JPH0738471A - Gain control method of optical amplifier repeater - Google Patents

Abstract

(57) [Abstract] [Purpose] Regarding the gain control method for optical amplifier repeaters such as optical submarine cables, the purpose is to simplify the control method and improve reliability. An optical amplifier repeater 10 includes an erbium-doped optical fiber 11, an excitation light source 12 including an excitation laser diode 12a and a drive control unit 12b thereof, and a power supply line 13.
And a current sensor 14 that adjusts the optical output level of the pumping light source by detecting the power supply current flowing through the optical amplifier repeater 1 with a variable power supply current from the signal light receiving end station.
The gain of 0 is adjusted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gain control method for an optical amplifier repeater, and more particularly to a gain control method for an optical amplifier repeater which improves the reliability of an optical repeater system using an optical fiber amplifier such as an optical submarine cable system.

Recently, neodymium (N
d), optical fiber amplification capable of amplifying signal light as it is by using an optical fiber doped with a rare earth element such as erbium (Er) as an amplification medium is drawing attention. In particular, an erbium-doped optical fiber doped with erbium ions Er ³⁺ is promising as an optical amplifier, and has high gain, low noise, polarization-independent gain characteristics, an amplification wavelength band of signal light, and a quartz system for transmission. It has excellent features such as good matching with the low loss wavelength band of the fiber and low coupling loss.

[0003]

2. Description of the Related Art Conventionally, in an optical communication system using an optical fiber, in addition to the optical fiber itself having low loss, wide band signal transmission characteristics, small core and light weight, It has the feature that various signals such as voice, data, and images can be combined and transmitted. When such an optical communication system is applied to a long-distance submarine cable, the maintenance of the optical fiber cable and the repeater cannot be facilitated after the operation thereof is started, and the communication capacity is large. Therefore, once a failure occurs, its effect becomes enormous and extremely high reliability is required.

FIG. 5 is a diagram showing a configuration example of a conventional optical amplifier repeater using an optical fiber amplifier for the repeater. In the figure, reference numeral 1 denotes an erbium-doped optical fiber which is an amplification medium for input signal light, and is inserted in series in the optical fiber for signal light transmission. A demultiplexer 2 is provided on the output side of the erbium-doped optical fiber 1 and is configured to split the output signal light at a predetermined rate and extract a part of the signal light. The light branched by the demultiplexer 2 is converted into an electric signal by the photodetector 3. This photodetector 3 is preferably constituted by an avalanche photodiode. The output of the photodetector 3 is input to the signal light monitor unit 4, measures the change in the optical output level of the output signal light, and is input to the drive control unit 5. The drive control unit 5 drives and controls the pump laser diode 6 by using the signal from the signal light monitor unit 4 as a control feedback signal. The drive controller 5 and the pump laser diode 6 constitute a pump light source for the erbium-doped optical fiber 1, and supply the controlled pump light to the erbium-doped optical fiber 1 via the multiplexer 7. The input signal light has a wavelength of, for example, 1.55 μm band, and the pumping laser diode 6 has a pumping wavelength of, for example, 1.48 μm.

In the example shown in the drawing, the pumping light is sent from the signal light output side of the erbium-doped optical fiber 1, and the pumping light is sent from the signal light input side of the erbium-doped optical fiber 1. There may be a case of forward pumping, or bidirectional pumping in which pumping light is sent from the signal light input / output side of the erbium-doped optical fiber 1.

As described above, the optical amplifier repeater uses the pump laser diode 6 to make the erbium-doped optical fiber 1
The pumping light is sent to, the signal light optically amplified by this is partly branched, the current optical output level is detected, the information of the optical output level is fed back to the drive control section 5, and the light of the pumping laser diode 6 is sent. Adjust the output to the desired level. For example, when the output level of the erbium-doped optical fiber 1 is low, the pumping light output level of the pumping laser diode 6 is increased, and when it is high, the pumping light output level of the pumping laser diode 6 is decreased to increase the gain of the optical amplifier. Are controlled so that the output level of the signal light becomes constant.

As another embodiment for controlling the gain of the optical amplifier, the main signal light is phase-modulated into a gain control command for the optical amplifier of the repeater, which is read and decoded by the optical amplifier repeater. There is also a method used for gain control of an optical amplifier. Therefore, the repeater requires a circuit for detecting such a command and supplying it to the laser diode drive control unit.

[0008]

Meanwhile, particularly high reliability is required in a repeater for an optical submarine cable. However, in the conventional optical amplifier repeater, a circuit of a system for monitoring the signal light output level including the demultiplexer 2, the photodetector 3, and the signal light monitor unit 4 or a gain command detection circuit is essential, and the circuit configuration Was complicated. Further, since the demultiplexer 2 that branches the output signal light and extracts a part thereof has a temperature dependence in its distribution rate, a circuit that detects the temperature of the demultiplexer 2 and corrects the temperature of the branched light is provided. This is necessary and makes the configuration of the signal light monitor circuit 4 more complicated.

The present invention has been made in view of the above circumstances, and provides a gain control system for an optical amplifier repeater capable of improving reliability by reducing the number of parts causing a failure as much as possible. With the goal.

[0010]

FIG. 1 is a principle block diagram of a gain control system of an optical amplifier repeater of the present invention which achieves the above object. In this figure, an optical amplifier repeater 10 is an erbium-doped optical fiber 1 which is an amplification medium for input signal light.
1, a pumping light source 12 including a pumping laser diode 12a and a drive controller 12b for the pumping laser diode 12a, and a current sensor 14 for detecting a power supply current flowing through a power supply line 13.
The pumping light source 12 is optically connected to the erbium-doped optical fiber 11 to supply pumping light to the erbium-doped optical fiber 11 via a multiplexer, and the current sensor 14 has its control input to provide its output to the pumping light source 12. It is connected to the.

[0011]

In FIG. 1, a current corresponding to the required optical amplification is passed through the power supply line 13. The value of this current is detected by the current sensor 14 and given to the excitation light source 12. The pumping light source 12 controls the optical output of the pumping light of the pumping laser diode 12a according to the value of the detected current, and thereby controls the gain of the optical amplifier. As described above, the configuration in which the power supply current is varied to control the gain of the optical amplifier allows the components of the optical amplifier repeater to be significantly reduced.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 2 is a configuration diagram showing a specific example of the gain control system of the optical amplifier repeater of the present invention. In the figure, an optical amplifier repeater 10 is inserted in the middle of an optical fiber for transmitting signal light, and an erbium-doped optical fiber 11 is connected to the optical fiber for transmitting signal light, for example, by fusion. A multiplexer 15 is provided on the output side of the erbium-doped optical fiber 11 and the pumping light source 1 is attached to the multiplexer 15.
2 are optically connected.

The pumping light source 12 is a pumping laser diode 12
The pump laser diode 12a is configured by a and its drive control unit 12b, and changes the output level of the pump light, that is, the gain of the optical amplifier, depending on the magnitude of the drive current 12c from the drive control unit 12b.

The output of the current sensor 14 is connected to the control input 12d of the excitation light source 12. This current sensor 14
Is configured to detect the magnitude of the feed current flowing through the feed line 13 and input a detection signal corresponding to the magnitude of the feed current to the control input 12d of the excitation light source 12.

Further, optical isolators 16 and 17 for suppressing the reflectance at the end face are provided on the input side of the erbium-doped optical fiber 11 and the signal light output side of the multiplexer 15, that is, at the input and output ends of the optical amplifier. Each is provided.

In the illustrated example, the optical power amplifier or the optical booster amplifier has a backward pumping structure having excellent characteristics such as gain, output, and economical efficiency, but other pumping structures can be adopted. .

Next, the operation of the gain control system of the optical amplifier repeater of the present invention will be described. The power supply line 13 is laid along with an optical fiber for signal light transmission for supplying power to the optical amplifier repeater 10, and is supplied with a constant current by a power supply device provided in the terminal device. This power line 13
The current flowing through is detected by the current sensor 14. The detected current value is the control input 12d of the excitation light source 12.
Is input as a gain control signal. The drive control unit 12b of the excitation light source 12 determines the value of the drive current 12c according to the detected current value from the current sensor 14, and the excitation laser diode 1
2a. Therefore, the pump laser diode 1
2a generates excitation light having an optical output according to the value of the supply current.
The pumping light is multiplexed into the input signal light via the multiplexer 15, and brings the erbium-doped optical fiber 11 into a pumped state. In this state, when the input signal light is input to the erbium-doped optical fiber 11, stimulated emission occurs, and the output of the input signal light is amplified along the optical fiber with a gain determined by the feeding current value.

Here, for example, when the optical output level in the terminal device is high, the power supply device of the terminal device reduces the value of the constant current and supplies it. The change in the power supply current is detected by the current sensor 14 and sent to the drive control unit 12b of the excitation light source 12. The drive control unit 12b reduces the drive current 12c according to the amount of change in the power supply current. As a result, the optical output level of the pump laser diode 12a is lowered, and the gain of the erbium-doped optical fiber 11 is lowered. On the contrary, when the optical output level in the terminal device is small, the value of the constant current of the power feeding device is increased, the optical output level of the pump laser diode 12a is increased, and the gain of the erbium-doped optical fiber 11 is increased. .

FIG. 3 shows a plurality of optical amplifier repeaters 10a-10.
It is the figure which showed the optical communication system of the optical submarine cable to which n was cascade-connected. In the figure, a plurality of optical amplifier repeaters 10a to 10n are connected in a cascade by an optical fiber for signal light transmission and a power supply line 13, and a terminal station device 20 and a power supply device are provided on the receiving end side of the optical fiber for signal light transmission. 30 is connected. The terminal device 20 and the power feeding device 30 are installed on land, and the operator observes the reception level of the signal light at the terminal device 20 and changes the feeding current value of the power feeding device as necessary. . As a result, the plurality of optical amplifier repeaters 10a to 10n can collectively change their gains.

FIG. 4 is a block diagram showing an embodiment of a power supply current changing means for automatically changing the power supply current value in the power supply device without intervention of an operator. In the figure, the terminal device 20 has a demultiplexer 20a and a photodetector 20b for detecting the level at the receiving end of an optical fiber for signal light transmission,
Further, it has a power supply current controller 20c that changes the power supply current according to the reception level of the signal light. These duplexers 2
0a, the photodetector 20b, and the feeding current control unit 20c constitute a detection device that detects the optical output level of the signal light.
The output of the power supply current controller 20c is connected to supply the control signal to the constant current source 30a of the power supply device 30.

Here, for example, when the reception level of the signal light is high, the power supply current control unit 20c commands the constant current source 30a of the power supply device 30 to reduce the value of the power supply current and supply power. In response to this, the constant current source 30a supplies the power supply current having a value reduced according to the increase in the reception level.
Supply to 3. When the reception level becomes small, the power supply current control unit 20c detects the decrease and the constant current source 3
0a increases the constant current value of the feeding current.

The above example has been described for the case where the optical amplifier repeater is used as a repeater for an optical submarine cable, but it can be similarly applied to the case where it is used as a repeater for an optical land cable.

[0023]

As described above, in the present invention, the gain of the optical amplifier is controlled by changing the current supplied to the optical amplifier repeater. Therefore, the demultiplexer, the photodetector, and the signal light monitor unit, which were conventionally required to monitor the output level of the signal light, are not required, the number of parts can be reduced, and the optical device by the demultiplexer intervenes. Transmission loss can be eliminated. In addition, a circuit for receiving the control command on the optical signal is not required even in comparison with the conventional gain control method of the optical amplifier in which the main signal light is phase-modulated and used as the gain control command for the optical amplifier of the repeater. Furthermore, since the structure of the optical amplifier repeater is simple and the control method is simple, the reliability can be further improved.

[Brief description of drawings]

FIG. 1 is a principle configuration diagram of a gain control system of an optical amplifier repeater of the present invention.

FIG. 2 is a configuration diagram showing an embodiment of a gain control system of an optical amplifier repeater of the present invention.

FIG. 3 is a diagram showing an optical communication system using a plurality of optical amplifier repeaters.

FIG. 4 is a configuration diagram showing an example of a supply current changing unit.

FIG. 5 is a diagram showing a configuration example of a conventional optical amplifier repeater.

[Explanation of symbols]

 10 Optical Amplifier Repeater 11 Erbium Doped Optical Fiber 12 Excitation Light Source 12a Excitation Laser Diode 12b Drive Control Section 13 Feed Line 14 Current Sensor 15 Combiner 16 Optical Isolator 17 Optical Isolator

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location H04B 10/17 10/16 10/14 10/06 10/04

Claims (5)

[Claims] 1. A gain control system for an optical amplifier repeater for controlling the gain of an optical amplifier repeater comprising an erbium-doped optical fiber and its pumping light source, wherein the pumping is performed by detecting a power supply current flowing through a power supply line (13). A current sensor (1 for adjusting the light output level of the light source (12)
4) The gain control system for an optical amplifier repeater, characterized in that the gain of the optical amplifier repeater (10) is controlled by a variable power supply current from a signal light receiving terminal station. 2. The plurality of optical amplifier repeaters (10) are connected in series, and the gains of the plurality of optical amplifier repeaters are collectively controlled by the variable power supply current. A gain control system for an optical amplifier repeater according to claim 1. 3. A detecting device (20a, 20a) for detecting an optical output level of the signal light in a receiving terminal device (20) for the signal light.
20b, 20c) and a power supply device (30) capable of varying a power supply current according to the optical reception level of the signal light detected by the detection device, the optical amplifier according to claim 1. Repeater gain control method. 4. The gain control method for an optical amplifier repeater according to claim 1, wherein the optical amplifier repeater (10) is installed as a repeater of an optical submarine cable. 5. The gain control method for an optical amplifier repeater according to claim 1, wherein the optical amplifier repeater (10) is installed as an optical land cable repeater.