JPH08149084A - Optical transmission device - Google Patents

Abstract

PURPOSE: To provide an optical transmitting device which can automatically control the gain of an optical fiber amplifier in response to the loss of a transmission line. CONSTITUTION: The transmission lines 105 and 107 which transmit the Signal light and the excited light are connected to the optical fiber amplifier 103 which amplifies the signal light. An excited light reflecting means 108 is provided at a single end of the transmission lines to reflect the excited light. Then an amplifier control means 120 is contained in the amplifier 103 to detect the reflected return light and to control the gain of the amplifier 103 and the optical output level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmission device using an optical fiber amplifier for amplifying an optical signal, and more particularly to an optical transmission device capable of automatically adjusting the gain of the optical fiber amplifier according to the loss of the transmission line. It relates to the device.

[0002]

2. Description of the Related Art Conventionally, an optical transmission device using an optical fiber amplifier is generally used in an optical transmitter 10 as shown in FIG.
An optical fiber amplifier 503 is provided between the optical fiber amplifier 1 and the optical receiver 102. The optical signal output from the optical transmitter 101 is attenuated while being transmitted through the optical fibers 104 and 106. The optical signal is amplified by the optical fiber amplifier 503 to a level at which the optical receiver 102 can receive the optical signal. The optical fiber amplifier 503 includes an optical multiplexer / demultiplexer 112, an optical amplification medium (rare earth doped fiber) 110, an optical isolator 550, an optical filter 551, an optical branching device 552, an output signal light monitor light receiving element 553, a reference voltage 554, and an excitation light. It is composed of a control circuit 555 and an excitation light source 111. The optical branching device 552 branches a part of the optical output, the output signal light monitoring light receiving element 553 detects the intensity thereof, and the pumping light control circuit 555 controls the output of the pumping light in accordance with this detection. The gain of the optical fiber amplifier 503 is adjusted to stabilize the optical signal output level. The optical filter 551 is used to remove spontaneous emission light generated by amplification of the optical signal.

[0003]

As described above, a part of the optical output is conventionally branched by the optical branching device 552 in order to control the gain of the optical fiber amplifier 503. Therefore, the optical output sent to the optical receiver 102 decreases according to the branching ratio of the optical branching device 552, and as a result, the gain of the optical fiber amplifier 503 decreases according to the branching ratio.

When the loss of the transmission line due to the optical fiber 106 between the optical fiber amplifier 503 and the optical receiver 102 fluctuates, the conventional gain control method uses the optical fiber 1
Optical fiber amplifier 5 adapted to the loss of the transmission line due to 06
03 optical output level adjustment is required. Alternatively, it is necessary to install an optical attenuator in front of the optical receiver 102 and adjust the reception level with this optical attenuator. Both of them are very troublesome because they need to be individually adjusted for fluctuations in transmission line loss. If the reception dynamic range of the optical receiver 102 can be increased, no adjustment is possible, but this method has a problem that the circuit configuration of the optical receiver 102 becomes complicated.

In the method of adjusting the reception level on the optical receiver side, it is necessary to always set the optical output of the optical fiber amplifier near the maximum on the assumption that the transmission line loss is maximum. Therefore, when the loss of the transmission line is small, it means that the pumping light is emitted more than necessary, and wasteful power is consumed.

Therefore, an object of the present invention is to solve the above problems and to provide an optical transmission device capable of automatically adjusting the gain of an optical fiber amplifier according to the loss of a transmission line.

[0007]

To achieve the above object, the present invention provides a transmission line for transmitting signal light together with pumping light,
An optical fiber amplifier for amplifying the signal light is connected, a pumping light reflecting means for reflecting pumping light is provided at one end of the transmission line, and the reflected return light is detected in the optical fiber amplifier to detect the gain and the gain of the optical fiber amplifier. An amplifier control means for controlling the optical output level is provided.

The pumping light reflecting means may be composed of an optical multiplexer / demultiplexer for separating the pumping light and a total optical reflector for reflecting the separated pumping light.

The optical fiber amplifier may have an optical circulator that separates the reflected return light of the pump light from the transmission line.

The optical fiber amplifier has a sending pumping light level detecting means for detecting the pumping light level sent to the transmission line, and the amplifier controlling means sends out the level of the reflected return light of the pumping light from the transmission line. The gain and optical output level of the optical fiber amplifier may be controlled in comparison with the pumping light level.

The excitation light reflecting means may be composed of an optical multiplexer / demultiplexer for separating the excitation light and an end face of an optical fiber or an optical connector for Fresnel-reflecting the separated excitation light.

An optical switch or an optical modulator may be provided between the optical multiplexer / demultiplexer and the optical total reflector.

[0013]

With the above construction, the pumping light of the optical fiber amplifier is output to the transmission line together with the signal light, and the pumping light reaching one end of the transmission line is reflected by the pumping light reflecting means and returned to the optical fiber amplifier. The excitation light is attenuated by going back and forth in the transmission path. By detecting the optical level of the pumping light that has reciprocated in the transmission line, the rate of loss in the transmission line can be known. If the optical output (gain and optical output level) of the optical fiber amplifier is controlled in accordance with this, signal light having an optimum level at one end of the transmission line can be sent to the transmission line. Since the loss is detected by using the pumping light, the optical level of the signal light is not lowered or the loss is not increased. Moreover, when the loss in the transmission line is small, the optical output of the optical fiber amplifier can be reduced.

Since the pumping light reflecting means separates only the pumping light and totally reflects it, the signal light passes through without loss and does not return to the transmission path. On the contrary, the pumping light returns to the transmission line without loss and does not pass through.

Since the optical circulator is used to separate the output light of the optical fiber amplifier and the reflected return light of the pumping light, the output light of the optical fiber amplifier is output to the transmission line without loss during the separation, and The reflected return light is taken in without loss.

By comparing the level of the pumping light sent to the transmission line with the level of the reflected return light of the pumping light from the transmission line, the loss in the transmission line can be accurately known, and the optical output control of the optical fiber amplifier can be determined to be appropriate. Become.

Fresnel reflection by an end face of an optical fiber or an optical connector may be used instead of the total light reflector to return the excitation light.

When the pumping light is returned, the returning light is turned on / off or modulated to perform information transmission using the returning pumping light as a medium.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

As shown in FIG. 1, the optical transmission apparatus of the present invention is provided with an optical fiber amplifier 103 between an optical transmitter 101 and an optical receiver 102. Transmission line 1 including an optical fiber 104 connected to the output side of the optical transmitter 101
Reference numeral 05 denotes an input side of the optical fiber amplifier 103, and a transmission line 107 formed of the optical fiber 106 drawn from the output side of the optical fiber amplifier 103 is connected to the pumping light reflecting means 10.
8 is connected to the optical receiver 102. Optical transmitter 101, optical receiver 102, optical fibers 104 and 106
Is the same as the conventional one. A transmission line 109 made of an optical fiber is also formed in the optical fiber amplifier 103, and a part of the transmission line 109 is made of a rare earth-doped fiber 110. The pumping light source 111 and the optical multiplexer / demultiplexer 112 are also the same as the conventional ones, and the pumping light from the pumping light source 111 and the signal light from the transmission line 105 on the optical transmitter 101 side pass through the optical multiplexer / demultiplexer 112 to add a rare earth element. It is adapted to be input to the fiber 7.

Transmission line 109 in the optical fiber amplifier 103
The transmission path 107 on the optical receiver 102 side is connected to the optical circulator 113. Optical circulator 1
13 outputs the signal light and pumping light from the transmission line 109 including the rare earth-doped fiber 110 to the transmission line 107 on the optical receiver 102 side, and the transmission line 10 on the optical receiver 102 side.
The reflected return light of the excitation light from 7 is the reflected return light detector 114.
It is designed to be input to. In this way, the optical fiber amplifier 103 is configured so that the pumping light is output to the transmission line together with the signal light.

One end of the transmission line 107, that is, the optical receiver 102
The pumping light reflecting means 108 provided immediately before the
Optical multiplexer / demultiplexer 115 for separating the signal light and pumping light from 07 into signal light and pumping light, an optical total reflector 116 for reflecting the separated pumping light, and only the signal light to optical receiver 102 And an optical filter 117 for controlling the light.

In the optical fiber amplifier 103, the transmission line 1
Reflected return light detector 114 for detecting the reflected return light of the pumping light from 07, sending pumping light level detecting means 118 for detecting the pumping light level sent to transmission line 109, and pumping light control for controlling pumping light source 111. The circuit 119 constitutes amplifier control means 120 for controlling the gain and the optical output level of the optical fiber amplifier. This amplifier control means 120 compares the level of the reflected return light of the pumping light from the transmission line 107 with the level of the pumping light to be transmitted, and then the optical fiber amplifier 1
03 gain and optical output level.

Next, the operation of the embodiment will be described.

The signal light input to the optical fiber amplifier 103 passes through the optical multiplexer / demultiplexer 112 and the rare earth-doped fiber 7
Is input to The pumping light from the pumping light source 111 is also input to the rare earth-doped fiber 7 through the optical multiplexer / demultiplexer 112.
The signal light is amplified in the rare earth-doped fiber 7. The amplified signal light is output to the transmission path 107 through the optical circulator 113. At this time, of the pumping light input to the rare earth-doped fiber 7, the pumping light that has not contributed to signal light amplification is also output to the transmission line 107 through the optical circulator 113, and pumped at one end of the transmission line 107 together with the signal light. It reaches the light reflecting means 108.

In the pumping light reflecting means 108, the optical multiplexer / demultiplexer 1
The signal light and the pumping light are separated by 15, and the signal light passes through the optical filter 117 and is input to the optical receiver 102.
The excitation light is reflected by the total optical reflector 116, and the optical multiplexer / demultiplexer 1
It is returned to the transmission line 107 by 15. The excitation light that has become the reflected return light passes through the transmission path 107, passes through the optical circulator 113, and is input to the reflected return light detector 114.

When the loss in the transmission line 107 is large, the detected return light becomes small. When the loss in the transmission line 107 is small, the detected return light becomes large. The amplifier control means 120 controls the output of the pumping light source 111 based on the output of the reflected return light detector 114. The amplifier control unit 120 detects the magnitude of the loss in the transmission line 107 by using the pumping light level sent to the transmission line 109 detected by the sending pumping light level detection unit 118.

In this way, the optical signal output control according to the loss in the transmission line 107 is achieved. At this time, by transmitting the pumping light that has not contributed to the amplification of the signal light after passing through the rare earth-doped fiber 7 to one end of the transmission path 107 together with the signal light and reflecting and detecting only the pumping light,
The reception level of the optical receiver 102 can be made constant without lowering the usage efficiency of the pumping light and without degrading the signal light.

According to the present invention, not only the gain of the optical fiber amplifier 103 can be automatically controlled according to the loss in the transmission line 107, but also the receiving power range of the optical receiver 102 can be reduced, and only the receiving sensitivity can be obtained. Considered optical receiver 102
Therefore, it is possible to significantly increase the sensitivity of the optical receiver 102, and it is possible to cope with a further large fluctuation in the transmission line loss without adjustment. Thereby, the transmission distance and the dynamic range can be expanded.

The excitation light reflecting means 108 can also be realized by using Fresnel reflection of the end face of a half mirror or an optical fiber optical connector instead of the total light reflector 116 that reflects the excitation light. However, when the loss in the transmission line 107 is large or the reflectance is small, the reflected return photodetector 114
To use a more sensitive photodetector.

Next, another embodiment will be described.

The optical transmission device of FIG. 2 is an optical fiber amplifier 203 by changing the configuration of the optical fiber amplifier 103 of the optical transmission device of FIG. Optical fiber amplifier 203
Is a rare earth-doped fiber 110 and an optical circulator 11.
In the transmission line 109 between the optical multiplexer / demultiplexer 221 and the optical multiplexer / demultiplexer 221
By inserting a bypass for the pumping light between the optical multiplexers / demultiplexers 221 and 222, and further inserting an optical branching device 223 into this bypass, and the branched pumping light is transmitted by the pumping light level detecting means 2
It is configured to be detected at 18. The pumping light that has been input to the rare earth-doped fiber 7 and has not contributed to signal light amplification is partly branched and detected for monitoring the pumping light level. The remaining pumping light is output to the transmission line 107 together with the signal light, and the reflected return light is detected by the reflected return light detector 114 as in the case of FIG. The pumping light control circuit 119
The excitation light source 111 is controlled based on the comparison.

As described above, by comparing the level of the pumping light which did not contribute to the amplification of the signal light and the level of the reflected return light, the loss in the transmission line 107 can be obtained more accurately.

The optical transmission device of FIG. 3 is an optical fiber amplifier 303 in which the configuration of the optical fiber amplifier 103 of the optical transmission device of FIG. 1 is changed. Optical fiber amplifier 303
Does not input the output of the pumping light source 111 to the optical multiplexer / demultiplexer 112, branches it by the optical splitter 326, and connects it to the optical multiplexer / demultiplexer 324 and the optical multiplexer / demultiplexer 325. Optical multiplexer / demultiplexer 324, 32
5 is a rare earth-doped fiber 110 and an optical circulator 1
It is inserted in the transmission line 109 between the line 13 and the line 13. In this configuration, the pumping light from the pumping light source 111 is transmitted by the optical splitter 326.
One is input to the rare earth-doped fiber 110 through the optical multiplexer / demultiplexer 324, and the other is input to the optical multiplexer / demultiplexer 3
25, and is output to the transmission path 107 through the optical circulator 113. The excitation light passing through the rare earth-doped fiber 110 is in the opposite direction to the signal light.

With this configuration, the same effects as those of the configurations of FIGS. 1 and 2 can be obtained, but in the configuration of FIG. 3, the pumping light sent to the transmission line 107 is taken from the pumping light source 111 and is independent of the signal light amplification. .

Each of the embodiments described so far is based on the optical transmitter 1.
Although one optical fiber amplifier 103, 203, 303 is provided between 01 and the optical receiver 102, it is also possible to connect the optical fiber amplifiers in multiple stages to perform relay amplification.
In this case, by placing the pumping light reflecting means 108 on the signal light input side of each optical fiber amplifier, the optical signal intensity can be controlled to be constant for each stage.

In the optical transmission device of FIG. 4, unlike the conventional ones, the pumping light of the optical fiber amplifier 403 is used as the optical transmitter 10.
A pumping light reflecting means 408 including an optical multiplexer / demultiplexer 415 and a total optical reflector 416 is provided at one end of the transmission path 105, that is, immediately after the optical transmitter 101. The loss of the transmission line 105 on the input side of the optical fiber amplifier 403 is determined. The transmission line 409 in the optical fiber amplifier 403 and the transmission line 105 on the optical transmitter 101 side are connected via an optical circulator 413. The pumping light from the pumping light source 111 is input to the rare earth-doped fiber 110 by the optical multiplexer / demultiplexer 427, passes through the rare earth-doped fiber 110 in the opposite direction to the signal light, and is bypassed from the optical multiplexer / demultiplexer 428 to the optical circulator 413. . Optical multiplexer / demultiplexer 428 and optical circulator 4
A part of the pumping light that has not contributed to the signal light amplification is branched by the optical branching device 223 inserted between the optical fiber 13 and the optical splitter 13 and detected by the sending pumping light level detecting means 218. The excitation light input to the transmission path 105 through the optical circulator 413 is
The optical fiber amplifier 40 is reflected by the pumping light reflecting means 408 and returns, and passes through the optical circulator 413 together with the signal light.
3 is input to the transmission line 409. The optical multiplexer / demultiplexer 429 separates the reflected return light of the excitation light, and the reflected return light detector 114 detects this.

According to this structure, the gain of the optical amplifier can be controlled without detecting the level of the input signal light. Further, since the transmission line loss can be compensated, the output of the optical fiber amplifier 403 can be kept at the same level as the output of the optical transmitter 101.

Next, an application example of the present invention will be described.

The reflectance of the optical reflector used for returning the pumping light is modulated, and the modulated reflected return light is detected by the reflected return light detecting light receiving element, so that one end of the transmission line is transferred to the optical fiber amplifier. A signal different from the signal light can be transmitted without using a light emitting element or a light source. As a method of modulating the light reflectivity, for example, there is a method of placing an optical switch in front of the light reflector and turning the optical switch on and off. Also,
When connecting optical fiber amplifiers in multiple stages for relay amplification,
The optical fiber amplifier modulates the reflectance of the optical reflector based on the reflected return light, so that the relay transmission of the signal by the reflected return light becomes possible.

Since the optical fiber amplifier can detect the loss of the transmission line, it can be used for maintenance and monitoring of the transmission line at the same time while performing signal transmission.

Since the reflected return light detector 114 and the pumping light control circuit 119 do not require high-speed response characteristics, they can be realized with a simple structure and low cost.

[0043]

The present invention exhibits the following excellent effects.

(1) Since the signal light is not branched, the gain of the optical fiber amplifier does not decrease.

(2) Since the optical fiber amplifier automatically adjusts the optical output, the adjustment by the optical attenuator or the like in the optical receiver becomes unnecessary.

(3) Since the reception power range of the optical receiver can be reduced, high-sensitivity reception can be performed by the optical receiver considering only high sensitivity, and an increase in transmission loss can be easily dealt with.

(4) Since the gain of the optical fiber amplifier can be set in accordance with the loss of the transmission line and the receiving sensitivity of the optical receiver and the optical output is not increased more than necessary, the power consumption due to the optical signal amplification is suppressed. be able to.

[Brief description of drawings]

FIG. 1 is an optical circuit diagram of an optical transmission device showing an embodiment of the present invention.

FIG. 2 is an optical circuit diagram of an optical transmission device showing another embodiment of the present invention.

FIG. 3 is an optical circuit diagram of an optical transmission device showing another embodiment of the present invention.

FIG. 4 is an optical circuit diagram of an optical transmission device showing another embodiment of the present invention.

FIG. 5 is an optical circuit diagram of an optical transmission device showing a conventional example.

[Explanation of symbols]

 101 Optical Transmitter 102 Optical Receiver 103 Optical Fiber Amplifier 105, 107 Transmission Line 108 Excitation Light Reflecting Means 120 Amplifier Controlling Means

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display area H04B 10/28 10/26

Claims (6)

[Claims] 1. An optical fiber amplifier for amplifying the signal light is connected to a transmission line for transmitting the signal light together with the pumping light,
Pumping light reflecting means for reflecting the pumping light is provided at one end of the transmission line, and amplifier control means for detecting the reflected return light in the optical fiber amplifier to control the gain and the optical output level of the optical fiber amplifier are provided. An optical transmission device characterized by. 2. The light according to claim 1, wherein the pumping light reflecting means comprises an optical multiplexer / demultiplexer for separating the pumping light and an optical total reflector for reflecting the separated pumping light. Transmission equipment. 3. The optical transmission device according to claim 1, wherein the optical fiber amplifier has an optical circulator that separates the reflected return light of the pumping light from the transmission line. 4. The optical fiber amplifier has a sending pumping light level detecting means for detecting a pumping light level sent to a transmission line, and the amplifier controlling means has a level of reflected return light of the pumping light from the transmission line. 5. The optical transmission device according to claim 1, wherein the gain and the optical output level of the optical fiber amplifier are controlled by comparing with the output pumping light level. 5. The excitation light reflecting means comprises an optical multiplexer / demultiplexer for separating the excitation light and an end face of an optical fiber or an optical connector for Fresnel reflecting the separated excitation light. 1. The optical transmission device according to 1. 6. The optical transmission device according to claim 2, wherein an optical switch or an optical modulator is provided between the optical multiplexer / demultiplexer and the optical total reflector.