JPH06268600A - Duplex optical repeater - Google Patents

Abstract

PURPOSE:To simplify the configuration of the duplex optical repeater. CONSTITUTION:The system employing the duplex optical repeaters has directional photocouplers 11, 12 connecting respectively to optical fiber transmission lines 15, 16 and optical amplifiers 13, 14 connected in a mutually opposite direction between the directional photocouplers 11, 12. The directional photocoupler 11 passes an optical signal proceeding to the optical amplifier 13 from the optical fiber transmission line 15 and the optical signal proceeding to the optical fiber transmission line 15 from the optical amplifier 14. Moreover, the directional photocoupler 12 passes an optical signal proceeding to the optical amplifier 14 from the optical fiber transmission line 16 and the optical signal proceeding to the optical fiber transmission line 16 from the optical amplifier 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bidirectional optical repeater, and more particularly to a bidirectional optical repeater used for optical bidirectional communication using a single optical fiber transmission line.

[0002]

2. Description of the Related Art A bidirectional optical repeater is a repeater transmission device for directly amplifying an optical signal attenuated by propagating through an optical fiber transmission line in bidirectional optical communication. A conventional bidirectional optical repeater is shown in FIG. This bidirectional optical repeater has an upstream optical amplifier 61, a downstream optical amplifier 62, optical isolators 63 and 64 that propagate light only in one direction, and optical couplers 65 and 66.

An optical signal traveling from the optical fiber transmission line 67 to the optical fiber transmission line 68 enters the optical coupler 65. The optical coupler 65 guides the incident light to the optical amplifier 61 and the optical isolator 64. However, the optical isolator 64 blocks the optical signal going to the amplifier 62. Therefore, the optical signal incident on the optical coupler 65 is eventually guided only to the optical amplifier 61. The optical amplifier 61 directly amplifies the input optical signal and outputs it to the optical isolator 63. Optical isolator 6
3 passes only the optical signal from the optical amplifier 61 to the optical coupler 66. Therefore, the optical signal output from the optical amplifier 61 is emitted to the optical fiber transmission line 68 via the optical isolator 63 and the optical coupler 66.

An optical signal traveling from the optical fiber transmission line 68 to the optical fiber transmission line 67 enters the optical coupler 66. The optical coupler 66 guides the incident light to the optical amplifier 62 and the optical isolator 63. Again, the optical isolator 63
Block the optical signal going to the amplifier 61. Optical amplifier 6
2 is an optical isolator 6 which directly amplifies the input optical signal.
Output to 4. The optical isolator 64 passes only the optical signal from the optical amplifier 62 to the optical coupler 65. Therefore, the optical signal output from the optical amplifier 62 is output to the optical fiber transmission line 67 via the optical isolator 64 and the optical coupler 65. Such a bidirectional optical repeater is disclosed in Japanese Patent Application Laid-Open No. 4-23628.

By the way, in an optical transmission line equipped with such a bidirectional optical repeater, an OTDR (Optical Time Domain Reflecti
on) By making measurements, fault points can be located over the entire line. Because the optical fiber transmission line 67
This is because the backscattered light generated by the OTDR measurement optical pulse traveling from the optical fiber transmission line 68 to the optical fiber transmission line 68 propagates from the optical fiber transmission line 68 to the optical fiber transmission line 67 as it is. For example, in the optical transmission line shown in FIG.
When an optical pulse for OTDR measurement that is directed in the direction is incident,
Backscattered light traveling in the direction of arrow B is observed. The time distribution of this backscattered light is shown in FIG. 7 when there is no obstacle in the optical transmission line.
As shown in (b). That is, the light power of the backscattered light regularly repeats monotonically decreasing and increasing by a certain amount by the amplifier.

On the other hand, when a failure occurs at the point C on the optical transmission line, as shown in FIG. 7C, the optical power of the backscattered light sharply decreases. Therefore, the failure occurrence point can be located from the relationship between the decrease in the optical power and the time.

[0007]

The conventional bidirectional optical repeater has a problem in that it requires an optical isolator and an optical coupler between the optical fiber transmission line and the optical amplifier, and has many components. Further, there is a problem that the optical signal loss due to the optical isolator and the optical coupler is large. The loss on the output side of the optical amplifier means an increase in the amplification factor of the optical amplifier, and the loss on the input side of the optical amplifier deteriorates the noise figure of the optical amplifier.

Further, the conventional bidirectional optical repeater has a problem that it is impossible to distinguish between a failure occurring near the optical repeater in the optical fiber transmission line and a failure occurring inside the repeater. More specifically, in the optical transmission line of FIG.
When a failure occurs (in the vicinity of the repeater), a time distribution as shown in FIG. 7D is obtained. That is, the backscattered light is amplified and simultaneously sharply reduced. On the other hand, point E
If a failure occurs inside the repeater, the amplification factor is low. However, these graphs are very similar and difficult to distinguish.

It is an object of the present invention to provide a bidirectional optical repeater having a small number of constituent elements and a low loss of optical signals.

It is another object of the present invention to provide a bidirectional optical repeater capable of locating fault points near and inside the repeater by using the OTDR method.

[0011]

According to the present invention, the optical signal is connected to the first and second optical fibers, the optical signal incident from the first optical fiber is amplified, and the amplified optical signal is emitted to the second optical fiber. In the bidirectional optical repeater that amplifies the optical signal incident from the second optical fiber and emits the optical signal to the first optical fiber, first and second optical amplifiers that amplify the incident optical signal, The light input from the first optical fiber is connected to the first optical fiber, the input end of the first optical amplifier, and the output end of the second optical amplifier, and the light incident from the first optical fiber is input to the first optical amplifier. A first bidirectional optical coupler for guiding an optical signal output from the second optical amplifier to the first optical fiber, the second optical fiber, and the first optical fiber.
Connected to the output end of the optical amplifier and the input end of the second optical amplifier, and guides the light incident from the second optical fiber to the input end of the second optical amplifier, and the first optical amplifier And a second bidirectional optical coupler that outputs the optical signal output from the second optical fiber to the second optical fiber.

Further, according to the present invention, the optical signal incident from the first optical fiber is demultiplexed at either the input end side or the output end side of the first amplifier, and Demultiplexing / combining for multiplexing to either one of the input end side and the output end side of the second amplifier so as to be amplified by at least one of the two optical amplifiers, and outputting to the first optical fiber. The bidirectional optical repeater according to claim 1 is provided with means.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a first embodiment of the present invention. This bidirectional optical repeater includes two bidirectional optical couplers 11 and 12 and two optical amplifiers 13 and 14. The two optical amplifiers 13 and 14 are opposite to each other in the bidirectional optical couplers 11 and 12.
Are connected to and form an uplink and a downlink. The bidirectional optical couplers 11 and 12 are connected to the optical fiber transmission lines 15 and 16, respectively.

The optical signal propagating through the optical fiber transmission line 15 in the direction of arrow A is guided to the amplifier 13 by the directional optical coupler 11. Here, the directional optical coupler 1
1 blocks the optical signal in the opposite direction. The amplifier 13 amplifies the input optical signal and outputs it to the directional coupler 12. The directional coupler 12 outputs the input optical signal to the optical fiber transmission line 16. Again, the directional optical coupler 12 blocks the backward optical signal.

Similarly, the optical signal propagating through the optical fiber transmission line 16 in the direction of arrow B is directional optical coupler 1.
2 leads to the amplifier 14. Here, the directional optical coupler 12 blocks an optical signal in the reverse direction. The amplifier 14 amplifies the input optical signal and outputs it to the directional coupler 11. The directional optical coupler 11 outputs the input optical signal to the optical fiber transmission line 15. Again, the directional optical coupler 11 blocks the optical signal in the opposite direction.

As described above, according to the present embodiment, since the directional optical couplers 11 and 12 are provided, bidirectional communication with low loss can be realized with a simple structure. Incidentally, such a directional optical coupler is a high-isolation optical nonreciprocal circuit without polarization dependence that can be used as a circulator by Koga and Matsumoto.
IEICE technical report, optical communication system, OC
S91-9, 1991.

Next, a second embodiment of the present invention will be described with reference to FIG. Here, the same parts as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted. The bidirectional optical repeater of this embodiment includes an optical coupler 21 for demultiplexing the output of the optical amplifier 13, an optical coupler 22 for guiding the optical signal demultiplexed by the optical coupler 21 to the optical amplifier 14, and an optical coupler. It has an optical coupler 23 for demultiplexing the output of the amplifier 14 and an optical coupler 24 for guiding the optical signal demultiplexed by the optical coupler 23 to the optical amplifier 13.

In practice, a remotely operated optical switch is provided between the optical coupler 21 and the optical coupler 22 and between the optical coupler 23 and the optical coupler 24. In normal operation, these optical switches are in the off state, so
The same operation as in the embodiment of When performing OTDR measurements, these optical switches are selectively turned on remotely. That is, when propagating the optical pulse for OTDR measurement in the direction of arrow A in the optical fiber transmission line 15,
An optical switch provided between the optical coupler 21 and the optical coupler 22 is turned on to turn back the OTDR measurement optical pulse,
The light is emitted to the optical fiber transmission line 15. On the contrary, when propagating the OTDR measurement optical pulse in the direction of the arrow B in the optical fiber transmission line 16, the optical switch provided between the optical coupler 23 and the optical coupler 24 is turned on to perform the OTDR measurement. The optical pulse for use is returned and emitted to the optical fiber transmission line 16.

An optical transmission line having such an optical repeater is shown in FIG.
It shows in (a). When no fault has occurred in this transmission line, OTDR measurement is performed using the optical pulse for OTDR measurement in the direction of arrow A, and the result shown in FIG. 3B is obtained. This is due to the backscattered light and the folded OT
It has a waveform obtained by adding the DR measurement optical pulse F.

When a failure occurs at a point C on the optical fiber transmission line, a drastic decrease in optical power is observed as shown in FIG. 3 (c). Therefore, the fault point can be located as in the conventional case.

Further, in the transmission line having the optical repeater of the present embodiment, it is possible to locate a fault near and inside the optical repeater. More specifically, if a failure occurs at a point D near the optical repeater on the optical fiber transmission line, the optical pulse for OTDR measurement is amplified and returned twice inside the optical repeater.
Therefore, in the OTDR waveform in this case, as shown in FIG. 3D, the optical power of the folded OTDR measurement optical pulse is the same as in the normal state, and only the optical power of the backscattered light is reduced. . On the other hand, if a failure occurs at the internal point E of the repeater, the OTD folded back as shown in FIG.
The optical power of the R measurement optical pulse decreases, and the optical power of the backscattered light also decreases.

As described above, in the optical transmission line having the repeater of the present embodiment, it is possible to identify whether the failure occurs near the optical repeater or inside the optical repeater.

Next, a third embodiment of the present invention will be described with reference to FIG. The optical repeater of this embodiment is also configured to return the optical pulse for OTDR measurement similarly to the second embodiment, but the optical couplers 41 and 42 perform demultiplexing and multiplexing respectively. Is configured. These optical couplers 41 and 42 are connected to the output sides of the optical amplifiers 13 and 14, respectively.

In the optical repeater of the present embodiment, since the demultiplexing and the multiplexing are performed by one optical coupler, the structure becomes simple. Further, since there is no optical coupler on the input side of the optical amplifiers 13 and 14, the noise figure of the amplifier can be improved.

Next, a fourth embodiment of the present invention will be described with reference to FIG. The optical repeater of this embodiment differs from the third embodiment in that the optical couplers 41 and 42 are connected to the input sides of the optical amplifiers 13 and 14, respectively. In the optical repeater of the present embodiment, since there is no optical coupler on the output side of the optical amplifiers 13 and 14, it is not necessary to increase the amplification factor of the amplifier.

[0026]

According to the present invention, the structure of the bidirectional optical repeater can be simplified by connecting the optical amplifier and the optical fiber transmission line by using the directional coupler, and the optical signal loss can be reduced. Can be suppressed.

Further, according to the present invention, the input OTD
By providing the optical coupler so as to amplify and return the R measurement pulse, it is possible to locate a fault that has occurred in the vicinity of or inside the optical repeater.

[Brief description of drawings]

FIG. 1 is a block diagram of a first embodiment of the present invention.

FIG. 2 is a block diagram of a second embodiment of the present invention.

3 is an OTD of a transmission line having the bidirectional optical repeater of FIG.
3A and 3B are diagrams for explaining the R measurement, where FIG. 3A is a block diagram of a transmission line having the bidirectional optical repeater of FIG. 2, FIG. 2B is an OTDR waveform diagram when there is no failure, and FIG. FIG. 5D is an OTDR waveform diagram when there is a fault at C, FIG. 8D is an OTDR waveform diagram when there is a fault at point D, and FIG.

FIG. 4 is a block diagram of a third embodiment of the present invention.

FIG. 5 is a block diagram of a fourth embodiment of the present invention.

FIG. 6 is a block diagram of a conventional bidirectional optical repeater.

FIG. 7: OTD of a transmission line having a conventional bidirectional optical repeater
FIG. 6 is a diagram for explaining R measurement, (a) is a block diagram of a transmission line having a conventional bidirectional optical repeater, (b) is an OTDR waveform diagram when there is no failure, and (c) is a point C. 2D is an OTDR waveform diagram when there is a fault, FIG. 7D is an OTDR waveform diagram when there is a fault at point D, and FIG.

[Explanation of symbols]

 11, 12 Bidirectional optical coupler 13, 14 Optical amplifier 15, 16 Optical fiber transmission line 21 Optical coupler 22 Optical coupler 23 Optical coupler 24 Optical coupler 41, 42 Optical coupler 61 Uplink optical amplifier 62 Downlink Optical amplifier for line 63,64 Optical isolator 65,66 Optical coupler 67 Optical fiber transmission line 68 Optical fiber transmission line

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuya Amagi 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited

Claims (3)

[Claims] 1. Connected to first and second optical fibers,
Amplify an optical signal incident from the first optical fiber and output it to the second optical fiber, amplify an optical signal incident from the second optical fiber and output it to the first optical fiber. In the optical repeater, first and second optical amplifiers for amplifying an incident optical signal, the first optical fiber, an input end of the first optical amplifier, and an output end of the second optical amplifier. Connected to the first optical fiber, guides the light incident from the first optical fiber to the input end of the first optical amplifier, and outputs the optical signal output from the second optical amplifier to the first optical fiber. 1 bidirectional optical coupler, the second optical fiber, the output end of the first optical amplifier, and the input end of the second optical amplifier, and are incident from the second optical fiber. The light is guided to the input end of the second optical amplifier, and the first optical amplifier is Bidirectional optical repeater, wherein the output optical signal to have a second bidirectional optical coupler emitted to the second optical fiber from. 2. The optical signal incident from the first optical fiber is demultiplexed on either the input end side or the output end side of the first amplifier, and the optical signal is divided into the first and second optical amplifiers. It has a demultiplexing / combining means for multiplexing at least one of an input end side and an output end side of the second amplifier so as to be amplified at least on one side, and emitting the multiplexed light to the first optical fiber. The bidirectional optical repeater according to claim 1. 3. The optical signal incident from the second optical fiber is demultiplexed at one of the input end side and the output end side of the second amplifier, and the optical signal is divided among the first and second optical amplifiers. It has a demultiplexing / combining means for multiplexing at least one of an input end side and an output end side of the first amplifier so as to be amplified at least on one side and emitting the multiplexed light to the second optical fiber. The bidirectional optical repeater according to claim 1 or 2.