loss. As described above, even when the monitoring optical pulses are combined, the gain of the optical communication signal received from the optical fiber amplifier does not change, so that the transmission characteristics do not deteriorate.

[0013]

As described above, the in-service monitoring method for an optical amplification repeater transmission line according to the present invention can propagate a monitoring optical pulse to a transmission line without affecting the transmission characteristics of an optical communication signal. it can. Further, since the intensity of the backscattered light generated by the monitoring light pulse can be measured with the passage of time, when a loss abnormality occurs in the optical amplification repeater transmission line, the content and location of the abnormality can be specified. As described above, the in-service monitoring method of the optical amplification relay transmission line according to the present invention has an effect that the transmission line can be monitored with higher accuracy than the conventional technology.

[Brief description of the drawings]

FIG. 1 is a diagram showing a system configuration to which an in-service monitoring method of the present invention is applied.

FIG. 2 is a diagram showing a measurement example of the backscattered light intensity with respect to the elapse of time after the monitoring light pulse is transmitted.

FIG. 3 is a diagram showing a time change of the input light intensity of the optical fiber amplifier.

FIG. 4 is a diagram showing the relationship between the gain of the optical fiber amplifier and the input light intensity.

FIG. 5 is a diagram showing a system configuration to which a conventional in-service monitoring method is applied.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 optical transmitting unit 2 multiplexer 3 optical fiber amplifier 4 optical repeater 5 optical path 6 optical receiving unit 7 optical filter 8 modulator 9 optical loopback 10 separator 11 supervisory signal receiver

Claims (1)

[Claims] An in-service monitoring method for an optical amplification repeater transmission line in which an optical fiber amplifier for directly amplifying an optical communication signal without converting it into an electric signal is inserted, wherein a pulse width is longer than a transient response time of the optical fiber amplifier. To generate a monitoring optical pulse whose wavelength is different from the wavelength of the optical communication signal, multiplexes the monitoring optical pulse with the optical communication signal, and sends the multiplexed optical communication signal to the optical amplification relay transmission line. Receiving the backscattered light generated by the light pulse for use, measuring the reception level of the backscattered light corresponding to the elapsed time after transmitting the monitoring light pulse, and measuring the loss abnormality in the optical amplification relay transmission line. An in-service monitoring method for an optical amplifying repeater transmission line, characterized in that the content and the position of occurrence are specified.