JPH04351935A - Beam path test monitoring system - Google Patents

Abstract

PURPOSE:To sensitively test and monitor connection loss due to shaft shift and bending loss separately without the deterioration of transfer quality by using both longer and shorter tesing wavelength than signal wavelength and using a light band path filter. CONSTITUTION:Light pulse testers 31, 32 have both longer and shorter wavelength testing light than signal light, and a light band path filter 21 is provided to transmit the signal light between an optical fiber 1 and a light coupler 2 and shield the testing light. With the longer wavelength testing light than the signal light, the backward scattering waveform of the optical fiber 1 is obtained to sensitively test and monitor the bending loss of the optical fiber 1. With the shorter wavelength testing light than the signal light, the backward scattering waveform of the optical fiber 1 is obtained to sensitively test and monitor the connection loss of the optical fiber 1. In this case, both longer and shorter wavelength testing light is shielded by the light band path filter 2 to prevent the deterioration of transfer quality.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvements in testing and monitoring of optical communication systems, particularly optical communication systems that utilize optical lines constructed of optical fibers.

0002

2. Description of the Related Art FIG. 5 shows two configuration examples of optical line test and monitoring systems according to the prior art. (Reference: Tomita et al.
"Automatic Fault Isolation Method for Optical Lines" B890, Proceedings of the 1990 Spring National Conference of the Institute of Electronics, Information and Communication Engineers, 4-69)

000
3] FIG. 5(a) shows a schematic configuration of a subscriber system that connects a station and a subscriber. An optical coupler 2 is installed near the station side in the middle of an optical fiber 1 that connects two optical transmission devices 4, 4. An optical pulse tester (OTDR) 12 is provided on the optical fiber 13 drawn out from the optical coupler 2 via an optical switch 11, and an optical fiber 1 near each optical transmission device 4 is provided on both sides of the optical coupler 2. Long wavelength cutoff optical filters (SWPF) 3, 3 are provided in the middle. The wavelength of the test light possessed by the optical pulse tester 12 (
λt (hereinafter referred to as the test wavelength) is the wavelength of the signal light used in the optical transmission device 4 (hereinafter referred to as the signal wavelength) λs
longer. That is, there is a relationship of λs < λt.

The operation of the optical line test monitoring system shown in FIG. 5(a) will be explained. When the test light is input from the optical pulse tester 12 to one end of the optical fiber 13, the test light is transmitted through any optical fiber 1 set by the optical switch 11 and the optical coupler 2, and is passed through the long wavelength cutoff optical filter on the subscriber side. reflected at 3,
It passes through the optical fiber 1, optical coupler 2, and optical fiber 13 and returns to the optical pulse tester 12. The optical pulse tester 12 measures the intensity of the returned test light to monitor failure conditions such as breakage of the optical fiber 1 serving as the optical path.

FIG. 5(b) shows a schematic configuration of a relay system connecting stations, in which an optical coupler 2 is installed near each station in the middle of an optical fiber 1 connecting two optical transmission devices 4, 4. , an optical pulse tester (OTDR) 12 is connected to the optical fiber 13 drawn out from each optical coupler 2, 2 via an optical switch 11.
Further, long wavelength cutoff optical filters (SWPF) 3, 3 are provided in the middle of the optical fiber 1 between each optical coupler 2, 2 and the optical transmission device 4, 4 nearby. In this case as well, λs
<λt. Note that the operation is similar to that of the subscriber system shown in FIG. 5(a), and a description thereof will be omitted.

Here, the test wavelength λt and the signal wavelength λs
The main reason why the relationship was λs < λt was to test and monitor the state of bending, which is the main cause of optical fiber breakage. That is, in general, there is a relationship between the bending radius and bending loss of an optical fiber as shown in FIG. 6, using wavelength as a parameter. As is clear from FIG. 6, the longer the wavelength, the greater the bending loss, so by setting the test wavelength longer than the signal wavelength, the bending state can be tested and monitored more sensitively than the signal wavelength. .

[0007]

[Problem to be Solved by the Invention] On the other hand, splice loss due to axis misalignment at the connection point of the optical fiber 1 is also an important test monitoring item, but there is a problem that effective test monitoring cannot be performed if the test wavelength is long. The reason is as follows.

[0008] There is a relationship between axis misalignment and connection loss as shown in FIG. 7 using wavelength as a parameter. As is clear from Fig. 7, the connection loss due to axis misalignment decreases as the wavelength becomes longer. Therefore, under the condition of λs < λt, the loss at the signal wavelength λs is large, and the connection state can be monitored with high sensitivity at the test wavelength λt. It is difficult to do so. For example, the test wavelength is λt = 1.65 μm, and the signal wavelength is λs = 1
．． In the case of 31 μm, the splice loss at the test wavelength is at most half of the value at the signal wavelength. Therefore,
The conventional system shown in FIG. 5 cannot be said to be capable of effectively testing and monitoring the state of the optical line, including connection loss.

It is possible to replace the optical pulse tester 12 with an optical pulse tester having a test wavelength shorter than the signal wavelength, for example 1.2 μm, but in this case, the backscattered light from the optical fiber 1 Since the long wavelength cutoff optical filter 3 cannot block the output light from the optical pulse tester or the optical pulse tester,
There is a problem in that these lights pass through the optical filter 3 and enter the optical transmission device 4, degrading the transmission quality.

In view of the above-mentioned problems of the prior art, the present invention provides a practical optical line test and monitoring system that can individually test and monitor connection loss and bending loss with high sensitivity without degrading transmission quality. The purpose is to

[0011]

[Means for Solving the Problems] The configuration of the optical line test monitoring system of the present invention that achieves the above object includes an optical fiber, an optical coupler for inputting and outputting signal light and test light to and from this optical fiber, and an optical coupler for inputting and outputting signal light and test light to and from this optical fiber. In an optical line test monitoring system equipped with an optical pulse tester that inputs and outputs test light,

00
12. The optical pulse tester has both a test light with a shorter wavelength and a test light with a longer wavelength than the signal light,
Furthermore, the present invention is characterized by comprising an optical bandpass filter provided between the optical fiber and the optical coupler, which transmits the signal light and blocks the test light.

In this case, the optical bandpass filter is not particularly limited, but it is preferable to use, for example, an optical fiber doped with thulium.

[0014]

[Function] The backscattered waveform of the optical fiber is obtained using a test light with a longer wavelength than the signal light to sensitively test and monitor the bending loss of the optical fiber, and the backscattered waveform of the optical fiber is obtained using the test light with a shorter wavelength than the signal light. This enables sensitive testing and monitoring of optical fiber splice loss. In this case, the optical bandpass filter blocks test light of both long and short wavelengths to prevent deterioration in transmission quality.

[0015] The optical fiber doped with thulium is 1.3
Transmission loss is extremely small for light with wavelengths from around 1.55 μm to around 1.2 μm and 1.65 μm.
Since the transmission loss is extremely large for light with a wavelength around μm, it works well as an optical bandpass filter.

[0016]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 1 to 4. In the drawings, parts that are the same as those in the prior art are given the same symbols and redundant explanation will be omitted.

[Embodiment 1] FIG. 1 is a diagram showing the configuration of a first embodiment of the present invention. In FIG. 1, 21 is an optical band pass filter (optical BPF), 31 is an optical pulse tester having a test wavelength λt1 shorter than the signal wavelength λs, and 32 is a signal wavelength λ
This is an optical pulse tester having a test wavelength λt2 longer than s, and an optical bandpass filter 21 is provided between the optical fiber 1 and the optical coupler 2, and both optical pulse testers 31, 32 are connected. In addition,
Although the illustration of the right end side of the optical fiber 1 is omitted in FIG. 1, in the case of an optical line for a subscriber system, optical transmission to the subscriber side is performed via an optical bandpass filter as shown in FIG. 5(a). The device is connected. In addition, in the case of a repeating optical line, an optical transmission device on another station side is connected via an optical coupler and an optical bandpass filter as shown in Figure 5(b), and the optical transmission equipment of another station is connected to this optical coupler as in Figure 1. An optical pulse tester 31 for a short test wavelength and an optical pulse tester 32 for a long test wavelength are connected via an optical switch 11.

The operation of the embodiment shown in FIG. 1 will be explained. The optical pulse testers 31 and 32 input test light into an arbitrary optical fiber 1 set by an optical switch 11 and an optical coupler 2 among a large number of optical fibers in an optical line, and detect backscattered light from the optical fiber 1. receives light.

FIG. 2 shows an example of backscattered waveforms in both optical pulse testers 31 and 32. In FIG. 2, the solid line waveform A
is an example of a backscattered waveform in the optical pulse tester 31 with a short test wavelength, and the broken line waveform B is an example of a backscattered waveform in the optical pulse tester 32 with a long test wavelength. In the case of FIG. 2, at a certain connection point 1, the loss is large at a short test wavelength, and at another connection point 2, conversely, the loss is large at a long test wavelength. From this, connection point 1
It is found that the connection loss is large at connection point 2, and the bending loss is large at connection point 2. Therefore, it is possible to estimate the cause of characteristic deterioration in the optical path.

In this case, the optical bandpass filter 21 provided immediately after the optical transmission device 4 blocks the test light crosstalked in the direction of the optical transmission device 4, thereby preventing deterioration in transmission quality. Therefore, the optical line can be tested and monitored while the signal light is being transmitted, that is, in-line.

[Experiment] In order to confirm the effects described above, an experiment was conducted using the following wavelength conditions and the optical bandpass filter 21. The cutoff wavelength for optical fiber 1 is 1.1
A 5 μm single mode optical fiber is used, and the fiber length is approximately 10 km. (1) Signal light: Signal wavelengths 1.31μm and 1.55μm
Wavelength multiplex transmission of m (2) Test light: test wavelengths of 1.21 μm (short wavelength) and 1.65 μm (long wavelength) (3) Note that a thulium-doped optical fiber was used as the optical bandpass filter 21. The loss wavelength characteristics of this thulium-doped optical fiber are shown in FIG. From Figure 3, the transmission loss is 20 at the test wavelengths of 1.21 μm and 1.65 μm.
dB/m or more, and the signal wavelength is 1.31 μm and 1
．． Since the transmission loss is less than 1 dB/m at 55 μm,
It can be seen that it operates as an optical bandpass filter that can sufficiently block the test light.

As a result of the experiment, no change was observed in the bit error rate at both signal wavelengths even when the optical pulse tester was in operation, and the cause of the increase in loss could be estimated from the backscattered waveforms at both test wavelengths.

Furthermore, instead of the thulium-doped optical fiber, a dielectric multilayer filter is used as the optical bandpass filter 21.
We also conducted experiments to confirm the effectiveness when used in As a result of this experiment, although the loss due to the dielectric multilayer filter increased, the test was similar to that of the thulium-doped optical fiber, and no change was observed in the bit error rate at both signal wavelengths even when the optical pulse tester was operating. Furthermore, we were able to infer the cause of the increased loss from the backscattered waveforms at both test wavelengths.

[Embodiment 2] FIG. 4 is a diagram showing the configuration of a second embodiment of the present invention, which differs from the example in FIG.
The surroundings of numbers 1 and 32 are different. That is, the optical switch 11
A multiplexing/demultiplexing coupler 2 is installed between the optical pulse testers 31 and 32.
2 is provided. This multiplexing/demultiplexing coupler 22 is connected to the test wavelength 1.
21 μm and 1.65 μm, and the test light of each wavelength is connected to the corresponding short wavelength optical pulse tester 31 (1
．． 21μm) and long wavelength optical pulse tester 32 (1.65μm)
μm). With the configuration shown in FIG. 4, it is possible to simultaneously perform an optical pulse test on the optical fiber 1 selected by the optical switch 11 using short wavelength test light and long wavelength test light. This makes it possible to shorten the time required to test and monitor all optical fibers.

[0025]

[Effects of the Invention] As explained above, according to the present invention,
By using both shorter and longer wavelengths than the signal wavelength as test wavelengths and using an optical bandpass filter, connection loss due to axis misalignment and bending loss can be tested individually and sensitively without degrading transmission quality. Monitor. Therefore, it is easier to separate and estimate the cause of loss change in an optical line than in the past, and by introducing the present invention, it is expected that the failure state of the optical line can be understood and maintenance operations will be made more efficient. The quality of optical communication services can be improved.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a first embodiment of the present invention.

FIG. 2 is a diagram showing an example of a backscattered waveform in an optical pulse tester.

FIG. 3 is a diagram showing loss wavelength characteristics of a thulium-doped optical fiber.

FIG. 4 is a diagram showing the configuration of a second embodiment of the present invention.

FIG. 5 is a diagram showing the configuration of a conventional example.

FIG. 6 is a diagram showing the wavelength dependence of the relationship between the bending radius and bending loss of an optical fiber.

FIG. 7 is a diagram showing the wavelength dependence of splice loss due to axis misalignment.

[Explanation of symbols]

1 Optical fiber 2 Optical coupler 4 Optical transmission device 11 Optical switch 21 Optical bandpass filter 22 Multiplexing/demultiplexing coupler 31 with test wavelengths of 1.21 μm and 1.65 μm Optical pulse tester 32 with test wavelength λt1 shorter than signal wavelength λs Signal Optical pulse tester with test wavelength λt2 longer than wavelength λs

Claims (2)

[Claims] Claim 1: An optical line test monitoring system comprising an optical fiber, an optical coupler that inputs and outputs signal light and test light to and from the optical fiber, and an optical pulse tester that inputs and outputs test light to and from the optical coupler. , the optical pulse tester has both a test light with a shorter wavelength and a test light with a longer wavelength than the signal light, and furthermore, the optical pulse tester has a test light with a shorter wavelength and a test light with a longer wavelength than the signal light, and further, the optical pulse tester transmits the signal light provided between the optical fiber and the optical coupler. An optical line test monitoring system characterized by comprising an optical bandpass filter that blocks test light. 2. The optical line test and monitoring system according to claim 1, further comprising an optical fiber doped with thulium as the optical bandpass filter.