JP2000352547A - System and method for monitoring of branch ray-of-light passage - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a branch ray-of-light passage monitoring system which can be constituted at low costs. SOLUTION: This branch ray-of-light passage monitoring system 1 is provided with a light source which outputs rays of monitoring light λ1 to λ4. The monitoring system is provided with a directional coupler 30 which introduces the rays of light λ1 to λ4 to a branch ray-of-light passage. The monitoring system is provided with four optical filters 41 to 44 which are installed respectively at branched optical fiber passages 11 to 14. The monitoring system is provided with a detection part 63 which detects rays of backscattered light of the rays of monitoring light λ1 to λ4. The monitoring system is provided with a computing part 64 which computes the state of the branched optical fiber passages 11 to 14 on the basis of the detection result of the rays of backscattered light. The optical fiber 41 transmits only the ray of monitoring light λ1. The optical filter 42 transmits only the rays of light λ1 to λ2. The optical filter 43 transmits only the rays of monitoring light λ1 to λ3. The optical filter 44 transmits the rays of light λ1 to λ4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a branch optical line monitoring system and method for monitoring the state of a 1: n branch optical line.

[0002]

2. Description of the Related Art As an optical line monitoring system for monitoring breakage and loss distribution in the longitudinal direction of an optical fiber line, OTDR is known.
(Optical Time Domain Reflectometer) is known. The OTDR propagates monitoring light through an optical fiber line, detects the intensity of light (backscattered light) that is scattered due to loss of the optical fiber line and the like and travels backward (backscattered light) as a function of time. This is a method of monitoring the loss distribution and failure (breakage or the like) in the longitudinal direction of the optical fiber line based on the information.

[0003] This OTDR is connected to a one-to-n branch optical line (n ≧ n).
For example, Japanese Patent Application Laid-Open No. 2-1416 describes
A branch optical line monitoring system as described in Japanese Patent Publication No. 41 is known. This branch optical line monitoring system
Each of the n optical fiber lines after branching is provided with a band-pass filter for selectively transmitting any one of the n monitoring lights having different wavelengths. Then, each of the n-wave monitor lights is input from the position before the branch, and n
The status of each of the optical fiber lines is sequentially monitored.

[0004]

However, in the above-described branch optical line monitoring system according to the prior art, it is necessary to provide bandpass filters having different cutoff characteristics for each of the n optical fiber lines after branching. There is a problem that the cost increases.

Accordingly, an object of the present invention is to provide a branch optical line monitoring system and a branch optical line monitoring method which can solve the above problems and can be configured at low cost.

[0006]

In order to solve the above-mentioned problems, a branch optical line monitoring system according to the present invention is arranged such that a signal light propagating through one optical line before branching is branched by a branching unit and is divided by n.
A branch optical line monitoring system for monitoring a branch optical line to be propagated to the (n ≧ 2) branched optical lines, wherein each of the n-wave monitor lights having a wavelength different from the signal light and different from each other. A monitoring light introducing unit that introduces each of the n-wave monitoring lights output from the light source into the optical line before the branch and propagates the same toward the branch unit;
Each of the n branched optical lines is provided,
In the wavelength band including the monitoring light of the wave, any one of the monitoring light of the n waves different from the monitoring light of the n
N light transmitting portions that transmit monitoring light having a shorter wavelength than the monitoring light of a wave and block monitoring light having a wavelength longer than the monitoring light of one wave, and the n branched optical lines A backscattered light detector for extracting and detecting the backscattered light of each of the n-wave monitor lights generated in the above, from the optical line before branching, and a backscatter of each of the n-wave monitor light by the backscattered light detector. A calculation unit that performs a calculation based on a light detection result and obtains a state of each of the n branched optical lines.

[0007] A low-pass filter (light transmitting portion having the above-mentioned characteristics), which can be configured at a lower cost than a band-pass filter, is provided on the branched optical line, and n is calculated by an operation based on the detection result of the backscattered light of each of the n-wave monitor light. By obtaining the state of each optical line after branching, the branch optical line monitoring system can be configured at low cost.

In the branch optical line monitoring system according to the present invention, the arithmetic unit may be configured such that when the i-th monitoring light is output from the light source in order from the shorter wavelength side of the n-wave monitoring light, the detection result of the back-scattered light detecting section when the m _i, the n-number of shorter wavelength than the i-th monitoring light and the i-th monitoring light in the light transmitting portion transmits a monitoring light together is, the i-th optical supervisory state Ri of the ray path after branching light transmission portion for blocking the monitoring light having a long wavelength is provided _{than, Ri = m i - m i} + 1 (i ≦ n Ri = m _i (When i = n) It may be characterized by being obtained by an arithmetic expression:

By using the above arithmetic expression, it is possible to easily obtain the state of the optical line after branching.

In order to solve the above-mentioned problems, a branch optical line monitoring system according to the present invention is arranged such that a signal light propagating through one optical line before branching is branched by a branching unit and n (n ≧ 2).
A branch light line monitoring system for monitoring a branch light line to be propagated to the optical line after branching, wherein the light source outputs n-wave monitor lights having different wavelengths from the signal light and different wavelengths from each other; A monitoring light introducing unit that introduces each of the n-wave monitoring lights output from the light source into the optical line before the branch and propagates the same toward the branch unit, and is provided on each of the n optical lines after the branch. In the wavelength band including the n-wave monitor light, any one of the n-wave monitor lights different from the other monitor light and the monitor light having a longer wavelength than the one monitor light are transmitted. At the same time, n light transmitting portions that block monitoring light having a shorter wavelength than the one monitoring light, and backscattered light of each of the n monitoring lights generated in the n branched optical lines. Take out from the optical line before branching and detect Calculation based on the detection results of the backscattered light of the n-wave monitoring light by the backscattered light detection unit and the backscattered light detection unit, and calculating the state of each of the n branched optical lines. And a unit.

A high-pass filter (light transmitting portion having the above-described characteristics), which can be configured at a lower cost than a band-pass filter, is provided on the branched optical line, and n is calculated by an operation based on the detection result of the backscattered light of each of the n-wave monitor lights. By obtaining the state of each optical line after branching, the branch optical line monitoring system can be configured at low cost.

Further, in the branch optical line monitoring system of the present invention, the arithmetic unit may be configured such that when the j-th monitoring light is output from the light source in order from the longer wavelength side of the n-wave monitoring light, When the detection result of the backscattered light detection unit is m _j , the j-th monitoring light and the monitoring light having a longer wavelength than the j-th monitoring light among the n light transmission units are transmitted. together is, the j-th state Rj of light path after branching light transmission portion is provided for blocking the monitoring light having a shorter wavelength than the monitoring _{light, Rj = m j - m j} + 1 (j ≦ n Rj = m _j (When j = n).

By using the above arithmetic expression, the state of the optical line after the branch can be easily obtained.

Further, in the branch optical line monitoring system of the present invention, each of the n light transmitting portions may be constituted by an optical fiber grating.

The optical fiber grating makes it possible to form a light transmitting portion having a highly accurate cutoff characteristic.

Further, in the branch optical line monitoring system of the present invention, each of the n light transmitting portions may be configured by combining an optical fiber grating and a dielectric multilayer film.

By combining an optical fiber grating capable of realizing high-precision cut-off characteristics with a dielectric multilayer film that can be formed relatively inexpensively, a light-transmitting portion having high-precision cut-off characteristics can be formed at low cost. It becomes possible.

Further, the branch optical line monitoring system of the present invention is further characterized by further comprising a cutoff characteristic control section for controlling the light cutoff characteristics of each of the n light transmitting sections to be substantially constant irrespective of the ambient temperature. Is also good.

By providing the cutoff characteristic control unit, the light cutoff characteristics of each of the n light transmission units can be kept substantially constant regardless of the surrounding environment, and high measurement accuracy can be maintained.

In order to solve the above-mentioned problem, a method for monitoring a branched optical line according to the present invention is characterized in that a signal light propagating through one optical line before branching is branched by a branching unit to n (n ≧ 2). A branch optical line monitoring method for monitoring a branch optical line to be propagated to an optical line after branching, wherein the wavelength is different from the wavelength of the signal light,
In addition, each of the n-wave monitor lights having a different wavelength from each other is output from the light source, and each of the n-wave monitor lights is introduced into the optical line before the branch and propagates toward the branch section.
In the wavelength band including the monitoring light of the wave, any one of the monitoring light of the n waves different from the monitoring light of the n
After the n branches, each of which is provided with n light transmission portions for transmitting the monitoring light having a shorter wavelength than the monitoring light of the wave and blocking the monitoring light having the longer wavelength than the monitoring light of the single wave. The backscattered light of each of the n-wave monitor light generated in the optical line is taken out from the optical line before branching and detected, and the n-wave monitor light is detected.
It is characterized in that a calculation is performed based on the detection result of the backscattered light of each of the monitoring lights of the wave, and the state of each of the n branched optical lines is obtained.

A low-pass filter (light transmitting portion having the above-mentioned characteristics), which can be constructed at a lower cost than a band-pass filter, is provided on the branched optical line, and n is calculated by an operation based on the detection result of the backscattered light of each of the n-wave monitor lights. Obtaining the state of each of the optical lines after branching makes it possible to monitor the branched optical lines at low cost.

In the method for monitoring a branched optical line according to the present invention, the detection of the backscattered light when the i-th monitoring light is output from the light source in order from the short wavelength side of the n-wave monitoring light. When the result is m _i , the i-th monitoring light and the monitoring light having a shorter wavelength than the i-th monitoring light out of the n light transmitting portions are transmitted, and the i-th monitoring light is transmitted. than monitoring light of long wavelength state Ri of light path after branching light transmission portion is provided for blocking the monitoring light, Ri = m _i - (when i ≦ n-1) m i + 1 Ri = The characteristic may be obtained by an arithmetic expression of m _i (when i = n).

By using the above arithmetic expression, the state of the optical line after branching can be easily obtained.

According to another aspect of the present invention, there is provided a method for monitoring a branched optical line, comprising the steps of branching a signal light propagating through one optical line before branching into n (n ≧ 2). A branch optical line monitoring method for monitoring a branch optical line to be propagated to an optical line after branching, wherein the wavelength is different from the wavelength of the signal light,
In addition, each of the n-wave monitor lights having a different wavelength from each other is output from the light source, and each of the n-wave monitor lights is introduced into the optical line before the branch and propagates toward the branch section.
In the wavelength band including the monitoring light of the wave, any one of the monitoring light of the n waves different from the monitoring light of the n
After the n branches, each of which is provided with n light transmitting portions for transmitting the monitoring light having a longer wavelength than the monitoring light of the wave and blocking the monitoring light having the shorter wavelength than the monitoring light of the single wave. The backscattered light of each of the n-wave monitor light generated in the optical line is taken out from the optical line before branching and detected, and the n-wave monitor light is detected.
It may be characterized in that a calculation is performed based on the detection result of the backscattered light of each of the monitoring lights of the wave, and the state of each of the n branched optical lines is obtained.

A high-pass filter (light transmitting portion having the above characteristics), which can be constructed at a lower cost than a band-pass filter, is provided in the branched optical line, and n is obtained by an operation based on the detection result of each backscattered light of the n-wave monitor light. Obtaining the state of each of the optical lines after branching makes it possible to monitor the branched optical lines at low cost.

In the method for monitoring a branched optical line according to the present invention, the detection of the backscattered light when the j-th monitoring light is output from the light source in order from the longer wavelength side of the n-wave monitoring light. When the result is m _j , the j-th monitoring light and the monitoring light having a longer wavelength than the j-th monitoring light among the n light transmitting portions are transmitted, and the j-th monitoring light is transmitted. of a shorter wavelength than the monitoring light conditions Rj of light path after branching light transmission portion is provided for blocking the monitoring light, Rj = m _j - (when j ≦ n-1) m j + 1 Rj = m _j (when j = n).

By using the above arithmetic expression, the state of the optical line after the branch can be easily obtained.

Further, in the branch optical line monitoring method of the present invention, each of the n light transmitting portions may be constituted by an optical fiber grating.

With the optical fiber grating, it is possible to form a light transmitting section having a highly accurate cutoff characteristic.

Further, in the branch optical line monitoring method of the present invention, each of the n light transmitting portions may be configured by combining an optical fiber grating and a dielectric multilayer film.

By combining an optical fiber grating capable of realizing high-precision cut-off characteristics with a dielectric multilayer film that can be formed relatively inexpensively, a light-transmitting portion having high-precision cut-off characteristics can be formed at low cost. It becomes possible.

Further, the branch optical line monitoring method of the present invention may be characterized in that the light blocking characteristics of each of the n light transmitting sections are controlled to be substantially constant regardless of the ambient temperature.

By keeping the light-blocking characteristics of the light transmitting portion substantially constant, high measurement accuracy can be maintained.

[0034]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A branch optical line monitoring system according to an embodiment of the present invention will be described with reference to the drawings. The branch optical line monitoring system according to the present embodiment is a branch optical line monitoring system that monitors one-to-four branch optical lines (n = 4).

First, the configuration of the branch optical line monitoring system according to the present embodiment will be described. FIG. 1 is a system configuration diagram of the branch optical line monitoring system according to the present embodiment.

The one-to-four branch optical line to be monitored is shown in FIG.
As shown in FIG.
It is configured to include the optical fiber lines 11 to 14 after branching and the branching unit 20. Here, the branching unit 20 includes three branching elements 21 to 23, each of which branches into two. In addition,
It is preferable that the branching section 20 is a star coupler because it can be configured at a low cost. In this one-to-four branch optical line, the signal light propagating through the optical fiber line 10 is branched into four by the branch part 20, and propagates through the optical fiber lines 11 to 14, respectively.

The branch optical line monitoring system 1 according to the present embodiment includes a directional coupler 30 (monitoring light introducing unit), four optical filters 41 to 44 (light transmitting unit), and four termination filters 51. To 54, the OTDR device 60,
An optical fiber selector 70 and an optical filter 80 are provided. Hereinafter, each component will be described in detail.

The OTDR device 60 includes a light source 61, a directional coupler 62, a detection unit 63 (backscattered light detection unit), and a calculation unit 64. As shown in FIG. 2, the light source 61 outputs four monitoring light beams having different wavelengths from the signal light and different wavelengths from each other. That is, the light source 61 includes a pulse-like monitoring light having a wavelength λ1 (hereinafter, referred to as monitoring light λ1), a pulse-like monitoring light having a wavelength λ2 (hereinafter, monitoring light λ2), and a pulse-like monitoring light having a wavelength λ3 (hereinafter, monitoring light λ2). , Monitoring light λ3) and pulse-like monitoring light of wavelength λ4 (hereinafter referred to as monitoring light λ4) can be sequentially output. Here, the monitoring lights λ1 to λ4
Each wavelength satisfies the relationship of equation (1).

Λ1 <λ2 <λ3 <λ4 (1) Such a light source 61 can be easily realized by, for example, combining a semiconductor light emitting element and a plurality of optical fiber gratings having mutually different lattice intervals.

The directional coupler 62 allows the monitoring lights λ1 to λ4 output from the light source 61 to pass through the optical fiber selector 70 and backscatters the monitoring lights λ1 to λ4 arriving from the optical fiber selector 70. Light is input and output to the detection unit 63. Note that the detection unit 63 and the calculation unit 64
Will be described later.

The optical fiber selector 70 is a one-to-n optical switch. By the switching operation of the optical fiber selector 70, the monitoring lights λ1 to λ4 output from the light source 61 and passed through the directional coupler 62 are transmitted to desired positions. The light can be incident on the monitoring target (branch optical line).

The directional coupler 30 is provided on the optical fiber line 10 before branching. The directional coupler 30 allows the signal light to pass through as it is and propagates through the optical fiber line 10, and also outputs the directional coupler 6 from the light source 61.
2. Monitoring light λ1 that has passed through the optical fiber selector 70
To λ4 are introduced into the optical fiber line 10 and propagated toward the branch portion 20. Also, the directional coupler 30
Inputs the backscattered light of the monitoring lights λ1 to λ4 arriving from the side of the branching unit 20, and outputs the backscattered light toward the optical fiber selector 70 and the directional coupler 62.

Each of the four optical filters 41 to 44 includes
It is provided on each of the four branched optical fiber lines 11 to 14, and more specifically, is provided near the connection with the branching unit 20. Transmittance T of four optical filters 41 to 44
3 (a) to 3 (d) are shown in FIGS. 3 (a) to 3 (d), respectively. In a wavelength band including four monitoring lights, four waves are monitored. Among the lights, any one of the monitoring lights different from each other and the monitoring light having a shorter wavelength than the one monitoring light are transmitted, and the monitoring light having a longer wavelength than the one monitoring light is cut off.

That is, as shown in FIG. 3A, the optical filter 41 provided on the branched optical fiber line 11 transmits the monitor light λ1 in the wavelength band including the monitor lights λ1 to λ4 and transmits the monitor light λ1. , The monitoring light λ2 to λ4 having a longer wavelength than the monitoring light λ1 is blocked. As shown in FIG. 3B, the optical filter 42 provided in the branched optical fiber line 12 has the monitor light λ2 and a shorter wavelength than the monitor light λ2 in the wavelength band including the monitor lights λ1 to λ4. Of the monitoring light λ1 and the monitoring light λ3, λ4 having a longer wavelength than the monitoring light λ2. As shown in FIG. 3C, the optical filter 43 provided in the branched optical fiber line 13 has the monitoring light λ3 and the shorter wavelength than the monitoring light λ3 in the wavelength band including the monitoring lights λ1 to λ4. Of the monitoring light λ1 and λ2, while blocking the monitoring light λ4 having a longer wavelength than the monitoring light λ3. As shown in FIG. 3D, the optical filter 44 provided in the branched optical fiber line 14 has the monitoring light λ4 and a wavelength shorter than the monitoring light λ4 in the wavelength band including the monitoring lights λ1 to λ4. Of the monitoring light λ1 to λ3.

Each of the four optical filters 41 to 44 is
It is configured by combining an optical fiber grating and a dielectric multilayer filter (dielectric multilayer). Hereinafter, the configuration of the optical filter 41 will be described using the optical filter 41 as an example. As shown in FIG. 4, the optical filter 41 includes an optical fiber grating 41a including a diffraction grating built in the branched optical fiber line 11, and a dielectric multilayer filter 41b inserted into the branched optical fiber line 11. Are configured in combination.

As shown in FIG. 5 (a), the cutoff characteristics of the optical fiber grating 41a are such that only light in a relatively narrow wavelength band longer than the monitor light λ1 is cut off, and the transmittance falls extremely sharply. It has the feature of. Such a cutoff characteristic can be realized by adjusting the lattice spacing of the optical fiber grating 51a.

On the other hand, as shown in FIG. 5B, the blocking characteristic of the dielectric multilayer filter 41b blocks only light in a relatively wide wavelength band longer than the monitoring light λ1, but the transmittance rises. It has the characteristic that the fall is slow. Such a cutoff characteristic can be realized by adjusting the thickness of each dielectric film constituting the dielectric multilayer filter 51d.

Therefore, the optical fiber grating 41a
FIG. 5C shows the cutoff characteristics of the optical filter 41 in which the light filter 41 and the dielectric multilayer filter 41b are combined with each other. However, an extremely sharp low-pass filter is realized.

Four termination filters 51 to 5
4 are four optical fiber lines 11 to 1 after branching.
4 at the end. Each of the termination filters 51 to 54 reflects the monitoring light λ1 to λ4 propagating through the four branched optical fiber lines 11 to 14.

The optical filter 80 is provided before the directional coupler 30 (on the signal light incident side). Optical filter 8
0 is an optical fiber line 10
While blocking the backscattered light of the monitoring lights λ1 to λ4 arriving from the directional coupler 30 side.

The detector 63 of the OTDR device 60 detects the backscattered light of the four monitoring lights λ1 to λ4 generated in the four branched optical fiber lines 11 to 14, respectively. More specifically, a directional coupler 6 using a photodetector or the like is used.
By observing the intensity of the light output from 2 with time, the backscattered light of the monitoring lights λ1 to λ4 is detected. The backscattered light is extracted by the directional coupler 30 from the optical fiber line 10 before branching.

The operation unit 64 of the OTDR device 60 performs an operation based on the detection results of the backscattered light of each of the four monitoring lights λ1 to λ4 detected by the detection unit 63, and performs the operation of the four branched optical fibers. The state of each of the lines 11 to 14 is obtained. More specifically, when the detection results by the detection unit 63 when the monitoring lights λ1 to λ4 are output from the light source 61 are respectively m _{1 to} m ₄ , the branched optical fiber lines 11
状態 14 states R1 to R4 are determined by equations (2) to (5). _{R1 = m 1 - m 2 (} 2) R2 = m 2 - m 3 (3) R3 = m 3 - m 4 (4) R4 = m 4 (5) where, m ₁ ~m _4, the monitoring light λ1 Represents the intensity of backscattered light of λ4, which is an amount that changes with time (a function of time). States R1 to R determined from the above equations (2) to (5)
4 specifically represents the intensity pattern of the backscattered light when each of the optical fiber lines 11 to 14 is measured independently.

Next, the operation of the branch optical line monitoring system according to the present embodiment will be described, and the branch optical line monitoring method according to the embodiment of the present invention will be described. FIG. 6 is a diagram illustrating the propagation of the monitoring lights λ1 to λ4 output from the light source 61. FIG. 7 is a diagram illustrating the detection unit 64 when the monitoring lights λ1 to λ4 are output from the light source 61.
FIG. 6 is a diagram showing a detection result by the.

When the monitoring light λ1 is output from the light source 61,
The monitoring light λ1 is supplied to the directional coupler 62 and the optical fiber selector 7.
0, and is introduced into the optical fiber line 10 before branching by the directional coupler 30. Optical fiber line 1 before branching
The monitoring light λ1 introduced into the optical fiber line 10
The light propagates toward the branching portion 20 and is branched into four by the branching portion 20. The monitoring light λ1 branched into four by the branching unit 20 enters the optical filters 41 to 44. Here, due to the cutoff characteristics of the optical filters 41 to 44 described with reference to FIGS. 3A to 3D, they are introduced into the branched optical fiber lines 11 to 14 as shown in FIG. The monitored light λ1 passes through each of the optical filters 41 to 44,
Termination filter 51 while emitting backscattered light
Propagating toward .about.54.

The backscattered light of the monitoring light λ1 introduced into the branched optical fiber lines 11 to 14 is introduced into the optical fiber line 10 before branching by the branching unit 20, and is changed by the directional coupler 30 into the optical fiber selector. 70 is output. On the other hand, even if a part of the backscattered light of the monitoring light λ1 passes through the directional coupler 30 to the signal source side, the backscattered light of the monitoring light λ1 is blocked by the optical filter 80. The backscattered light of the monitoring light λ1 output to the optical fiber selector 70 passes through the optical fiber selector 70 and is guided to the detection unit 63 by the directional coupler 62.

If there is no failure in the branch optical line, the detecting unit 63
Detection result m ₁ detected by is as shown in FIG. 7 (a), which will represent the sum of the intensity pattern of the backscattered light in the case of measuring the optical fiber lines 11 to 14 alone .

On the other hand, when the monitoring light λ2 is output from the light source 61, as shown in FIG. 6B, the monitoring light λ2 introduced into the branched optical fiber lines 12 to 14 is applied to the optical filters 42 to 44. And propagates toward the termination filters 52 to 54 while emitting backscattered light. The backscattered light of the monitoring light λ2 introduced into the branched optical fiber lines 12 to 14 is detected by the detection unit 63. FIG. 7B shows a detection result m ₂ detected by the detection unit 63.
It represents the sum of the intensity patterns of the backscattered light when each of 2 to 14 is measured independently.

When the monitoring light λ3 is output from the light source 61, as shown in FIG. 6C, the monitoring light λ3 introduced into the branched optical fiber lines 13 and 14 is applied to the optical filters 43 and 44. And propagates toward the termination filters 53 and 54 while emitting backscattered light. The backscattered light of the monitoring light λ3 introduced into the branched optical fiber lines 13 and 14 is detected by the detection unit 63. The detection result m ₃ detected by the detection unit 63 is as shown in FIG. 7C.
3 and 14 represent the sum of the intensity patterns of the backscattered light when measured independently.

When the monitoring light λ4 is output from the light source 61, as shown in FIG. 6D, only the monitoring light λ4 introduced into the branched optical fiber line 14 is used as the optical filter 4.
4 and propagates toward the termination filter 54 while emitting backscattered light. The backscattered light of the monitoring light λ4 introduced into the branched optical fiber line 14 is detected by the detection unit 63. FIG. 7D shows the detection result m ₄ detected by the detection unit 63, which represents the intensity pattern of the backscattered light when the optical fiber line 14 is measured alone.

Thereafter, the operation unit 64 calculates the above equation (2)
Based on (5), the branched optical fiber lines 11 to 1
Four states R1 to R4 are obtained. Such states R1 to R
4 specifically represents the intensity pattern of the backscattered light when each of the optical fiber lines 11 to 14 is measured independently.

Here, as shown in FIG. 8, for example, when a failure such as a break occurs in the middle of the optical fiber line 12 after branching, each of the detection results m _{1 to} m ₄ detected by the detection unit 63 is: 9 (a) to 9 (d).
That is, the detection results m ₃ and m ₄ are shown in FIGS.
As shown in FIG. 9D, there is no change in comparison with the case where no failure has occurred, but the detection results m ₁ and m ₂ are shown in FIG.
As shown in FIG. 9B, a constant attenuation pattern is generated corresponding to the location where the failure has occurred. Here, FIG.
Since the attenuation patterns shown in FIGS. 9A and 9B are the same, if the calculation is performed based on the above equations (2) to (5), only the state R2 changes. As a result, it is possible to specify that a failure has occurred in the optical fiber line 12 after branching, and to specify the location of the failure.

When it is desired to detect only the state of the optical fiber line after a specific branch, it is sufficient to introduce two types of monitoring light into the branch optical line. That is, in order to detect the state R2 of the optical fiber line 12 after the branch, only m ₂ and m ₃ are necessary from the above equation (3), and therefore, the monitoring lights λ2 and λ3 are introduced into the branch optical line. That will be enough.

Next, effects of the branch optical line monitoring system according to the present embodiment will be described. The branch optical line monitoring system 1 according to the present embodiment includes an optical fiber line 11 after branching the optical filters 41 to 44, which are low-pass filters.
, And the states R1 to R4 of the four branched optical fiber lines 11 to 14 by an operation based on the detection results of the backscattered lights of the monitoring lights λ1 to λ4.
Seeking. In general, a low-pass filter can be configured at a lower cost than a band-pass filter. Therefore, the low-pass filter is compared with a case in which a band-pass filter is provided to introduce monitoring lights λ1 to λ4 having different wavelengths into the branched optical fiber lines 11 to 14, respectively. Thus, the branch optical line monitoring system can be configured at low cost.

The branch optical line monitoring system 1 according to this embodiment calculates the states R1 to R4 of the branched optical fiber lines 11 to 14 based on the above equations (2) to (5). Therefore, the optical fiber lines 11 to 11 after branching
Each of the fourteen states R1 to R4 can be obtained extremely easily.

The branch optical line monitoring system 1 according to the present embodiment is an optical filter 41 that combines an optical fiber grating capable of realizing high-precision cutoff characteristics with a dielectric multilayer filter that can be constructed relatively inexpensively. ~ 44
With this configuration, the optical filters 41 to 44 having high-precision cutoff characteristics can be configured at low cost.

In the branch optical line monitoring system 1 according to the above embodiment, the cutoff characteristics of the optical filters 41 to 44 are as shown in FIGS. 3A to 3D. Is set to 1 (= 100%), and the transmittance of the wavelength to be cut off is set to 0 (= 0%). However, if the transmittance of the wavelength to be cut is sufficiently larger than the transmittance of the wavelength to be cut off, 30 % Is sufficient, 90%
It is preferable that this is the case. Similarly, if the transmittance at the wavelength to be cut off is sufficiently smaller than the transmittance at the wavelength to be transmitted, 70% or less is sufficient, and preferably 10% or less.

In the branch optical line monitoring system 1 according to the above embodiment, the optical filters 41 to 44 are formed by combining an optical fiber grating and a dielectric multilayer filter.
However, the optical filters 41 to 44 may be configured only by the optical fiber grating.

Further, in the branch optical line monitoring system 1 according to the above-described embodiment, the optical filter 14 may not be provided when noise in a long wavelength range does not pose a problem. In this case, the optical fiber line 14 itself after branching is a light transmitting unit that transmits the monitoring light λ4 and the monitoring lights λ1 to λ3 having a shorter wavelength than the monitoring light λ4 in the wavelength band including the monitoring lights λ1 to λ4. Act as

Each of the four monitoring lights λ1 to λ4 output from the light source 61 has a finite wavelength bandwidth and
Each of the optical filters 41 to 44 also has a finite cutoff wavelength bandwidth (at least one side is finite). The wavelength band of the monitoring light λ1 is not included in the cutoff wavelength band of the optical filters 41 to 44, and the wavelength band of the monitoring light λ2 is
And not included in the cut-off wavelength bands of the optical filters 42 to 44, the wavelength band of the monitoring light λ3 is included in the cut-off wavelength bands of the optical filters 41 and 42 and the cut-off wavelength bands of the optical filters 43 and 44. It is preferable that the wavelength band of the monitoring light λ4 is included in the cutoff wavelength band of the optical filters 41 to 43 and not included in the cutoff wavelength band of the optical filter 44. However, when such a condition is not satisfied due to, for example, a change in the temperature of the optical filters 41 to 44, the S / N ratio is reduced due to a decrease in the amount of necessary monitoring light and the incorporation of unnecessary monitoring light. . So 4
It is preferable that the cutoff characteristics of each of the optical filters 41 to 44 be constant regardless of the temperature. Alternatively, when the cutoff wavelength of each of the four optical filters 41 to 44 depends on the temperature, it is preferable to further include a temperature control unit that controls these temperatures.

FIG. 10 is a block diagram of the cutoff characteristic control section 90 for making the cutoff wavelength constant regardless of the temperature when each of the four optical filters 41 to 44 includes an optical fiber grating. Cutoff characteristic control section 90
Is an iron member 91 having a concave cross section as shown in FIG.
And two rectangular aluminum members 92 and 93 that are spaced apart from each other on the iron member 91, and each of the branched optical fiber lines 11 to 14 includes:
The tension is applied to the aluminum members 92 and 93 appropriately so that the optical filters 41 to 44 including the optical fiber gratings are located between the aluminum members 92 and 93, and the adhesives 94 and 95 are applied. Is fixedly arranged.
The bonding position by the adhesives 94 and 95 is located inside the position where the aluminum members 92 and 93 are fixed to the iron member 91.

When the temperature rises, the aluminum members 92 and 93 each having a larger thermal expansion coefficient than the iron member 91 thermally expand, so that the tension of the optical fiber grating is loosened and the cutoff wavelength shifts to the shorter wavelength side. On the other hand, as the average refractive index of the optical fiber grating increases, the cutoff wavelength shifts to the longer wavelength side, so that the shift of the cutoff wavelength is canceled out, and the cutoff wavelength is constant regardless of the temperature. Is kept. Similarly, when the temperature decreases, the cutoff wavelength shifts to the longer wavelength side due to thermal contraction of each of the aluminum members 92 and 93, while the average refractive index of the optical fiber grating decreases. The cutoff wavelength shifts to the shorter wavelength side, and the shift of the cutoff wavelength is eventually canceled out,
The cutoff wavelength is kept constant regardless of the temperature.

Further, in the branch optical line monitoring system 1 according to the above embodiment, the cutoff characteristics of the optical filters 41 to 44 are as shown in FIGS. 3A to 3D, respectively. This may be as shown in FIGS. 11 (a) to 11 (d). That is, the optical filter 41 provided on the optical fiber line 11 after the branch is the same as that shown in FIG.
As shown in FIG. 1A, in the wavelength band including the monitoring lights λ1 to λ4, the monitoring light λ4 is transmitted and the monitoring lights λ1 to λ3 having a shorter wavelength than the monitoring light λ4 are cut off.
Optical filter 4 provided on optical fiber line 12 after branching
As shown in FIG. 11B, reference numeral 2 denotes a monitor light λ3 and a monitor light λ3 in a wavelength band including the monitor lights λ1 to λ4.
While transmitting the monitoring light λ4 having a wavelength longer than 3
The monitoring lights λ1 and λ2 having a shorter wavelength than the monitoring light λ3 are blocked. As shown in FIG. 11C, the optical filter 43 provided in the optical fiber line 13 after the branching includes monitoring light λ1 to λ
In the wavelength band including 4, the monitor light λ2 and the monitor lights λ3 and λ4 having a longer wavelength than the monitor light λ2 are transmitted, and the monitor light λ1 having a shorter wavelength than the monitor light λ2 is blocked. As shown in FIG. 11D, the optical filter 44 provided on the branched optical fiber line 14 has the monitoring lights λ1 to λ1.
In the wavelength band including λ4, the monitoring light λ1 and the monitoring lights λ2 to λ4 having a longer wavelength than the monitoring light λ1 are transmitted.

In this case, when the detection results by the detector 63 when the monitoring lights λ1 to λ4 are output from the light source 61 are respectively m _{1 to} m ₄ , the branched optical fiber line 11
The 14 states R1 to R4 are obtained by the equations (6) to (9). _{R1 = m 4 - m 3 (} 6) R2 = m 3 - m 2 (7) R3 = m 2 - m 1 (8) R4 = m 1 (9)

In the branch optical line monitoring system 1 according to the above embodiment, the wavelength of the monitoring light is 1.55 μm.
In the case where band light is used, an erbium-doped optical fiber amplifier for amplifying the monitoring light may be provided as necessary in order to solve the shortage of the dynamic range.

[0075]

According to the branch optical line monitoring system and the branch optical line monitoring method of the present invention, an optical line after branching a low-pass filter or a high-pass filter (light transmitting portion having the above characteristics), which can be constructed at a lower cost than a band-pass filter. And the state of each of the n branched optical lines is obtained by an operation based on the detection result of the backscattered light of each of the n-wave monitoring lights, whereby the branch optical line monitoring system can be configured at low cost.

Further, in the branch optical line monitoring system and the branch optical line monitoring method of the present invention, it is possible to easily obtain the state of the optical line after branching by using the above-mentioned constant arithmetic expression.

Further, in the branch optical line monitoring system and the branch optical line monitoring method according to the present invention, the light transmission section is constituted by an optical fiber grating, so that the light transmission section having a high-precision cutoff characteristic is constituted. Becomes possible.

Further, in the branch optical line monitoring system and the branch optical line monitoring method according to the present invention, the light transmitting portion is made of an optical fiber grating capable of realizing a high-precision cutoff characteristic and a dielectric multilayer structure which can be formed relatively inexpensively. By combining the film and the film, it is possible to inexpensively configure the light transmitting unit having the highly accurate blocking characteristic.

Further, in the branch optical line monitoring system and the branch optical line monitoring method of the present invention, the provision of the cut-off characteristic control unit makes it possible to keep the cut-off characteristic of the light transmitting unit substantially constant, thereby achieving high measurement accuracy. Can be maintained.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram of a branch optical line monitoring system.

FIG. 2 is a diagram illustrating a wavelength spectrum of four monitoring lights λ1 to λ4 output from a light source.

FIG. 3 is a diagram illustrating cutoff characteristics of an optical filter.

FIG. 4 is a configuration diagram of an optical filter.

FIG. 5 is a diagram illustrating cutoff characteristics of an optical filter.

FIG. 6 is a diagram illustrating the propagation of each of monitoring lights λ1 to λ4 output from a light source.

FIG. 7 is a diagram illustrating a detection result by a detection unit when monitoring light beams λ1 to λ4 are output from a light source.

FIG. 8 is a diagram illustrating a location of a failure in a branch optical line.

FIG. 9 is a diagram illustrating a detection result by a detection unit when each of monitoring lights λ1 to λ4 is output from a light source.

FIG. 10 is a configuration diagram of a cutoff characteristic control unit.

FIG. 11 is a diagram illustrating wavelength characteristics of transmittance of an optical filter.

[Explanation of symbols]

10-14: Optical fiber line, 20: Branch part, 21-2
DESCRIPTION OF SYMBOLS 3 ... Branch element, 30 ... Directional coupler, 41-44 ... Optical filter, 51-54 ... Termination filter, 60
... OTDR device, 61 ... light source, 62 ... directional coupler, 6
3 ... Detection unit, 64 ... Calculation unit, 90 ... Blocking characteristic control unit.

Claims (14)

[Claims] 1. A branch optical line for monitoring a branch optical line that is branched by a branching unit and propagates to an n (n ≧ 2) branched optical line that propagates a signal light propagating in one optical line before branching. In the monitoring system, a light source that outputs each of n-wave monitoring lights having a different wavelength from the signal light and different wavelengths from each other, and an optical line before the branching that outputs each of the n-wave monitoring lights output from the light source. A monitoring light introducing unit for introducing the light into the optical fiber and propagating the light toward the branching unit;
In the wavelength band including the monitoring light of the wave, any one of the monitoring light of the n waves different from the monitoring light of the n
N light transmitting portions for transmitting monitor light having a shorter wavelength than the wave monitor light and blocking monitor light having a longer wavelength than the one monitor light; and the n branched optical lines. A backscattered light detection unit that extracts and detects the backscattered light of each of the n-wave monitor lights generated in the above, from the optical line before branching; and a backscatter of the n-wave monitor light by the backscattered light detection unit. An operation is performed based on the light detection result, and
A branching optical line monitoring system, comprising: a calculation unit for determining a state of each of the optical lines after branching. 2. The arithmetic unit according to claim 1, wherein the detection result of the backscattered light detection unit when the i-th monitoring light is output from the light source in order from a short wavelength side of the n-wave monitoring light is _mi. When transmitting, the i-th monitoring light and the monitoring light having a shorter wavelength than the i-th monitoring light among the n light transmitting portions are transmitted, and the i-th monitoring light is also state Ri of light path after branching light transmission portion is provided for blocking the monitoring light of long wavelength, Ri = m _i - (when _{i ≦ n-1) m i} + 1 Ri = m i (i 2. The branch optical line monitoring system according to claim 1, wherein the value is obtained by an arithmetic expression: 3. A branch optical line for monitoring a branch optical line that is split by a branching unit to propagate signal light propagating through one pre-branch optical line and propagated to n (n ≧ 2) post-branch optical lines. In the monitoring system, a light source that outputs each of n-wave monitoring lights having a different wavelength from the signal light and different wavelengths from each other, and an optical line before the branching that outputs each of the n-wave monitoring lights output from the light source. A monitoring light introducing unit for introducing the light into the optical fiber and propagating the light toward the branching unit;
In the wavelength band including the monitoring light of the wave, any one of the monitoring light of the n waves different from the monitoring light of the n
N light transmitting portions that transmit monitoring light having a longer wavelength than the monitoring light of a wave and block monitoring light having a shorter wavelength than the monitoring light of one wave; and the n branched optical lines. A backscattered light detection unit for extracting and detecting the backscattered light of each of the n-wave monitor light generated in the above, from the optical line before branching; and a backscattering of the n-wave monitor light by the backscattered light detection unit An operation is performed based on the light detection result, and
A branching optical line monitoring system, comprising: a calculation unit that obtains the state of each of the branched optical lines. 4. The arithmetic unit calculates a detection result by the backscattered light detection unit when the j-th monitoring light is output from the light source in order from a long wavelength side among the n-wave monitoring light, by m _j And, while transmitting the j-th monitoring light and the monitoring light having a longer wavelength than the j-th monitoring light out of the n light transmitting portions, also state Rj of light path after branching light transmission portion for blocking the monitoring light of short wavelength is _{provided, Rj = m j - m j} + 1 ( when j ≦ n-1) Rj = m j (j The branch optical line monitoring system according to claim 3, wherein the value is obtained by an arithmetic expression: 5. The branch optical line monitoring system according to claim 1, wherein each of the n light transmitting sections is configured by an optical fiber grating. 6. The split light beam according to claim 1, wherein each of the n light transmitting portions is configured by combining an optical fiber grating and a dielectric multilayer film. Road monitoring system. 7. The light-shielding device according to claim 1, further comprising a light-blocking characteristic control unit that controls light-blocking characteristics of each of said n light-transmitting units to be substantially constant regardless of ambient temperature. 2. The branch optical line monitoring system according to 1. 8. A branch optical line for monitoring a branch optical line that is branched by a branching unit and propagates to n (n ≧ 2) branched optical lines by propagating signal light propagating in one optical line before branching. In the monitoring method, each of the n-wave monitoring lights having a wavelength different from the signal light and different from each other is output from a light source, and the n-wave monitoring lights are respectively introduced into the optical line before the branch and the branch is performed. In the wavelength band including the n-wave monitoring light,
The monitor light of any one of the different wave monitor lights and the monitor light of a shorter wavelength than the monitor light of the one wave are transmitted, and the monitor light of a longer wavelength than the monitor light of the one wave is cut off. The backscattered light of each of the n-wave monitor light generated in the n branched optical lines provided with the n light transmitting portions to be extracted is extracted from the optical line before the branch, and detected. A method for monitoring a branched optical line, comprising: performing a calculation based on a detection result of backscattered light of each of the monitoring lights of a wave to obtain a state of each of the n branched optical lines. The method according to claim 9, wherein said detection result of the back-scattered light when the i-th optical supervisory from the short wavelength side of the n wave optical supervisory is sequentially outputted from the light source is taken as m _i, the n While transmitting the i-th monitoring light and the monitoring light having a shorter wavelength than the i-th monitoring light, the monitoring light having a longer wavelength than the i-th monitoring light is transmitted. the state Ri of light path after the light transmitting unit for blocking is provided branching, Ri = m _i - (when _{i ≦ n-1) m i} + 1 ( when _i = n) Ri = m i becomes operational 9. The method according to claim 8, wherein the value is obtained by an equation. 10. A branch optical line for monitoring a branch optical line that causes a signal light propagating through one optical line before branching to be branched by a branching unit and propagated to n (n ≧ 2) branched optical lines. In the monitoring method, n wavelengths of monitoring light different from the wavelength of the signal light and different from each other are output from a light source, and the n wavelengths of monitoring light are introduced into the optical line before the branch and the branch is performed. In the wavelength band including the n-wave monitoring light,
Among the monitoring lights of the waves, any one of the different monitoring lights and the monitoring light having a longer wavelength than the one monitoring light are transmitted, and the monitoring light having a shorter wavelength than the one monitoring light is blocked. The backscattered light of each of the n-wave monitor light generated in the n branched optical lines provided with the n light transmitting portions to be extracted is extracted from the optical line before the branch, and detected. A method for monitoring a branched optical line, comprising: performing a calculation based on a detection result of backscattered light of each of the monitoring lights of a wave to obtain a state of each of the n branched optical lines. 11. When the j-th monitoring light is output from the light source in order from the long wavelength side of the n-wave monitoring light, the detection result of the backscattered light is m _j , While transmitting the j-th monitoring light and the monitoring light having a longer wavelength than the j-th monitoring light among the light transmitting portions, the monitoring light having a shorter wavelength than the j-th monitoring light is transmitted. the state Rj of light path after the light transmitting unit for blocking is provided branching, Rj = m _j - (when _{j ≦ n-1) m j} + 1 ( when _j = n) Rj = m j becomes operational The method for monitoring a branched optical line according to claim 10, wherein the method is obtained by an equation. 12. The branch optical line monitoring method according to claim 8, wherein each of the n light transmitting portions is constituted by an optical fiber grating. 13. The branched light beam according to claim 8, wherein each of the n light transmitting portions is configured by combining an optical fiber grating and a dielectric multilayer film. Road monitoring method. 14. The branch optical line monitoring according to claim 8, wherein the light blocking characteristics of each of the n light transmitting portions are controlled to be substantially constant regardless of the ambient temperature. Method.