JPH09116502A - High output optical amplifier repeater with monitoring loopback circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high output optical amplifier repeater which can amplify an optical signal with high gain and also can satisfactorily monitor the line of an optical submarine cable system. SOLUTION: First and second amplifiers 3a ad 3b and the 3rd and 4th amplifiers 4a and 4b are inserted into the lines composed of a pair of fibers respectively. Then a 1st loopback circuit 5 secures the optical connection between the amplifiers 3a/3b and 4a/4b, and the 2nd loopback circuits 6a to 6c secure the optical connection between the output terminals of amplifiers 3b and 4b. The signal light transmitted via a line 1 is amplified by the amplifiers 3a and 3b with high gains. The output signal light of the amplifier 3a is returned to a line 2 set opposite to the line 1 via the circuit 5. The scattered light generated at the downstream side of the amplifier 3b is returned to the line 2 via the circuits 6a to 6c.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-power optical amplifier repeater having a monitoring loopback circuit, and particularly to a monitoring loopback suitable for installation in a place where the repeater spacing of optical submarine cables is large. The present invention relates to a high-power optical amplification repeater having a circuit.

[0002]

2. Description of the Related Art An example of a conventional optical submarine cable system configuration will be described with reference to FIG. Usually, the optical submarine cable has a basic configuration of one optical fiber pair consisting of an upstream optical fiber cable 51 and a downstream optical fiber cable 52. The upstream and downstream optical fiber cable 5
Optical amplification repeaters 53a, 53b, 53c, etc. are arranged at intervals of 50 to 100 km in each of 1, 52. A specific configuration example of this optical amplification repeater is shown in FIG. 6 as a representative of the optical amplification repeater 53b.

As shown, an optical amplification repeater 53
b is an erbium-doped optical fiber 61, 66, WDM
It is composed of couplers 62 and 67, pump LDs 63 and 68, isolators 64 and 69, and a loopback circuit 65. Further, the loopback circuit 65 is connected between the upstream and downstream optical fiber cables 51 and 52.
0 dB couplers 65a and 65b and loopback circuit 6
25 dB couplers 65c and 65d provided in the middle of 5.

In the transmission system having the above configuration, line monitoring by the LME device is performed as follows. Signal lights S1 and S input to the optical amplification repeater 53b
2 is attenuated by a certain amount by the loopback circuit 65 in the repeater, and the input signal light S1 of the uplink is returned to the downlink and the input signal light S2 of the downlink is returned to the uplink. Then, the loopback signal is set to HLLB.
It is taken out from the circuit 54 or 55 and the line monitoring device (Line
Monitoring Equipment: LME) 56 or 57,
Measure its power. By this measurement, the LME devices 56 and 57 are able to detect the failure of the optical fiber cables 51 and 52,
The relay circuits 53a, 53b, 53c and the like are monitored for failures.

In addition, a coherent optical pulse test (Coheren
t-Optical Time Domain Reflectometry (C-OTDR) to perform upstream or downstream optical fiber cables 51, 5
A path for returning the scattered light of 2 to the opposite line is also secured in the loopback circuit 65 as described above. The coherent light pulse test is performed by replacing the LTE 58 and 59 with a C-OTDR measuring device. Where the LM
The line monitoring by E and the coherent optical pulse test will be briefly described.

The optical signal output from the optical amplifier 53b1 is always attenuated by 10 dB by the 10 dB coupler 65a and is guided to the loopback circuit 65. Then, 25d
Attenuated by 25 dB by B coupler 65c, and further 1
It is attenuated by the 0 dB coupler 65b and is returned to the downstream optical fiber cable 52 which is the opposite line. afterwards,
It is guided to the LME device 56 via the HLLB circuit 54,
If necessary, the LME device 56 allows the optical amplifier 5
The output light of 3b1 is monitored. In this way, the signal for the LME receives a loss of about 45 dB in total and is guided to the LME device 56. For example, the repeater circuit 53
If some failure occurs in the optical amplifier 53b1 of b, the LME device detects that there is a failure in the optical amplifier 53b1 by monitoring the output signal of the optical amplifier 53b1 having a loss of about 45 dB. .

On the other hand, the signal light of C-OTDR is scattered by the optical fiber of the path and travels in the direction opposite to the traveling direction of the signal light. For example, the point 51a of the upstream optical fiber cable 51
The scattered light generated in (see FIG. 5) is attenuated by 10 dB by the 10 dB coupler 65a of the loopback circuit 65, then passes through the two 25 dB couplers 65d and 65c without being attenuated, and is transmitted by the 10 dB coupler 65b. 10d
After being lost by B, the call is returned to the opposite line 52. And
The scattered light that has been returned is measured by a C-OTDR measurement device that is installed in place of the LTE 58. As a result, for example, when a failure such as disconnection occurs at the point 51a of the upstream optical fiber cable 51, the scattered light after the point 51a becomes small or the reflected light from the disconnection point is generated, and C- Since the measurement is performed by the OTDR measuring device, the fault at the point 51a is detected. In this case, 2
When passing through the 5 dB couplers 65d and 65c, the passing path is the path without loss, so the total loss is about 21.
It becomes about dB.

[0008]

As described above, in the ordinary optical submarine cable, the optical amplification repeaters 53a, 53b, 5 are used.
3c are inserted at substantially equal intervals, but due to geographical conditions in which the optical submarine cable is laid, or for reasons such as reduction in installation cost, only before and after a certain optical amplification repeater, for example, before and after the optical amplification repeater 53b. However, the relay interval may need to be lengthened. In such a case, a high gain optical amplification repeater 53b is required, and the inventor of the present invention, as the high gain optical amplification repeater (hereinafter referred to as a high output optical amplifier),
Consider the one shown in FIG.

As the high-power optical amplification repeater 60, an optical amplifier in which two optical amplifiers 53b1 and 53b2 are connected in series is arranged in each of the upstream and downstream optical fiber cables, and the upstream and downstream optical fibers are connected. It is considered that the conventional loopback circuit 65 is arranged between the cables. If this optical amplification repeater is used, the input signal light can be amplified with high gain and output, so that it can be dealt with even if the repeater interval before and after the optical amplification repeater becomes long.

However, when the high power optical amplification repeater 60 of FIG. 7 is applied to the optical submarine cable, there is a problem that the line monitoring by the LME device cannot be sufficiently performed. For example, in the upstream optical fiber cable of FIG.
If some trouble occurs in the optical fiber cable 51a on the upstream side of the high output optical amplification repeater 60, and the power of the signal light input to the high output optical amplification repeater 60 decreases,
This signal light power is amplified by the two-stage optical amplifier 53b1, guided to the downstream optical fiber cable through the loopback circuit 65 as described above, and input to the LME device 56 provided in the transmission terminal station. However, if two optical amplifiers 53b1 operated in the gain saturation region are used in series, the output approaches the steady value even if there is a large fluctuation in the input signal light power.
It is hard to appear on the device 56. As a result, as described above, there is a problem that the line monitoring by the LME device cannot be performed sufficiently. An object of the present invention is to eliminate the above-mentioned problems of the prior art, to amplify the signal light with a high gain, and to perform line monitoring of the optical submarine cable system sufficiently. To provide.

[0011]

In order to achieve the above-mentioned object, the present invention is a high-power optical amplifier repeater inserted in an optical line formed by a pair of upstream and downstream optical fibers, First and second optical amplifiers sequentially arranged in an upstream line, third and fourth optical amplifiers sequentially arranged in a downstream line, between the first and second optical amplifiers, and between the third and the third optical amplifiers. A first loopback circuit for optically coupling between the fourth optical amplifier and a second loopback circuit for optically coupling the output end of the second optical amplifier and the output end of the fourth optical amplifier. It is characterized by having a loopback circuit of. Also, other features are
It is characterized in that the second and fourth amplifiers are composed of amplifiers having an automatic gain control function.

According to the present invention, since the signal light transmitted through the upstream or downstream line is sequentially amplified by the two optical amplifiers, the output power becomes high. Further, the output light of the first or third amplifier is returned to the opposite line via the first loopback circuit, and therefore the LME device observes the power of the returned signal light to detect the power of the line. Can be monitored. Further, since the scattered light generated in the line is returned to the opposite line via the second loopback circuit, the coherent light pulse test device connected instead of the LTE device measures the scattered light. , Track status can be monitored.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a high-power optical amplification repeater according to an embodiment of the present invention. Same figure
As shown in (a), the high-power optical amplification repeater 10 according to the present embodiment includes the first and second optical amplifiers 3a and 3b inserted into the upstream optical fiber cable 1 and the downstream optical amplifier. The third and fourth optical amplifiers 4a inserted in the fiber cable 2,
4b and the output of the first optical amplifier 3a are attenuated to the downstream optical fiber cable 2 which is the opposite line, or the output of the third optical amplifier 4a is attenuated to the upstream optical fiber cable 1 which is the opposite line. The signal light scattered in the LME loopback circuit 5 and the optical fiber cable 1 on the downstream side of the second optical amplifier 3b is returned to the downstream optical fiber cable 2 which is the opposite line, or the fourth optical fiber cable 2 It comprises a C-OTDR loopback circuit 6 for guiding the signal light scattered in the optical fiber cable 2 on the downstream side of the optical amplifier 4b to the upstream optical fiber cable 1 which is the opposite line.

Here, the first to fourth optical amplifiers 3a to 4 are provided.
Each b has a structure as shown in FIG. That is, the erbium-doped optical fiber 1
1, a WDM coupler 12, a pump LD 13 and an isolator 14. FIG. 2 shows the optical amplifier 3a.
4b show the amplification characteristics of the respective optical amplifiers. The horizontal axis represents the input power and the vertical axis represents the gain. As is clear from the figure, the gain characteristic with respect to the input signal is constant in a region where the input signal is relatively small, but the gain decreases as the repeater input signal power increases. Therefore, when the operating point X is set in the gain saturation region as shown in the figure, the gain automatically changes with respect to the fluctuation of the input signal, and the output power can be made constant. That is, when the input signal is smaller than the reference value corresponding to the operating point X, the gain increases, whereas when the input signal is larger than the reference value, the gain decreases, so that the output power of the optical amplifier is constant. To be kept. When the input signal is significantly reduced below the reference value, the operating point is outside the saturation region and the gain is constant, so that the repeater output signal light power is reduced below the expected level. As the output decreases, the folded LME signal also decreases, so that the decrease in repeater input power can be sensed.

The LME loopback circuit 5 is also provided.
Are two couplers (for example, 10 dB couplers) 5a, 5
b and two attenuators (eg 25 dB attenuators) 5c,
5d. The C-OTDR loopback circuit 6 has two couplers (for example, 10 dB couplers) 6a and 6b and one attenuator (for example, 1 dB attenuator) 6c.

Next, the operation of this embodiment will be described with reference to FIG. FIG. 3 shows a system diagram when the high-power optical amplification repeater 10 of the present embodiment is applied to an optical submarine cable system, and the reference numerals in the drawing are the same as or equivalent to those in FIG. 1 and FIG. Indicates a thing. As shown in the figure, the repeater interval before and after the high-power optical amplification repeater 10 is larger than other repeater intervals, for example, 100 to 200 km.

The signal light input to the high-power optical amplifier repeater 10 through the upstream optical fiber cable 1 is greatly amplified by the first and second optical amplifiers 3a and 3b and output with high optical power. . At this time, a part of the signal light amplified by the first optical amplifier 3a is returned to the downstream optical fiber cable 2 by the LME loopback circuit 5, and HLLB
Input to the LME device 56 via the circuit 54.

Now, suppose that some trouble has occurred in the optical fiber cable 1 on the upstream side of the high power optical amplification repeater 10 or the first optical amplifier 3a in the high power optical amplification repeater 10. The LM is looped back by the LME loopback circuit 5 and passed through the downstream optical fiber cable 2 to the LM.
The power of the signal light input to the E device 56 is greatly attenuated. As a result, the optical fiber cable 1 on the upstream side of the high output optical amplification repeater 10 or the high output optical amplification repeater 1
It can be seen that a failure has occurred in the first optical amplifier 3a in 0. In addition, the second optical amplifier 3 of the high output optical amplification repeater 10
When some failure occurs in the optical fiber cable 1 on the side b or the downstream side thereof, the signal light returned by the loopback circuit of the optical amplification repeater 53c is sent to the LME device 56.
It can be detected by measuring with.

Further, the above-mentioned obstacle is caused by the second optical amplifier 3b.
It is possible to discriminate between the optical fiber cable 1 on the downstream side and the optical fiber cable 1 on the downstream side by connecting a C-OTDR measuring device instead of the LTE device 58. That is, for example, the high output optical amplification repeater 10
When a failure such as disconnection occurs at a point 1a in the optical fiber cable 1 between the optical amplifier repeater 53c and the optical amplification repeater 53c, the scattered light of the signal light after the failure point becomes weak, or the failure point 1
a is reflected, and the scattered light and the reflected light are C-OTD.
It is guided to the downstream optical fiber cable 2 through the R loopback circuit 6 and detected by the C-OTDR measuring device. However, when a failure occurs in the second optical amplifier 3b, the scattered light does not change, so C-
Abnormalities of scattered light are not detected by the OTDR measuring device. Therefore, by integrating the measurement results by the LME device and the C-OTDR measuring device, it is possible to distinguish whether the fault has occurred in the optical amplifier or in the optical fiber cable.

Next, the second embodiment of the high-power optical amplification repeater of the present invention
An embodiment will be described with reference to FIG. The high-power optical amplification repeater 20 of this embodiment is different from the first embodiment in that the second optical amplifier 3b and the fourth optical amplifier 4b are different.
The optical amplifiers 3b 'and 4b' having the automatic gain control function (AGC function) are used as the above. That is, the second and fourth optical amplifiers 3b 'and 4b' of the present embodiment.
Are couplers 21a and 21b for monitoring the output power of these optical amplifiers 3b 'and 4b', and photodiodes 22a and 2b for converting the monitored signal light into electric signals.
2b and an automatic gain control circuit (ALC circuit) 23a for generating a control signal for returning the electric signal to a predetermined value when the electric signal changes and adjusting the pump laser current of the pump LD by the control signal. , 23b.

According to this embodiment, the signal light transmitted through the upstream or downstream optical fiber cable 1 or 2 is amplified by the first or the third optical amplifier 3a 'or 4a', and further the second or the second optical amplifier. It is amplified by the optical amplifier 3b 'or 4b' having the automatic gain control function of 4. As a result, stable high output power signal light is output from the high output optical amplification repeater 20. In the present embodiment, the output signal light is the second or fourth optical amplifier 3b '.
Alternatively, since the AGC control is performed by 4b ', it is possible to obtain a high output signal light with more stable power as compared with the high output optical amplification repeater 10 of the first embodiment.

Further, as shown in the figure, the LME loopback circuit 5 is provided between the first and second optical amplifiers 3a 'and 3b' of the upstream optical fiber cable 1 and the third optical fiber cable 2 of the downstream optical fiber cable 2. And the fourth optical amplifier 4
Between a'and 4b ', the first and second couplers 5
Since it is provided via a and 5b, for example, the first optical amplifier 3
When some trouble occurs on the upstream side of a ′ and the signal light is attenuated, the signal light is amplified by the first optical amplifier 3a ′ and then returned to the downstream optical fiber cable 2 by the LME loopback circuit 5. Will be. Therefore, the LME device 56 (see FIG. 3) provided in the transmitting terminal station can detect the attenuation of the signal light and can perform predetermined line monitoring. The C-OTDR loopback circuit 6 includes third and fourth couplers 6a and 6b provided at the output ends of the upstream and downstream optical fiber cables of the high-power optical amplification repeater 20, as shown in the figure. Since it is provided via the optical fiber, the scattered light generated on the downstream side of the high-power optical amplification repeater 20 can be reliably returned to the optical fiber cable on the opposite side. As a result, L
With the C-OTDR device connected instead of the TE device,
The scattered light can be detected.

[0023]

As is apparent from the above description, according to the present invention, since two stages of amplifiers are inserted in each of the up and down lines, a large gain can be obtained, and the LME device and the C- The line monitoring by the OTDR device can be performed without any trouble. Therefore, when the high-power optical amplification repeater of the present invention is used in a geographical condition such as between remote islands where the repeat interval is not long enough to use several ordinary optical repeaters, the optical submarine cable The laying can be performed technically and cost effectively.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing amplification characteristics of the optical amplifier of FIG.

FIG. 3 is a diagram showing a system configuration when the high-power optical amplification repeater of this embodiment is applied to a submarine cable.

FIG. 4 is a circuit diagram showing a configuration of a second exemplary embodiment of the present invention.

FIG. 5 is a diagram showing a system configuration of a conventional submarine cable.

FIG. 6 is a circuit diagram showing a configuration example of a conventional optical amplification repeater.

FIG. 7 is a block diagram showing a configuration of a high-power optical amplification repeater that can be easily conceived.

[Explanation of symbols]

1 ... upstream optical fiber cable, 2 ... downstream optical fiber cable, 3a, 3b, 4a, 4b, 3a ', 3b',
4a ', 4b' ... Optical amplifier, 5 ... LME loopback circuit, 6 ... C-OTDR loopback circuit, 10, 2
0 ... High output optical amplification repeater, 22a, 22b ... Photodiodes, 23a, 23b ... Automatic gain control circuit.

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Tomohiro Otani 2-3-2 Nishishinjuku, Shinjuku-ku, Tokyo International Telegraph and Telephone Corporation (72) Inventor Koji Goto 2-3-2 Nishishinjuku, Shinjuku-ku, Tokyo No. International Telegraph and Telephone Corporation (72) Inventor Haruo Abe 2-3-2 Nishishinjuku, Shinjuku-ku, Tokyo International Telegraph and Telephone Corporation (72) Masato Tanaka 2-3-2 Nishishinjuku, Shinjuku-ku, Tokyo No. International Telegraph and Telephone Corporation (72) Inventor Shingo Ito 2-3-2 Nishishinjuku, Shinjuku-ku, Tokyo International Telegraph and Telephone Corporation

Claims (6)

[Claims] 1. A high-power optical amplification repeater to be inserted into an optical line formed by a pair of upstream and downstream optical fibers, the first and second optical amplifiers being sequentially arranged on the upstream line, A third and a fourth optical amplifiers which are sequentially arranged in a down line, and a first optical coupling between the first and the second optical amplifiers and between the third and the fourth optical amplifiers. A loopback circuit for monitoring, comprising: a loopback circuit; and a second loopback circuit that optically couples the output end of the second optical amplifier and the output end of the fourth optical amplifier. High power optical amplifier repeater with circuit. 2. A high-power optical amplifier repeater having a monitoring loopback circuit according to claim 1, wherein each of the first to fourth optical amplifiers includes an erbium-doped optical fiber and a signal light for amplifying the signal light. A high-power optical amplification repeater having a monitoring loopback circuit, comprising a pump LD for exciting an erbium-doped optical fiber and an isolator for transmitting amplified signal light in one direction. 3. A high-power optical amplification repeater having a monitoring loopback circuit according to claim 1, wherein the second and fourth amplifiers are amplifiers having an automatic gain control function. High power optical amplifier repeater with buck circuit. 4. A high-power optical amplification repeater having a monitoring loopback circuit according to claim 1, wherein an attenuator having a predetermined attenuation value is inserted in each of the first and second loopback circuits. A high-power optical amplifier repeater having a loopback circuit for monitoring characterized in that 5. A high-power optical amplification repeater having a monitoring loopback circuit according to claim 1, wherein the first loopback circuit branches the output light of the first optical amplifier, and branches the output light. A high output optical amplification repeater having a loopback circuit for monitoring, comprising: a unit for giving a predetermined loss to the output light thus produced and a unit for merging with the input of the third optical amplifier. 6. The high-power optical amplification repeater having the monitoring loopback circuit according to claim 1, wherein the second loopback circuit returns from an optical line on the output side of the second optical amplifier. A monitoring loopback circuit comprising: means for branching scattered light; means for imparting a predetermined loss to the branched scattered light; and means for merging with the output of the second optical amplifier. High power optical amplifier repeater.