JP3336613B2 - Branch line monitoring system and branch line monitoring method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a 1-to-n (≧ 3)
TECHNICAL FIELD The present invention relates to a branch line monitoring system and a branch line monitoring method for monitoring a loss distribution state along a longitudinal direction including a break of the branch line of each of n branched lines in an optical communication line.

[0002]

2. Description of the Related Art Conventionally, as an optical line monitoring system for monitoring a loss distribution state along a longitudinal direction including a break of an optical fiber line as an optical communication line, an OTDR (Optical Tire) has been known.
A system using me Domain Reflectometer) is known. The OTDR introduces monitoring light into an optical fiber line, detects the intensity of a part (backscattered light) of the monitoring light scattered backward due to a loss or the like in the optical fiber line as a function of time, and detects the detection result. Monitoring the breakage of the optical fiber line and the loss distribution along the longitudinal direction of the optical fiber line based on

An example in which the OTDR is applied to monitoring of each of a plurality of branched optical fiber lines is disclosed in, for example, Japanese Patent Application Laid-Open No. 2-141641 (hereinafter referred to as a first conventional example).
Is disclosed. In the loss distribution measuring device according to the first conventional example, a band for selectively transmitting any one of a plurality of monitoring lights having different wavelengths from each other corresponding to each of a plurality of optical fiber lines as branch lines. A pass filter is provided. In the first conventional example, only one monitoring light is propagated through a corresponding one of the optical fiber lines, so that the state of each of the optical fiber lines (including breakage and fluctuation of loss distribution) is sequentially changed. It has a configuration to monitor.

The IEICE Spring 1997, SB-11-
The device described in No. 3 (hereinafter referred to as a second conventional example) is an AWG (Arrayed Waveguide Grat) as a monitoring light branching means.
ing) is applied, and a configuration is provided for individually monitoring the state of each of a plurality of branched optical fiber lines.

[0005]

Normally, when monitoring a plurality of branched optical fiber lines, monitoring light beams having substantially the same amount of light are distributed to each of the plurality of optical fiber lines, that is, after branching guided to each optical fiber line. Are configured such that the intensity of each monitoring light becomes 1 / n. In such a configuration, in the first conventional example, since a plurality of optical fiber lines are monitored by propagating one corresponding monitoring light, the dynamic range of each monitoring light wavelength (measurement wavelength band) is monitored. ) Is small and the SN ratio is poor. On the other hand, in the second conventional example, since the operation of the AWG is sensitive to a temperature change, temperature control using a Peltier element or the like is required, which is expensive.

[0006] Further, IEICE Fall 1991 B-588
In the OTDR device using a light source having a narrow oscillation wavelength band of the monitoring light, fading noise occurs due to the high coherence of the light source, and good measurement cannot be performed.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and has an improved SN ratio of measurement information, enables high-precision measurement, and has a structure capable of being manufactured at low cost. It is an object to provide a system and a branch line monitoring method.

[0008]

A branch line monitoring system and a branch line monitoring method according to the present invention monitor each of n (≧ 3) branch lines to which signal light of a predetermined wavelength is guided via a branching unit. A system and method, comprising a configuration that improves a signal-to-noise ratio of measurement information by extending a measurement wavelength band of each optical fiber line as an optical communication line, and enables highly accurate line monitoring.

That is, a branch line monitoring system for realizing the branch line monitoring method according to the present invention includes a light source that emits n-wave monitoring light having a wavelength different from the signal light and different from each other, and a light emitted from the light source. Monitoring light introducing means for guiding the n-wave monitoring light to each branch line via the branching means, and an optical filter provided on the branch line or at an end of the branch line corresponding to each of the branch lines A backscattered light detection means for detecting, via a branching means, backscattered light of each monitoring light generated in these branch lines; and at least a branch line based on a detection result obtained by the backscattered light detection means. Calculation means for specifying a loss distribution state along each longitudinal direction (including a disconnection of each branch line, a loss variation along each longitudinal direction in each branch line, a portion where these occur, etc.) That.

In particular, the optical filter blocks any one of the guided monitor lights (including reflection and absorption), while transmitting the remaining (n-1) waves and signal light. By providing an optical filter having such a cutoff characteristic in each branch line, each branch line is monitored by (n-1) -wave monitor light excluding the monitor light cut off by the correspondingly provided optical filter. Therefore, it is possible to monitor each branch line using a wider measurement wavelength band than before, and the SN ratio of the measurement information is improved. That is, according to the branch line monitoring system and the branch line monitoring method of the present invention, the measurement result (detection result by the backscattered light detection unit) obtained for each monitoring light is divided into the branch lines provided with the optical filters that are cut off. Since information on (n-1) branch lines excluding the line is included, focusing on one branch line that is a monitoring target, the monitoring target excludes the interrupted monitoring light (n-1). ) It will be monitored by the wave monitoring light. Therefore, since the SN ratio of the measurement information is improved as compared with the conventional system, it is possible to specify the broken portion, the loss variation portion, and the like of each of the n branch lines with high accuracy. It should be noted that the state of each branch line is determined by detecting the intensity of the backscattered light of each of the monitoring lights generated in the branch line by the backscattered light detection unit, and then calculating the calculation unit based on the detection result. Is obtained through a special calculation process. The n-wave monitor light may be simultaneously emitted from the light source to each branch line, or may be sequentially emitted to each branch line at a predetermined time interval.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a branch line monitoring system and a branch line monitoring method according to the present invention will be described below with reference to FIGS.
This will be described with reference to FIG. The same elements in the drawings have the same reference characters allotted, and overlapping description will be omitted.

In the branch optical line monitoring system according to the present invention, one of the n-wave monitor lights is provided for each of n (≧ 3) optical fiber lines (branch lines) branched through the branch means. An optical filter is provided which has a blocking characteristic of blocking (including reflection and absorption) one wave while transmitting monitoring light and signal light of the remaining (n-1) waves. That is, the branch line monitoring system includes a light source that emits n (≧ 3) monitoring lights different from the wavelength of the signal light and different from each other, and transmits the n monitoring lights emitted from the light source to each optical fiber line. Monitoring light introducing means for guiding the light to the optical path, n optical filters provided on the optical line or at the end of the optical line corresponding to each of the n branch lines, Backscattered light detecting means for detecting backscattered light of each monitoring light through the branching means,
On the basis of the result of detection of the backscattered light by the backscattered light detection means, the state of each of the n branch lines (including the state of the breakage of the optical fiber which is the branch line and the loss variation along the longitudinal direction) is specified. Computing means at least. The n-wave monitor light may be simultaneously emitted from the light source to each optical fiber line, or may be emitted to each optical fiber line at a predetermined time interval.

The n-wave monitor light emitted from the light source is guided to each branch line by the monitor light introducing means via the branch means. Therefore, in each of the n branch lines, the monitor light of (n-1) waves propagates in each branch line, except for the monitor light cut off by the optical filters prepared corresponding to the respective optical fiber lines. Becomes As described above, when the (n-1) -wave monitor light propagates through the n branch lines except for the monitor light cut off by the optical filter, backscattered light is generated according to the state of these branch lines. Then, based on the detection result (measured intensity of the backscattered light) detected by the backscattered light detection means, the calculation means performs a special calculation to obtain the state of each of the n branch lines, for example, the branch line. , The loss distribution state (including the break of the branch line) along the longitudinal direction is specified. In other words, in the branch line monitoring system according to the present invention, each branch line is monitored by the (n-1) -wave monitor light excluding the monitor light blocked by the corresponding optical filter. As a result, the S / N ratio of the measurement information is improved by using a wider measurement wavelength band than before, and more precise monitoring of each branch line becomes possible.

Each of the n optical filters is
It is preferable that the n-wave monitor light has a cutoff rate of 30% or more, more preferably 90% or more with respect to the monitor light to be cut off. If the cutoff ratio is 30% or more, the state of each of the n branch lines can be measured with a better SN ratio than the SN ratio in measurement using a conventional bandpass filter. In addition, when the cutoff ratio is 90% or more, the noise component is slight, and the state of each of the n branch lines can be measured with a good SN ratio.

It is preferable that an optical fiber grating is applied to each of the n optical filters. This is because, since the reflection wavelength of the optical fiber grating is in a narrow band, the wavelength interval of each monitor light can be narrowed to narrow the wavelength band of the entire monitor wavelength band light, and the temperature compensation becomes easy. On the other hand, it is preferable to use a star coupler for the branching means. In this case, the branching means is realized at lower cost.

Further, in the branch line monitoring system according to the present invention, the wavelength bandwidth of each monitor light emitted from the light source is finite, and the cutoff wavelength bandwidth of each of the n optical filters is also finite. The wavelength band of each monitor light is included in any of the cutoff wavelength bands of the n optical filters. By setting the wavelength band of each monitoring light to be included in one of the cutoff wavelength bands of each optical filter in this manner, transmitted noise is reduced, and the state of each of the n branch lines with a good SN ratio is obtained. Measurement becomes possible.

The branch line monitoring system according to the present invention comprises:
A temperature controller for controlling the temperature of each of the n optical filters may be further provided, and it is more preferable that the cutoff wavelength of each of the n optical filters is constant regardless of the temperature. In any case, the state of each of the n branch lines can be stably measured.

In the first embodiment of the present invention, the calculating means sets the wavelength of the monitoring light to λi (i = 1, 2,..., N) and sets the detection result of the backscattering light of the monitoring light having the wavelength λi. To m (λ
i), and when the proportional coefficient is k, a loss distribution state along a longitudinal direction of a branch line provided with an optical filter for blocking the monitoring light of the wavelength λi among the n branch lines (breakage of the branch line) Is included in the parameter Ri.

(Equation 5) It is obtained by the following arithmetic expression. That is, according to the first embodiment, the state of each of the n branch lines with the improved S / N ratio of the measurement information can be obtained with high accuracy using such a simple arithmetic expression. In the above-described first embodiment, the state of each branch line is monitored using the n-wave monitor light different from the signal light wavelength. However, both the signal light wavelength and the n-wave monitor light wavelength are used. Even if probe light of a different wavelength (wavelength not blocked by any optical filter) is used, it is possible to detect the occurrence of a failure (for example, breakage of one or more branch lines) in any of the branch lines. . By combining such a configuration with the configuration of the first embodiment, it is possible to simultaneously monitor all of the n branch lines and to simplify monitoring during normal operation.

Further, in the second embodiment of the branch line monitoring system according to the present invention, the above-described probe light (having a wavelength that is not blocked by any optical filter) and n-wave monitoring light (wavelength λi) are used. There is provided a configuration relating to the state of each branch line by utilizing. That is, the calculating means according to the second embodiment sets the wavelength of the probe light to λ0,
When the detection result for the backscattered light of the probe light obtained by the backscattered light detection means is m (λ0),
The parameter Ri indicating the loss distribution state (including the break of the branch line) along the longitudinal direction of the branch line provided with the optical filter that blocks the monitoring light of the wavelength λi is

(Equation 6) It is obtained by the following arithmetic expression. According to this configuration, a desired state of the branch line can be specified by at least two measurements of the backscattered light. In the case where the loss of the shunt to be measured has wavelength dependency (for example, bending loss), an error occurs in the absolute value (measured value) of the loss. It is sufficiently possible to specify the degree of the branch line.

Next, as a more specific configuration of each of the above-described embodiments, monitoring of a branch line branched into one to four, that is, a branch line monitoring system of n = 4 will be described.

First, the configuration of a branch line monitoring system common to the embodiments will be described. FIG. 1 is a diagram illustrating a configuration of a branch line monitoring system that monitors four branch lines branched via a branching unit.

The one-to-four optical communication line shown in FIG. 1 includes an optical fiber line 10 as a main trunk line, four optical fiber lines 11 to 14 as branch lines, and a branching unit 20 as branching means. ing. In addition, each of the branch portions 20
It is composed of three branch elements 21 to 23 that branch. In addition, it is preferable to use a star coupler as the branching portion 20 because it can be configured at low cost. In this one-to-four optical communication line, the signal light propagating in the optical fiber line 10 is branched into four by the branch part 20 and
To 14 respectively.

In this one-to-four optical communication line, the branch part 2
A directional coupler 30 (included in the monitoring light introducing means) is provided at a predetermined position of the optical fiber line 10 located on the near side. The directional coupler 30 propagates the signal light through the optical fiber transmission line 10 as it is, while monitoring light output from the OTDR device 60 so as to propagate through the optical fiber lines 11 to 14 via the branching unit 20. Into the optical fiber line 10. Further, the directional coupler 30 guides the backscattered light of each monitoring light propagating through the optical fiber line 10 via the branching section 20 to the OTDR device 60.

Each of the four optical fiber lines 11 to 14 is provided with an optical filter 41 to 44 on the optical fiber line or at least one end of the optical fiber lines 11 to 14. Optical filters 41 to 44
Each selectively blocks (including reflection and absorption) any one of four monitoring lights λ1 to λ4 (λ1 to λ4 have different wavelengths) emitted from the OTDR device 60. That is, the optical filter 41 transmits monitoring light of wavelengths λ2, λ3, and λ4 in addition to signal light, but blocks monitoring light of wavelength λ1. The optical filter 42 includes, in addition to the signal light,
The monitor light of wavelengths λ1, λ3, and λ4 is transmitted, but the monitor light of wavelength λ2 is blocked. The optical filter 43 transmits monitoring light of wavelengths λ1, λ2, and λ4 in addition to signal light, but blocks monitoring light of wavelength λ3. The optical filter 44
In addition to transmitting the signal light, the monitor light of wavelengths λ1, λ2, and λ3 is transmitted, but the monitor light of wavelength λ4 is blocked. Preferably, each of the optical filters 41 to 44 is provided at a position immediately behind the branching section 20 in that the length of the line section that can be monitored can be increased. Also, the optical filters 41 to 4
4 each is an optical fiber grating, the reflection wavelength band is narrow, so that even if the wavelength intervals of the four monitoring lights λ1 to λ4 are close to each other, the whole measurement wavelength band can be narrowed, and temperature compensation is easy. Preferred in certain respects.

Monitoring light reflection optical filters 51 to 54 are provided at the ends of the monitorable line sections of the four optical fiber lines 11 to 14, respectively. Each of the monitoring light reflected light filters 51 to 54 reflects the arrived monitoring light (at least a part of which is blocked by the optical filters 41 to 44).

The OTDR device 60 includes a wavelength variable light source 61,
A directional coupler 62, a detection unit 63, and a calculation unit 64 are provided. The wavelength tunable light source 61 is, as shown in FIG.
Four monitoring lights λ1 to λ4 having different wavelengths from the signal light and different wavelengths are sequentially emitted. The directional coupler 62 guides the monitoring lights λ1 to λ4 output from the tunable light source 61 to the directional coupler 30 and sends backscattered light of each monitoring light arriving from the directional coupler 30 to the detection unit 63. Lead. The detection unit 63 detects the backscattered light as a function of time, and the calculation unit 64 performs a calculation based on the detection result (intensity of the detected backscattered light) by the detection unit 63 and performs four optical fiber The state of each of the lines 11 to 14 is monitored.

Next, the operation of the embodiment of the branch line monitoring system according to the present invention will be described.
The branch line monitoring method according to the present invention will be described with reference to FIGS. FIG. 3 is a diagram for explaining the propagation of each of the monitoring lights λ1 to λ4 emitted from the variable wavelength light source 61. In this figure, optical fiber lines 10-1
The portion indicated by the bold line in FIG. 4 indicates a path through which each monitor light propagates. FIG. 4 is a diagram for explaining a temporal change in the intensity of the backscattered light detected by the detection unit 63 when the monitoring lights λ1 to λ4 are emitted from the variable wavelength light source 61.

When the monitoring light λ 1 is emitted from the variable wavelength light source 61, the monitoring light λ 1 is branched into four by the branching unit 20 as shown in FIG. Since this monitoring light λ1 is cut off by the optical filter 41, it does not propagate through the optical fiber line 11 thereafter.
The optical fiber line 12 transmits through the optical filter 42, the optical fiber line 13 transmits through the optical filter 43, and
The light passes through the optical filter 44 in the optical fiber line 14. Accordingly, assuming that the states of the optical fiber lines 11 to 14 are R1 to R4, the intensity m (λ1) of the backscattered light of the monitoring light λ1 detected by the detection unit 63 at this time is as shown in FIG.
As shown in (a),

(Equation 7) It is represented by R1 to R4 are the optical fiber lines 11
To 14 represent the intensity of backscattered light when measured independently.

When the monitoring light λ 2 is emitted from the wavelength tunable light source 61, the monitoring light λ 2 is cut off by the optical filter 42 after being split into four by the splitter 20 as shown in FIG. Therefore, it does not propagate through the optical fiber line 12 thereafter. However, this monitoring light λ2
Is transmitted through the optical filter 41 in the optical fiber line 11,
In the optical fiber line 13, the light passes through the optical filter 43, and in the optical fiber line 14, the light passes through the optical filter 44. Accordingly, the intensity m (λ2) of the backscattered light of the monitoring light λ2 detected by the detection unit 63 at this time is as shown in FIG.
As shown in

(Equation 8) It is represented by

When the monitoring light λ 3 is emitted from the wavelength tunable light source 61, the monitoring light λ 3 is split into four by the splitter 20 and then to the optical filter 43 as shown in FIG. , And does not propagate through the optical fiber line 13 thereafter. However, this monitoring light λ
3 is transmitted through the optical filter 41 in the optical fiber line 11, transmitted through the optical filter 42 in the optical fiber 12, and transmitted through the optical filter 44 in the optical fiber line 14. Accordingly, the intensity m (λ3) of the backscattered light of the monitoring light λ3 detected by the detection unit 63 at this time is as shown in FIG.
As shown in

(Equation 9) It is represented by

Further, the monitoring light λ 4
Is emitted, as shown in FIG.
After the monitoring light λ4 is branched into four by the branching unit 20,
The light is not blocked by the optical filter 44 and does not propagate through the optical fiber line 14 thereafter. However, this monitoring light λ4 passes through the optical filter 41 in the optical fiber line 11, transmits through the optical filter 42 in the optical fiber line 12,
Then, the light passes through the optical filter 43 in the optical fiber line 13. Accordingly, at this time, the intensity m (λ4) of the backscattered light of the monitoring light λ4 detected by the detection unit 63 is as shown in FIG.
As shown in (d),

(Equation 10) It is represented by

The operation unit 64 calculates the above m (λ1)
The sum M of m (λ4)

[Equation 11] And obtain the state R1 of each of the optical fiber lines 11 to 14.
~ R4

(Equation 12) It is calculated by the following formula. Alternatively, the optical fiber lines 11 to 14
Each state R1 to R4

(Equation 13) It may be calculated by the following formula.

Alternatively, in general, the optical fiber lines 11 to
14 states R1 to R4

[Equation 14] It may be calculated by the following formula. Here, k is a proportional coefficient.

As described above, according to the above-described specific example, the monitoring light can be effectively used, and thus the monitoring light of the (n-1) wave is used for monitoring each of the n (= 4) optical fiber lines. The wavelength band of the measurement is large and the S / N ratio of the measurement information is improved as compared with the related art in which one wave of monitoring light is used for monitoring one optical fiber line. Further, since a commonly used demultiplexing element can be used for the branching unit 20 without using an expensive AWG, the configuration can be made at low cost. Further, according to the above-described specific example, the intensities m (λ1) to m (λ
4) is added, which is due to the coherence of the monitoring light.
Fading noise is reduced.

The wavelength tunable light source 61 is provided with monitoring lights λ 1 to
In addition to λ4, a configuration may be employed in which probe light including a signal light and a wavelength λ5 (a wavelength not blocked by any of the optical filters 41 to 44) different from any of these wavelength components is emitted. FIG. 5 is a diagram for explaining the propagation of the monitoring light λ5 emitted from the variable wavelength light source 61. FIG. 6 is a diagram for explaining a temporal change in the intensity of the backscattered light detected by the detection unit 63 when the monitoring light λ5 is emitted from the variable wavelength light source 61.

In this specific example, when the monitoring light λ5 is emitted from the wavelength tunable light source 61, as shown in FIG. The light passes through each of the optical filters 41 to 44 and propagates through each of the optical fiber lines 11 to 14. Therefore, at this time, the intensity m (λ5) of the backscattered light of the monitoring light λ5 detected by the detection unit 63 is, as shown in FIG. 6A, the backscattered light generated in each of the optical fiber lines 11 to 14. It is the sum of all light. However, for example, as shown in FIG. 5B, when a break occurs in the middle of the optical fiber line 14 (indicated by X in the figure), the intensity of the backscattered light of the monitoring light λ5 detected by the detection unit 63 m (λ5) is shown in FIG.
As shown in (b), the optical fiber line 14 is obtained by adding the backscattered light generated up to the break point.

That is, normally, the operation unit 64 can monitor the entire one-to-four optical communication line by emitting the monitoring light λ5 by the wavelength variable light source 61 and detecting the intensity of the backscattered light by the detection unit 63. Become. With such a configuration, when it is detected that a failure such as breakage has occurred in any part of the optical fiber line which is a branch line, the wavelength tunable light source 61 emits monitoring lights of wavelengths λ1 to λ4 again, respectively. When the detection unit 63 detects the intensity of the backscattered light of the monitoring light, the calculation unit 64 detects which of the optical fiber lines 11 to 14 has failed, including the location of the failure. By doing so, the monitoring at the normal time is simplified and the efficiency is improved.

In the case of the specific example corresponding to the second embodiment, the probe light having the wavelength λ5 and the four monitoring lights λ1 are used.
The monitoring of each of the optical fiber lines 11 to 14 is performed by .about..lambda.4. That is, the arithmetic unit 64 is configured to output the optical fiber 11
~ 14 each state R1 ~ R4

(Equation 15) It is calculated by the following formula. With such a configuration, a desired optical fiber line can be measured in two measurements, and
It is possible to specify at least a broken part or a part where the loss largely changes.

In the above description, the cutoff rate of the optical filter 41 for the monitor light of wavelength λ1 is 100%, the cutoff rate of the optical filter 42 for the monitor light of wavelength λ2 is 100%, and the monitor light of wavelength λ3 is Is 100%, and the cutoff ratio of the optical filter 44 for the monitoring light having the wavelength λ4 is 100%. But,
Even if the cutoff rate of each optical filter is not 100%, it is preferable that the cutoff rate is 90% or more, and at least 30% or more is sufficient.

Next, a case where the cutoff rate R of the optical filter 41 among the four optical filters 41 to 44 is 30% and the cutoff rate R of each of the remaining optical filters 42 to 44 is 100% will be described. I do. FIG. 7 shows four optical filters 4.
It is a figure for explaining propagation of surveillance light when cutoff rate R of optical filter 41 is 30% among 1-4. FIG.
Is the optical filter 41 among the four optical filters 41 to 44
FIG. 9 is a diagram for describing a temporal change in the intensity of the backscattered light detected by the detection unit 63 when the cutoff ratio R of the light beam is 30%.

In this case, the monitoring light of wavelength λ 1 emitted from the wavelength tunable light source 61 is divided into four by the branching unit 20 and then to the optical fiber line 11 as shown in FIG. Is transmitted through the optical fiber line 11 while 30% is cut off by the optical filter 41 and the remaining 70% is transmitted, and the monitoring light component traveling to the optical fiber line 12 is transmitted through the optical filter 42 by 100%. Optical fiber line 1
2, the monitoring light component traveling toward the optical fiber line 13 passes through the optical filter 43 by 100%, propagates through the optical fiber line 13, and the monitoring light component traveling toward the optical fiber line 14. The component is 100% of the optical filter 44
The light passes through and propagates through the optical fiber line 14. Therefore, at this time, the monitoring light (wavelength λ1) propagated through each of the optical fiber lines 11 to 14 detected by the detection unit 63.
As shown in FIG. 8, the intensity m (λ1) of the backscattered light

(Equation 16) It is represented by

The operation unit 64 calculates m (λ1) to m (λ4)
M (λ1) is subtracted from one-third of the sum of

[Equation 17] Get. This is because the cutoff rate R of the optical filter 41 is 100%.
Although the S / N ratio is reduced to one half as compared with the case where the SNR is lower than the case where the S / N ratio is reduced to one fourth when the band-pass filter of the related art 1 is used, a favorable result is obtained. It has an SN ratio.

Next, a case where the cutoff ratio R of each of the four optical filters 41 to 44 is 90% will be described. FIG. 9 shows the cutoff ratio R of each of the four optical filters 41 to 44.
FIG. 9 is a diagram for explaining the propagation of monitoring light when is 90%. FIG. 10 is a diagram for describing a temporal change in the intensity of the backscattered light detected by the detection unit 63 when the cutoff ratio R of each of the four optical filters 41 to 44 is 90%.

In this case, the monitoring light of the wavelength λ 1 emitted from the wavelength variable light source 61 is divided into four by the branching unit 20 and then to the optical fiber line 11 as shown in FIG. 90% is blocked by the optical filter 41, and the remaining 10% propagates through the optical fiber line 11. The monitoring light component traveling to the optical fiber line 12 passes through the optical filter 42 by transmitting 100% through the optical filter 42, and the monitoring light component traveling toward the optical fiber line 13 transmits 100% through the optical filter 43. Then, the monitoring light component traveling to the optical fiber line 14 is transmitted through the optical filter 44 and propagates through the optical fiber line 14. The same applies to monitoring light of another wavelength. Therefore, at this time, the intensities m (λ1) to m (λ
4) Each is as shown in FIG.

(Equation 18) It is represented by

The operation unit 64 calculates m (λ1) to m (λ4)
M (λ1) is subtracted from one-third of the sum of

[Equation 19] Get. Although the second term in the equation (19) is noise, the effect of the second term is sufficiently small as compared with the first term, so that there is no practical problem.

The two cases described above, that is, the optical filter 4 out of the four optical filters 41 to 44,
The cutoff rate R of one is 30% and the other three optical filters 4
A case where the cutoff rate R of each of 2 to 44 is 100%,
And the four optical filters 41 including the case where the cutoff rate R of each of the four optical filters 41 to 44 is 90%.
To 44, the cutoff rate R of any one of the optical filters is 100.
%, The intensity corresponding to the cutoff rate R of each of the four optical filters 41 to 44 is assigned to each of the intensities m (λ1) to m (λ4) of the backscattered light detected by the detection unit 63. After multiplying, calculate according to equations (10) to (12),
By obtaining the states R1 to R4 of the optical fiber lines 11 to 14, noise components appearing in the second term of the equation (16) can be removed.

Next, the relationship between the wavelength of the monitoring light emitted from the wavelength variable light source 61 and the cutoff characteristics of the optical filters 41 to 44 will be described with reference to FIG. FIG.
As shown in (a), each of the four monitoring lights emitted from the tunable light source 61 has a finite wavelength bandwidth, and each of the n optical filters 41 to 44 has a cut-off wavelength bandwidth. Finite. The wavelength band of the monitoring light having the wavelength λ1 is included in the cutoff wavelength band of the optical filter 41, and the wavelength λ1
The wavelength band of the monitoring light of No. 2 is included in the cutoff wavelength band of the optical filter 42, and the wavelength band of the monitoring light of the wavelength λ3 is
3 is included in the cutoff wavelength band, and the wavelength band of the monitoring light having the wavelength λ4 is preferably included in the cutoff wavelength band of the optical filter 44.

However, as shown in FIG.
When the wavelength band of the monitoring light of a certain wavelength has a portion (hatched portion in the drawing) that is not included in the cutoff wavelength band of the optical filter, that portion of the monitoring light becomes noise without being cut off by the optical filter. Becomes Therefore, four optical filters 4
It is preferable that each of the cut-off wavelengths 1 to 44 is constant regardless of the temperature. Alternatively, four optical filters 41 to 44
When each of the cutoff wavelengths depends on temperature, it is preferable to further include a temperature control device for controlling these temperatures.

FIG. 12 is a perspective view showing an apparatus for making the cutoff wavelength constant regardless of the temperature when each of the four optical filters 41 to 44 is realized by an optical fiber grating. As shown in this figure, this device comprises an iron member 71 having a concave cross section,
And two rectangular aluminum members 72 and 73 disposed apart from each other on the optical fiber lines.
4 are optical filters 41 to 44 made of optical fiber gratings, respectively.
3 and are fixedly disposed on the aluminum members 72 and 73 with adhesives 74 and 75 under appropriate tension. The positions of the adhesives 74 and 75 (adhesion positions) are located inside positions where the aluminum members 72 and 73 are fixed to the iron member 71.

If the temperature rises, an aluminum member 72 having a larger coefficient of thermal expansion than the iron member 71,
The thermal expansion of each of the fibers 73 relaxes the tension of the optical fiber grating and shifts the cutoff wavelength to the shorter wavelength side, while increasing the average refractive index of the optical fiber grating causes the cutoff wavelength to become longer. In the end, the shift of the cutoff wavelength is canceled out, and the cutoff wavelength is kept constant regardless of the temperature. Similarly,
When the temperature decreases, the cutoff wavelength shifts to the longer wavelength side due to thermal contraction of each of the aluminum members 72 and 73, while the cutoff wavelength decreases due to a decrease in the average refractive index of the optical fiber grating. As a result, the shift of the cutoff wavelength is canceled out, and the cutoff wavelength is kept constant regardless of the temperature.

[0051]

As described above, according to the present invention, each of the n-wave monitoring lights having different wavelengths emitted from the light source is guided to the n branch lines to be monitored via the branching means. , While it is desired to propagate the branch line provided with the optical filter for blocking the monitoring light among the n branch lines, the remaining (n-1) branch lines are propagated. Backscattered light is generated depending on the state. Then, the state of each of the n branch lines is specified by a calculation based on the detection result regarding the backscattered light of each of the detected n-wave monitoring lights.

As described above, since the monitoring light can be effectively used (the monitoring light of the (n-1) wave is used for monitoring one branch line), the measurement wavelength band is larger than that of the related art. The S / N ratio is improved. Further, since a normal branch element can be used without using an expensive AWG for the branch part, an inexpensive system can be realized. Furthermore, since the intensities of the backscattered light of each of the n-wave monitoring light are added, fading noise caused by the coherence of the monitoring light is reduced.

Even if each of the n optical filters has a cut-off rate of 30% or more with respect to the monitor light of the wavelength to be cut out of the n-wave monitor light, a conventional band-pass filter is used. The state of each of the n branch lines is obtained with a better SN ratio as compared with the SN ratio at the time of the occurrence. Also,
When each of the n optical filters blocks the monitoring light of the wavelength to be cut out of the n-wave monitoring light at a cut-off ratio of 90% or more, the noise component is small and the noise is good. The state of each of the n branch lines is obtained from the SN ratio.

When each of the n optical filters is an optical fiber grating, it has a narrow band, so that even if the wavelength bands of the n-wave monitor light are close to each other, the entire measurement wavelength band can be narrowed. , Temperature compensation is easy. When the branching section is a star coupler, an inexpensive branch line monitoring system can be realized.

The wavelength bandwidth of each of the n-wave monitor lights emitted from the light source is finite, the cutoff wavelength bandwidth of each of the n optical filters is finite, and the wavelength band of each of the n-wave monitor lights is n. When included in any of the cutoff wavelength bands of the optical filters, noise transmitted through the optical filters is reduced, and the state of each of the n branch lines is obtained with a good SN ratio.

The branch line monitoring system may further include a temperature control device for controlling the temperature of each of the n optical filters. Even if the cutoff wavelength of each of the n optical filters is constant regardless of the temperature. Good. In each case,
The state of each of the n branch lines is stably obtained.

Further, one of the wavelengths of the n-wave monitor light is λi (i = 1, 2,..., N), the detection result by the backscattered light detection means is m (λi), and the proportional coefficient is k When
When the state Ri of the branch line provided with the optical filter for blocking the monitoring light of the wavelength λi among the n branch lines is obtained by a predetermined arithmetic expression, the state of each of the n branch lines is determined by this simple state. It can be obtained with a good S / N ratio simply by using an arithmetic expression.

Further, when the light source also outputs a probe light having a wavelength different from each of the signal light and the n-wave monitor light, all of the n branch lines can be monitored simultaneously, Time monitoring can be simplified. Further, the state of the n branch lines can be obtained by using the probe light and the n-wave monitor light.

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic configuration of an embodiment of a branch line monitoring system according to the present invention.

FIG. 2 is a diagram illustrating a wavelength spectrum of four monitoring lights included in the monitoring light emitted from the variable wavelength light source.

FIG. 3 is a diagram for explaining a state of propagation of monitor light having wavelengths λ1 to λ4 emitted from a variable wavelength light source.

FIG. 4 is a diagram for describing a temporal change in the intensity of backscattered light detected by a detection unit with respect to monitoring light having wavelengths λ1 to λ4 emitted from a wavelength tunable light source.

FIG. 5 is a diagram for explaining a state of propagation of probe light having a wavelength λ5 emitted from a variable wavelength light source.

FIG. 6 is a diagram for explaining a time change of the intensity of the backscattered light detected by the detection unit with respect to the probe light having the wavelength λ5 emitted from the variable wavelength light source.

FIG. 7 is a diagram for explaining propagation of monitoring light when one of the four optical filters has a cutoff rate of 30%.

FIG. 8 is a diagram for explaining a temporal change in the intensity of the backscattered light detected by the detection unit when the cutoff rate of one of the four optical filters is 30%.

FIG. 9 is a diagram for explaining propagation of monitoring light when the cutoff rate of each of four optical filters is 90%.

FIG. 10 shows that the cutoff rate of each of the four optical filters is 90%.
FIG. 9 is a diagram for describing a time change of the intensity of the backscattered light detected by the detection unit in the case of.

FIG. 11 is a diagram for explaining the relationship between the wavelength of the monitoring light output from the variable wavelength light source and the cutoff characteristics of each of the four optical filters.

FIG. 12 is a perspective view showing an apparatus for making a cutoff wavelength constant regardless of temperature when each of four optical filters 41 to 44 is realized by an optical fiber grating.

[Explanation of symbols]

10 optical fiber line (main line), 11-14 optical fiber line (branch line), 20 branch part (branch means),
21 to 23 branch elements, 30 directional couplers, 41 to 4
4: optical filter, 51 to 54: monitoring light reflected light filter,
60 OTDR device, 61 tunable light source, 62 directional coupler, 63 detector, 64 arithmetic unit.

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) H04B 10/00-10/28 H04J 14/00-14/08 G01M 11/00 H04B 3/46

Claims (15)

(57) [Claims] 1. A branch line monitoring system for monitoring n (≧ 3) branch lines to which signal light of a predetermined wavelength is guided via a branching means, wherein n has a wavelength different from the signal light and different from each other. A light source for emitting wave monitoring light; a monitoring light introducing unit for guiding the n-wave monitoring light emitted from the light source to each of the n branch lines via the branching unit; Are provided on the branch line or on the signal incident end side of the branch line corresponding to the n branch lines.
Of one wave with different wavelength assigned to each branch line
While blocking the monitor light, the monitor light of the remaining (n-1) waves and
N optical filters having a function of transmitting signal light, and transmitting through the corresponding one of the n optical filters
The n branch lines through which the (n-1) -wave monitoring light propagates
Backscattered light of n-wave monitoring light propagating from each path
A back scattered light detection unit that detects the scattered light through the n optical filters and the branching unit, based on a detection result of the back scattered light obtained by the back scattered light detection unit, at least the n A branch line monitoring system comprising: a calculating unit that specifies a loss distribution state along a longitudinal direction of each branch line. 2. The apparatus according to claim 1, wherein each of the n optical filters has a cutoff rate of 30% or more with respect to monitor light of a wavelength to be cut off among the monitor lights of the n waves. Branch line monitoring system. 3. The apparatus according to claim 2, wherein each of the n optical filters has a cut-off ratio of 90% or more with respect to the monitor light of the wavelength to be cut off among the monitor lights of the n waves. Branch line monitoring system. 4. The apparatus according to claim 1, wherein each of the n optical filters is an optical fiber grating.
The branch line monitoring system described in the above. 5. The branch line monitoring system according to claim 1, wherein said branching means is a star coupler. 6. The wavelength band of each of the n-wave monitor lights emitted from the light source is finite, the cutoff wavelength bandwidth of each of the n optical filters is finite, and each of the n-wave monitor lights is 2. The branch line monitoring system according to claim 1, wherein the wavelength band is included in any one of the cut-off wavelength bands of the n optical filters. 3. 7. The branch line monitoring system according to claim 1, further comprising a temperature controller for controlling a temperature of each of the n optical filters. 8. The branch line monitoring system according to claim 1, wherein a cutoff wavelength of each of the n optical filters is constant regardless of a temperature. 9. The calculation means sets the wavelength of each of the n-wave monitor lights to λi (1, 2,..., N), and sets the detection result obtained by the backscattered light detection means to m (λi). , When the proportional coefficient is k, the wavelength λ of the n branch lines is
A parameter Ri indicating a loss distribution state along the longitudinal direction of a branch line provided with an optical filter for blocking the monitoring light of i.
Is given by 2. The branch line monitoring system according to claim 1, wherein the branch line monitoring system is obtained by the following arithmetic expression. 10. The branch line monitoring system according to claim 1, wherein the light source emits a probe light having a wavelength different from each of the signal light and the n-wave monitoring light. 11. The arithmetic means is obtained by the backscattered light detecting means, wherein the wavelength of each of the n-wave monitoring lights is λi (1, 2,..., N) and the wavelength of the probe light is λ0. The detected results are m (λi) and m (λ0), and the proportional coefficient is k
Where, a parameter Ri indicating a loss distribution state along a longitudinal direction of a branch line provided with an optical filter for blocking the monitoring light of the wavelength λi among the n branch lines is expressed by the following equation. 11. The branch line monitoring system according to claim 10, wherein the branch line monitoring system is obtained by the following arithmetic expression. 12. A branch line monitoring method for monitoring n (≧ 3) branch lines to which signal light of a predetermined wavelength is guided via a branching unit, wherein n has a wavelength different from the wavelength of the signal light and different from each other. A light source for emitting wave monitoring light is prepared, and each light source is assigned to the n branch lines.
While one monitor light having a different wavelength is blocked, the remaining (n−
1) n having a function of transmitting wave monitoring light and signal light
Optical filters are provided for each of the n branch lines.
On the branch line or on the signal incident end side of the branch line, and transmits through the corresponding one of the n optical filters.
The n branch lines through which the (n-1) -wave monitoring light propagates
Backscattered light of n-wave monitoring light propagating from each path
Is detected through the n optical filters and the branching unit, and based on the obtained detection result regarding the backscattered light, at least a loss distribution state along the longitudinal direction of each of the n branch lines. A branch line monitoring method characterized in that: 13. The wavelength of each of the n-wave monitor lights is λ.
i (1,2, ..., n), the detection result of the backscattered light of the monitor light of the wavelength λi is m (λi), and the proportional coefficient is k. The parameter Ri indicating the loss distribution state along the longitudinal direction of the branch line provided with the optical filter for blocking the monitoring light of λi is given by: 2. The method according to claim 1, wherein the value is obtained by the following arithmetic expression.
2. The branch line monitoring method according to 2. 14. The branch line monitoring method according to claim 12, wherein the light source emits probe light having a wavelength different from each of the signal light and the n-wave monitoring light. 15. The wavelength of each of the n-wave monitor lights is λ.
i (1,2, ..., n), the wavelength of the probe light is λ0,
When the detection results of the monitor light of the wavelength λi and the backscattered light of the probe light are m (λi) and m (λ0), and the proportional coefficient is k, the wavelength λi of the n branch lines is used.
Parameter Ri indicating the loss distribution state along the longitudinal direction of the branch line provided with the optical filter for blocking the monitoring light
Is: 2. The method according to claim 1, wherein the value is obtained by the following arithmetic expression.
0. The branch line monitoring method according to 0.