JPH05126673A - Failure detecting device for optical line - Google Patents

Abstract

PURPOSE:To provide a failure detecting device of an optical line invariably monitoring the optical line and capable of instantly detecting a failure when the failure occurs on the optical line. CONSTITUTION:Part of the communication light transmitted to a receiver 2 side in an optical line 3 is branched at a fixed ratio by a light merging/diverting unit such as an optical fiber coupler, it is reflected by a reflector 6 installed at the far end of the optical line 3, and part of the reflected return light of the communication light returning to a transmitter 1 side is branched at a fixed ratio. Light quantities of the branched communication light and the reflected return light are detected by light quantity detectors 10, 11, and the ratios of the light quantities are invariably compared by a comparing circuit 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical line failure detection device for detecting a failure such as cracking or breakage in an optical line.

[0002]

2. Description of the Related Art Conventionally, an optical pulse tester (OTDR) has been used as a technique for monitoring failures such as cracks and breaks in optical lines.
A system using is known (see FIG. 2). According to this system, the communication light transmitted from the transmitter 1 and the test light having a wavelength different from this communication light are multiplexed in the optical multiplexer / demultiplexer 5, and then transmitted to the optical line 3. A reflector 6 is provided near the receiver 2 at the far end of the optical line 3, and the reflector 6 transmits the communication light and reflects only the test light at a constant ratio. The failure of the optical line 3 is detected by monitoring the level of the reflected test light with the optical pulse tester 4. Further, when a large number of optical lines are monitored by one optical pulse tester 4, as shown in FIG. 2, a core wire selection device 7 is provided between the optical pulse tester 4 and the optical multiplexer / demultiplexer 5. An intervening system is also known.

[0003]

However, when a plurality of optical lines are monitored by the single optical pulse tester 4 using the optical fiber selecting device 7 as described above, the test optical lines are sequentially supplied to the respective optical lines. Will be sent and each optical line will be measured one by one. Therefore, when a failure occurs in one of a large number of optical lines, there is a drawback that this failure can be detected only after the other optical lines are measured once. For this reason, it cannot be used at all for a communication system in which a large amount of communication light propagates in the optical line, and from the viewpoint of safety measures, the transmission of communication light must be instantaneously stopped in the event of a failure. .. Further, since the optical pulse tester is expensive and relatively large, it is not necessary to provide an optical pulse tester on each of the optical lines sent from the transmitting station.
It was extremely impossible because it resulted in an extreme increase in equipment costs.

The present invention has been made in order to solve the above-mentioned drawbacks, in which each optical line is constantly monitored, and when a failure occurs in the optical line, the failure can be instantly detected. An object is to provide a detection device.

[0005]

An optical line failure detecting apparatus according to the present invention comprises first branching means for branching communication light sent to a receiving side in the optical line at a constant ratio, and A first light amount detecting unit that detects the amount of light branched by the first branching unit and a reflected return light of the communication light that is reflected by the reflector installed at the far end of the optical line and returns to the transmission side are set at a fixed ratio. And a second light amount detecting unit for detecting the light amount branched by the second branching unit.

The first branching means and the second branching means may be separately arranged as separate bodies or integrally molded.

[0007]

The communication light sent to the receiving side in the optical line is branched by the first branching means, and the light quantity thereof is detected by the first light quantity detecting means. On the other hand, a part of the communication light is reflected by the reflector installed near the receiver at the far end of the optical line, and the reflected return light of the communication light returning to the transmitting side in this optical line is branched by the second branching means. Then, the light amount is detected by the second light amount detecting means. Since the detected communication light and reflected return light are branched by the respective branching means at a constant ratio, by constantly monitoring the ratio of the detected light amount, if the value of this ratio deviates from the predetermined level. Alternatively, when it changes to a certain value or more, it is detected that a failure has occurred in the optical line.

[0008]

Embodiments of the present invention will be described below with reference to the accompanying drawings. The same elements as those shown in FIG. 2 are designated by the same reference numerals, and the description thereof will be omitted.

FIG. 1 shows the configuration of an optical line failure detection apparatus according to this embodiment. The failure detection device branches a part of the communication light transmitted to the receiver 2 side through the optical line 3 at a constant ratio,
An optical multiplexer / demultiplexer 9 such as an optical fiber coupler that branches a part of the reflected return light of the communication light returning to the transmitter 1 side through the optical path 3 at a constant ratio is provided. Further, the light quantity of the branched communication light is detected by the light quantity detector 10, the light quantity of the branched reflected return light is detected by the light quantity detector 11, and the ratio of the respective light quantities is constantly compared by the comparison circuit 12.

Next, the detection principle of the failure detection device will be described. Assuming that the light amount of the communication light transmitted from the transmitter 1 and passing through the optical multiplexer / demultiplexer 9 is P _0, and the branching ratio of the optical multiplexer / demultiplexer 9 is γ, the light amount P received by the light amount detector 10 is P.
₁ is

[0011]

[Equation 1]

Is given by Also, the loss of the optical line 3 up to the reflector 6 is α [dB], and the reflectance of the reflector 6 is R
Assuming [dB], the amount of communication light P _r reflected by the reflector 6 and returning to the transmitting station side is

[0013]

[Equation 2]

Is given by Further, the light amount P ₂ of the reflected return light split by the optical multiplexer / demultiplexer 9 and received by the light amount detector 11 is

[0015]

[Equation 3]

Is given by In the comparison circuit 12, by detecting the ratio of the respective light amounts P ₁ and P ₂ received by the light amount detectors 10 and 11,

[0017]

[Equation 4]

Is obtained. This value is the apparent reflectance of the reflector 6 viewed from the transmitter 1 side.

Here, when the reflectance R [dB] of the reflector 6 is set so that the apparent reflectance of the reflector 6 is larger than the maximum reflectance from the optical connector 8 at the near end, When there is no abnormality in the path 3, the comparison circuit 12 detects a constant reflectance (R-2α).

On the other hand, when a failure such as a crack occurs in the optical line 3 and the loss of the optical line 3 increases, the apparent reflectance (R-2α) decreases. Further, when a failure such as disconnection occurs and reflection occurs at that point, it is extremely rare that the reflectance thereof matches the reflectance of the reflector 6, so that the apparent reflectance suddenly changes. Is detected by the comparison circuit 12. Therefore, if the comparison circuit 12 detects an apparent decrease in reflectance or a rapid change, the failure of the optical line 3 can be constantly monitored.

In the above-mentioned optical line failure detection device,
When the maximum reflectance of the optical connector 8 is -35 [dB] and there are a maximum of two optical connectors 8 near the optical multiplexer / demultiplexer 9, the maximum reflectance by the optical connector is -32 [dB]. Becomes Therefore, the apparent reflectance of the reflector 6 is -30
It is necessary to set it above [dB]. Also, the reflector 6
When the set reflectance of -10 is set to -10 [dB], the apparent reflectance is -30 in the range where the optical line loss is 10 [dB] or less.
It becomes more than [dB], and this is the range where failure detection is possible.

Further, in response to the comparison result of the comparison circuit 12,
For example, when an apparent reflectance changes by 1 [dB] or more, an alarm is generated to easily detect the failure of the optical line. Particularly when the loss of the optical line is small, a large amount of reflected return light returns to the transmitter 1, which may adversely affect the transmitted communication light. Therefore, the transmitter 1 and the optical multiplexer / demultiplexer 9 It is preferable to insert an optical isolator between and.

In this embodiment, an optical fiber coupler is shown as an example of the optical multiplexer / demultiplexer, but it is not particularly limited as long as it can split light at a constant ratio. The branching ratio of the coupler is preferably about 1 to 5% in consideration of insertion loss. Further, as the reflector, a dielectric multilayer filter having a constant reflectance can be formed by inserting it into a groove formed in an optical fiber, and the reflectance is -10 [dB] or less in consideration of insertion loss. desirable.

[0024]

As described above, the apparatus for detecting a failure of an optical line according to the present invention makes it possible to detect the communication light transmitted through the optical line as a first line.
And the reflected return light of the communication light reflected by the reflector installed at the far end of the optical line is detected by the first light quantity detecting means. And the light amount is detected by the second light amount detecting means. Therefore, by constantly monitoring the ratio of the detected amounts of communication light and reflected return light,
It is possible to instantly detect the occurrence of a failure such as a crack or a break in the optical line.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an optical line failure detection device according to an exemplary embodiment of the present invention.

FIG. 2 is a configuration diagram showing a conventional optical line failure detection device.

[Explanation of symbols]

 9 ... Optical multiplexer / demultiplexer 10 ... Light intensity detector 11 ... Light intensity detector 12 ... Comparison circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Eigo Yoneda 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (3)

[Claims] 1. A failure detecting device for an optical line provided on a transmitting side, comprising: first branching means for branching communication light sent to a receiving side at a constant ratio, and branching by the first branching means. A first light amount detecting means for detecting the amount of light and a reflected return light of the communication light which is reflected by the reflector installed at the far end of the optical line and returns to the transmission side at a constant ratio. A failure detecting device for an optical line, comprising: a second branching means; and a second light quantity detecting means for detecting the quantity of light branched by the second branching means. 2. A detection means for comparing the light quantity detected by the first light quantity detection means with the light quantity detected by the second light quantity detection means to detect a failure of the optical line. The optical fiber failure detection device according to claim 1. 3. The optical line failure detection device according to claim 1, wherein the first branching means and the second branching means are integrally formed.