JPH09113413A - Branched light line with optical pulse-testing function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To individually test respective downstream-side optical fibers in a branched light line network by a method wherein a light branching means, an optical pulse testing means and a reflected light filter are provided, wavelength light, for communication, from the upstream side is passed to the downstream side, intrinsic wavelength light for maintenance is passed through optical fibers which are allocated individually in advance and light other than them is cut off. SOLUTION: Wavelength light, for maintenance, which is sent out from an optical pulse testing means 8 is incident on an upstream-side optical fiber 1 via a signal-light input/output means 9. Then, the light is distributed equally into (n) pieces of dowastream-side optical fibers 201 to 206 by a wavelength-independent light branching element 3. The wavelength of beams of branched wavelength light for maintenance is sorted by respective optical band-pass filters 501 to 506, and only the wavelength light which agrees with transmission bands of the filters 501 to 506 is passed. The light is reflected by an optical band-pass filter 60, with a reflection function, which is installed immediately in front of a subscriber terminal 701, it is changed into returned light together with light generated in an optical fiber 1 or the optical fiber 201, and it is propagated in a route in the reverse direction so as to be incident on the testing means 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a branched optical line having an optical pulse test function, and more particularly to an optical pulse test used for construction or maintenance of a branched optical line network for providing video distribution service at low cost. It relates to technology that is effective when applied.

[0002]

2. Description of the Related Art Conventionally, in constructing or maintaining an optical fiber communication network, it has been essential to carry out a test on an optical fiber unit basis from the cable termination in the station to immediately before the user equipment.

The above-mentioned tests include an optical pulse test for judging the quality of an optical fiber core wire during construction work, an equipment failure isolation test for isolating a communication equipment and a user equipment when a failure occurs, and a failure location is specified. There is a failure search test for this purpose, and a regular test for the purpose of preventive maintenance of the working line.

For a so-called single star configuration in which one intra-station transmission device and one subscriber terminal are connected by one optical fiber, a test method as shown in FIG. 9 is currently implemented.

In the test shown in FIG. 9, a test signal light (a signal light of a maintenance wavelength light) is sent from the optical pulse test apparatus 8 to the optical fiber 1 requiring the test through the signal light input / output means 9. Incident.

The incident test signal light is transmitted to the subscriber terminal 7
The optical bandpass filter 6 with a reflection function installed immediately before is reflected as terminal reflected light, and the backscattered light and the Fresnel reflected light generated in the optical fiber 1 are passed through the signal light input / output means 9 to be reflected again. Return to the pulse test equipment 8 and OTD
R (Optical Time Domain Ref
Lectometer) waveform.

At this time, an optical fiber coupler, a waveguide type directional coupler, or the like is used as the signal light input / output unit 9, or the optical fiber 1 is directly connected without using the signal light input / output unit 9. The test signal light enters from the end face.

Further, the optical pulse test apparatus for the single star configuration usually has a light source drive circuit 2 as shown in FIG.
Semiconductor laser 29 driven by pulse modulation under control of 8
And a light receiving element for transmitting pulse test signal light in synchronization with the light source drive circuit 28 and for receiving backscattered light, Fresnel reflected light and terminal reflected light (hereinafter, referred to as return light) generated by this pulsed light. And an acousto-optic switch 31 for guiding to 30.

As a light source for the test signal, an LD (Lesar) having the same wavelength as the communication wavelength light is used when the optical line is constructed.
A diode) light source is used, and an LD light source having a longer wavelength than the communication wavelength light is used so as not to affect the communication wavelength light during in-service.

As described above, in the single star configuration, one preset test signal light is sent from the semiconductor laser 29 of the optical pulse test apparatus 8 to the optical fiber 1, and the return caused by the signal light is returned. The light pulse test is performed by receiving light with the light receiving element 30 of the light pulse test apparatus 8.

On the other hand, in the case of so-called optical conversion, in which each user's building or home is connected by an optical fiber, from the viewpoint of providing a video distribution service or the like at a low cost, as shown in FIG. A line configuration is being considered in which the intra-station transmission device and a plurality of subscriber terminals are connected via a wavelength-independent branch optical line, and in some areas, a multi-line system using such a branch optical line network is being studied. Media communication experiments are being conducted.

However, as is apparent from FIG. 10, when the conventional test method for a single star configuration is applied to a wavelength-independent branch optical line network, the test signal light is wavelength-independent optical branching element 3. To n downstream optical fibers 20
1 to 206, the return light generated by the test signal light of each downstream optical fiber 201 to 206 is received by the light receiving section of the optical pulse test apparatus 8 at the same time. Downstream optical fibers 201-206
Since the return light from is overlapped, the return light cannot be individually distinguished and tested.

Therefore, at present, the downstream optical fiber 2
Focusing only on the change in the position information and the peak level of the terminal reflected light from the optical bandpass filters with reflection function 601 to 606 installed at the far ends of 01 to 206, the communication equipment and the user equipment at the time of failure occurrence We are isolating equipment failures.

[0014]

SUMMARY OF THE INVENTION As a result of studying the above prior art, the present inventor has found the following problems.

However, in the conventional branch optical line having the optical pulse test function, the downstream optical fibers 201 to 20 are provided.
If there is a downstream optical fiber with the same length in any of 6, the terminal reflected light from the optical bandpass filter with a reflection function of the downstream optical fiber with the same length will overlap, and even the isolation of equipment failure There was a problem that I could not do it.

Therefore, in order to prevent the terminal reflected lights from the optical bandpass filters with reflection function 601 to 606 from overlapping, all the downstream optical fibers 201 to 206 are installed when the downstream optical fibers 201 to 206 are laid. There was a problem that the laying work had to be done so that the 206 had different track lengths.

Further, each downstream optical fiber 201-206
There is a problem that the individual failure position search test of the downstream side optical fibers 201 to 206 cannot be performed because the return lights from the optical fibers overlap each other.

An object of the present invention is to provide a technique capable of individually testing each downstream optical fiber of a branch optical line network.

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

[0020]

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.

(1) One upstream optical fiber, a plurality of downstream optical fibers, optical branching means for connecting one end of the upstream optical fiber and one end of the downstream optical fiber, and the downstream A reflected light filter provided at the farthest end of the other end of the side optical fiber, and an optical pulse test means provided at the near end of the other end of the upstream optical fiber, wherein the optical branching means is , The wavelength light for communication included in the optical signal from the upstream is passed through the optical fiber on the downstream side, and the maintenance wavelength light peculiar to each optical fiber previously individually assigned to each of the optical fibers on the downstream side is supplied. Passes through the optical fiber and blocks all wavelengths for maintenance other than the specific wavelength for maintenance, and the reflected light filter passes the wavelength light for communication, for maintenance specific to the optical fiber on the downstream side. Blocks light of wavelengths and And, the light pulse testing means,
A branched optical line having an optical pulse test function that sequentially supplies the wavelength light for maintenance peculiar to the downstream optical fiber to be tested by switching one wavelength at a time and receives the returned light individually in sequence.

(2) The optical pulse test means of (1) above is
A wavelength tunable light source that individually generates maintenance wavelength light uniquely assigned to the downstream optical fiber, and light output from the wavelength tunable light source is incident on the upstream optical fiber,
A signal light input / output unit that guides the return light from the upstream optical fiber to the light receiving unit, and a light receiving unit that can receive a unique maintenance wavelength previously assigned to the optical fiber on the downstream side of the return light are provided.

(3) The optical pulse test means of (1) above is
At least one light source having a wavelength spectrum width that includes all of the maintenance wavelength light uniquely assigned to the downstream optical fiber, and the light output from the light source is incident on the upstream optical fiber, and the upstream light A signal light input / output unit that guides the return light from the fiber to the light receiving unit, and a light receiving unit that can receive the unique maintenance wavelength previously assigned to the optical fiber on the downstream side of the return light are provided.

(4) The optical pulse test means described in (1) to (3) performs the test after previously identifying the return light of the maintenance wavelength light uniquely assigned to the optical fiber on the downstream side.

(5) The optical branching means of (1) to (4) above allows the wavelength-independent light to pass through the downstream optical fiber without depending on the wavelength of the optical signal from the upstream optical fiber. Of the optical signals from the branching element and the optical fiber on the upstream side, the wavelength light for communication and the wavelength light for maintenance peculiarly assigned to the optical fiber are allowed to pass through, and the wavelength peculiar to the other downstream side optical fiber is peculiar to The maintenance wavelength light is composed of an optical bandpass filter that blocks all of the maintenance wavelength light.

(6) The optical branching means described in (1) to (4) above are peculiar maintenances assigned in advance to the wavelength light for communication and the optical fiber on the downstream side of the optical signal from the optical fiber on the upstream side. It is a wavelength-dependent optical branching element that allows the maintenance wavelength light to pass therethrough and blocks the maintenance wavelength light uniquely assigned to the other optical fiber on the downstream side.

According to the above-mentioned means (4) to (6), the wavelength of the maintenance wavelength light is assigned to each downstream optical fiber in advance, and the wavelength assigned to each downstream optical fiber by the optical branching means. Of the return light including the reflected light from the reflected light filter provided at the farthest end on the user side of the downstream side optical fiber by passing only the maintenance wavelength light and the communication wavelength light from the downstream side optical fiber Therefore, the downstream optical fiber can be tested even if the wavelength assigned to the downstream optical fiber on the optical pulse testing means side is not accurately grasped in advance.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings together with embodiments (examples) of the invention.

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

(Embodiment 1) FIG. 1 is a block diagram showing a schematic configuration of a branched optical line having an optical pulse test function of Embodiment 1 of the present invention, in which 1 is an upstream optical fiber and 20 is an optical fiber.
1 to 206 are downstream side optical fibers, 3 is a wavelength independent optical branching element (optical branching means), 501 to 506 are optical bandpass filters, 601 to 606 are optical bandpass filters with reflection function (reflected light filters), 7 is a subscriber terminal, 8 is an optical pulse test means, and 9 is a signal light input / output means.

FIG. 2 shows the optical pulse test means 8 of the first embodiment.
Is a block diagram showing a schematic configuration of 10 is a variable wavelength light source, 11 is an optical amplifier, 12 and 13 are acousto-optic switches, 14 is a light receiving element (light receiving section), 15 is a timing generator, and 18 is main control / identification. Reference numeral 28 denotes a light source drive circuit.

In FIG. 2, the wavelength variable light source 10 is a well-known wavelength variable LD, and the wavelength (frequency) of the output light can be changed by pulse-modulating the drive signal for driving the LD.

The optical amplifier 11 is a known optical amplifier,
The input light is amplified by a predetermined amplification factor and output.

The acousto-optic switch 12 is a well-known acousto-optic switch, and has maintenance wavelength light (pulse test signal light).
During the time when no light is being sent, the return light is received by suppressing the noise light (spontaneous emission light) from the optical amplifier 11 that is input to the downstream optical fibers 201 to 206 (measured optical fibers) that have been measured. The decrease of the S / N ratio at the time is suppressed.

The acousto-optic switch 13 is a known acousto-optic switch, and switches transmission / reception of maintenance wavelength light and return light generated by the maintenance wavelength light.

The light receiving element 14 is, for example, an APD (Av
It is a well-known optical conversion element such as alanche Photo Diode, and converts received light into an electric current.

The timing generator 15 is a well-known pulse generator that generates a pulse signal having a predetermined cycle, and operates the acousto-optic switches 12, 13 and the light source drive circuit 28 based on the signal output from the timing generator 15. By operating the acousto-optic switches 12 and 13, the light source drive circuit 28 is synchronized.

The main controller / identifier 18 includes a light source drive circuit 28.
And the wavelength of the peculiar maintenance wavelength light assigned to the downstream optical fibers 201 to 206 is identified from the return light received by the light receiving element 14.

The light source drive circuit 28 comprises a well-known pulse modulation circuit, and outputs a signal synchronized with the signal output from the timing generator 15.

FIG. 3 is a diagram showing the light transmission characteristics of the optical bandpass filters 501 to 506 of the first embodiment.
(Thin line) is the light transmission characteristic of the optical bandpass filter 501,
512 (thick line) is the light transmission characteristic of the optical bandpass filter 502, and 513 (thick line) is the optical bandpass filter 503.
2 shows the light transmission characteristics thereof.

As is apparent from FIG. 3, for example, the light transmission characteristics 511 of the optical bandpass filter 501 are as follows: the wavelength λs of the wavelength light for communication and the wavelength maintenance light pre-allocated to the downstream optical fiber 201. The optical bandpass filter 501 has a wavelength of λs because the transmittance is large around the wavelength λ1 and is low in other wavelength regions.
The communication wavelength light and the maintenance wavelength light having the wavelength λ1 are selectively transmitted, and the other maintenance wavelength light having the wavelengths λ2 to λn are blocked.

Similarly, the optical bandpass filter 502 selectively transmits the wavelength light for communication having the wavelength λs and the wavelength light for maintenance having the wavelength λ2, and transmits the wavelength light for maintenance having other wavelengths λ1 and λ3 to λn. Shut off.

The wavelength λn is the maintenance wavelength light assigned to the n-th downstream optical fiber 206.

Further, this characteristic shown in FIG.
It is known that the transmission characteristics can be accurately designed and produced by the fiber grating using the photochromic effect.

Next, the operation of the branched optical line having the optical pulse test function according to the first embodiment will be described with reference to FIGS. 1 and 2. For example, the variable wavelength light source pulse-modulated by the light source drive circuit 28 is driven. When maintenance wavelength light of wavelength λ1 is output from 10, the output maintenance wavelength light is amplified by the optical amplifier 11 and then is synchronized with the maintenance wavelength light by the acousto-optic switch 12 and the acoustic It passes through the optical switch 13.

The maintenance wavelength light that has passed through the acousto-optic switch 13, that is, sent from the optical pulse test means 8 is first made incident on the upstream optical fiber 1 via the signal light input / output means 9.

Next, the wavelength-independent light for maintenance is processed by the wavelength-independent optical branching element 3 regardless of its wavelength, n (however,
(n is a natural number) is distributed substantially evenly to the downstream optical fibers 201 to 206.

The maintenance wavelength light, which is substantially evenly distributed to the downstream optical fibers 201 to 206, is supplied to the downstream optical fibers 20.
The wavelengths are selected by the optical bandpass filters 501 to 506 installed in the optical bandpass filters 1 to 206, respectively, and only the maintenance wavelength light that matches the transmission band of the optical bandpass filters 501 to 506 can pass.

The maintenance wavelength light having the wavelength λ1 is selectively transmitted through the optical bandpass filter 501, and the optical bandpass filter 60 with a reflection function is installed immediately before the subscriber terminal 701.
At the same time as being blocked by 1, the light reflected by the terminal is reflected light, and the light generated in the upstream optical fiber 1 or the downstream optical fiber 201 due to the incidence of the maintenance wavelength light is returned along with the same path as the maintenance wavelength light as return light. The light propagates in the opposite direction, enters the optical pulse test means 8, and is received by the light receiving element 14.

By performing the above-described test on the other downstream optical fibers 202 to 206, it is possible to test all the downstream optical fibers 201 to 206.

Further, in the optical pulse test means 8, even if the wavelengths assigned to the downstream optical fibers 201 to 206 are unknown, the downstream optical fiber 20
In the wavelength range including all the wavelengths assigned to Nos. 1 to 206, the optical bandpass filters 501 to 5 from the wavelength variable light source 10 controlled by the main control / identification unit 18
The total amount of return light generated by outputting the maintenance wavelength light by changing it by a step smaller than half the full width at half maximum of the transmission band of 06, or the downstream optical fibers 201 to 206.
The terminal reflected light reflected by the optical bandpass filters with reflection function 601 to 606 installed at the farthest end of the
When the main control / identification unit 18 determines the maximum value of the received light, the downstream optical fibers 201 to 201
The wavelength of the peculiar maintenance wavelength light assigned to 206 can be identified.

By the method described above, the downstream optical fiber 2
After specifying the maintenance wavelength lights assigned to 01 to 206, the downstream optical fibers 201 to 206 are tested again to obtain the downstream optical fibers 201 to 206.
206 tests can be performed.

FIG. 4 shows the results of observation of OTDR waveforms of the conventional branch line having the optical pulse test function and the branch optical line having the optical pulse test function of the first embodiment when the number of branches is three. It is a figure and (a) is O of the conventional branch optical line.
TDR waveform, (b) is the branch optical line of the first embodiment,
The OTDR waveform by the return light of the first downstream optical fiber, (c) is the OTDR waveform by the return light of the second downstream optical fiber in the branch optical line of the first embodiment, (d)
3 shows an OTDR waveform due to the return light of the third downstream side optical fiber in the branched optical line of the first embodiment.

In FIG. 4, 401 (thick line) is the OTDR waveform of the conventional branch line, and 402 (thin line) is the first embodiment.
OTDR waveform of the return light of the first downstream optical fiber of the branch optical line of 403, OTDR of the return light of the second downstream optical fiber of the branch optical line of 403 (middle thick line)
A waveform 404 (dotted line) is the OTDR due to the return light of the third downstream optical fiber in the branch optical line of the first embodiment.
The waveform is shown.

As is apparent from FIG. 4, in the conventional branched optical line having the optical pulse test function, due to the structure of the branched optical line, the wavelength-independent branching optical element is used for maintenance on each downstream side optical fiber after branching. Since the wavelength light is not allocated and the maintenance wavelength light is distributed almost uniformly to each downstream optical fiber, the return light generated in each downstream optical fiber is simultaneously transmitted to the light receiving element of the optical pulse test means. The light is received.

That is, as shown by the OTDR waveform 401, since the backscattered light generated in each downstream optical fiber, the Fresnel reflected light, and the terminal reflected light are combined waveforms, the connection position, the connection loss, the Fresnel reflection amount, or The terminal reflection amount and terminal position from the optical filter with reflection function installed at the farthest end of each downstream optical fiber are not clear, and accurate line information cannot be obtained for the downstream optical fiber after branching.

On the other hand, in the branch line of the first embodiment, as shown in FIG.
As shown in (b) to (d), the optical bandpass filter installed in each downstream optical fiber allocates the maintenance wavelength light to each downstream optical fiber after branching, and also performs the optical pulse test. Since the means can set the wavelength of the output light according to the maintenance wavelength light assigned to the downstream optical fiber,
The downstream optical fiber to be tested can be individually tested.

Therefore, the same construction and maintenance as the conventional single star optical line can be performed.

(Embodiment 2) FIG. 5 is a block diagram showing a schematic configuration of an optical pulse test means 8 of a branched optical line having an optical pulse test function of Embodiment 2 of the present invention, and 16 is a wide wavelength spectrum. A width light source, 17 is an optical bandpass filter for wavelength selection.

The wide wavelength spectrum width light source 16 outputs light including all wavelength regions of the wavelength of the maintenance wavelength light assigned to the downstream side optical fibers 201 to 206.

The wavelength selection optical bandpass filter 17 comprises:
It is provided between the acousto-optic switch 13 and the light receiving element 14, and makes a selection for causing the light receiving element 14 to receive only the return light of a predetermined wavelength among the return light of the downstream optical fibers 201 to 206.

The selection wavelength is determined based on the output of the main controller / identifier 18.

Next, referring to FIG. 5, the operation of the branched optical line having the optical pulse test function of the second embodiment will be described. Output from the wide wavelength spectrum width light source 16 pulse-modulated and driven by the light source drive circuit 28. The maintenance wavelength light is amplified by the optical amplifier 11, and then passes through the acousto-optic switch 12 and the acousto-optic switch 13 synchronized with the maintenance wavelength light.

The maintenance wavelength light that has passed through the acousto-optic switch 13, that is, sent from the optical pulse test means 8 is first made incident on the upstream optical fiber 1 via the signal light input / output means 9.

Next, the maintenance wavelength light is transmitted by the wavelength-independent optical branching element 3 regardless of the wavelength, n (however,
(n is a natural number) is distributed substantially evenly to the downstream optical fibers 201 to 206.

The maintenance wavelength light distributed almost evenly to the downstream optical fibers 201 to 206 is the downstream optical fiber 20.
The wavelengths are selected by the optical bandpass filters 501 to 506 installed in the optical bandpass filters 1 to 206, respectively, and only the maintenance wavelength light that matches the transmission band of the optical bandpass filters 501 to 506 can pass.

The maintenance wavelength light transmitted through the optical bandpass filters 501 to 506 is provided with an optical bandpass filter 601 with a reflection function installed immediately before the subscriber terminals 701 to 706.
At the same time as being blocked by ˜606, it is reflected as terminal reflected light and is generated as a return light together with the light generated in the upstream side optical fiber 1 or the downstream side optical fibers 201 to 206 by the incidence of the maintenance wavelength light, and the maintenance wavelength light. The light propagates through the same path in the opposite direction and enters the optical pulse test means 8.

At this time, the return light incident on the optical pulse test means 8 has a wavelength spectrum including all the maintenance wavelength lights of different downstream optical fibers 201 to 206, that is, all the downstream optical fibers 201 to 206. It contains track information of.

Therefore, the downstream side optical fiber 2 to be tested is selected by the wavelength selecting optical bandpass filter 17.
By selecting the maintenance wavelength lights 01 to 206 and causing the light receiving element 14 to receive the light, it is possible to test the downstream optical fiber for which the test is desired.

On the other hand, as in the case of the above-described first embodiment, even if the wavelengths assigned to the downstream optical fibers 201 to 206 are unknown, the main control / identification unit 18
By changing the wavelength selection optical bandpass filter 17 in steps smaller than half the full width at half maximum of the transmission band of the optical bandpass filters 501 to 506, the total amount of return light received correspondingly, Alternatively, the terminal reflected light reflected by the optical bandpass filters with reflection function 601 to 606 installed at the farthest ends of the downstream optical fibers 201 to 206 is received by the light receiving element 14, and the maximum value of the received light is detected. Since the main control / identification unit 18 makes the determination, it is possible to identify the wavelength of the peculiar maintenance wavelength light assigned to the downstream optical fibers 201 to 206.

By the method described above, the downstream optical fiber 2
After specifying the maintenance wavelength lights assigned to 01 to 206, the downstream optical fibers 201 to 206 are tested again to obtain the downstream optical fibers 201 to 206.
206 tests can be performed.

FIG. 6 shows the wavelength spectrum of the return light generated by the maintenance wavelength light obtained from the wide wavelength spectrum width light source 16, and the wavelength selection optical bandpass filter 17 from the wavelength spectrum.
It is a figure which shows the wavelength transmission spectrum of the return light selectively permeate | transmitted by 65, (thin line) is the return light of the downstream optical fibers 201-206 produced by the maintenance wavelength light obtained from the wide wavelength spectrum light source 16. 61 is return light 65
From the downstream optical fiber 20 selected by the wavelength selection optical bandpass filter 17 and received by the light receiving element 14.
1 return light, 62 is selected from the return light 65 by the wavelength selection optical bandpass filter 17, and is returned light of the downstream optical fiber 202 received by the light receiving element 14, 63 is a wavelength selection optical band from the return light 65. The return light of the downstream optical fiber 203 which is selected by the pass filter 17 and is received by the light receiving element 14, 64 is selected from the return light 65 by the wavelength selection optical bandpass filter 17, and the light receiving element 1
4 shows the return light of the n-th downstream optical fiber 206 received.

In FIG. 6, the central wavelengths of the return lights 61 to 64 selected by the wavelength selecting optical bandpass filter 17 are λ1, λ2, λ3, ..., λn, respectively, in order, and the downstream optical fibers 201 to 206. Coincides with the wavelength of the maintenance wavelength light assigned in advance.

According to the optical pulse test means 8 of the second embodiment described above, for example, the transmission band of the wavelength selection bandpass filter 17 is as wide as the transmission band of the wavelength-independent optical branching element 3 in advance. By ensuring the above, fading noise that occurs when a light source with a narrow spectral line width is used as a light source for maintenance wavelength light can be suppressed to a small level.

(Third Embodiment) FIG. 7 is a block diagram showing a schematic structure of a branch optical line having an optical pulse test function according to a third embodiment of the present invention, and 4 is a wavelength-dependent optical branch element.

In FIG. 7, the wavelength-dependent optical branching element 4 comprises an upstream optical fiber 1 and downstream optical fibers 201-206.
Connect.

FIG. 8 is a diagram showing an example of the structure of a wavelength-dependent optical branching element, 19 is a wavelength optical input fiber for maintenance, and 20 is a wavelength optical input fiber for maintenance.
Is WDM (Wavelength Division)
(Multiplex) coupler, 21 is an arrayed waveguide diffraction grating, 22 is a communication wavelength light input waveguide, 23 is a signal light output waveguide, 24 is a maintenance wavelength light input waveguide, 25 is a slab waveguide, and 26 is a dielectric. Multilayer filter, 27 is 1/4
A wave plate is shown.

The wavelength-dependent optical branching device 4 shown in FIG. 8 communicates the wavelength light for communication input from the upstream optical fiber 1 by the WDM coupler 20 connected to the upstream optical fiber 1 and having wavelength dependency. After being guided to the optical wavelength optical input waveguide 22 and developed in the lateral direction of the paper by the slab waveguide 25, the n optical signals are equally distributed to the n optical signal output waveguides 23 and are connected to the optical signal output waveguides 23. Downstream optical fiber 201-
The wavelength light for communication is output to 206.

On the other hand, the maintenance wavelength light input from the upstream optical fiber 1 is guided to the maintenance wavelength light input fiber 19 via the WDM coupler 20 having wavelength dependency, and further, the maintenance wavelength light input guide. After being guided to the waveguide 24 and developed in the lateral direction of the drawing by the slab waveguide 25, it is distributed to the arrayed waveguide diffraction grating 21 arranged in parallel.

The maintenance wavelength light distributed to the arrayed waveguide diffraction grating 21 is reflected by the dielectric multilayer film filter 26, and again returns to the slab waveguide 25 via the same arrayed waveguide diffraction grating 21.

At this time, the arrayed waveguide diffraction grating 21 is
By designing the optical path lengths so that they are different at equal intervals, the maintenance wavelength light causes a phase shift in the arrayed waveguide diffraction grating 21 by the difference in optical path length. Causes interference of multiple light beams.

As a result, the position where the light is focused changes depending on the wavelength of the maintenance wavelength light (hereinafter referred to as the wavelength-dependent optical branching element 4).
Is called an optical branching device with wavelength routing function).

The quarter-wave plate 27 is provided to eliminate the wavelength shift due to the polarization dependence of the maintenance wavelength light.

In the case of an intra-station branch type branch optical line network in which the wavelength-dependent optical branching element 4 is installed near the signal light input / output means 9, the signal light input / output means 9 is connected to the WDM coupler 20. Can be replaced with

For details of the optical branching device with wavelength routing function, see "Silica-based arrayed-wavegu
ide grating circuit as optical splitter / router, Ele
ctronics Letters, Vol.3, No.9, pp.726-729, April 199
See section 5.

Next, the operation of the branched optical line having the optical pulse test function according to the third embodiment will be described with reference to FIGS. 7 and 8. For example, from the optical pulse test means 8 to the wavelength λ.
When the maintenance wavelength light of No. 1 is output, the output maintenance wavelength light is first incident on the upstream optical fiber 1 via the signal light input / output unit 9.

Next, the wavelength-dependent optical branching element 4 selects the wavelength of the maintenance wavelength light having the wavelength λ1 and the pre-allocated wavelength of the maintenance wavelength light enters the downstream optical fiber 201 having the wavelength λ1. Downstream optical fiber 20
The maintenance wavelength light incident on the first optical fiber 1 is provided with an optical bandpass filter 601 with a reflection function installed immediately before the subscriber terminal 701.
At the same time as being blocked by the light source, the light reflected by the terminal and reflected by the maintenance wavelength light is returned along with the light generated in the upstream optical fiber 1 or the downstream optical fiber 201 by the incidence of the maintenance wavelength light, and the same path as the maintenance wavelength light is reversed. The light propagates in the direction, enters the optical pulse test means 8, and is received by the light receiving element 14.

By performing the above-described test on the other downstream optical fibers 202 to 206, it is possible to test all the downstream optical fibers 201 to 206.

As described above, in the branched optical line having the optical pulse test function of the third embodiment, the arrayed-waveguide diffraction grating 25 and the slab waveguide 21 realize the multi-beam interference phenomenon, and the optical wavelength router. Since the maintenance wavelength light is distributed as described above, there is an effect that the structural distribution loss due to the wavelength-independent optical branching element 3 generated in the first and second embodiments can be eliminated.

Further, since the output of the wavelength light for maintenance can be reduced by eliminating the distribution loss by the wavelength-independent optical branching element 3, it is possible to reduce the optical output during the test in the construction and maintenance of the branched optical line network. A sufficient dynamic range of the pulse test means 8 and the like can be secured.

Although the number of subscriber terminals 7 (the number of subscribers) is 6 in the drawings showing the first to third embodiments, the number of subscriber terminals 7 is not limited to this, and FIGS. , Figure 1
As is clear from 0, it goes without saying that the number of subscribers may be 1 or more.

As described above, the invention made by the present inventor is
Although specifically described based on the embodiments of the present invention, the present invention is not limited to the embodiments of the present invention, and it is needless to say that various modifications can be made without departing from the gist of the present invention. .

[0093]

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

Since the downstream optical fiber can be identified from the wavelength of the return light, the downstream optical fiber can be identified even if the wavelength assigned to the optical fiber on the downstream side is not accurately grasped in advance by the optical pulse test means. Fiber testing can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a branched optical line having an optical pulse test function according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a schematic configuration of an optical pulse test means according to the first embodiment.

FIG. 3 is a diagram showing light transmission characteristics of the optical bandpass filter according to the first embodiment.

FIG. 4 is a diagram showing an observation result of OTDR waveforms of a branch line having a conventional optical pulse test function and a branch optical line having an optical pulse test function of the first embodiment when the number of branches is three. .

FIG. 5 is a block diagram showing a schematic configuration of an optical pulse test means for a branched optical line having an optical pulse test function according to a second embodiment of the present invention.

FIG. 6 shows a wavelength spectrum of return light generated by maintenance wavelength light obtained from a wide wavelength spectrum light source, and a wavelength transmission spectrum of return light selectively transmitted by the wavelength selection optical bandpass filter. It is a figure.

FIG. 7 is a block diagram showing a schematic configuration of a branched optical line having an optical pulse test function according to a third embodiment of the present invention.

FIG. 8 is a diagram showing a configuration example of a wavelength-dependent optical branching device.

FIG. 9 is a block diagram showing a schematic configuration of a branched optical line having an optical pulse test function of a single star configuration.

FIG. 10 is a block diagram showing a schematic configuration of a conventional branched optical line having an optical pulse test function.

FIG. 11 is a block diagram showing a schematic configuration of a conventional optical pulse test means.

[Explanation of symbols]

1 ... Upstream optical fiber, 3 ... Wavelength-independent optical branching element,
4 ... Wavelength-dependent optical branching element, 7 ... Subscriber terminal, 8 ... Optical pulse test means, 9 ... Signal light input / output means, 10 ... Wavelength variable light source, 11 ... Optical amplifier, 12, 13 ... Acousto-optic switch, 14 , 30 ... Light receiving element, 15 ... Timing generator, 16 ... Wide wavelength spectrum width light source, 17 ... Wavelength selection optical bandpass filter, 18 ... Main control / identification section, 19 ...
Wavelength optical input fiber for maintenance, 20 ... WDM coupler, 21
Array waveguide diffraction grating, 22 ... Communication wavelength light input waveguide, 23 ... Signal light output waveguide, 24 ... Maintenance wavelength light input waveguide, 25 ... Slab waveguide, 26 ... Dielectric multilayer film filter, 27 ... quarter wave plate, 28 ... light source drive circuit, 29
... Semiconductor laser, 201-206 ... Downstream optical fiber,
501-506 ... Optical bandpass filter, 601-60
6 ... Optical bandpass filter with reflection function.

Claims (6)

[Claims] 1. An upstream optical fiber, a plurality of downstream optical fibers, an optical branching unit connecting one end of the upstream optical fiber and one end of the downstream optical fiber, and the downstream side. A reflected light filter provided at the farthest end portion of the other end of the optical fiber, and an optical pulse test means provided at the near end portion of the other end of the upstream optical fiber, the optical branching means, The wavelength light for communication included in the optical signal from the upstream is passed through the downstream optical fiber, and the maintenance wavelength light peculiar to each optical fiber individually assigned to each of the downstream optical fibers corresponds to the downstream light. The wavelength of light for maintenance other than the wavelength of light for maintenance unique to the fiber is blocked, and the reflected light filter allows the wavelength of light for communication to pass, and the wavelength of maintenance light unique to the downstream optical fiber. Block and reflect, before The optical pulse test means sets the maintenance wavelength light peculiar to the downstream optical fiber to be tested to 1
A branched optical line having an optical pulse test function, characterized in that the light is sequentially switched and supplied for each wavelength, and the returned light is sequentially received individually. 2. The tunable light source for individually generating wavelength light for maintenance, which is uniquely assigned to the downstream side optical fiber, and the light output from the tunable light source for the upstream side light source. A signal light input / output unit that guides the return light from the upstream side optical fiber to the light receiving section by making it enter the fiber, and a light receiving section that receives the unique maintenance wavelength of the return light previously assigned to the downstream side optical fiber. The branched optical line having the optical pulse test function according to claim 1, further comprising: 3. The optical pulse test means includes at least one light source having a wavelength spectrum width including all the maintenance wavelength lights uniquely assigned to the downstream optical fiber, and the light output from the light source to the upstream side. Signal light input / output means for guiding the return light from the upstream side optical fiber to the light receiving part and receiving light for receiving a unique maintenance wavelength previously assigned to the downstream side optical fiber of the return light. A branch optical line having an optical pulse test function according to claim 1, further comprising: 4. The optical pulse test means performs the test after previously identifying the return light of the maintenance wavelength light uniquely assigned to the downstream optical fiber. A branched optical line having the optical pulse test function according to any one of 1. 5. The wavelength-independent optical branching element, which allows the optical branching means to pass through the downstream optical fiber without depending on the wavelength of the optical signal from the upstream optical fiber, and the upstream optical fiber. From among the optical signals from the above, the communication wavelength light and the peculiar maintenance wavelength light pre-allocated to the optical fiber are allowed to pass, and all the peculiar maintenance wavelength light pre-allocated to the other downstream optical fibers are blocked. 2. An optical bandpass filter for
A branched optical line having the optical pulse test function according to claim 4. 6. The optical branching unit allows, among the optical signals from the upstream optical fiber, the wavelength light for communication and the wavelength light for maintenance unique to the downstream optical fiber to pass therethrough, and The optical pulse test function according to any one of claims 1 to 4, characterized in that the optical pulse test function is a wavelength-dependent optical branching element that blocks a wavelength for maintenance specific to a downstream optical fiber in advance. A branch optical line having.