JPH03287204A - Optical fiber line monitoring system - Google Patents

Abstract

PURPOSE:To improve the monitoring performance by coupling inspection light which is different in wavelength from signal light, separating the inspection light by an optical filter at the terminal side of a signal light beam line, and amplifying back scattered light based upon the incidence of the inspection light in front of a photodetector. CONSTITUTION:A distribution device 4 is installed in the signal light beam path L1 to couple the inspection light from a line monitoring device 3 with the signal light beam path L1, and an optical filter 5 and an amplifier 6 are connected on the terminal side of the signal light beam path L1 to amplify the signal light and also separate the inspection light. An optical filter 5 and an amplifier 11 are connected in front of the photodetector 9 in the inspection light beam path L2 of the inspection light monitoring device 3 to amplify the back scattered light of the inspection light and also separate and monitor unnecessary light. The inspection light is therefore separated by the optical filter 5 on the terminal side and amplified by the amplifier 11 without being inputted as noise to a terminal device 2, so the afterward addition and averaging processing time is shortened. Consequently, the monitoring performance is improved.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a line monitoring system for an optical fiber line in which the terminal device is a subscriber device or the like.

[Conventional technology]

Conventionally, for optical lines using optical fibers, a monitoring method has been used that focuses on understanding the characteristics of the optical fibers. for example,
Normal line condition monitoring involves only checking the quality of the communication condition or line loss. However, with these methods alone, it is difficult to carry out preventive maintenance such as how the track condition will change in the future. Therefore, as a method for performing this preventive maintenance, a method that measures changes in line loss with high sensitivity, such as the optical pulse reflection method (O
TDR) has been proposed.

[Problem to be solved by the invention]

However, this optical pulse reflection method had a poor S/N ratio, and there was room for improvement. This is because this method uses backscattered light generated at various points along the length of the optical fiber for monitoring purposes, but the basic problem is that the light intensity of this inspection light is extremely low. Another problem is that the inspection light is further weakened by the distributor, optical filter, etc. of the line monitoring device. For this reason, in order to improve this S/N ratio, inspection light has been repeatedly measured, added, and averaged, but the time required for this addition and averaging has been reduced to several minutes (about 3 to 4 minutes). It also has the disadvantage that it is difficult to respond to changes that occur over a short period of time (several tens of seconds). The present invention has been made in view of such conventional circumstances.

[Means to solve the problem]

The present invention is characterized by a track monitoring system that measures events at each point by introducing inspection light (monitoring light) of a wavelength different from that of the signal light into a track made of optical fiber, and maintains the track. A distribution device is installed in the signal light line to couple the inspection light from the line monitoring device to the signal light line, and an optical filter and an amplifier are connected to the terminal side of the signal light line to transmit the signal light. On the other hand, an optical filter and an amplifier are connected in front of the light receiver in the inspection light line of the line monitoring device to amplify the backscattered light of the inspection light and separate unnecessary light. There is a fiber optic line monitoring system to monitor.

[Effect]

In this way, in the present invention, the test light having a different wavelength from the signal light is combined, and since this test light is separated by the optical filter on the terminal side of the signal optical path, it is possible to combine the test light with a wavelength different from that of the signal light. In addition, the backscattered light caused by the incidence of the inspection light is amplified by the amplifier in front of the receiver, significantly shortening the subsequent addition and averaging processing time and improving monitoring performance. A significant improvement will be achieved.

【Example】

FIG. 1 shows an embodiment of an optical fiber line monitoring system according to the present invention. In the figure, reference numeral 1 denotes a signal light transmission device, which is connected to a terminal bag W2, such as a subscriber device, through a signal light line. Reference numeral 3 denotes a line monitoring device, the inspection optical line L2 of which is coupled to the signal optical line L1 by a distribution device 4 installed in the signal optical path L1, and this distribution device 4 and the terminal device 2 An optical filter 5 for separating test light and an amplifier 6 for amplifying signal light (an element having an amplification function may also be used) are connected to the signal light line L1 on the terminal side. The line monitoring device 3 includes a pulsed light source 8 that sends a test light to the signal light line L1 through a distributor 7, and a light receiver 9 that receives backscattered light due to the input of the test light. An optical filter 10 for separating unnecessary light and an amplifier 11 (an element having an amplification function may also be used) for amplifying backscattered light by the test light are connected to the front test light line L2. According to this system, the test light (for example, light with a wavelength of 1.55 μm) emitted from the pulsed light source 8 is transmitted to the terminal device through the distributor 7, the test light line L2, and the signal light line. The light is transmitted to the optical filter 5 for separating the inspection light on the second side, and is selectively separated and absorbed by the optical filter 5. Therefore, the signal light (for example, light with a wavelength of 1.3 μm) emitted from the signal light transmission device 1 is
The signal is amplified by the signal light amplifying amplifier 6 in a noise-free state and is transmitted to the terminal device 2 side. On the other hand, backscattered light generated in the line immediately before the optical filter 5 due to the incidence of the inspection light is transmitted to the distribution device 4 of the signal optical path L1, the distribution device 7 in the line monitoring device 3, and the unnecessary light separation device. Optical filter 10 and amplifier 11 for amplifying backscattered light
The light is received by the light receiver 9 through the light. At this time, the optical filter IO separates and absorbs unnecessary light, and only the backscattered light is amplified by the amplifier 11 and reaches the light receiver 9. Due to this amplification, the number of measurements can be reduced, and the addition and averaging processing time can be significantly shortened compared to the conventional method. For example, the time can be set from several minutes to several tens of seconds. Therefore, it becomes possible to respond to changes that occur in minute time (several tens of seconds).The optical filter 5.10 used in the present invention includes:
Although not particularly limited, for example, a semiconductor filter may be used. In particular, filters using semiconductor lasers allow wavelength control, such as distributed feedback (DFB) filters.
Filters using lasers or Fabry-Bello type (FD) lasers can have a light amplification function, and are therefore optimal as filters with gain. An amplifier 6 inserted together with these optical filters 5 and 10
, 11 may be an element having an amplification function as described above. In particular, in the semiconductor filter having the above-mentioned light amplification function, this element can be used as an optical filter that also serves as an amplifier. Incidentally, when the present inventors conducted a confirmation test using the system shown in Fig. 1 above, using the signal light as light with a wavelength of 1.3 μm and the test light as light with a wavelength of 1.55 μm, we found the following. I got similar results. First, the signal input from the signal light transmission device 1 to the distribution device 4 was -10 dBm. The coupler in this distribution device 4 is 1
The branching ratio was 0:1, and the loss, including the internal anti-reflection filter, was 3 dB. Line loss is 10 dB, and -23 at the terminal of signal optical line L1.
It was dBm. Furthermore, this terminal required 10 dB for distribution, and the reception level was -33 dBm. Here, as an optical filter that also serves as an amplifier, a gain of 20
Using a semiconductor wavelength tunable filter with a performance of dB and wavelength tuning width of 188 GHz (15 A), a 1°55 μm test light was separated and a 1.3 μm signal light was amplified. This chip gain is 20 dB as mentioned above, but the actual gain is 14 dB, and this gain reduces the reception level to -19 dB.
improved to m. Further, the level of the remaining test light that was not separated by the semiconductor wavelength tunable filter portion was -70 dBm or less, which was not a value that would pose a problem for the signal light. On the other hand, the level of backscattered light due to the incidence of the above-mentioned 1.55 μm inspection light was extremely small at -60 to -70 dB, but in the line monitoring device 3, it was also used as an optical filter that also served as an amplifier, with a gain of 20 dB and a wavelength variable width. 188GHz
When a semiconductor wavelength tunable filter with a performance of (15 A) was used, a gain of 10 dB or more was obtained, which was improved to about -50 dBm. As a result, the S/N ratio of the optical pulse reflection method has been improved, and conventionally the addition and averaging processing required 65,000
The number of times that was required was only about 8,200 times, and the measurement time, which conventionally required about 3 minutes, was reduced to about 20 seconds.

Effects of the Invention As is clear from the above description, according to the present invention, test light having a different wavelength from the signal light is combined, and this test light is separated by an optical filter on the terminal side of the signal light line. Since the backscattered light caused by the incidence of this test light is amplified by the amplifier in front of the receiver, the subsequent addition, An excellent optical fiber line monitoring system is provided in which the averaging processing time is significantly shortened and, as a result, the monitoring performance is significantly improved.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram showing an embodiment of an optical fiber line monitoring system according to the present invention. In the figure, 1... Signal optical transmission device, 2... Terminal device, 3... Line monitoring device, 4... Distribution device, 5... Filter, 6... Amplifier, 8... Pulse light source, 9... Photoreceiver, lO... Filter, 11... Amplifier, Ll... Signal light line, L2... Inspection light line, 0

Claims (2)

[Claims] (1) In a line monitoring system that maintains the line by introducing inspection light (monitoring light) with a wavelength different from that of the signal light into a line made of optical fiber and measuring events at each point, a distribution device is used in the signal light line. is installed to couple the test light from the line monitoring device to the signal light line, and connect an optical filter and an amplifier to the terminal side of the signal light line to amplify the signal light and separate the test light, On the other hand, the optical fiber is characterized in that an optical filter and an amplifier are connected in front of the light receiver in the inspection light line of the line monitoring device to amplify the backscattered light of the inspection light and separate unnecessary light for monitoring. Track monitoring system. (2) The optical fiber line monitoring system according to claim 1, wherein the optical filter and the amplifier are semiconductor filters having an amplification function.