JP2002005784A - Light amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light amplifier capable of realizing early recovery of a system by immediately determining an abnormal portion and an abnormal cause after abnormality of a transmission line is detected. SOLUTION: This light amplifier has a monitoring signal light source 20 emitting a monitoring signal light independent of an excitation light source 4 for exciting erbium added optical fibers 3a, 3b, and a pulse generating circuit 21 for generating pulses having specific duty ratio when abnormality is detected, and by emitting a pulsed light corresponding to the pulse from the excitation light source 4, the excitation light source 4 is used as a light source for emitting the pulsed light for measuring back scattered light in addition to the light source for exciting the erbium added optical fibers 3a, 3b. Since the a back scattered light detecting circuit 22 is installed, the abnormal portion and the abnormal cause can be determined at almost the same time as circuit abnormality detection.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplifier having a function of monitoring a broken portion or the like of an optical fiber transmission line, and more particularly to an optical amplifier capable of specifying an abnormal location and an abnormal cause.

[0002]

2. Description of the Related Art Attention has been focused on optical fibers having special functions such as amplification effect, non-linearity, dispersibility, non-reciprocity and sensor effect added to the optical fiber. In particular, in recent years,
2. Description of the Related Art Optical fibers having an amplification function have been actively researched to reduce attenuation due to long-distance transmission of signal light.

In general, an optical fiber having an amplification function is used as a component of an optical amplifier together with a pumping light source for pumping the optical fiber. In recent years, among these optical amplifiers, an optical amplifier having a function of monitoring an abnormality such as a disconnection of a signal light transmission line (optical fiber) has been developed. As such an optical amplifier with a supervisory control function, for example, an "optical amplifier with a supervisory control function" disclosed in No. B-10-124 of "2000 IEICE General Conference Proceedings" is known. .

FIG. 3 is a block diagram showing a schematic configuration of the above-mentioned conventional optical amplifier with a supervisory control function. The optical amplifier with a monitoring control function shown in FIG. 3 has a signal input terminal 101 for inputting a main signal light in a 1.55 μm wavelength band, a signal output for outputting the amplified main signal light and a monitoring signal light to be described later. The terminal 102, a first erbium-doped optical fiber 103a and a second erbium-doped optical fiber 103b as amplification media, and a 1.48 μm wavelength for exciting the first and second erbium-doped optical fibers 103a and 103b. Light source 10 for outputting band pump light
4 and the light in the 1.48 μm wavelength band are output from the signal output terminal 10.
Excitation light removal filter 107 for preventing leakage from filter 2
And an optical isolator 108 having a function of giving directionality to the main signal light and preventing laser oscillation.

The optical amplifier with the monitoring and control function comprises a signal input terminal 101 and a first erbium-doped optical fiber 1.
A fiber grating reflector 105 is provided between the first erbium-doped optical fiber 103a and the second erbium-doped optical fiber 103a.
The optical circulator 106 is provided between the erbium-doped optical fibers 103b.

The fiber grating reflector 10
No. 5 has a reflection characteristic of reflecting 95% of the light in the 1.48 μm wavelength band and transmitting 5% of the light. The optical circulator 106 guides the pump light output from the excitation light source 104 to the first erbium-doped optical fiber 103a, and thereby converts the pump light reflected from the fiber grating reflector 105 to the second erbium-doped optical fiber. Lead to 103b. This optical circulator 1
06 further has a function of giving directionality to light incident from the signal input terminal 101 and preventing laser oscillation.

The optical amplifier with a monitoring control function includes an LD driving circuit 113 for driving the excitation light source 104 and a monitoring signal generating circuit 114. Monitoring signal generation circuit 11
Reference numeral 4 generates a monitoring signal for detecting an abnormality such as a disconnection of a transmission line. The monitoring signal generated by the monitoring signal generation circuit 114 is input to the LD drive circuit 113 and superimposed on the pump light, which is a DC component, as the monitoring signal light.

Thus, the monitoring signal light is transmitted to the optical circulator 106 and the first erbium-doped optical fiber 103.
a, via the fiber grating reflector 105 and the signal input terminal 101, to the same optical amplifier (hereinafter, referred to as a front node) located at the preceding stage.

Further, the optical amplifier with a supervisory control function includes an optical coupler 109 for branching supervisory signal light output from the same optical amplifier (hereinafter, referred to as a next node) located at a subsequent stage and input to the signal output terminal 102. A light receiving element 110 for receiving the monitoring signal light branched by the optical coupler 109, a monitoring signal detecting circuit 111 for detecting the monitoring signal light received by the light receiving element 110, and the monitoring signal detecting circuit 111 disconnecting the monitoring signal light. And a line switching control circuit 112 for switching a line for transmitting an optical signal such as a main signal light to a protection line upon detection.

Next, the operation of the optical amplifier with a monitoring and control function will be described with reference to the pump light and the monitoring signal light.
Transmission of light having a wavelength of 48 μm (hereinafter, referred to as pumping light) and light having a wavelength of 1.55 μm which is main signal light will be described in order. First, regarding the transmission of the excitation light, the excitation light source 1
The pumping light emitted from the optical circulator 104 is supplied to the optical circulator 106 regardless of whether the monitoring signal light is superimposed.
Is guided to the first erbium-doped optical fiber 103a by the first erbium-doped optical fiber 103a.
To excite.

First erbium-doped optical fiber 103a
Has a short shape for the purpose of approaching a completely inverted population state in order to reduce the noise figure, and most of the excitation light reaches the fiber grating reflector 105 without being absorbed. In the fiber grating reflector 105, 95% of the light that has reached is reflected and is again incident on the first erbium-doped optical fiber 103a. The light returns to the optical circulator 106 without being absorbed.

Here, the optical circulator 106 is a first circulator.
Of the second erbium-doped optical fiber 103a with respect to the light incident from the side of the erbium-doped optical fiber 103a.
The pumping light returning from the first erbium-doped optical fiber 103a side has the directionality leading to the b side.
Incident on the second erbium-doped optical fiber 103b side,
This excites the second erbium-doped optical fiber 103b.

The second erbium-doped optical fiber 1
03b is elongated to obtain high output,
Excitation light in the 1.48 μm wavelength band is almost absorbed but slightly transmits the excitation light. However, the transmitted excitation light is supplied to the excitation light removal filter 107.
, So that it is not transmitted to the transmission line.

On the other hand, the supervisory signal light is transmitted to the supervisory signal generation circuit 1.
When the modulation signal of the frequency f1 generated at 14 is input to the LD drive circuit 113, it is superimposed on the DC component of the pump light, and the optical circulator 1 is used as the excitation light.
06. Then, the excitation light that has entered the optical circulator 106 reaches the fiber grating reflector 105 via the first erbium-doped optical fiber 103a, as described above.

At this time, the fiber grating reflector 1
In FIG. 05, 95% of the arriving light is reflected.
Reenters the erbium-doped optical fiber 103a side, but the remaining 5% of the light is transmitted. This transmitted light is output from the signal input terminal 101 as effective monitoring signal light, and is transmitted toward the transmission path toward the previous node in a direction opposite to the main signal light. In other words, the optical amplifier with a supervisory control function receives supervisory signal light from the next node via the signal output terminal 102.

The monitoring signal light input from the signal output terminal 102 is guided to the light receiving element 110 by the optical coupler 109, and is converted into an electric signal by the light receiving element 110. The reception of the monitoring signal light by the light receiving element 110 is detected by the monitoring signal detection circuit 111. If the monitoring signal light is not detected by the monitoring signal detection circuit 111, it is determined that an abnormality such as disconnection of the transmission line has occurred, and the line switching control circuit 112 sets the line for transmitting the optical signal such as the main signal light to the standby state. Switch to line.

As described above, in the optical amplifier, it is common to use the monitoring signal light by superimposing it on the pump light.
For example, "Monitoring control method in optical amplification repeater transmission system" disclosed in No. B-944 of "1992 Spring Meeting of the Institute of Electronics, Information and Communication Engineers", and "Optical repeater repeater" disclosed in Japanese Patent Application Laid-Open No. 6-6309. Monitoring method ".

Next, transmission of light having a wavelength of 1.55 μm, which is the main signal light, will be described. The main signal light having a wavelength of 1.55 μm incident on the signal input terminal 101 is transmitted through the fiber grating reflector 105 and is incident on the first erbium-doped optical fiber 103a.
It is amplified by the action of the pump light guided by 6.

First erbium-doped optical fiber 103a
The main signal light amplified in the optical circulator 10
The light enters the second erbium-doped optical fiber 103b through the optical fiber 6, and is further amplified to a desired optical output by the action of the pump light. The main signal light amplified in the second erbium-doped optical fiber 103b is
The signal is transmitted from the signal output terminal 102 via the excitation light removal filter 107, the optical isolator 108, and the optical coupler 109. That is, as described above, the optical coupler 109 branches the monitoring signal light input to the signal output terminal 102 to the light receiving element 110, and also outputs the main signal light transmitted through the optical isolator 108 to the signal output terminal 102. It also has the function of deriving.

Next, a description will be given of a supervisory control method in the optical amplifier with a supervisory control function described above. FIG. 4 is a diagram showing a schematic configuration of an optical transmission system for explaining a supervisory control method. In particular, FIG. 4A shows a normal state in which no disconnection or the like of the transmission line occurs, that is, a state in which the working line is used as a line for transmitting an optical signal such as a main signal light. Further, FIG. 4B shows a state at the time of abnormality due to a disconnection of the transmission line, that is, a state in which a protection line is used as a line for transmitting an optical signal such as a main signal light.

FIG. 4 shows an optical transmission system,
In particular, a state in which the main signal light and the supervisory signal light are transmitted and received between the first node 200a and the second node 200b is also shown. In FIG. 4, the first node 20
Reference numeral 0a denotes a working line optical amplifier 201a and a protection line optical amplifier 202a having the same configuration as the optical amplifier with a monitoring control function shown in FIG. And

Similarly, for the second node 200b, the working line optical amplifier 201b and the protection line optical amplifier 202b having the same configuration as the optical amplifier with the supervisory control function shown in FIG. An optical switch (not shown) for switching the path from the transmission path 203 to the protection line transmission path 204.

Here, a description will be given of a series of flows for detecting an abnormality, switching a line, and identifying and restoring an abnormality detection point in the working line transmission line 203. First, FIG.
As shown in (a), when the supervisory signal light transmitted from the second node 200b to the working line transmission line 203 is normally received by the first node 200a, the optical switch 205 switches to the working line. The main signal light output from the working optical amplifier 201a is sent to the working line transmission line 203.

On the other hand, when an abnormality such as disconnection occurs on the working line transmission line 203, as shown in FIG.
In the node 200a, the monitoring signal detection circuit 111 shown in FIG. 3 cannot detect the monitoring signal light, whereby the line switching control circuit 112 operates to switch the path in the optical switch 205 to the protection line transmission line 204. Can be

At this time, in order to identify an abnormal portion such as a disconnection on the working line transmission line 203, generally, light for detecting an abnormal portion is incident on the transmission line, and backscattered light due to the disconnection portion is detected. The measurement is performed using a device that measures a large amount of reflected return light or a transmission path loss at a disconnection location and specifies an abnormal location. This device uses OTDR (Optical Time)
This is called a “Domain Reflectometer”, and is not usually incorporated in the optical transmission system, but is provided as a measuring device used only when an abnormality occurs. When an abnormal location is specified by using the OTDR, the maintenance worker goes to the abnormal location and reconnects the disconnected location. Thus, the restoration of the transmission path is completed.

[0026]

However, in the above-described monitoring and control system in the conventional optical amplifier, the section where the optical amplifier is arranged, that is, the abnormality occurs, due to the detection of the abnormality from the specific optical amplifier. Although the section can be specified, it is necessary to re-diagnose the disconnection point using the OTDR in order to specify the detailed abnormal part and the cause of the abnormality, so that there is a problem that it takes a long time to recover.

A conventional optical amplifier having a monitoring function generates a monitoring signal light by superimposing a signal of a predetermined frequency on the pump light, and the pumping light source 104 outputs the pump light and the monitoring signal. In general, in an optical amplifier using a silica-based erbium-doped optical fiber as an amplification medium, its reliability,
That is, there is a problem that the reliability of the system may be reduced because the component that determines the service life is the excitation light source.

In order to improve the reliability of the system, it is conceivable to prepare a spare pumping light source. However, this causes a problem that the cost of each optical amplifier increases.

The present invention has been made in order to solve the above-mentioned problems, and an optical amplifier capable of realizing an early recovery of a system by immediately detecting an abnormality of a transmission line and identifying the abnormality location and the cause of the abnormality. The purpose is to obtain.

[0030]

Means for Solving the Problems The above-mentioned problems are solved,
In order to achieve the object, in the optical amplifier according to the present invention, in the optical amplifier used in the optical network,
A rare-earth-doped optical fiber serving as an amplification medium; and a first light-emitting device that emits pulsed light in response to the input of the first or second pulse signal.
A light source, a second light source that emits a monitoring signal light transmitted on the transmission path to detect an abnormality on a transmission path of the optical network, monitoring signal detection means for detecting the monitoring signal light, and the monitoring When the monitoring signal light is detected by the signal detection means, a first pulse signal for using the pulse light as excitation light of the rare-earth-doped optical fiber is output, and the monitoring signal detection means performs the monitoring. A pulse generation unit that outputs a second pulse signal for using the pulse light as backscattered light measurement pulse light for detecting backscattered light on the transmission path when no signal light is detected; and Backscattered light detecting means for detecting the backscattered light in order to identify the cause of the abnormality and the location of the abnormality on the transmission path.

According to the present invention, the light source for emitting the monitor signal light is provided independently of the first light source for excitation as the second light source, and when the abnormality is detected, the specific duty ratio is set. Pulse generating means for generating a pulse of the type described above, and by emitting a pulse light corresponding to the pulse from the first light source, the first light source can be used only as a light source for exciting the rare earth-doped optical fiber. But not
It can also be used as a light source for emitting backscattered light measurement pulse light, and by providing a backscattered light detection means, it is possible to specify an abnormal location and an abnormal cause almost simultaneously with line abnormality detection. .

In the optical amplifier according to the next invention,
In an optical amplifier used in an optical network, a rare earth-doped optical fiber as an amplification medium, a first light source that emits pulsed light in response to input of a first or second pulse signal, and a transmission line of the optical network. A second emitting a monitoring signal light transmitted on the transmission line to detect an abnormality;
A light source, a monitoring signal detecting means for detecting the monitoring signal light, and when the monitoring signal light is detected by the monitoring signal detecting means, the pulse light is used as excitation light for the rare earth-doped optical fiber. Pulse signal for detecting backscattered light on the transmission path when the monitor signal light is not detected by the monitor signal detecting means. Pulse generation means for outputting a second pulse signal for use as a signal; backscattered light detection means for detecting the backscattered light to identify the cause of the abnormality and the location of the abnormality on the transmission line; When the monitoring signal light is not detected by the means, the backscattered light measurement pulse is provided on a path through which the backscattered light measurement pulse light is transmitted. An optical switching means for forming a path that bypasses the particular optical components a loss of light occurs, characterized by comprising a.

According to the present invention, the light source for emitting the monitoring signal light is provided as the second light source independently of the first light source for excitation, and when the abnormality is detected, the specific duty ratio is set. Pulse generating means for generating a pulse of the type described above, and by emitting a pulse light corresponding to the pulse from the first light source, the first light source can be used only as a light source for exciting the rare earth-doped optical fiber. But not
It can also be used as a light source for emitting backscattered light measurement pulsed light, and by providing backscattered light detection means, it is possible to specify an abnormal location and cause almost simultaneously with line abnormality detection. In addition, since the optical switch means for forming a detour path when the backscattered light measurement pulse light is transmitted is provided, the optics causing a loss of the backscattered light measurement pulse light such as a fiber grating reflector. Parts can be bypassed.

In the optical amplifier according to the next invention,
In the above invention, the rare earth-doped optical fiber is an erbium-doped optical fiber.

According to the present invention, an erbium-doped optical fiber can be used as an amplifying medium, and even in an optical amplifier to which this erbium-doped optical fiber is applied, the function of detecting the above-mentioned backscattered light can be exhibited. .

In the optical amplifier according to the next invention,
In the above invention, the first light source is a semiconductor laser that oscillates light in a 1.48 μm wavelength band.

According to the present invention, 1.48 is used as the first light source for emitting the excitation light and the pulse light for measuring the backscattered light.
A semiconductor laser that oscillates light in the μm wavelength band can be used.

In the optical amplifier according to the next invention,
In the above invention, the monitoring signal detecting means and the backscattered light detecting means use an avalanche photodiode as a light receiving means for receiving the monitoring signal light and the backscattered light.

According to the present invention, an avalanche photodiode can be used to receive the monitoring signal light and the backscattered light, so that higher-speed detection is possible.

[0040]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the optical amplifier according to the present invention will be described below in detail with reference to the drawings. The present invention is not limited by the embodiment.

Embodiment 1 First, an optical amplifier according to the first embodiment will be described. The optical amplifier according to the first embodiment includes a light source that generates a monitoring signal independently of an excitation light source for outputting pump light, and further includes a circuit that detects the backscattered light described above in advance.
It is characterized in that the function of the OTDR can be exhibited immediately after detecting the abnormality of the transmission path.

FIG. 1 is a block diagram showing a schematic configuration of the optical amplifier according to the first embodiment. The optical amplifier shown in FIG. 1 includes a signal input terminal 1 for inputting a main signal light in a 1.55 μm wavelength band, a signal output terminal 2 for outputting an amplified main signal light and inputting a monitoring signal, and an amplification medium. Certain first and second erbium-doped optical fibers 3a and 3b, and 1.4 for exciting the first and second erbium-doped optical fibers 3a and 3b.
An excitation light source 4 that oscillates a pump light in the 8 μm wavelength band, an excitation light removal filter 7 that prevents the light in the 1.48 μm wavelength band from leaking out of the signal output terminal 2, and gives directionality to the main signal light. And an optical isolator 8 having a function of preventing laser oscillation. Note that a semiconductor laser is preferably used as the excitation light source 4.

In this optical amplifier, a fiber grating reflector 5 is provided between the signal input terminal 1 and the first erbium-doped optical fiber 3a, and the first erbium-doped optical fiber 3a and the second erbium-doped optical fiber are provided. Fiber 3b
An optical circulator 6 is provided between them.

The fiber grating reflector 5 and the optical circulator 6 function in the same manner as the fiber grating reflector 105 and the optical circulator 106 shown in FIG. 3, respectively.

The optical amplifier according to the first embodiment has
An LD drive circuit 13a for driving the excitation light source 4 and a pulse generation circuit 21 are provided. The pulse generation circuit 21
This is a circuit for outputting the excitation light generated from the excitation light source 4 as pulse light by supplying a pulse current to the LD drive circuit 13a. By changing the duty ratio of the pulse light, the average intensity of the pump light can be reduced. It is possible to adjust.

The optical amplifier includes a monitor signal light source 20 that oscillates a monitor signal light in a 1.48 μm wavelength band, an LD drive circuit 13b that drives the monitor signal light source 20, a monitor signal generation circuit 14, An optical coupler 9b for guiding the monitoring signal light to the signal output terminal 2. The monitoring signal generation circuit 14 is a circuit that generates a monitoring signal for detecting an abnormality such as a disconnection of a transmission line. The monitoring signal generated by the monitoring signal generating circuit 14 is
b, and as a result, the monitoring signal light is emitted from the monitoring signal light source 20. The supervisory signal light output from the supervisory signal light source 20 is input to the optical coupler 9b and transmitted via the signal output terminal 2 to the same optical amplifier (hereinafter, referred to as the next node) located at the next stage.

Further, this optical amplifier comprises an optical coupler 9a for branching a monitoring signal input to the signal input terminal 1 from the optical amplifier (hereinafter, referred to as a preceding node) located at the preceding stage;
A light receiving element 10 for receiving the monitoring signal branched by the optical coupler 9a, a monitoring signal detecting circuit 11 for detecting the monitoring signal light received by the light receiving element 10, and when the monitoring signal detecting circuit 11 detects that the monitoring signal is disconnected. A line switching control circuit 12 for switching a line transmitting an optical signal such as a main signal light to a protection line. In addition, it is preferable to use an avalanche photodiode as the light receiving element 10 because higher speed detection is possible.

Here, when the monitoring signal detection circuit 11 detects the disconnection of the monitoring signal, the pulse generation circuit 21
By supplying a pulse current having a duty ratio of about 10% to the D drive circuit 13a, the excitation light source 4 outputs pulse light for measuring backscattered light. That is, when an abnormality in the transmission path is detected, the light output from the excitation light source 4 is:
It is used not to excite the first erbium-doped optical fiber 3a and the second erbium-doped optical fiber 3b, but to output backscattered light based on the OTDR function to the transmission line in which an abnormality has occurred.

Therefore, the optical amplifier according to the first embodiment includes a backscattered light detection circuit 22 for detecting backscattered light output from the excitation light source 4. here,
Since the backscattered light has the same wavelength (1.48 μm) as the monitoring signal light, it is received by the light receiving element 10 via the optical coupler 9a when input to the signal input terminal 1. The received backscattered light is transmitted to the monitoring signal detection circuit 1
Since the signal is input to the above-described backscattered light detection circuit 22 through 1, the backscattered light can be detected as a result.

Next, regarding the operation of the optical amplifier according to the first embodiment, the pump light and the pulse light for measuring the backscattered light output from the excitation light source 4 and the monitoring signal light output from the monitoring signal light source 20 will be described. The transmission of the main signal light will be described in order. First, regarding the transmission of the pump light, the pump light emitted from the excitation light source 4 is supplied to the first erbium-doped optical fiber 3a by the optical circulator 6.
And the first erbium-doped optical fiber 3a
To excite.

The first erbium-doped optical fiber 3a is
In order to reduce the noise figure, it is made short so as to approach a completely inverted distribution state, and most of the excitation light reaches the fiber grating reflector 5 without being absorbed.
In the fiber grating reflector 5, the reached 95%
Is reflected again and is incident on the first erbium-doped optical fiber 3a. However, since it is close to a completely inverted distribution state as described above, most of the light is returned to the optical circulator 6 without being re-absorbed. Come.

Here, the optical circulator 6 has a directivity for guiding the light incident from the first erbium-doped optical fiber 3a side to the second erbium-doped optical fiber 3b side. Then, the pump light returned from the first erbium-doped optical fiber 3a is incident on the second erbium-doped optical fiber 3b, thereby exciting the second erbium-doped optical fiber 3b.

The second erbium-doped optical fiber 3
b has a long shape in order to obtain high output.
Most of the pump light in the 48 μm wavelength band is absorbed, but slightly transmitted. However, the transmitted pump light is completely removed by the excitation light removal filter 7 and is not transmitted to the transmission line.

On the other hand, the monitoring signal light is transmitted to the monitoring signal generating circuit 1.
The signal of the frequency f1 generated in 4 is input to the LD drive circuit 13b, so that the signal is emitted from the monitoring signal light source 20. The monitoring signal light emitted from the monitoring signal light source 20 is input to the optical coupler 9b, and is transmitted to the next node via the signal output terminal 2. In other words, the optical amplifier inputs the monitoring signal light from the previous node via the signal input terminal 1.

The monitoring signal light input from the signal input terminal 1 is guided to the light receiving element 10 by the optical coupler 9a, and is converted into an electric signal by the light receiving element 10. The reception of the monitoring signal light by the light receiving element 10 is detected by the monitoring signal detection circuit 11. When the monitoring signal light is not detected by the monitoring signal detection circuit 11, it is determined that an abnormality such as disconnection of the transmission path has occurred, and the line switching control circuit 12 sets the line for transmitting the optical signal such as the main signal light to the standby state. Switch to line.

When the switching of the line is completed, the pulse generating circuit 21 is simultaneously operated to detect a disconnection or the like of the transmission line, the duty ratio of the pulse light is reduced to 10%, and the detection of the disconnection or the like of the transmission line is performed. A backscattered light measurement pulse is generated. In addition, 1.4 which is generally used as an excitation light source
8 μm LD (laser diode) has a cavity length of 900
In the case of pulse driving with less heat generation, even if a high peak intensity is generated, the possibility that the inside of the crystal is damaged is very small, and no particular problem occurs.

The pulse for measuring the backscattered light generated in the pulse generation circuit 21 is input to the LD drive circuit 13a.
Pulse light for measuring backscattered light having a duty ratio of 10% is emitted.

The backscattered light measuring pulse light emitted from the excitation light source 4 is incident on the optical circulator 6 and reaches the fiber grating reflector 5 via the first erbium-doped optical fiber 3a as described above. I do. At this time, the fiber grating reflector 5 reflects 95% of the arriving light, so that most of the backscattered light measurement pulse light is re-incident on the first erbium-doped optical fiber 3a side. 5% is transmitted. The signal input terminal 1 is used as pulse light for measuring the backscattered light in which the transmitted light is effective.
And is transmitted toward the transmission path toward the previous node in a direction opposite to the main signal light.

The pulse light for measuring the backscattered light transmitted from the signal input terminal 1 reaches an abnormal part, and causes Rayleigh scattering or Fresnel reflection peculiar to the abnormal mode, and returns to the signal input terminal 1 as backscattered light. come. The backscattered light is received by the light receiving element 10 via the optical coupler 9a, and detected by the backscattered light detection circuit 22 via the monitoring signal detection circuit 11. Here, the backscattered light detection circuit 22
Is synchronized with the pulse generation circuit 21, so that the time from pulse transmission to pulse reception can be measured, and as a result, the distance to the abnormal part can be specified. In particular, when there is a disconnection in the transmission path, the Fresnel reflected light at the break point has higher intensity than the Rayleigh scattered light, so that the break point can be easily specified.

Next, transmission of light having a wavelength of 1.55 μm, which is the main signal light, will be described. The main signal light having a wavelength of 1.55 μm incident on the signal input terminal 1 passes through the optical coupler 9a and the fiber grating reflector 5, is incident on the first erbium-doped optical fiber 3a, and is guided by the optical circulator 6. It is amplified by the action of the pump light.

The main signal light amplified in the first erbium-doped optical fiber 3a is incident on the second erbium-doped optical fiber 3b via the optical circulator 6, and further desired light is produced by the action of the pump light described above. The output is amplified. Then, the main signal light amplified in the second erbium-doped optical fiber 3b is transmitted from the signal output terminal 2 via the excitation light removing filter 7, the optical isolator 8, and the optical coupler 9b. That is, the optical coupler 9b
Has a function of guiding the monitor signal light emitted from the monitor signal light source 20 to the signal output terminal 2 and of leading the main signal light transmitted through the optical isolator 8 to the signal output terminal 2 as described above. Also have.

As described above, according to the optical amplifier of the first embodiment, the light source for emitting the monitor signal light
The monitoring signal light source 20 includes a pulse generation circuit 21 that is provided independently of the pumping light source 4 and generates a pulse having a specific duty ratio when an abnormality is detected. Because we fire from 4,
The excitation light source 4 can be used not only as a light source for exciting the first erbium-doped optical fiber 3a and the second erbium-doped optical fiber 3b, but also as a light source for measuring backscattered light. The provision of the backscattered light detection circuit 22 makes it possible to identify an abnormal location and an abnormal cause almost simultaneously with the detection of a line abnormality and to recover the optical transmission system at an early stage.

In the first embodiment, the reflectivity of the fiber grating reflector 5 for reflecting the pump light is set to 95%. However, the same monitoring control function can be obtained by using a different reflectivity. Needless to say. Also,
In the first embodiment described above, an erbium-doped optical fiber for amplifying light in the 1.55 μm wavelength band is used as an amplification medium, but an optical fiber doped with another rare earth element may be used.

Embodiment 2 Next, an optical amplifier according to a second embodiment will be described. In the first embodiment, since the pulse light for measuring the backscattered light is transmitted through the fiber grating reflector 5, loss of the pulse light for measuring the backscattered light occurs in the fiber grating reflector 5. The optical amplifier according to the second embodiment has a high peak intensity by providing two optical switches that are operated before and after the fiber grating reflector 5 in response to the transmission of the above-described pulsed light for backscattered light measurement. It is characterized in that pulsed light for backscattered light measurement can be transmitted.

FIG. 2 is a block diagram showing a schematic configuration of the optical amplifier according to the second embodiment. In FIG. 2, portions common to FIG. 1 are denoted by the same reference numerals, and description thereof is omitted. In particular, the optical amplifier according to the second embodiment shown in FIG. 2 has optical switches 30a and 30b for forming a path bypassing the fiber grating reflector 5 before and after the fiber grating reflector 5, An optical switch drive circuit 31 that activates the optical switches 30a and 30b when a pulse for the backscattered light measurement pulse light is emitted from the generation circuit 21.

Next, the operation of the optical amplifier according to the second embodiment will be described. The transmission of the pump light output from the excitation light source 4, the monitoring signal light output from the monitoring signal light source 20, and the main signal light are described in the first embodiment.
The description is omitted here.
Therefore, regarding the backscattered light measurement pulse light output from the excitation light source 4, first, the line switching control circuit 12
Is completed, the pulse generation circuit 21 operates to detect a disconnection of the transmission line at the same time, the duty ratio of the pulse light is reduced to 10%, and the back scattering for detecting the disconnection of the transmission line is performed. An optical measurement pulse is generated.

At this time, the optical switch drive circuit 31 detects the operation of the pulse generation circuit 21 and switches the path of the optical switches 30a and 30b to the one without the fiber grating reflector 5.

The backscattered light measurement pulse generated in the pulse generation circuit 21 is input to the LD drive circuit 13a, and the LD drive circuit 13a outputs the pulse from the excitation light source 4.
Pulse light for measuring backscattered light having a duty ratio of 10% is emitted.

The backscattered light measuring pulse light emitted from the excitation light source 4 enters the optical circulator 6 and is transmitted to the first erbium-doped optical fiber 3a as described above. Since a path bypassing the fiber grating reflector 5 is formed by 30b, it does not reach the fiber grating reflector 5. As a result, the backscattered light measurement pulse light is reduced only by the insertion loss of the optical switches 30a and 30b as compared with the case where the backscattered light measurement pulse light passes through the fiber grating reflector 5, so that a high peak intensity can be maintained. Become.

The backscattered light measurement pulse light bypassing the fiber grating reflector 5 is transmitted from the signal input terminal 1 via the optical coupler 9a. And the signal input terminal 1
The backscattered light measurement pulsed light transmitted from the optical communication device reaches an abnormal portion, thereby causing Rayleigh scattering or Fresnel reflection peculiar to the abnormal mode, and returns to the signal input terminal 1 as backscattered light. The backscattered light is received by the light receiving element 10 via the optical coupler 9a, and is detected by the backscattered light detection circuit via the monitoring signal detection circuit 11.

As described above, according to the optical amplifier according to the second embodiment, in addition to the configuration shown in the first embodiment, the transmission of the pulse light for measuring the backscattered light before and after the fiber grating reflector 5 is performed. Embodiment 2 is provided with two optical switches 30a and 30b that form a path bypassing the fiber grating reflector 5 according to the first embodiment.
, The pulse light for measuring the backscattered light can be maintained at a high peak intensity, and the break point can be specified even in a system having a long distance node interval.

[0072]

As described above, according to the present invention, the light source for emitting the monitoring signal light is used as the second light source.
Provided independently of the first light source for excitation,
A pulse generating means for generating a pulse having a specific duty ratio when an abnormality is detected is provided, and a pulse light corresponding to the pulse is emitted from the first light source, so that the first light source emits rare-earth added light. It can be used not only as a light source for exciting the fiber, but also as a light source for emitting backscattered light measurement pulse light. At the same time, the location and cause of the abnormality can be specified, so that the optical transmission system can be quickly restored.

According to the next invention, the light source for emitting the monitor signal light is provided independently of the first light source for excitation as the second light source, and when the abnormality is detected, the specific duty is set. A pulse generating means for generating a pulse having a ratio is provided, and a pulse light corresponding to the pulse is emitted from the first light source, so that the first light source is used as a light source for exciting the rare earth-doped optical fiber. Not only that, it can also be used as a light source for emitting backscattered light measurement pulse light, and by providing a backscattered light detection means, it is possible to identify an abnormal location and cause almost simultaneously with line abnormality detection Therefore, the optical transmission system can be recovered at an early stage, and the optical switch means for forming a detour path when the backscattered light measurement pulse light is transmitted is provided. As a result, it is possible to maintain a high peak intensity of the backscattered light measurement pulse light by bypassing optical components such as a fiber grating reflector, which may cause a loss of the backscattered light measurement pulse light, and maintain a long distance. There is an effect that a break point can be specified even in a system with node intervals.

According to the next invention, an erbium-doped optical fiber can be used as an amplification medium, and even in an optical amplifier to which this erbium-doped optical fiber is applied, the function of detecting the backscattered light described above can be exhibited. It has the effect of being able to.

According to the next invention, 1.4 is used as the first light source for emitting the excitation light and the pulse light for measuring the backscattered light.
Since a semiconductor laser that oscillates light in the 8 μm wavelength band can be used, there is an effect that an optical amplifier can be easily and inexpensively formed.

According to the next invention, since an avalanche photodiode can be used to receive the monitoring signal light and the backscattered light, there is an effect that higher-speed detection becomes possible.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of an optical amplifier according to a first embodiment;

FIG. 2 is a block diagram illustrating a schematic configuration of an optical amplifier according to a second embodiment;

FIG. 3 is a block diagram showing a schematic configuration of a conventional optical amplifier with a supervisory control function.

FIG. 4 is a diagram showing a schematic configuration of an optical transmission system for explaining a supervisory control method in a conventional optical amplifier with a supervisory control function.

[Explanation of symbols]

Reference Signs List 1 signal input terminal, 2 signal output terminal, 3a, 3b erbium-doped optical fiber, 4 excitation light source, 5 fiber grating reflector, 6 optical circulator, 7 excitation light removal filter, 8 optical isolator, 9a, 9b
Optical coupler, 10 light receiving element, 11 monitoring signal detection circuit, 1
2 line switching control circuit, 13a, 13b LD drive circuit, 14 supervisory signal generation circuit, 20 supervisory signal light source,
21 pulse generation circuit, 22 backscattered light detection circuit, 3
0a, 30b Optical switch, 31 Optical switch drive circuit.

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (reference) H04B 10/17 H04B 9/00 K 10/16 J 17/00 F term (reference) 2G086 CC02 CC06 5F072 AB09 AK06 JJ20 KK30 PP07 YY17 5F088 AA05 BA20 BB01 JA14 5K002 AA06 BA15 CA13 EA06 EA07 FA01 5K042 AA08 CA07 CA10 DA18 DA33 EA09 FA05 FA13 FA21 FA25 JA01 LA11 MA01 NA03

Claims (5)

[Claims] 1. An optical amplifier used in an optical network, comprising: a rare earth-doped optical fiber serving as an amplification medium; a first light source for emitting pulse light in response to input of a first or second pulse signal; A second light source that emits a monitoring signal light to be transmitted on the transmission path to detect an abnormality on a transmission path of the network; a monitoring signal detection unit that detects the monitoring signal light; Outputting a first pulse signal for using the pulse light as excitation light for the rare-earth-doped optical fiber when signal light is detected, and when the monitor signal light is not detected by the monitor signal detecting means; A second pulse signal for using the pulsed light as a backscattered light measurement pulsed light for detecting the backscattered light on the transmission path is output. A pulse generating means for optical amplifier, characterized in that it and a back-scattered light detecting means for detecting the backscattered light to identify the cause of abnormality and the abnormal point of the transmission path. 2. An optical amplifier used in an optical network, comprising: a rare earth-doped optical fiber as an amplification medium; a first light source for emitting pulse light in response to input of a first or second pulse signal; A second light source that emits a monitoring signal light to be transmitted on the transmission path to detect an abnormality on a transmission path of the network; a monitoring signal detection unit that detects the monitoring signal light; Outputting a first pulse signal for using the pulse light as excitation light for the rare-earth-doped optical fiber when signal light is detected, and when the monitor signal light is not detected by the monitor signal detecting means; A second pulse signal for using the pulsed light as a backscattered light measurement pulsed light for detecting the backscattered light on the transmission path is output. Pulse generating means, and backscattered light detecting means for detecting the backscattered light to identify the cause of the abnormality and the abnormal location on the transmission line, and when the monitoring signal light is not detected by the monitoring signal detecting means, On a path through which the backscattered light measurement pulse light is transmitted, there is provided an optical switch means for forming a path that bypasses a specific optical component in which loss of the backscattered light measurement pulse light occurs. Optical amplifier. 3. The optical amplifier according to claim 1, wherein the rare-earth-doped optical fiber is an erbium-doped optical fiber. 4. The optical amplifier according to claim 1, wherein the first light source is a semiconductor laser that oscillates light in a 1.48 μm wavelength band. 5. The monitoring signal detecting means and the backscattered light detecting means use an avalanche photodiode as a light receiving means for receiving the monitoring signal light and the backscattered light. The optical amplifier according to any one of claims 1 to 4.