JPH1127211A - Branch optical line checking device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To test each optical branch fiber individually even when drift occurs in a test channel by measuring Rayleigh back scattering light from a branch optical fiber or wavelength of maximum intensity of reflected light from an optical filter. SOLUTION: A variable wavelength light source 9 which has received control of a main control/identifying part 13 outputs pulse testing light, changing test wavelength with a notch that is smaller than the half of full width at half maximum of a test channel, and the part 13 identifies the maximum intensity of returned light from a brand optical fiber which is measured by a photodetector 11. The part 13 calculates a drift amount from the difference between the wavelength of the maximum intensity and the reference wavelength of a wavelength selective optical branch device which is preliminarily acquired as an initial condition in an optical pulse testing device 6. Thereby, it is possible to estimate the maximum transparent wavelength of each test channel by adding correctionally the drift amount to the initial condition of each test channel even to the test channel of the wavelength selective optical branch device under an optional temperature environment.

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 test apparatus, and more particularly to an optical pulse required for construction and maintenance of a PDS optical transmission system which is promising for economically constructing an optical access network. It relates to a test device.

[0002]

2. Description of the Related Art In the construction or maintenance of an optical fiber communication network, it is essential to conduct a test for each optical fiber core from the cable termination in a station to immediately before user equipment. This work includes an optical pulse test to determine the quality of the optical fiber cable during construction work, a facility fault isolation test to determine the fault between the communication equipment and the user equipment when a fault occurs, and a fault search test to identify the fault location Or periodic tests for the purpose of preventive maintenance of the working line.

At present, when an optical system is used in a user building or each home, one intra-station transmission device and a plurality of subscriber transmission devices are wavelength-independent, such as a star coupler, so that a video distribution service can be provided at low cost. PDS connecting with the type of optical branching device (P assive D ouble
( Star) Optical transmission systems are being developed.

[0004] This PDS optical transmission system is in a practical experiment stage, and a multimedia communication experiment is being carried out in some districts (“OPTICAL FIBER LINE”).
TEST AND MEASUREMENT SYSTE
M FOR PASSIVEDOUBLE STAR
NETWORKS AND WDM TRANSMIS
SION SYSTEMS ”, 44th IWCS P
rosedings, pp. 640-646).

In such a wavelength-independent type optical splitter, since the test light is equally distributed to each of the split optical fibers, a conventional PDS optical transmission system using a wavelength-independent type optical splitter is not available. In addition, the loss distribution of each branch optical fiber cannot be measured individually from the optical fiber before branching.
Only the length of each branch optical fiber is designed to be different, and based on the position information of the terminal reflected light from each branch optical fiber and its level change, whether the communication equipment is faulty or the user equipment is faulty Equipment failure determination is currently being performed. For this reason, in the conventional PDS optical transmission system using the wavelength-independent type optical splitter, not only the reliability of construction and maintenance is reduced, but also the degree of freedom in designing the PDS optical transmission system is limited. become.

In order to solve the above problems, a PDS optical transmission system in which one intra-station transmission device and a plurality of subscriber transmission devices are connected via a wavelength-selective optical splitter having wavelength dependency, and a test method therefor. Is being considered.

[0007] optical divider of this communication mode, the array waveguide grating made of silica glass waveguide (AWG; A r
rayed W aveguide G rating) configured optical splitter (hereinafter, referred to as AWG splitter.)
Is used. Since the transmission band port (channel) of this AWG branching device is periodically repeated, one of the
Using the period for the test wavelength band, a different test wavelength (test channel) can be assigned to each of the branch optical fibers. Therefore, by adjusting the wavelength of the test light output from the optical pulse test device to the target test wavelength,
Each branch optical fiber can be tested individually (see Japanese Patent Application No. 7-270025).

[0008]

However, in the above-mentioned PDS optical transmission system, there is a problem that the transmission band of the AWG splitter changes (hereinafter, referred to as drift) due to a temperature change. That is, when the AWG splitter is installed in an environment where the temperature changes (such as outdoors), a drift occurs in the test channel. Therefore, if the AWG splitter is used without performing the temperature control, the wavelength of the predetermined wavelength may be reduced. When the test light is output from the optical pulse test device, A
Due to the drift of the WG optical splitter, the effective transmission loss may increase even if the input is not input to a different channel or to a different test channel, and the loss distribution of the split optical fiber may not be measured.

In order to solve the above problem, a method has been proposed in which a test channel of an AWG optical branching device under an arbitrary temperature environment is detected in advance by an optical pulse tester, and an individual test of each branching optical fiber is performed. I have.

FIG. 8 is a diagram for explaining a conventional method for correcting a test channel drift of a PDS optical transmission system.

Hereinafter, a conventional method for correcting the drift of the test channel of the PDS optical transmission system will be described with reference to FIG.

In FIG. 1, reference numeral 1 denotes a single optical fiber;
, 2-n are branch optical fibers, 3 is a wavelength-selective optical splitter (AWG optical splitter), 4-1, 4-2,
, 4- (n-1) are optical bandpass filters, 5-1
5-2,..., 5- (n-1) are subscriber transmission devices, 6 is an optical pulse test device, 7 is test light input / output means, 8 is an intra-office transmission device, and 17 is a mirror.

As shown in FIG.
To one branch optical fiber (2-n) (hereinafter referred to as
It is called a reference channel. 2), a mirror 17 which has been subjected to a total reflection process is installed. Then, when the test light output from the optical pulse test device 6 is swept in the wavelength range including all of the test channels, the test light from the optical pulse test device 6 is reflected by the mirror 17 in the reference channel. The incoming reflected light is reflected relatively strongly in the reference channel.

By reading the wavelength of the reflected light, the maximum transmission wavelength of the reference channel under an arbitrary temperature condition can be measured. Here, since the interval between the test channels including the reference channel hardly changes due to the temperature change, if the reference channel at an arbitrary temperature can be detected, the reference channel branch optical fiber can be individually tested (particularly, No. 5-230266; optical branch line monitoring system.

However, in this test method,
Since one of the branch optical fibers is used as a reference port for drift monitoring and is subjected to total reflection processing, the number of communication channels is one.
As a result, the economical effect of the PDS optical transmission system is reduced. The reflected light generated from the reference channel is the PDS
There is a problem that the PDS optical transmission system needs to be designed in consideration of the influence on the intra-office transmission device because the optical transmission is accompanied by stronger reflection than other optical components constituting the optical transmission system.

The present invention has been made to solve the problems of the prior art, and an object of the present invention is to provide a PDS.
In a branch optical line test device used in an optical transmission system, even if a drift occurs in a test channel of a wavelength-selective optical splitter due to a temperature change in an outdoor environment or the like, each optical branch fiber is individually tested. It is to provide a technology that makes it possible.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0018]

SUMMARY OF THE INVENTION Among the inventions disclosed in the present application, the outline of a representative one will be briefly described.
It is as follows.

An intra-station transmission device, a wavelength-selective optical splitter for distributing communication light and test light of a plurality of different wavelengths to a plurality of different optical fibers according to the respective wavelengths, the intra-station transmission device and the wavelength selection device. A single optical fiber provided between the optical branching device and the optical fiber for transmitting the communication light and the test light, a plurality of subscriber transmission devices, and the wavelength-selective optical branching device and the plurality of subscriber transmission devices. What is claimed is: 1. A branch optical line test apparatus used in a PDS optical transmission system comprising a plurality of branch optical fibers provided therebetween, comprising: an optical pulse test apparatus that outputs test light; and a test light from the optical pulse test apparatus. An optical coupler for inputting / outputting the optical fiber to / from the one optical fiber, and an optical filter which is installed immediately before the plurality of subscriber transmission devices and cuts off the test light. Light A wavelength tunable light source that outputs test light in the entire wavelength range of the test wavelength band assigned to each of the optical fibers, and Rayleigh backscattered light from the branch optical fiber generated by the test light from the wavelength tunable light source, or the light. It has a light receiver for detecting the reflected light from the filter, and identification means for identifying a maximum transmission wavelength in a test wavelength band assigned to each of the branch optical fibers based on a detection result of the light receiver.

Further, the optical pulse test apparatus includes at least one test light source that outputs a broadband test light including all wavelengths of a test wavelength band allocated to each of the branch optical fibers; From the Rayleigh backscattered light from the branch optical fiber generated by the broadband test light from the test light source, or the reflected light from the optical filter, the wavelength within the test wavelength band assigned to each of the branch optical fibers A variable transmission wavelength optical bandpass filter for individually selecting and outputting a light, a light receiver for detecting transmitted light from the variable transmission wavelength optical bandpass filter, and the branch light based on a detection result of the light receiver. Within the test wavelength band assigned to each of the fibers,
Identification means for identifying the maximum transmission wavelength.

Further, the optical pulse test apparatus outputs at least one broadband test light including all wavelengths of a test wavelength band allocated to each of the branch optical fibers.
A transmission light source for individually selecting and outputting a wavelength within a test wavelength band assigned to each of the branch optical fibers from one test light source and a broadband test light output from the at least one test light source. Wavelength tunable optical bandpass filter, and a light receiver for detecting Rayleigh backscattered light from the branch optical fiber generated by test light from the transmission wavelength tunable optical bandpass filter, or reflected light from the optical filter, Based on the detection result of the light receiver,
Identification means for identifying a maximum transmission wavelength in a test wavelength band assigned to each of the branch optical fibers.

That is, in the present invention, in a PDS optical transmission system using a wavelength-selective optical splitter, a test channel drift caused by a temperature change of the wavelength-selective optical splitter is reduced by a Rayleigh from a specific branch optical fiber. By measuring the wavelength of the maximum intensity of the backscattered light or the reflected light from the optical filter, the test channels allocated to all the branch optical fibers are estimated, and the test wavelength light of the branch optical fiber to be tested is converted to an optical signal. Each of the branched optical fibers can be individually tested by outputting from a pulse test apparatus.

[0023]

Embodiments of the present invention will be described below in detail with reference to the drawings.

In all the drawings for describing the embodiments, those having the same functions are denoted by the same reference numerals, and their repeated description will be omitted.

[First Embodiment] FIG. 1 is a block diagram showing a schematic configuration of a PDS optical transmission system using a branch optical line test apparatus according to an embodiment of the present invention.

In the figure, 1 is a single optical fiber, 2-
, 2-n are branch optical fibers, 3 is a wavelength-selective optical splitter (AWG optical splitter), 4-1, 4-2,
.., 4-n are optical bandpass filters, 5-1, 5-2,
..., 5-n is a subscriber transmission device, 6 is an optical pulse test device,
Reference numeral 7 denotes a test light input / output unit, and reference numeral 8 denotes an intra-station transmission device.

Here, the intra-station transmission device 8 is an intra-station transmission device that transmits and receives using one or a plurality of different wavelengths of communication light. The wavelength-selective optical branching device 3 is a wavelength-selective optical branching device that distributes communication light and test light of a plurality of different wavelengths to a plurality of different branching optical fibers according to each wavelength, or one wavelength. Wavelength-selective optical splitter for equally distributing communication light to a plurality of different optical fibers and distributing communication light and test light of different wavelengths to a plurality of different branch optical fibers according to each wavelength. It is.

FIG. 2 shows a wavelength-selective optical splitter 3 shown in FIG.
6 is a graph showing the transmission spectrum of the test channel of FIG.

The number of branches is 14, and # 1, # 2,..., # 14
Represents a transmission channel assigned to each branch optical fiber. The full width at half maximum of the test channel is about 0.4 nm,
The spacing between each test channel is about 1 nm, and the insertion loss is on average about 7.5 dB.

FIG. 3 shows a wavelength-selective optical splitter 3 shown in FIG.
5 is a graph showing a relationship between a temperature and a test channel drift amount in FIG.

FIG. 3 shows the measured temperature characteristics of the first channel and the eighth channel. The drift amount of each channel is almost the same, and about 0.0149 per 1 ° C.
± 0.0006 nm.

FIG. 4 is a block diagram showing a schematic configuration of the optical pulse test apparatus 6 of the present embodiment.

In FIG. 1, reference numeral 9 denotes a variable wavelength light source, 10 denotes an acousto-optical switch, 11 denotes a light receiving element, 12 denotes a timing generator, 13 denotes a main control / identification unit, 14 denotes a light source drive circuit, and 15 denotes an adder. .

In the optical pulse test apparatus 6 shown in FIG.
The light source drive circuit 14 receives the control of the main control / identification unit 13 and drives the variable wavelength light source 9 by pulse modulation. The pulse test light output from the wavelength tunable light source 9 passes through the acousto-optic switch 10 which operates in synchronization with the pulse modulation drive of the light source drive circuit 14 by the timing generator 12. Here, the acousto-optic switch 10 switches between transmission and reception of the pulse test light and the return light generated thereby.

As described above, the pulse test light output from the optical pulse test apparatus 6 is incident on the single optical fiber 1 via the test light input / output means 7 and further transmitted by the wavelength-selective optical splitter 3. The light is distributed to the branch optical fibers (2-1 to 2-n) according to the wavelength of the pulse test light.

That is, the pulse test light that has selectively passed through the test channel of the wavelength-selective optical branching device 3 further propagates through the branch optical fibers (2-1 to 2-n) and is transmitted to the subscriber transmission device (5-). 1-5-n) are cut off by the optical band-pass filters (4-1 to 4-n) installed immediately before, and are also reflected as terminal reflected light at the same time. Along with the return light generated in (2-1 to 2-n), the light propagates backward along the same path as the pulse test light, returns to the optical pulse test device 6 again, and is received by the light receiving element 11. The received return light (Rayleigh backscattered light or terminal reflected light) is subjected to an addition process by an adder 15 operating in synchronization with the timing generation device 12, and the main control /
The OTDR waveform is displayed on a monitor in the identification unit 13.

Next, a method of estimating each test channel according to the present embodiment will be described. In the present embodiment, in order to estimate the test channel of the wavelength-selective optical splitter 3 as accurately as possible, the port (# 8) with the steepest channel loss change is used as the monitoring channel. The optical pulse test apparatus 6 acquires the initial conditions of the channel (# 8) at the specific temperature Tc.

That is, the reference wavelength of the test channel of the wavelength-selective optical splitter 3; λ8, the minimum insertion loss of the test channel port; Gc, the full width at half maximum of the test channel; Wc, the distance between the test channels; Δλ1, Δλ2. …, Δλ
(N−1) is acquired by the optical pulse test apparatus 6. Here, it is assumed that all test channels drift uniformly with changes in temperature.

The test channel assigned to each of the branch optical fibers (2-1 to 2-n) is a wavelength-selective optical branching device 3.
If the drift occurs due to the temperature change of the test channel (# 8), the wavelength tunable light source 9 controlled by the main control / identification unit 13 changes the test wavelength assigned to the reference channel (# 8) to half the full width at half maximum of the test channel (# 8). Pulse test light is output while changing the test wavelength in smaller increments, return light from the branch optical fiber generated by each is measured by the light receiving element 11, and the maximum intensity of the return light is determined by the main control / identification unit 13. Identify. From the difference between the wavelength of the maximum intensity at that time and the reference wavelength (λ8) of the wavelength-selective optical branching device 3 acquired in advance as the initial condition by the optical pulse test apparatus 6, the drift amount is determined by the main control / identification unit 13. (Δλt) is obtained.

Thus, the drift amount (Δλt) of the test channel of the wavelength-selective optical splitter 3 under an arbitrary temperature environment is also reduced by the initial condition of each test channel of the wavelength-selective optical splitter 3. Is corrected, the maximum transmission wavelength of each test channel can be estimated, so that the optical pulse test apparatus 6 outputs the test wavelength light of the target branch optical fiber (2-1 to 2-n). This makes it possible to individually test each of the branch optical fibers (2-1 to 2-n).

FIG. 5 is a graph showing a change in the intensity (OTDR waveform) of the backscattered light from the eighth branch optical fiber with a change in the temperature of the wavelength-selective optical splitter 3.

FIG. 5A shows the case where the temperature of the wavelength-selective optical branching device 3 is 25 ° C. and the test wavelength is 1648.1 nm.
5 shows a TDR waveform, which is the maximum transmission wavelength (reference wavelength) of the test light at 25 ° C. in the eighth branch optical fiber of the wavelength-selective optical branching device 3 of the present embodiment, and the wavelength selection at that time. The transmission loss (hereinafter, referred to as a level difference) of the optical splitter 3 was about 7 dB.

FIG. 5B shows a case where the temperature of the wavelength-selective optical branching device 3 is 40 ° C. and the test wavelength is 1648.1 nm, that is, the temperature of the wavelength-selective optical branching device 3 changes from 25 ° C. to 40 ° C. 10 shows the OTDR waveform after the change. This FIG. 5 (b)
It can be seen from FIG. 4 that the temperature of the wavelength-selective optical splitter 3 changes, thereby increasing the transmission loss of the wavelength-selective optical splitter 3 and changing (moving) the test channel from 1648.1 nm. The transmission loss at this time was about 11 dB.

FIG. 5C shows the OTD when the temperature of the wavelength-selective optical branching device 3 is 40 ° C. and the test wavelength is 1648.2 nm.
The R waveform is shown. FIG. 5C shows the OT when the reference wavelength is changed by only +0.1 nm in order to determine the drift direction of the test channel due to the temperature change.
It is a DR waveform. The transmission loss at that time was about 9 dB. At this time, since the level difference is decreasing,
It can be confirmed that the test channel drifts to the longer wavelength side.

FIG. 5D shows the OT when the temperature of the wavelength selective optical branching device 3 is 40 ° C. and the test wavelength is 1648.4 nm.
It shows a DR waveform. This FIG.
The operation of (c) was repeated to obtain a test wavelength at which the transmission loss was minimized, and a transmission loss of 7 dB similar to that at the reference wavelength was found at 1648.4 nm. That is, the temperature of the wavelength-selective optical branching device 3 is 25 ° C.
The test channel drift value Δλt due to the change from to 40 ° C. was about 0.3 nm.

As described above, according to the present embodiment, in the PDS optical transmission system in which the channel of the wavelength-selective optical splitter 3 drifts due to a temperature change in an outdoor environment or the like, a specific light pulse test apparatus 6 is used. By monitoring the drift of the test channel and correcting the initial condition of each test channel with the drift amount, each of the branch optical fibers (2-1 to 2-n) can be individually tested. This makes it possible to construct a PDS optical transmission system having a degree of freedom in design that is not restricted by temperature changes such as outdoors.

[Second Embodiment] FIG. 6 is a block diagram showing a schematic configuration of an optical pulse test apparatus 6 'of the present embodiment.

The present embodiment is the same as the first embodiment except that the optical pulse test device 6 in the first embodiment is replaced with an optical pulse test device 6 'shown in FIG.

In FIG. 6, 6 'is an optical pulse test apparatus,
9 'is a wide wavelength spectrum width light source, 10 is an acousto-optic switch, 11 is a light receiving element, 12 is a timing generator, 13
Is a main control / identification unit, 14 is a light source drive circuit, 15 is an adder, and 16 is an optical bandpass filter for wavelength selection.

In the optical pulse test apparatus 6 'shown in FIG. 6, the light source drive circuit 14 receives the control of the main control / identification unit 13 and drives the wide wavelength spectrum width light source 9' in a pulse modulation manner. The pulse test light output from the wide-wavelength spectral width light source 9 ′ passes through the acousto-optical switch 10 that operates in synchronization with the pulse modulation drive of the light source drive circuit 14 by the timing generator 12. Here, the acousto-optic switch 10 switches between transmission and reception of the pulse test light and the return light generated thereby.

In this way, the pulse test light output from the optical pulse test device 6 ′ is incident on the single optical fiber 1 via the test light input / output means 7, and is further transmitted by the wavelength-selective optical splitter 3. Are distributed to the branch optical fibers (2-1 to 2-n) according to the wavelength of the pulse test light.

That is, the pulse test light that has selectively passed through the test channel of the wavelength-selective optical splitter 3 further propagates through each of the branch optical fibers (2-1 to 2-n), and is transmitted to the subscriber transmission device (5). -1 to 5-n) are cut off by the optical bandpass filters (4-1 to 4-n) installed immediately before, and are simultaneously reflected as terminal reflected light, before which the single optical fiber 1 or the branch optical fiber Along with the return light generated in (2-1 to 2-n), the light propagates backward along the same path as the pulse test light, returns to the optical pulse test device 6 'again, and is received by the light receiving element 11.

Here, the return light returning to the optical pulse test device 6 'includes all the test wavelength spectra allocated to the branch optical fibers (2-1 to 2-n). Therefore, under the control of the main control / identification unit 13, the test wavelength of the target branch optical fiber (for example, # 8) is selected in the wavelength selection optical bandpass filter 16 and received by the light receiving element 11. The received return light is subjected to an addition process by an adder 15 synchronized with the timing generator 12, and the monitor in the main control / identification unit 13 performs OTD.
Display as an R waveform.

As described above, according to the present embodiment, each of the branched optical fibers (2-1 to 2-
A pulse test light including all of the test wavelengths assigned to n) is output, and under the control of the main control / identification unit 13, the wavelength selection light installed immediately before the light receiving element 11 of the optical pulse test device 6 '. The band-pass filter 16 is changed in steps smaller than half of the full width at half maximum of the test channel of the wavelength-selective optical splitter 3, and the return light of the test channel assigned to the specific branch optical fiber is measured by the light receiving element 11. The main control / identification unit 13 identifies the maximum intensity of the return light. The drift amount (Δλt) can be obtained from the difference between the test wavelength of the maximum intensity at that time and the reference wavelength of the test channel of the wavelength-selective optical branching device 3 previously grasped on the optical pulse test device 6 ′ side. .

As a result, the drift amount (Δλt) of the test channel of the wavelength-selective optical splitter 3 under an arbitrary temperature environment is also reduced by the initial condition of each test channel of the wavelength-selective optical splitter 3. , The maximum transmission wavelength of each test channel can be estimated, so that each of the branch optical fibers (2-1 to 2-n) is individually tested in the same manner as in the first embodiment. It becomes possible.

As described above, according to the present embodiment, in the PDS optical transmission system in which the channel of the wavelength-selective optical splitter 3 drifts due to a temperature change in an outdoor environment or the like, the optical pulse test apparatus 6 ′ By monitoring the drift of the test channel of (1) and correcting the initial condition of each test channel with the drift amount, each of the branch optical fibers (2-1 to 2-n) can be individually tested. This makes it possible to construct a PDS optical transmission system having a degree of freedom in design that is not restricted by temperature changes such as outdoors.

[Embodiment 3] FIG. 7 is a block diagram showing a schematic configuration of an optical pulse test apparatus 6 ″ of the present embodiment.

This embodiment is the same as the first embodiment except that the optical pulse test device 6 in the first embodiment is replaced with an optical pulse test device 6 ″ shown in FIG.

In FIG. 7, 6 ″ is an optical pulse tester, 9 ″ is a wide wavelength spectrum width light source, 10 is an acousto-optic switch, 11 is a light receiving element, 12 is a timing generator, and 13 is a main control / identification unit. , 14 are light source drive circuits, 15
Is an adder, and 16 is an optical bandpass filter for wavelength selection.

In the optical pulse test apparatus 6 ″ shown in FIG. 7, the light source drive circuit 14 receives the control of the main control / identification unit 13 and drives the wide wavelength spectrum width light source 9 ″ by pulse modulation. The test light output from the wide wavelength spectrum width light source 9 ″ includes all the test wavelength spectra assigned to the branch optical fibers (2-1 to 2-n). The pulse test light output from the wide-wavelength spectral width light source 9 ″ is passed through a wavelength selection optical bandpass filter 16 controlled by the main control / identification unit 13 to a specific branch optical fiber (for example, # 8). The test wavelength is selected, and passes through the acousto-optic switch 10 which operates in synchronization with the pulse modulation drive of the light source drive circuit 14 by the timing generator 12. Here, the acousto-optic switch 10 switches between transmission and reception of the pulse test light and the return light generated thereby.

In this way, the optical pulse test apparatus 6 ″
Is output to the single optical fiber 1 via the test light input / output means 7 and further branched by the wavelength-selective optical splitter 3 in accordance with the wavelength of the pulse test light. 2-1 to 2-n).

That is, the pulse test light that has selectively passed through the test channel of the wavelength-selective optical branching device 3 further propagates through the branch optical fibers (2-1 to 2-n) and is transmitted to the subscriber transmission device (5-). 1-5-n) are cut off by the optical band-pass filters (4-1 to 4-n) installed immediately before, and are simultaneously reflected as terminal reflected light. Along with the return light generated in -1 to 2-n), the light propagates backward along the same path as the pulse test light, returns to the optical pulse test device 6 ″ again, and is received by the light receiving element 11. The received return light (Rayleigh backscattered light or terminal reflected light) is subjected to an addition process by an adder 15 operating in synchronization with the timing generation device 12, and the main control /
It is displayed as an OTDR waveform on a monitor in the identification unit 13.

As described above, in the present embodiment, the specific optical fibers (2-1 to 2-1) are transmitted from the optical pulse test apparatus 6 ″.
2-n) selectively outputs the pulse test light of the test wavelength allocated to the test wavelength of the wavelength-selective optical branching device 3 under the control of the main control / identification unit 13. The return light of the test channel assigned to the specific branch optical fiber is measured by the light receiving element 11 and the maximum intensity of the return light is identified by the main control / identification unit 13. . The drift amount (△ λt) is obtained from the difference between the test wavelength of the maximum intensity at that time and the reference wavelength of the reference channel of the wavelength-selective optical splitter 3 previously grasped by the optical pulse test apparatus 6 ″.
Can be requested.

As a result, the drift amount (Δλt) of the test channel of the wavelength-selective optical splitter 3 under an arbitrary temperature environment is also reduced by the initial condition of each test channel of the wavelength-selective optical splitter 3. , The maximum transmission wavelength of each test channel can be estimated, so that each of the branch optical fibers (2-1 to 2-n) is individually tested in the same manner as in the first embodiment. It becomes possible.

As described above, according to the present embodiment, in the PDS optical transmission system in which the channel of the wavelength-selective optical splitter 3 drifts due to a temperature change in an outdoor environment or the like, the optical pulse test apparatus 6 ″ By monitoring the drift of a specific test channel and correcting the initial condition of each test channel with the drift amount, each of the branch optical fibers (2-1 to 2-n) can be individually tested. This makes it possible to construct a PDS optical transmission system having a degree of freedom in design that is not restricted by temperature changes such as outdoors.

[Embodiment 4] The present embodiment is directed to an optical band-pass filter (4-1) used in the first embodiment.
4 to n) is the same as that of the first embodiment except that the optical band-pass filter with a reflection function having a reflection intensity characteristic larger than that of ordinary Fresnel reflected light is replaced.

The reflected light generated by the optical band-pass filter having the reflection function returns to the light pulse test device 6 as normal Fresnel reflected light or reflected light stronger than the backscattered light. PDS not only can be expanded, but also has a long testable distance
When monitoring the channel drift of an optical transmission system,
Alternatively, it is effective as a means for reducing the averaging time required for monitoring.

As described above, in the present embodiment, the specific test of the PDS optical transmission system is performed in accordance with the procedure of the first embodiment while using the reflected light from the optical band-pass filter with the reflection function as the test light of the channel drift. By monitoring the drift of the channel and correcting the drift amount to the initial condition of each test channel, each of the branch optical fibers (2-1 to 2-
n) can be tested individually. As a result, a PDS having a degree of design freedom that is not restricted by temperature changes such as outdoors
It becomes possible to construct an optical transmission system.

As described above, the invention made by the present inventor is:
Although a specific description has been given based on the above-described embodiment, the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the gist of the invention.

[0070]

The effects obtained by typical ones of the inventions disclosed in the present application will be briefly described as follows.

(1) According to the present invention, one communication channel is sacrificed in a PDS optical transmission system in which a test channel of a wavelength-selective optical branching device changes forcefully due to a temperature change such as outdoors. Each branch optical fiber can be individually tested while detecting the test channel drift only by the optical pulse test apparatus.

(2) According to the present invention, it is possible to construct a PDS optical transmission system that is economical and has a degree of freedom in design that is not restricted by an external temperature environment.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a PDS optical transmission system using a branch optical line test apparatus according to an embodiment of the present invention.

FIG. 2 is a graph showing a transmission spectrum of a test channel of the wavelength-selective optical branching device shown in FIG.

FIG. 3 is a graph showing a relationship between a temperature and a test channel drift amount in the wavelength-selective optical branching device shown in FIG.

FIG. 4 is a block diagram illustrating a schematic configuration of the optical pulse test apparatus according to the first embodiment.

FIG. 5 shows the change in the intensity of the Rayleigh backscattered light from the eighth branch optical fiber (O
4 is a graph showing measured TDR waveforms.

FIG. 6 is a block diagram illustrating a schematic configuration of an optical pulse test apparatus according to a second embodiment.

FIG. 7 is a block diagram illustrating a schematic configuration of an optical pulse test apparatus according to a third embodiment.

FIG. 8 is a diagram for explaining a conventional method for correcting a test channel drift of a PDS optical transmission system.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Single optical fiber, 2-1 to 2-n ... Branch optical fiber, 3 ... Wavelength selective type optical splitter, 4-1 to 4-n ... Optical bandpass filter, 5-1 to 5-n ... Addition Transmission equipment,
6, 6 ', 6'': optical pulse test device, 7: test light input / output means, 8: intra-station transmission device, 9: variable wavelength light source, 9',
9 ″: wide wavelength spectrum width light source, 10: acousto-optic switch, 11: light receiving element, 12: timing generator, 1
3: Main control / identification unit, 14: Light source drive circuit, 15: Adder, 16: Optical bandpass filter for wavelength selection.

Claims (4)

[Claims] An intra-station transmission device, a wavelength-selective optical splitter for distributing communication light and test light of a plurality of different wavelengths to a plurality of different optical fibers according to respective wavelengths, and a plurality of subscriber transmission devices. A single optical fiber provided between the intra-station transmission device and the wavelength-selective optical splitter to propagate the communication light and the test light; and the wavelength-selective optical splitter and the plurality of subscriber transmission devices. A branch optical line test apparatus used in a PDS optical transmission system including a plurality of branch optical fibers provided between the optical pulse test apparatus, the optical pulse test apparatus outputting test light, and a test from the optical pulse test apparatus. An optical coupler that inputs and outputs light to and from the one optical fiber; and an optical filter that is installed immediately before the plurality of subscriber transmission devices and blocks the test light, the optical pulse test device includes: Split light A wavelength tunable light source that outputs test light in the entire wavelength range of the test wavelength band assigned to each of the fibers, a Rayleigh backscattered light from the branch optical fiber generated by the test light from the wavelength tunable light source, or the light A light receiver for detecting reflected light from a filter, and identification means for identifying a maximum transmission wavelength in a test wavelength band assigned to each of the branch optical fibers based on a detection result of the light receiver. A branch optical line test apparatus characterized by the above-mentioned. 2. An intra-station transmission device, a wavelength-selective optical splitter for distributing communication light and test light of a plurality of different wavelengths to a plurality of different optical fibers according to respective wavelengths, and a plurality of subscriber transmission devices. A single optical fiber provided between the intra-station transmission device and the wavelength-selective optical splitter to propagate the communication light and the test light; and the wavelength-selective optical splitter and the plurality of subscriber transmission devices. A branch optical line test apparatus used in a PDS optical transmission system including a plurality of branch optical fibers provided between the optical pulse test apparatus, the optical pulse test apparatus outputting test light, and a test from the optical pulse test apparatus. An optical coupler that inputs and outputs light to and from the one optical fiber; and an optical filter that is installed immediately before the plurality of subscriber transmission devices and blocks the test light, the optical pulse test device includes: Split light At least one test light source that outputs a broadband test light including all wavelengths of a test wavelength band assigned to each of the fibers, and the branch optical fiber generated by the broadband test light from the at least one test light source From the Rayleigh backscattered light from the optical filter or from the reflected light from the optical filter, a transmission wavelength tunable optical bandpass that individually selects and outputs wavelengths within a test wavelength band allocated to each of the branch optical fibers. A filter, and a photodetector for detecting transmitted light from the variable transmission wavelength optical bandpass filter, based on a detection result of the photodetector, among test wavelength bands assigned to each of the branch optical fibers, An apparatus for testing a branched optical line, comprising: identification means for identifying a transmission wavelength. 3. An intra-station transmission device, a wavelength-selective optical splitter for distributing communication light and test light of a plurality of different wavelengths to a plurality of different optical fibers according to each wavelength, and a plurality of subscriber transmission devices. A single optical fiber provided between the intra-station transmission device and the wavelength-selective optical splitter to propagate the communication light and the test light; and the wavelength-selective optical splitter and the plurality of subscriber transmission devices. A branch optical line test apparatus used in a PDS optical transmission system including a plurality of branch optical fibers provided between the optical pulse test apparatus, the optical pulse test apparatus outputting test light, and a test from the optical pulse test apparatus. An optical coupler that inputs and outputs light to and from the one optical fiber; and an optical filter that is installed immediately before the plurality of subscriber transmission devices and blocks the test light, the optical pulse test device includes: Split light At least one test light source that outputs a broadband test light including all wavelengths of a test wavelength band allocated to each of the fibers; and among the broadband test light output from the at least one test light source, A transmission wavelength tunable optical bandpass filter that individually selects and outputs a wavelength within a test wavelength band assigned to each of the branch optical fibers, and the test light generated by the test light from the transmission wavelength tunable optical bandpass filter. Rayleigh backscattered light from the branch optical fiber, or a photodetector that detects reflected light from the optical filter, based on the detection result of the photodetector, in a test wavelength band assigned to each of the branch optical fibers And an identification means for identifying the maximum transmission wavelength. 4. The optical filter according to claim 1, wherein the optical filter is an optical bandpass filter that transmits the communication light and blocks and reflects the test light. Branch optical line test equipment.