JP3452521B2 - Optical fiber amplifier - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber amplifier for amplifying signal light by injecting signal light and pumping light into a rare earth element-doped optical fiber.

[0002]

2. Description of the Related Art The first prior art is shown below.

FIG. 14 shows the document “Efficient erbium-doped f
ibre amplifier with an integral isolator '', Michael
N. Zervas, Richard I. Laming, David N. Payne 16
It is a block block diagram of the 1st conventional optical fiber amplifier described in pages 2-165. In the figure, 1 is a signal light input terminal, 2 is a pumping light source, 3a is a first optical multiplexer / demultiplexer, 31
a is the first terminal of the first optical multiplexer / demultiplexer 3a, and 32a is the first terminal.
Second terminal of the optical multiplexer / demultiplexer 3a, 33a is the third terminal of the first optical multiplexer / demultiplexer 3a, and 34a is the first optical multiplexer / demultiplexer 3a.
, 4a is a first rare earth element-doped optical fiber, 3b is a second optical multiplexer / demultiplexer, 31b is a first terminal of the second optical multiplexer / demultiplexer 3b, and 32b is a second optical multiplexer / demultiplexer. The second terminal of the wave multiplexer 3b, 33b is the third terminal of the second optical multiplexer / demultiplexer 3b, 34b is the fourth terminal of the second optical multiplexer / demultiplexer 3b, 5a
Is an optical isolator, 3c is a third optical multiplexer / demultiplexer, 31c is a first terminal of the third optical multiplexer / demultiplexer 3c, 32c is a second terminal of the third optical multiplexer / demultiplexer 3c, and 33c is a third terminal. The third terminal of the optical multiplexer / demultiplexer 3c, 34c is the fourth terminal of the third optical multiplexer / demultiplexer 3c, 4b is the second rare earth element-doped optical fiber,
6 is a signal light output terminal, 7a is a first non-reflective terminal, 7b is a second non-reflective terminal, and 7c is a third non-reflective terminal.

Next, the operation will be described.

The first optical multiplexer / demultiplexer 3a includes a first terminal 31
The signal light is transmitted between a and the second terminal 32a and between the third terminal 33a and the fourth terminal 34a. Also, the first
The excitation light is transmitted between the terminal 31a and the fourth terminal 34a, and between the second terminal 32a and the third terminal 33a.
In addition, the second optical multiplexer / demultiplexer 3b and the third optical multiplexer / demultiplexer 3b
The operation of c is the same as the operation of the above first optical multiplexer / demultiplexer 3a.

The signal light input from the signal light input terminal 1 is transmitted between the first terminal 31a and the second terminal 32a of the first optical multiplexer / demultiplexer 3a, and the first rare earth element-doped optical fiber 4a. Entered in. The pumping light output from the pumping light source 2 is supplied to the third terminal 33a of the first optical multiplexer / demultiplexer 3a and the second terminal 33a.
After being transmitted between the terminals 32a, the light is input to the first rare earth element-doped optical fiber 4a. The excitation light is absorbed by the rare earth element in the first rare earth element-doped optical fiber 4a, and the signal light is amplified by the absorbed energy.

The signal light amplified and output in the first rare earth element-doped optical fiber 4a is output by the second optical multiplexer / demultiplexer 3b.
Between the first terminal 31b and the second terminal 32b, through the optical isolator 5a, between the first terminal 31c and the second terminal 32c of the third optical multiplexer / demultiplexer 3c, 2 is input to the rare earth element-doped optical fiber 4b. The pumping light output without being consumed in the first rare earth element-doped optical fiber 4a is the first terminal 3 of the second optical multiplexer / demultiplexer 3b.
After passing between 1b and the third terminal 33b, and passing through the fourth terminal 34c and the second terminal 32c of the third optical multiplexer / demultiplexer 3c, it is input to the second rare earth element-doped optical fiber 4b. . The excitation light is absorbed by the rare earth element in the second rare earth element-doped optical fiber 4b, and the signal light is amplified by the absorbed energy.

The amplified optical signal is output from the second rare earth element-doped optical fiber 4b and output from the signal light output terminal 6.

Among the first rare earth element-doped optical fiber 4a and the second rare earth element-doped optical fiber 4b,
Amplified spontaneous emission light (ASE light) is generated. A above
SE light has components in a wide wavelength range with the signal light wavelength as the center, and has components that travel in both directions in a rare earth element-doped optical fiber.

The optical isolator 5a prevents the ASE light generated in the first rare earth element-doped optical fiber 4a and the second rare earth element-doped optical fiber 4b from oscillating. At the same time, the optical isolator 5a prevents the ASE light generated in the second rare earth element-doped optical fiber 4b and traveling in the opposite direction of the signal light from flowing into the first rare earth element-doped optical fiber 4a. . This is because when the ASE light flows into the first rare earth element-doped optical fiber 4a, the first rare earth element-doped optical fiber 4a.
This is because the energy obtained by absorbing the pumping light inside is consumed for the amplification of the ASE light and the amplification characteristic of the signal light deteriorates.

Since the transmission wavelength of the optical isolator 5a is usually set according to the signal light wavelength, the loss at the signal light wavelength is small. However, especially when the difference between the signal light wavelength and the pumping light wavelength is large, the optical isolator 5 at the pumping light wavelength is used.
The loss of a becomes large. Therefore, in the first conventional example, the pumping light bypasses the optical isolator 5a by the second optical multiplexer / demultiplexer 3b and the third optical multiplexer / demultiplexer 3c to avoid the loss caused by the optical isolator 5a. .

However, the second optical multiplexer / demultiplexer 3b and the third optical multiplexer / demultiplexer 3b
The excitation light is attenuated by the loss of the optical multiplexer / demultiplexer 3c.
Normally, the total loss of these two optical multiplexers / demultiplexers is 0.5 dB.
It is about 1 dB.

The non-reflection terminations 7a to 7c are for preventing oscillation due to reflection of signal light or ASE light, and can be realized by polishing the end face of the optical fiber at an angle.

Also in the optical fiber amplifier, like the general electric amplifier, in the two-stage configuration, it is possible to improve the overall characteristics by making the front stage an amplifier having a low noise figure and the rear stage an amplifier having a high output. Connect

In the first conventional example, the pumping light input direction to the rare earth element-doped optical fiber is the same as the signal light traveling direction. Therefore, in the rare earth element doping optical fiber, the pumping light is closer to the signal light input side. The light intensity is strong. The stronger the pumping light intensity is, the higher the gain is, the higher the maximum optical output is and the lower the noise is. Therefore, the closer to the signal light input side, the lower the noise is.

FIG. 15 is a technical research report of Institute of Electronics, Information and Communication Engineers, Vol. 90, No. 155, OCS90-23,
It is a block block diagram of the 2nd conventional optical fiber amplifier described in "Er doped optical fiber amplifier." In addition,
The same symbols are attached to the same elements as those of the first conventional example.
The same applies to the following conventional examples.

In the second conventional example, since the pumping light input direction to the rare earth element-doped optical fiber 4c is opposite to the signal light traveling direction, the rare earth element-doped optical fiber 4 is used.
In c, the closer to the signal light output side, the stronger the pumping light intensity, and as a whole, an optical fiber amplifier with high output can be obtained.

In the second conventional example described above, the rare earth element-doped optical fiber 4c is described as having only one stage, but even in the case where the rare-earth element-doped optical fiber 4c is formed in the two stages as in the first conventional example, the signal light traveling direction is also increased. By inputting the pumping light from the opposite direction, a high output optical fiber amplifier can be obtained.

FIG. 16 is a block diagram of a third conventional optical fiber amplifier disclosed in Japanese Patent Laid-Open No. 3-127885.

In the third conventional example, the pumping light is input from the same direction as the signal light traveling direction of the rare earth element-doped optical fiber 4c, and another direction is opposite to the signal light traveling direction of the rare earth element doped optical fiber 4c. Excitation light is input from the excitation light source 2b. In this case, in the rare earth element-doped optical fiber 4c, the intensity of the pumping light is stronger as it is closer to both ends of the signal light input side and the signal light output side, and an optical fiber amplifier with low noise and high output as a whole can be obtained.

Although the third conventional example describes the case where the rare earth element-doped optical fiber 4c has only one stage, even when the rare-earth element-doped optical fiber 4c has a two-stage structure as in the first conventional example, the excitation light is emitted from both directions. By inputting, an optical fiber amplifier with low noise and high output can be obtained.

The second conventional technique will be described below.

When the optical fiber amplifier is used in an actual transmission system, it is necessary to monitor the input level and the output level of the optical fiber amplifier to obtain a proper gain in order to obtain a stable operating state. Becomes

FIG. 17 is a technical research report Vol. 91, No. 282, OCS 91-32, a block configuration diagram of a fourth conventional optical fiber amplifier described in "EDFA by detecting spontaneous emission light from side surface of fiber".

In the figure, 8a is a first optical branching device, 81
a is an input terminal of the first optical branching device 8a, 82a is a first output terminal of the first optical branching device 8a, 84a is a second output terminal of the first optical branching device 8a, and 8b is a second output terminal. Optical splitter, 81b
Is an input terminal of the second optical branching device 8b, 82b is a first output terminal of the second optical branching device 8b, and 84b is a second optical branching device 8b.
2nd output terminal of b, 9a is 1st optical receiver, 9b is 2nd
Is a pump light source control circuit.

Next, the operation will be described. The signal light input from the signal light input terminal 1 is input to the input terminal 81a of the first optical branching device 8a. Most of the signal light input to the first optical branching device 8a is output from the first output terminal 82a, and part thereof is output from the second output terminal 84a.
Generally, the ratio of the output from the first output terminal 82a and the output from the second output terminal 84a is set to about 10 dB. Therefore, the input terminal 81 of the first optical branching device 8a is
The loss between a and the first output terminal 82a is about 0.5 dB due to the branch loss alone. Usually, an excessive loss is added to the branch loss, resulting in an insertion loss of about 0.5 dB to 1 dB.

The second output terminal 84 of the first optical branching device 8a
The output from a is received by the first optical receiver 9a and transmitted to the excitation light source control circuit 10 as a monitor of the input signal level.

The first output terminal 82 of the first optical branching device 8a
The output from a is transmitted between the first terminal 31a and the second terminal 32a of the optical multiplexer / demultiplexer 3a, transmitted through the first optical isolator 5b, and input to the rare earth element-doped optical fiber 4c. The pumping light output from the pumping light source 2 is transmitted between the third terminal 33a and the second terminal 32a of the optical multiplexer / demultiplexer 3a, the first optical isolator 5b, and the rare earth element-doped optical fiber 4c. Is entered. The excitation light is absorbed by the rare earth element in the rare earth element-doped optical fiber 4c, and the signal light is amplified by the absorbed energy.

The signal light amplified and output in the rare earth element-doped optical fiber 4c is input to the input terminal 81b of the second optical branching device 8b. Most of the signal light input to the second optical branching device 8b is output from the first output terminal 82b, and part thereof is output from the second output terminal 84b.

The first output terminal 82 of the second optical branching device 8b
The signal light output from b is the second optical isolator 5c.
And is output from the signal light output terminal 6.

The signal light output from the second terminal 84b of the second optical branching device 8b is received by the second optical receiver 9b,
It is transmitted to the excitation control circuit 10 as a monitor of the output signal level.

In the first optical isolator 5b, the ASE light traveling in the opposite direction to the signal light generated in the rare earth element-doped optical fiber 4 is temporarily connected to the input side from the signal light input terminal 1 by the transmission line fiber. After being output to the inside, it is prevented from being re-inputted to the rare earth element-doped optical fiber 4c due to reflection due to Rayleigh scattering in the transmission line fiber and deteriorating the amplification characteristic. Since the internal reflectances of the first optical branching device 8a and the optical multiplexing / demultiplexing device 3a are usually as weak as -50 dB, the first optical isolator 5b is located at the position of the first optical branching device 8a and the optical multiplexing / demultiplexing device. 3a, or between the signal light input terminal 1 and the first optical branching device 8a.

In the second optical isolator 5c, the signal light amplified in the rare earth element-doped optical fiber 4c and the ASE light generated in the rare earth element-doped optical fiber 4c and traveling in the same direction as the signal light are temporarily transmitted. After being output from the signal light output terminal 6 into the transmission line fiber connected to the output side,
This prevents the rare earth element-doped optical fiber 4c from entering the optical fiber 4c again due to Rayleigh scattering reflection in the transmission line fiber and deteriorating the amplification characteristic. Since the internal reflectance of the second optical branching device 8b is a negligible value of about -50 dB, the position of the second optical isolator 5c is located between the rare earth element-doped optical fiber 4c and the second optical branching device 8b. It doesn't matter if it's in between.

The pumping light source control circuit 10 controls the current supplied to the pumping light source 2 based on the monitor of the input level and the output level so that the gain of the rare earth element-doped optical fiber 4c becomes appropriate. An optical fiber amplifier capable of stable operation can be obtained.

As described above, the monitor of the input level and the output level is necessary for operating the optical fiber amplifier in a stable state. However, due to the insertion loss of the optical branching device for the monitor, the characteristics of the optical fiber amplifier. Deteriorates. The optical branching device for monitoring the input level is connected to the signal input side of the rare earth element-doped optical fiber 4c, but the noise characteristic is deteriorated by the insertion loss of the optical branching device. Further, the optical branching device for monitoring the output level is connected to the signal output side of the rare earth element-doped optical fiber, but the maximum optical output is reduced by the insertion loss of the optical branching device.

In the fourth conventional example, in order to operate the optical fiber amplifier in a stable manner, the input level and the output level of the optical fiber amplifier are monitored and controlled so as to obtain an appropriate gain.

In the case where the input level and the output level of the optical fiber amplifier are monitored to judge the input abnormality due to the disconnection of the transmission line on the signal input side or the abnormality such as the gain reduction of the rare earth element-doped optical fiber, Similarly, the insertion loss of the optical splitter for monitoring deteriorates the characteristics of the optical fiber amplifier.

In order to avoid the deterioration of the noise characteristic, in order to avoid the deterioration of the noise characteristic of the fourth conventional example, it is not necessary to monitor the input level by utilizing the change of the ASE light level generated in the rare earth element-doped optical fiber. There is a conventional example.

FIG. 18 is a block diagram of a fifth conventional optical fiber amplifier described in Japanese Patent Laid-Open No. 4-241328.

In the figure, 100 is an optical amplifier, 101
Is an optical amplifier, 102 is an input signal light, 103 is an amplifier output light, 104 is a narrow band optical filter, 105 is reflected light, 10
6 is a light splitting mirror, 107 is a light receiver, 108 is transmitted light,
Reference numeral 109 is an optical branching mirror, 110 is branched light, 111 is a light receiver, 112 is output signal light, and 113 is a control circuit. Next, the operation will be described. The amplifier output light 103 output from the optical amplifier 101 contains a signal light component and an ASE light component. Of these, the signal light wavelength component is transmitted through the narrow band optical filter 104, part of which is branched by the optical branching mirror 109, is received by the light receiver 111, and is transmitted to the control circuit 113 as an output monitor.

A wavelength component other than the signal light wavelength, that is, AS
The E light component is reflected by the narrow band optical filter 104, returned by the optical branching mirror 106, and then received by the light receiver 107.

When the signal input becomes large, the amplifier output light 1
03, the signal light component increases but the ASE light component decreases, so the level of the photodetector 111 rises, but the photodetector 10
Level 7 goes down. On the contrary, when the signal input becomes small, the signal component of the amplifier output light 103 decreases but the ASE light component increases, so that the level of the photodetector 111 decreases but the level of the photodetector 107 increases. As a result, the level of the light receiver 111 and the light receiver 107 with respect to the signal input level are
By grasping the relationship of the level ratios in advance, it is possible to monitor the signal input level without splitting and receiving the input signal light.

Therefore, it is possible to avoid the deterioration of the noise characteristic due to the insertion loss of the optical branching device, which occurs when the optical branching device for monitoring the input level is provided.

The third conventional technique will be described below.

The main evaluation items of the amplification characteristic of the optical fiber amplifier are the gain (output) and the noise figure as in the case of the electric amplifier. As a sixth conventional example of the method of measuring the gain and the noise figure, for example, Technical Report of IEICE, V.
ol. 90, No. 206, OQE 90-80, "Optical Fiber Amplifier Module".

The gain of the optical fiber amplifier is calculated by measuring and comparing the input signal light level and the output signal light level with an optical spectrum analyzer.

The noise figure can be calculated by measuring the optical fiber level of the ASE light generated in the rare earth element-doped optical fiber at the same wavelength as the signal light wavelength with an optical spectrum analyzer. However, since the optical spectrum analyzer cannot separate the signal light component and the ASE light component, the ASE light level at the same wavelength as the signal light cannot be measured. For this reason, a method of estimating the ASE light level at the same wavelength as the signal light based on the ASE light level at a wavelength sufficiently separated from the signal light wavelength is used. It is difficult to accurately estimate the ASE light level of, and the noise figure cannot be accurately measured.

As a seventh conventional example for the above problems,
It is described in Proceedings of the 1992 Autumn Meeting of the Institute of Electronics, Information and Communication Engineers, Volume 4, C-268, "Examination of High-Precision Noise Figure Measurement Method for Optical Fiber for Amplification".

In the seventh conventional method, the same polarization component as the signal light in the output light of the rare earth element-doped optical fiber is removed by the combination of the phase compensator and the polarizer, and then the optical spectrum analyzer is used. The signal light wavelength component input to the optical spectrum analyzer is removed (suppressed) by measurement, and the ASE light level at a wavelength closer to the signal light wavelength is used to estimate the ASE light level at the same wavelength as the signal light. Is what makes it possible.

As the eighth conventional example, there is a description of "1992 IEICE Autumn Meeting, C-269".

According to the eighth conventional example, the signal light component and the ASE light are subtracted by subtracting the same optical spectrum as the input signal light from the result of measuring the output light of the rare earth element-doped optical fiber with the optical spectrum analyzer. A method of separating the components is shown.

[0052]

However, according to the fourth conventional example described above, when the input signal light level and the output signal light level are monitored in order to stably control the operating state of the optical fiber amplifier. There is a first problem that the noise characteristic is deteriorated by providing an optical branching device for monitoring the input signal light level on the signal light input side of the rare earth element-doped optical fiber, and the output signal light level is There is a second problem that the maximum output of signal light is reduced by providing the optical branching device for monitoring on the signal light output side of the rare earth element-doped optical fiber.

Further, it is possible to determine whether the signal light input to the optical fiber amplifier is normal or abnormal and whether the amplification state of the optical fiber amplifier is normal or abnormal.
Also when monitoring the input signal light level and the output signal light level in order to make an abnormality determination, there are the above-mentioned first and second problems.

Further, according to the above-mentioned fifth conventional example made to solve the above-mentioned first problem, since the narrow band filter is inserted in the signal light path, the optical fiber in the long-distance optical transmission system is When the amplifiers are connected in multiple stages, there is a third problem that the signal transmission quality deteriorates due to variations in the transmission center wavelength of the narrow band filters in the respective optical fiber amplifiers.

The first invention of the present invention is made to solve the above first and third problems.
An object of the present invention is to obtain an optical fiber amplifier which suppresses the deterioration of noise characteristics without requiring an optical branching device for monitoring the input signal light level and does not cause deterioration of signal transmission quality.

The second aspect of the present invention is made to solve the above first and third problems, and determines whether the signal light input and the amplification state of the optical fiber amplifier are normal or abnormal. Another object of the present invention is to obtain an optical fiber amplifier that suppresses deterioration of noise characteristics and does not cause deterioration of signal transmission quality by eliminating the need for an optical branching device for monitoring the input signal light level.

The third invention of the present invention is made to solve the above-mentioned second and third problems, and eliminates the need for an optical branching device for monitoring the output signal light level. An object of the present invention is to obtain an optical fiber amplifier which suppresses the reduction of the maximum optical output and does not cause the deterioration of the signal transmission quality.

The fourth invention of the present invention is made to solve the above-mentioned second and third problems, and an optical branching device for monitoring the output signal light level is not necessary and the signal is eliminated. An object of the present invention is to obtain an optical fiber amplifier which suppresses the reduction of the maximum optical output and does not cause the deterioration of the signal transmission quality.

[0059]

Means for Solving the Problems An optical fiber amplifier according to the first aspect of the invention, a rare earth element doped optical fiber doped with a rare earth element for amplifying signal light to the optical fiber by the irradiation of the excitation light, the rare earth Element doped optical phi
Pump used as amplification energy of signal light in
A pumping light source that outputs light, an optical branching device that branches the optical output of the rare earth element-doped optical fiber, and a branching output light of the optical branching device that branches into a signal light wavelength component and a wavelength component other than the signal light wavelength. A wavelength filter, and a first light receiver for receiving the signal light wavelength component output from the optical wavelength filter,
A second photoreceiver for receiving wavelength components other than the signal light wavelength output from the optical wavelength filter, and the first photoreceiver and the first photoreceiver.
And the excitation based on the output level of the second photoreceiver
And an excitation light source control circuit for controlling the driving of the light source .

The optical fiber amplifier according to the second aspect of the present invention is a rare fiber which amplifies the signal light by irradiating the pumping light.
Rare earth element doped light with earth element doped in optical fiber
Fiber and optical output of the rare earth element-doped optical fiber
Optical branching device for branching the
Light split into wavelength components other than the signal light wavelength component and signal light wavelength
The wavelength filter and the signal output from the optical wavelength filter
A first light receiver for receiving the optical wavelength component and the optical wavelength component
Receives wavelength components other than the signal light wavelength output from the filter
A second photodetector that, the circuit for determining the normality / abnormality of the first light receiver and the second doped optical fiber gain of normal / abnormal and rare earth elements of the signal light input level from the output level of the photodetector Be prepared.

An optical fiber amplifier according to a third aspect of the present invention includes a signal light input terminal, a rare earth element-doped optical fiber in which the optical fiber is doped with a rare earth element that amplifies the signal light by irradiating the excitation light, The rare earth element doping
Used as amplification energy of signal light in optical fiber
Pumping light source for outputting pumping light, and the signal light input terminal
The light input from the first terminal connecting the
Branches outputted to the second terminal and the fourth terminal element doped optical fiber is connected, also, it is inputted from the second terminal
Generated in the rare earth element-doped optical fiber
An optical branching device for branching and outputting signal lights other than the input signal light to a first terminal and a third terminal, and a third terminal of the optical branching device .
An optical wavelength filter for removing the input signal light wavelength component from the signal light other than the input signal light outputted by the optical splitter,
The first for receiving the signal light wavelength component output from the terminal 4
Receiver and the input signal output from the optical wavelength filter.
A second light receiver for receiving a wavelength component other than the signal light wavelength ;
Note that the output levels of the first photoreceiver and the second photoreceiver
An excitation light source control circuit for controlling the drive of the excitation light source based on
It is equipped with a road .

An optical fiber amplifier according to a fourth aspect of the present invention includes a signal light input terminal, a rare earth element-doped optical fiber in which the optical fiber is doped with a rare earth element that amplifies the signal light by irradiation with excitation light, The rare earth element doping
Used as amplification energy of signal light in optical fiber
Pumping light source for outputting pumping light, and the signal light input terminal
First Oyo but the signal light input from an input terminal connected
Beauty and optical splitter for splitting the second output terminal, a first of said rare earth element doped optical fiber light input from the terminal contact
Output from the second terminal connection, is input from the second terminal
An optical circulator for outputting light from the third terminal,
Input output from the third terminal of the optical circulator
An optical wavelength filter that removes an input signal light wavelength component from a signal light other than the signal light, from the second output terminal of the pre-Symbol optical splitter
A first light receiver for receiving the output signal light wavelength component;
Other than the input signal light wavelength output from the optical wavelength filter
A second optical receiver for receiving the wavelength components, the first light receiving
Based on the output level of the detector and the second photoreceiver
An excitation light source control circuit for controlling driving of the excitation light source .

In the optical fiber amplifier according to the first aspect of the present invention, after the output light of the rare earth element-doped optical fiber is branched by the optical branching device, the signal light wavelength component and the wavelength other than the signal light wavelength are further filtered by the wavelength filter. The components are separated and received by separate photodetectors. The signal light output level of the rare earth element-doped optical fiber is monitored from the intensity of the signal light wavelength component, and the signal light to the rare earth element-doped optical fiber is calculated from the ratio of the intensity of the signal light wavelength component and the intensity of components other than the signal light wavelength. By calculating the input level, it is not necessary to provide an optical branching device to monitor the input level on the input side of the rare earth element-doped optical fiber, and loss due to the optical branching device does not occur, and a wavelength filter is installed in the signal light path. Since it is not included, it is possible to obtain an optical fiber amplifier in which the noise characteristic is not deteriorated and the signal deterioration does not occur even in the multi-stage connection.

Further, in the optical fiber amplifier according to the second aspect of the present invention, after the output light of the rare earth element-doped optical fiber is branched by the optical branching device, it is further filtered by the wavelength filter except the signal light wavelength component and the signal light wavelength. Of the respective wavelengths, and each of them is received by another photodetector, and the output of each photodetector is transmitted to the failure determination circuit. As a result, the failure determination circuit detects the change in the intensity of the signal light wavelength component and the change in the intensity of components other than the signal light wavelength to separately determine whether the signal light input and the amplification state of the optical fiber amplifier are normal or abnormal. In addition, since it is not necessary to provide an optical branching device for monitoring the input level on the input side of the rare earth element-doped optical fiber, there is no loss in the optical branching device. Further, since the signal light path does not include a wavelength filter, the signal light input and the amplification state of the optical fiber amplifier are judged to be normal / abnormal, there is no deterioration in noise characteristics, and signal deterioration does not occur even in multistage connection. A fiber amplifier can be obtained.

In the optical fiber amplifier according to the third aspect of the present invention, the input light of the rare earth element-doped optical fiber is branched by the optical branching device and then received by the photodetector to monitor the input level, and the rare earth element is also monitored. The ASE light generated in the doped optical fiber, traveling in the opposite direction to the signal light, and output to the input side is branched by the above optical branching device. After the signal wavelength component is removed by the wavelength filter, the light is received by the light receiver, and the signal light output level is calculated from the ratio of the input level and the ASE light level output to the input side. As a result, there is no need to provide an optical branching device for monitoring the output level on the output side of the rare earth element-doped optical fiber, and loss due to the optical branching device does not occur. be able to.

Also, in the optical fiber amplifier according to the fourth aspect of the present invention, the input light to the rare earth element-doped optical fiber is branched by the optical branching device and then received by the light receiving device to monitor the input level, and the rare earth element is also monitored. The ASE light generated in the element-doped optical fiber, traveling in the opposite direction to the signal light, and output to the input side is branched by the optical circulator. After removing the signal wavelength component with a wavelength filter, it is received by a photoreceiver,
The output level of the rare earth element-doped optical fiber is calculated from the ratio of the input level and the ASE light level output to the input side. As a result, there is no need to provide an optical branching device for monitoring the signal light output level, and no loss occurs due to the optical branching device, so that it is possible to obtain an optical fiber amplifier in which the maximum signal light output does not decrease.

[0067]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1. FIG. 1 shows a first embodiment according to the present invention. In the figure, 1 is a signal light input terminal, 2a is a pump light source, 3a is a first optical multiplexer / demultiplexer,
31a is a first terminal of the first optical multiplexer / demultiplexer 3a, 32a is a second terminal of the first optical multiplexer / demultiplexer 3a, 33a is a third terminal of the first optical multiplexer / demultiplexer 3a, and 34a is A fourth terminal of the first optical multiplexer / demultiplexer 3a, 4a is a first rare earth element-doped optical fiber, 3b is a second optical multiplexer / demultiplexer, and 31b is a first terminal of the second optical multiplexer / demultiplexer 3b. , 32b is the second optical multiplexer / demultiplexer 3
The second terminal of b, 33b is the third terminal of the second optical multiplexer / demultiplexer 3b.
, 34b is a fourth terminal of the second optical multiplexer / demultiplexer 3b,
Reference numeral 5 is an optical isolator, 4b is a second rare earth element-doped optical fiber, 6 is a signal light output terminal, and 7a is a reflectionless termination.

The first optical multiplexer / demultiplexer 3a includes a first terminal 31
a to the second terminal 32a and between the third terminal 33a and the fourth terminal 34a to transmit the signal light, and the first terminal 3
The excitation light is transmitted between 1a and the fourth terminal 34a and between the second terminal 32a and the third terminal 33a. The second optical multiplexer / demultiplexer 3b also operates similarly to the first optical multiplexer / demultiplexer 3a.

Next, the operation will be described.

The signal light input from the signal light input terminal 1 is transmitted between the first terminal 31a and the second terminal 32a of the first optical multiplexer / demultiplexer 3a, and the first rare earth element-doped optical fiber 4a. Entered in. The pumping light output from the pumping light source 2a passes between the third terminal 33a and the second terminal 32a of the first optical multiplexer / demultiplexer 3a, and is input to the first rare earth element-doped optical fiber 4a. . The excitation light is absorbed by the rare earth element in the first rare earth element-doped optical fiber 4a, and the signal light is amplified by the absorbed energy.

The signal light amplified and output in the first rare earth element-doped optical fiber 4a is output by the second optical multiplexer / demultiplexer 3b.
Between the first terminal 31b and the second terminal 32b of the second optical multiplexer 5 and the second optical multiplexer / demultiplexer 3b of the second optical multiplexer / demultiplexer 3b.
It is transmitted between the terminal 33b and the fourth terminal 34b, and is input to the second rare earth element-doped optical fiber 4b. The pumping light output without being consumed by the first rare earth element-doped optical fiber 4a is the first terminal 31b of the second optical multiplexer / demultiplexer 3b.
And the fourth terminal 34b, and is input to the second rare earth element-doped optical fiber 4b. The excitation light is absorbed by the rare earth element in the second rare earth element-doped optical fiber 4b, and the signal light is amplified by the absorbed energy.

The amplified optical signal is output from the second rare earth element-doped optical fiber 4b through the signal light output terminal 6.

The signal light path is composed of the first optical multiplexer / demultiplexer 3a,
A first rare earth element-doped optical fiber 4a, a second optical multiplexer / demultiplexer 3b, an optical isolator 5, a second optical multiplexer / demultiplexer 3b,
The order is the second rare earth element-doped optical fiber 4b and the signal light output terminal 6. This path is the same as the conventional one, and there is no increase in loss in the signal light path.

The optical isolator 5 prevents oscillation of signal light or ASE light. At the same time, the ASE light generated in the second rare earth element-doped optical fiber 4b and traveling in the opposite direction to the signal light flows into the first rare earth element-doped optical fiber 4a, and the amplification characteristic of the signal light deteriorates. Is being prevented.

On the other hand, the path of the pumping light includes the pumping light source 2a, the first optical multiplexer / demultiplexer 3a, the first rare earth element-doped optical fiber 4a, the second optical multiplexer / demultiplexer 3b, and the second rare earth element-doped light. The order is the fiber 4b. First rare earth element-doped optical fiber 4a and second rare earth element-doped optical fiber 4
There is only the second optical multiplexer / demultiplexer 3b between b and the conventional optical multiplexer / demultiplexer 3b.
The loss of one optical multiplexer / demultiplexer is reduced as compared with the case where there were one optical multiplexer / demultiplexer.

Therefore, with the same signal light input and pumping light input, the pumping light intensity input to the second rare earth element-doped optical fiber 4b corresponds to the loss of one optical multiplexer / demultiplexer as compared with the conventional case. Only big. In a two-stage optical fiber amplifier, the maximum output of signal light increases as the input of pumping light in the subsequent stage increases.

As described above, according to this embodiment, it is possible to obtain an optical fiber amplifier having a large maximum output of signal light with the same signal light input and pumping light input.

Further, according to this embodiment, it is possible to reduce one optical multiplexer / demultiplexer as a component compared to the conventional optical fiber amplifier.

Although omitted in the above embodiment, the signal light input terminal 1 and the first terminal 3 of the first optical multiplexer / demultiplexer 3a are used.
1a, or between the second terminal 32a of the first optical multiplexer / demultiplexer 3a and the first rare earth element-doped optical fiber 4a, light for preventing reflection due to Rayleigh scattering of the transmission line fiber on the input side. Even if you add an isolator,
The effect of this embodiment is the same.

Although omitted in the above embodiment, light for preventing reflection due to Rayleigh scattering of the transmission line fiber on the output side is provided between the second rare earth element-doped optical fiber 4b and the signal light output terminal 6. Even if an isolator is added, the effect of this embodiment does not change.

Embodiment 2. FIG. 2 shows the second embodiment of the present invention.
An embodiment of is shown. In the figure, 1 is a signal light input terminal, 2b is a pump light source, 3b is a first optical multiplexer / demultiplexer, 31b.
Is a first terminal of the first optical multiplexer / demultiplexer 3b, 32b is a second terminal of the first optical multiplexer / demultiplexer 3b, 33b is a third terminal of the first optical multiplexer / demultiplexer 3b, and 34b is a third terminal. The fourth terminal of the first optical multiplexer / demultiplexer 3b, 4a is the first rare earth element-doped optical fiber, 3c is the second optical multiplexer / demultiplexer, 31c is the first terminal of the second optical multiplexer / demultiplexer 3c, 32c is the second terminal of the second optical multiplexer / demultiplexer 3c, 33c is the third terminal of the second optical multiplexer / demultiplexer 3c, 34c is the fourth terminal of the second optical multiplexer / demultiplexer 3c, and 5 is An optical isolator, 4b is a second rare earth element-doped optical fiber, 6 is a signal light output terminal, and 7b is a reflectionless termination.

Next, the operation will be described.

The pumping light output from the pumping light source 2b is the fourth terminal 34c and the first terminal 3 of the second optical multiplexer / demultiplexer 3c.
A second rare earth element-doped optical fiber 4 that transmits between 1c
It is input to b and used as amplification energy of signal light.
The pumping light that is output without being consumed by the second rare earth element-doped optical fiber 4b passes between the fourth terminal 34b and the first terminal 31b of the first optical multiplexer / demultiplexer 3b, and the first rare earth element It is input to the element-doped optical fiber 4b.

The signal light inputted from the signal light input terminal 1 is inputted to the first rare earth element-doped optical fiber 4a, amplified and outputted.

The signal light output from the first rare earth element-doped optical fiber 4a passes between the first terminal 31b and the second terminal 32b of the first optical multiplexer / demultiplexer 3b, and the optical isolator 5. Then, the third terminal 3 of the first optical multiplexer / demultiplexer 3b
It is transmitted between 3b and the fourth terminal 34b, and is input to the second rare earth element-doped optical fiber 4b.

The signal light further amplified in the second rare earth element-doped optical fiber 4b is supplied to the second optical multiplexer / demultiplexer 3
c between the first terminal 31c and the second terminal 32c,
It is output after passing through the signal light output terminal 6.

The path of the signal light includes the first rare earth element-doped optical fiber 4a, the first optical multiplexer / demultiplexer 3b, the optical isolator 5, the first optical multiplexer / demultiplexer 3b, and the second rare earth element-doped optical fiber 4b. The order is the second optical multiplexer / demultiplexer 3c and the signal light output terminal 6. This path is the same as the conventional one, and there is no increase in loss in the signal light path.

The optical isolator 5 prevents oscillation of signal light or ASE light. At the same time, the ASE light generated in the second rare earth element-doped optical fiber 4b and traveling in the opposite direction to the signal light flows into the first rare earth element-doped optical fiber 4a, and the amplification characteristic of the signal light deteriorates. Is being prevented.

On the other hand, the path of the pumping light includes the pumping light source 2b, the second optical multiplexer / demultiplexer 3c, the second rare earth element-doped optical fiber 4b, the first optical multiplexer / demultiplexer 3b, and the first rare earth element-doped light. The order is the fiber 4a. Second rare earth element-doped optical fiber 4b and first rare earth element-doped optical fiber 4
There is only the first optical multiplexer / demultiplexer 3b between a and the conventional optical multiplexer / demultiplexer 3b.
The loss of one optical multiplexer / demultiplexer is reduced as compared with the case where there were one optical multiplexer / demultiplexer.

Therefore, with the same signal light input and pumping light input, the pumping light intensity input to the first rare earth element-doped optical fiber 4a is equivalent to the loss of one optical multiplexer / demultiplexer as compared with the conventional case. Only big. In the two-stage type optical fiber amplifier, the noise becomes low when the pumping light input in the preceding stage becomes large.

As described above, according to this embodiment, an optical fiber amplifier with low noise can be obtained with the same signal light input and pumping light input.

Further, according to the present embodiment, one optical multiplexer / demultiplexer can be reduced as a constituent component as compared with the conventional optical fiber amplifier.

Although omitted in the above embodiment, the signal light input terminal 1 and the first terminal 3 of the first optical multiplexer / demultiplexer 3b are used.
Even when an optical isolator for preventing reflection due to Rayleigh scattering of the transmission line fiber on the input side is added between 1b, the effect of the present embodiment does not change.

Although omitted in the above embodiment, light for preventing reflection due to Rayleigh scattering of the transmission line fiber on the output side is provided between the second rare earth element-doped optical fiber 4b and the signal light output terminal 6. Even if an isolator is added, the effect of this embodiment does not change.

Embodiment 3. FIG. 3 shows a third embodiment of the present invention.
An embodiment of is shown. In the figure, 1 is a signal light input terminal, 2a is a first pumping light source, 3a is a first optical multiplexer / demultiplexer,
31a is a first terminal of the first optical multiplexer / demultiplexer 3a, 32a is a second terminal of the first optical multiplexer / demultiplexer 3a, 33a is a third terminal of the first optical multiplexer / demultiplexer 3a, and 34a is A fourth terminal of the first optical multiplexer / demultiplexer 3a, 4a is a first rare earth element-doped optical fiber, 3b is a second optical multiplexer / demultiplexer, and 31b is a first terminal of the second optical multiplexer / demultiplexer 3b. , 32b is the second optical multiplexer / demultiplexer 3
The second terminal of b, 33b is the third terminal of the second optical multiplexer / demultiplexer 3b.
, 34b is a fourth terminal of the second optical multiplexer / demultiplexer 3b,
5 is an optical isolator, 4b is a second rare earth element-doped optical fiber, 2b is a second pumping light source, 3c is a third optical multiplexer / demultiplexer, 31c is a first terminal of the third optical multiplexer / demultiplexer 3c, Three
2c is the second terminal of the third optical multiplexer / demultiplexer 3c, 33c is the third terminal of the third optical multiplexer / demultiplexer 3c, 34c is the fourth terminal of the third optical multiplexer / demultiplexer 3c, and 6 is A signal light output terminal, 7a is a first non-reflection end, and 7b is a second non-reflection end.

Next, the operation will be described.

The pumping light output from the pumping light source 2a is the third terminal 33a and the second terminal 3 of the first optical multiplexer / demultiplexer 3a.
The first rare earth element-doped optical fiber 4 that transmits between 2a
It is input to a and used as amplification energy of signal light.
The pumping light that is output without being consumed by the first rare earth element-doped optical fiber 4a passes between the first terminal 31b and the fourth terminal 34b of the second optical multiplexer / demultiplexer 3b, and the second rare earth element It is input to the element-doped optical fiber 4b.

The pumping light output from the pumping light source 2b is transmitted between the fourth terminal 34c and the first terminal 31c of the third optical multiplexer / demultiplexer 3c, and the second rare earth element-doped optical fiber 4b. And is used as amplified energy of the signal light. The pumping light that is output without being consumed by the second rare earth element-doped optical fiber 4b passes between the fourth terminal 34b and the first terminal 31b of the second optical multiplexer / demultiplexer 3b, and the first rare earth element It is input to the element-doped optical fiber 4a.

The signal light input from the signal light input terminal 1 is transmitted between the first terminal 31a and the second terminal 32a of the first optical multiplexer / demultiplexer 3a, and the first rare earth element-doped optical fiber 4a. Is input to and amplified. The signal light output from the first rare earth element-doped optical fiber 4a passes between the first terminal 31b and the second terminal 32b of the second optical multiplexer / demultiplexer 3b, passes through the optical isolator 5, and The light is transmitted between the third terminal 33b and the fourth terminal 34b of the second optical multiplexer / demultiplexer 3ba, and is input to the second rare earth element-doped optical fiber 4b. The signal light further amplified in the second rare earth element-doped optical fiber 4b passes between the first terminal 31c and the second terminal 32c of the third optical multiplexer / demultiplexer 3c, and the signal light output terminal 6 It passes and is output.

The path of the signal light is the first optical multiplexer / demultiplexer 3a,
A first rare earth element-doped optical fiber 4a, a second optical multiplexer / demultiplexer 3b, an optical isolator 5, a second optical multiplexer / demultiplexer 3b,
The order is the second rare earth element-doped optical fiber 4b, the third optical multiplexer / demultiplexer 3c, and the signal light output terminal 6. This path is the same as the conventional one, and there is no increase in loss in the signal light path. The optical isolator 5 prevents oscillation of signal light or ASE light. At the same time, A generated in the second rare earth element-doped optical fiber 4b and traveling in the direction opposite to the signal light A
The SE light is prevented from flowing into the first rare earth element-doped optical fiber 4a and deteriorating the amplification characteristic of the signal light.

On the other hand, the path of the output of the first pumping light source 2a includes the first optical multiplexer / demultiplexer 3a, the first rare earth element-doped optical fiber 4a, the second optical multiplexer / demultiplexer 3b, and the second rare earth element. The order is the doped optical fiber 4b. Only the second optical multiplexer / demultiplexer 3b is provided between the first rare earth element-doped optical fiber 4a and the second rare earth element-doped optical fiber 4b, and in comparison with the conventional two optical multiplexers / demultiplexers. , Optical multiplexer / demultiplexer 1
The loss for the vehicle is reduced.

The output path of the second pumping light source 2b includes a third optical multiplexer / demultiplexer 3c, a second rare earth element-doped optical fiber 4b, a second optical multiplexer / demultiplexer 3b, and a first rare earth element. The order is the doped optical fiber 4a. Only the second optical multiplexer / demultiplexer 3b is provided between the second rare earth element-doped optical fiber 4b and the first rare earth element-doped optical fiber 4a, and in comparison with the conventional two optical multiplexers / demultiplexers. , Optical multiplexer / demultiplexer 1
The loss for the vehicle is reduced.

Therefore, in the same signal light input and pumping light input, the pumping light intensity input to the second rare earth element-doped optical fiber 4b and the first rare earth element doping optical fiber 4a are input as compared with the conventional case. The pumping light intensity is large as much as one optical multiplexer / demultiplexer corresponds to the loss. In the two-stage type optical fiber amplifier, when the pumping light input of the preceding stage becomes large, the noise becomes low, and when the pumping light input of the latter stage becomes large, the maximum output of the signal light increases.

As described above, according to the present embodiment, it is possible to obtain an optical fiber amplifier which has low noise at the same signal light input and pumping light input and has a large maximum output of signal light.

Further, according to this embodiment, one optical multiplexer / demultiplexer can be reduced as a constituent component as compared with the conventional optical fiber amplifier.

Although omitted in the above embodiment, the signal light input terminal 1 and the first terminal 3 of the first optical multiplexer / demultiplexer 3a are used.
1a, or between the second terminal 32a of the first optical multiplexer / demultiplexer 3a and the first rare earth element-doped optical fiber 4a, light for preventing reflection due to Rayleigh scattering of the transmission line fiber on the input side. Even if you add an isolator,
The effect of this embodiment is the same.

Although omitted in the above-mentioned embodiment, reflection due to Rayleigh scattering of the transmission line fiber on the output side is caused between the third terminal 33c of the third optical multiplexer / demultiplexer 3c and the signal light output terminal 6. Even if an optical isolator for prevention is added, the effect of the present embodiment does not change.

Fourth Embodiment FIG. 4 shows a fourth embodiment of the present invention.
An embodiment of is shown. In the figure, 1 is a signal light input terminal, 2a is a pumping light source, 3a is a first optical multiplexer / demultiplexer, and 31a.
Is a first terminal of the first optical multiplexer / demultiplexer 3a, 32a is a second terminal of the first optical multiplexer / demultiplexer 3a, 33a is a third terminal of the first optical multiplexer / demultiplexer 3a, and 34a is a third terminal. The fourth terminal of the first optical multiplexer / demultiplexer 3a, 4a is the first rare earth element-doped optical fiber, 3b is the second optical multiplexer / demultiplexer, 31b is the first terminal of the second optical multiplexer / demultiplexer 3b, 32b is the second terminal of the second optical multiplexer / demultiplexer 3b, 33b is the third terminal of the second optical multiplexer / demultiplexer 3b, 34b is the fourth terminal of the second optical multiplexer / demultiplexer 3b, and 5 is An optical isolator, 4b is a second rare earth element-doped optical fiber, 6 is a signal light output terminal, and 7a is a reflectionless termination.

Next, the operation will be described.

The signal light input from the signal light input terminal 1 is transmitted between the first terminal 31a and the second terminal 32a of the first optical multiplexer / demultiplexer 3a, and the first rare earth element-doped optical fiber 4a. Entered in. The pumping light output from the pumping light source 2a is transmitted between the fourth terminal 34b and the first terminal 31b of the second optical multiplexer / demultiplexer 3b, and travels to the first rare earth element-doped optical fiber 4a. Input is from the opposite direction. In the first rare earth element-doped optical fiber 4a, the rare earth element absorbs the excitation light, and the absorbed energy amplifies the signal light.

The signal light amplified and output in the first rare earth element-doped optical fiber 4a is output to the second optical multiplexer / demultiplexer 3b.
Between the first terminal 31b and the second terminal 32b of the first optical multiplexer / demultiplexer 3a.
It is transmitted between the terminal 34a and the third terminal 33a, and is input to the second rare earth element-doped optical fiber 4b. The pumping light output without being consumed by the first rare earth element-doped optical fiber 4a is the second terminal 32a of the first optical multiplexer / demultiplexer 3a.
And the third terminal 33a, and is input to the second rare earth element-doped optical fiber 4b. In the second rare earth element-doped optical fiber 4b, the rare earth element absorbs the excitation light, and the absorbed energy amplifies the signal light. The pumping light is input to the second rare earth element-doped optical fiber 4b from the same direction as the signal light traveling direction.

The amplified optical signal is output from the second rare earth element-doped optical fiber 4b through the signal light output terminal 6.

The path of the signal light is the first optical multiplexer / demultiplexer 3a,
The first rare earth element-doped optical fiber 4a, the second optical multiplexer / demultiplexer 3b, the optical isolator 5, the first optical multiplexer / demultiplexer 3a, the second rare earth element-doped optical fiber 4b, and the signal light output terminal 6 are in this order. . This path is the same as the conventional one, and there is no increase in loss in the signal light path.

The optical isolator 5 prevents oscillation of signal light or ASE light. At the same time, the ASE light generated in the second rare earth element-doped optical fiber 4b and traveling in the opposite direction to the signal light flows into the first rare earth element-doped optical fiber 4a, and the amplification characteristic of the signal light deteriorates. Is being prevented.

On the other hand, the path of the pumping light includes the pumping light source 2a, the second optical multiplexer / demultiplexer 3b, the first rare earth element-doped optical fiber 4a, the first optical multiplexer / demultiplexer 3a, and the second rare earth element-doped light. The order is the fiber 4b. First rare earth element-doped optical fiber 4a and second rare earth element-doped optical fiber 4
There is only the first optical multiplexer / demultiplexer 3a between b and the conventional optical multiplexer / demultiplexer 3a.
The loss of one optical multiplexer / demultiplexer is reduced as compared with the case where there were one optical multiplexer / demultiplexer.

Therefore, under the same signal light input and pumping light input, the pumping light intensity input to the second rare earth element-doped optical fiber 4b is equivalent to the loss of one optical multiplexer / demultiplexer as compared with the conventional case. Only big. In a two-stage optical fiber amplifier, the maximum output of signal light increases as the input of pumping light in the subsequent stage increases.

As described above, according to this embodiment, it is possible to obtain an optical fiber amplifier having a large maximum output of signal light with the same signal light input and pumping light input.

Further, according to this embodiment, one optical multiplexer / demultiplexer can be reduced as a constituent component as compared with the conventional optical fiber amplifier.

Although omitted in the above embodiment, the signal light input terminal 1 and the first terminal 3 of the first optical multiplexer / demultiplexer 3a are used.
Even if an optical isolator for preventing reflection due to Rayleigh scattering of the transmission line fiber on the input side is added between 1a, the effect of the present embodiment does not change.

Although omitted in the above-mentioned embodiment, light for preventing reflection due to Rayleigh scattering of the transmission line fiber on the output side is provided between the second rare earth element-doped optical fiber 4b and the signal light output terminal 6. Even if an isolator is added, the effect of this embodiment does not change.

Embodiment 5. FIG. FIG. 5 shows the fifth embodiment of the present invention.
An embodiment of is shown. In the figure, 1 is a signal light input terminal, 2b is a pump light source, 3a is a first optical multiplexer / demultiplexer, 31a.
Is a first terminal of the first optical multiplexer / demultiplexer 3a, 32a is a second terminal of the first optical multiplexer / demultiplexer 3a, 33a is a third terminal of the first optical multiplexer / demultiplexer 3a, and 34a is a third terminal. The fourth terminal of the first optical multiplexer / demultiplexer 3a, 4a is the first rare earth element-doped optical fiber, 3c is the second optical multiplexer / demultiplexer, 31c is the first terminal of the second optical multiplexer / demultiplexer 3c, 32c is the second terminal of the second optical multiplexer / demultiplexer 3c, 33c is the third terminal of the second optical multiplexer / demultiplexer 3c, 34c is the fourth terminal of the second optical multiplexer / demultiplexer 3c, and 5 is An optical isolator, 4b is a second rare earth element-doped optical fiber, 6 is a signal light output terminal, and 7b is a reflectionless termination.

Next, the operation will be described.

The pumping light output from the pumping light source 2b is the fourth terminal 34c and the first terminal 3 of the second optical multiplexer / demultiplexer 3c.
A second rare earth element-doped optical fiber 4 that transmits between 1c
It is input to b from the direction opposite to the signal light traveling direction and is used as amplified energy of the signal light. The pumping light output without being consumed by the second rare earth element-doped optical fiber 4b is the third terminal 33a and the second terminal 3 of the first optical multiplexer / demultiplexer 3a.
The first rare earth element-doped optical fiber 4 that transmits between 2a
It is input to a from the same direction as the signal light traveling direction.

The signal light input from the signal light input terminal 1 is transmitted between the first terminal 31a and the second terminal 32a of the first optical multiplexer / demultiplexer 3a, and the first rare earth element-doped optical fiber 4a. Is input to, output after amplification. The signal light output from the first rare earth element-doped optical fiber 4a is transmitted through the optical isolator 5 and the fourth signal of the first optical multiplexer / demultiplexer 3a.
It is transmitted between the terminal 34a and the third terminal 33a, and is input to the second rare earth element-doped optical fiber 4b. The signal light further amplified in the second rare earth element-doped optical fiber 4b is the first terminal 31 of the second optical multiplexer / demultiplexer 3c.
It is transmitted between c and the second terminal 32c, passes through the signal light output terminal 6, and is output.

The signal light path is composed of the first optical multiplexer / demultiplexer 3a,
First rare earth element-doped optical fiber 4a, optical isolator 5, second optical multiplexer / demultiplexer 3a, first rare earth element-doped optical fiber 4b, second optical multiplexer / demultiplexer 3c, and signal light output terminal 6 in this order. is there. This path is the same as the conventional one, and there is no increase in loss in the signal light path.

The optical isolator 5 prevents oscillation of signal light or ASE light. At the same time, the ASE light generated in the second rare earth element-doped optical fiber 4b and traveling in the opposite direction to the signal light flows into the first rare earth element-doped optical fiber 4a, and the amplification characteristic of the signal light deteriorates. Is being prevented.

On the other hand, the path of the pumping light includes the pumping light source 2b, the second optical multiplexer / demultiplexer 3c, the second rare earth element-doped optical fiber 4b, the first optical multiplexer / demultiplexer 3a, and the first rare earth element-doped light. The order is the fiber 4a. Second rare earth element-doped optical fiber 4b and first rare earth element-doped optical fiber 4
There is only the first optical multiplexer / demultiplexer 3a between a and the conventional optical multiplexer / demultiplexer 3a.
The loss of one optical multiplexer / demultiplexer is reduced as compared with the case where there were one optical multiplexer / demultiplexer.

Therefore, under the same signal light input and pumping light input, the pumping light intensity input to the first rare earth element-doped optical fiber 4a corresponds to the loss of one optical multiplexer / demultiplexer as compared with the conventional case. Only big. In the two-stage type optical fiber amplifier, the noise becomes low when the pumping light input in the preceding stage becomes large.

The pumping light input to the second-stage second rare earth element-doped optical fiber 4b is opposite to the signal light traveling direction as in the conventional case, and a large maximum output is obtained, and the first-stage first rare earth element is also supplied. Since the pumping light input to the element-doped optical fiber 4a is input from the same direction as the signal light traveling direction, low noise can be obtained. Conventionally, two or more pumping light inputs were required to realize a pumping light intensity distribution that achieves the characteristics of low noise and large maximum output as described above.

According to the present embodiment, it is possible to realize a pumping light intensity distribution that can obtain excellent amplification characteristics without using a single pumping light source and branching the pumping path.

As described above, according to this embodiment, a low noise optical fiber amplifier can be obtained with the same signal light input and pumping light input.

Further, according to this embodiment, it is possible to reduce one optical multiplexer / demultiplexer as a component compared to the conventional optical fiber amplifier.

Although omitted in the above embodiment, the signal light input terminal 1 and the first terminal 3 of the first optical multiplexer / demultiplexer 3a are used.
Even if an optical isolator for preventing reflection due to Rayleigh scattering of the transmission line fiber on the input side is added between 1a, the effect of the present embodiment does not change.

Although omitted in the above embodiment, light for preventing reflection due to Rayleigh scattering of the transmission line fiber on the output side is provided between the second rare earth element-doped optical fiber 4b and the signal light output terminal 6. Even if an isolator is added, the effect of this embodiment does not change.

Sixth Embodiment FIG. 6 shows a sixth embodiment of the present invention.
An embodiment of is shown. In the figure, 1 is a signal light input terminal, 2a is a pumping light source, 3a is a first optical multiplexer / demultiplexer, and 31a.
Is a first terminal of the first optical multiplexer / demultiplexer 3a, 32a is a second terminal of the first optical multiplexer / demultiplexer 3a, 33a is a third terminal of the first optical multiplexer / demultiplexer 3a, and 34a is a third terminal. The fourth terminal of the first optical multiplexer / demultiplexer 3a, 4a is the first rare earth element-doped optical fiber, 3b is the second optical multiplexer / demultiplexer, 31b is the first terminal of the second optical multiplexer / demultiplexer 3b, 32b is the second terminal of the second optical multiplexer / demultiplexer 3b, 33b is the third terminal of the second optical multiplexer / demultiplexer 3b, 34b is the fourth terminal of the second optical multiplexer / demultiplexer 3b, and 5 is Optical isolator, 4b is a second rare earth element-doped optical fiber, 2b is a second pumping light source, 3c is a third optical multiplexer / demultiplexer, 31c is a first terminal of the third optical multiplexer / demultiplexer 3c, 32
c is the second terminal of the third optical multiplexer / demultiplexer 3c, and 33c is the first terminal
Of the third optical multiplexer / demultiplexer 3c, 34c is a fourth terminal of the third optical multiplexer / demultiplexer 3c, 6 is a signal light output terminal, 7a is a first non-reflective terminal, and 7b is a second terminal. It is a reflection termination.

Next, the operation will be described.

The pumping light output from the pumping light source 2a is the fourth terminal 34b and the first terminal 3 of the second optical multiplexer / demultiplexer 3b.
The first rare earth element-doped optical fiber 4 which transmits between 1b
It is input to a and used as amplification energy of signal light.
The pumping light that is output without being consumed by the first rare earth element-doped optical fiber 4a passes between the second terminal 32a and the third terminal 33a of the first optical multiplexer / demultiplexer 3a, and the second rare earth element It is input to the element-doped optical fiber 4b.

The pumping light output from the pumping light source 2b passes between the fourth terminal 34c and the first terminal 31c of the third optical multiplexer / demultiplexer 3c, and the second rare earth element-doped optical fiber 4b. And is used as amplified energy of the signal light. The pumping light that is output without being consumed by the second rare earth element-doped optical fiber 4b passes between the third terminal 33a and the second terminal 32a of the first optical multiplexer / demultiplexer 3a, and the first rare earth element It is input to the element-doped optical fiber 4a.

The signal light input from the signal light input terminal 1 is transmitted between the first terminal 31a and the second terminal 32a of the first optical multiplexer / demultiplexer 3a and the first rare earth element-doped optical fiber 4a. Is input to and amplified. The signal light output from the first rare earth element-doped optical fiber 4a passes between the first terminal 31b and the second terminal 32b of the second optical multiplexer / demultiplexer 3b, passes through the isolator 5, and Optical multiplexer / demultiplexer 3
a between the fourth terminal 34a and the third terminal 33a,
It is input to the second rare earth element-doped optical fiber 4b.
The signal light further amplified in the second rare earth element-doped optical fiber 4b passes between the first terminal 31c and the second terminal 32c of the third optical multiplexer / demultiplexer 3c, and the signal light output terminal 6 It passes and is output.

The path of the signal light is the first optical multiplexer / demultiplexer 3a,
First rare earth element-doped optical fiber 4a, second optical multiplexer / demultiplexer 3b, optical isolator 5, first optical multiplexer / demultiplexer 3a,
The order is the second rare earth element-doped optical fiber 4b, the third optical multiplexer / demultiplexer 3c, and the signal light output terminal 6. This path is the same as the conventional one, and there is no increase in loss in the signal light path. The optical isolator 5 prevents oscillation of signal light or ASE light. At the same time, A generated in the second rare earth element-doped optical fiber 4b and traveling in the direction opposite to the signal light A
The SE light is prevented from flowing into the first rare earth element-doped optical fiber 4a and deteriorating the amplification characteristic of the signal light.

On the other hand, the path of the output of the first pumping light source 2a is
The order is the second optical multiplexer / demultiplexer 3b, the first rare earth element-doped optical fiber 4a, the first optical multiplexer / demultiplexer 3a, and the second rare earth element-doped optical fiber 4b. Only the first optical multiplexer / demultiplexer 3a is provided between the first rare earth element-doped optical fiber 4a and the second rare earth element-doped optical fiber 4b. In comparison with the conventional two optical multiplexer / demultiplexer, , The loss of one optical multiplexer / demultiplexer is reduced.

The output path of the second pumping light source 2b includes a third optical multiplexer / demultiplexer 3c, a second rare earth element-doped optical fiber 4b, a first optical multiplexer / demultiplexer 3a, and a first rare earth element. The order is the doped optical fiber 4a. There is only the first optical multiplexer / demultiplexer 3a between the second rare earth element-doped optical fiber 4b and the first rare earth element-doped optical fiber 4a, and in comparison with the conventional two optical multiplexer / demultiplexer, , Optical multiplexer / demultiplexer 1
The loss for the vehicle is reduced.

Therefore, in the same signal light input and pumping light input, the pumping light intensity input to the second rare earth element-doped optical fiber 4b and the first rare earth element doping optical fiber 4a are input as compared with the conventional case. The pumping light intensity corresponding to one optical multiplexer / demultiplexer is large. In the two-stage type optical fiber amplifier, when the pumping light input of the preceding stage becomes large, the noise becomes low, and when the pumping light input of the latter stage becomes large, the maximum output of the signal light increases.

As described above, according to the present embodiment, it is possible to obtain an optical fiber amplifier which has low noise and large maximum output of signal light when the same signal light input and pumping light input are used.

Further, according to this embodiment, one optical multiplexer / demultiplexer can be reduced as a constituent component as compared with the conventional optical fiber amplifier.

Although omitted in the above embodiment, the signal light input terminal 1 and the first terminal 3 of the first optical multiplexer / demultiplexer 3a are used.
Even if an optical isolator for preventing reflection due to Rayleigh scattering of the transmission line fiber on the input side is added between 1a, the effect of the present embodiment does not change.

Although omitted in the above embodiment, reflection due to Rayleigh scattering of the transmission line fiber on the output side is caused between the third terminal 33c of the third optical multiplexer / demultiplexer 3c and the signal light output terminal 6. Even if an optical isolator for prevention is added, the effect of the present embodiment does not change.

Seventh Embodiment FIG. 7 shows a seventh embodiment according to the present invention.
An embodiment of is shown. In the figure, 1 is a signal light input terminal, 5a is a first optical isolator, 2 is a pumping light source, 3a
Is an optical multiplexer / demultiplexer, 31a is the first terminal of the optical multiplexer / demultiplexer 3a,
32a is a second terminal of the optical multiplexer / demultiplexer 3a, 33a is a third terminal of the optical multiplexer / demultiplexer 3a, and 34a is a fourth terminal of the optical multiplexer / demultiplexer 3a.
, 4a is a rare earth element-doped optical fiber, 8b is an optical branch, 81b is an input terminal of the optical branch 8b, 82b is a first output terminal of the optical branch 8b, and 84b is a second output of the optical branch 8b. Output terminal, 5b is a second optical isolator, 6 is a signal light output terminal, 11 is an optical wavelength filter, 115 is an input terminal of the optical wavelength filter 11, 116 is an optical wavelength filter 11
Of the first output terminal 117 of the optical wavelength filter 11
Is an output terminal, 9b is a first light receiver, 9c is a second light receiver, and 10 is an excitation light source control circuit.

Next, the operation will be described.

The signal light input from the signal light input terminal 1 passes through the first optical isolator 5a, and the optical multiplexer / demultiplexer 3
a between the first terminal 31a and the second terminal 32a,
It is input to the rare earth element-doped optical fiber 4c.

The first optical isolator 5a is generated in the rare earth element-doped optical fiber 4c, travels in the direction opposite to the signal light traveling direction, and is input to the input side transmission line fiber.
The light is prevented from being re-inputted to the rare earth element-doped optical fiber 4c by reflection due to Rayleigh scattering in the transmission line fiber and deteriorating the amplification characteristic.

The pumping light output from the pumping light source 2 is transmitted between the third terminal 33a and the second terminal 32a of the optical multiplexer / demultiplexer 3a, and then input to the rare earth element-doped optical fiber 4c to amplify the signal light. Used as energy.

The signal light amplified and output in the rare earth element-doped optical fiber 4c is input to the input terminal 81 of the optical branching device 8b.
b, and most of them are output from the first output terminal 82b and some of them are output from the second output terminal 84b. First
Output from the output terminal 82b of the
The ratio of the output from is usually about 10 dB.

The output light from the first output terminal 82b of the optical branching device 8b passes through the second optical isolator 5b, passes through the signal light output terminal 6, and is output. The ASE light component generated in the rare earth element-doped optical fiber 4c is mixed with the output light of the rare earth element-doped optical fiber 4c in addition to the signal light component.

In the second optical isolator 5b, the signal light and the ASE light input to the output side transmission line fiber are re-inputted to the rare earth element-doped optical fiber 4c by reflection due to Rayleigh scattering in the transmission line fiber and amplified. It prevents deterioration of characteristics.

The output light from the second output terminal 84b of the optical branching device 8b is separated by the optical wavelength filter 11 into a signal light wavelength component and a wavelength component other than the signal light wavelength. A signal light wavelength component is output from the first output terminal 116 of the light wavelength filter 11, received by the first light receiver 9b, and used for monitoring the signal light output level. A wavelength component other than the signal light wavelength is output from the second output terminal 117 of the optical wavelength filter 11, and is received by the second light receiver 9c. This is the second
It means that the photodetector 9c of 1 monitors the ASE level output from the rare earth element-doped optical fiber 4c.

In the rare earth element-doped optical fiber 4c, when the signal light input level is higher than a certain level, the ASE light level generated when the input signal light level increases and the ASE light level generated when the input signal light level decreases are generated.
The light level rises.

When the input signal light level is lower than a certain level, the generated ASE light level is constant.

Therefore, the signal light output level obtained from the first light receiver 9b and the A obtained from the second light receiver 9c are obtained.
Depending on SE light level, rare earth element-doped optical fiber 4c
It is possible to know the input level of the signal light to the.

The result of monitoring the signal light output level and the result of monitoring the ASE light level are transmitted to the pumping light source control circuit 10 so that the pumping light source 2 can obtain an appropriate amplification characteristic according to the signal light input level and the output level. Is controlled.

According to the present embodiment, the optical branching device for monitoring the signal light input level is not required on the input side of the rare earth element-doped optical fiber 4c. Therefore, it is possible to avoid deterioration of the noise figure of about 0.5 dB to 1 dB due to the insertion loss of the optical branching device.

Since there is no optical wavelength filter for selecting the transmitted light wavelength in the signal light path, signal deterioration due to variations in the transmitted light wavelength of the optical wavelength filter does not occur when optical fiber amplifiers are connected in multiple stages.

As described above, according to the present embodiment, it is possible to obtain an optical fiber amplifier which has low noise and does not cause signal deterioration even when connected in multiple stages.

Although the first optical isolator 5a is connected between the signal light input terminal 1 and the first terminal 31a of the optical multiplexer / demultiplexer 3a in the above embodiment, the second terminal of the optical multiplexer / demultiplexer 3a is used. Even when the optical fiber 4c is connected between the optical fiber 32a and the rare earth element-doped optical fiber 4c, the effect of the present embodiment can be similarly obtained.

Further, in the above-mentioned embodiment, the second optical isolator 5b is connected between the first output terminal 82b of the optical branching device 8b and the signal light output terminal 6, but the second rare earth element-doped optical fiber 4c and the optical fiber 4c are connected. The same effect of the present embodiment can be obtained even when connected between the input terminals 81b of the branching device 8b.

In the above embodiment, the optical multiplexer / demultiplexer 3 is used.
The case where a is connected between the first optical isolator 5a and the rare earth element-doped optical fiber 4c and pumping light is input to the rare earth element-doped optical fiber 4c from the same direction as the signal light traveling direction is shown. 3a is connected between the rare earth element-doped optical fiber 4c and the input terminal 81b of the optical branching device 8b, and pumping light is input to the rare earth element-doped optical fiber 4c from the direction opposite to the signal light traveling direction. The effect of the embodiment can be obtained.

In the above embodiment, the optical multiplexer / demultiplexer 3 is used.
It is shown that a is connected only between the first optical isolator 5a and the rare earth element-doped optical fiber 4c, and the excitation light is input to the rare earth element-doped optical fiber 4c from the same direction as the signal light traveling direction. The wave device 3a is connected between the rare earth element-doped optical fiber 4c and the input terminal 81b of the optical branching device 8b, the second excitation light source is connected to the second optical multiplexer / demultiplexer, and both sides of the rare earth element-doped optical fiber 4c are connected. The same effect of the present embodiment can be obtained even when the excitation light is input.

Eighth Embodiment FIG. 8 shows the eighth embodiment of the present invention.
An embodiment of is shown. In the figure, 1 is a signal light input terminal, 5a is a first optical isolator, 2 is a pumping light source, 3a
Is an optical multiplexer / demultiplexer, 31a is the first terminal of the optical multiplexer / demultiplexer 3a,
32a is a second terminal of the optical multiplexer / demultiplexer 3a, 33a is a third terminal of the optical multiplexer / demultiplexer 3a, and 34a is a fourth terminal of the optical multiplexer / demultiplexer 3a.
, 4c is a rare earth element-doped optical fiber, 8b is an optical branch, 81b is an input terminal of the optical branch 8b, 82b is a first output terminal of the optical branch 8b, and 84b is a second branch of the optical branch 8b. Output terminal, 5b is a second optical isolator, 6 is a signal light output terminal, 11 is an optical wavelength filter, 115 is an input terminal of the optical wavelength filter 11, 116 is an optical wavelength filter 11
Of the first output terminal 117 of the optical wavelength filter 11
Is an output terminal, 9b is a first light receiver, 9c is a second light receiver, and 20 is a failure determination circuit.

Next, the operation will be described.

The signal light input from the signal light input terminal 1 passes through the first optical isolator 5a, and the optical multiplexer / demultiplexer 3
a between the first terminal 31a and the second terminal 32a,
It is input to the rare earth element-doped optical fiber 4c.

The pumping light output from the pumping light source 2 is transmitted between the third terminal 33a and the second terminal 32a of the optical multiplexer / demultiplexer 3a, and then input to the rare earth element-doped optical fiber 4c to amplify the signal light. Used as energy.

The signal light amplified and output in the rare earth element-doped optical fiber 4c is input to the input terminal 81 of the optical branching device 8b.
b, and most of them are output from the first output terminal 82b and some of them are output from the second output terminal 84b.

The output light from the first output terminal 82b of the optical branching device 8b passes through the second optical isolator 5b, passes through the signal light output terminal 6, and is output. The ASE light component generated in the rare earth element-doped optical fiber 4c is mixed with the output light of the rare earth element-doped optical fiber 4c in addition to the signal light component.

The output light from the second output terminal 84b of the optical branching device 8b is separated by the optical wavelength filter 11 into a signal light wavelength component and a wavelength component other than the signal light wavelength. A signal light wavelength component is output from the first output terminal 116 of the optical wavelength filter 11, received by the first light receiver 9b, and used for monitoring the signal light output level.

Second output terminal 11 of optical wavelength filter 11
A wavelength component other than the signal light wavelength is output from 7 and is received by the second light receiver 9c. This is the second light receiver 9c.
Is output from the rare earth element-doped optical fiber 4c.
This means that the SE level is being monitored.

The monitoring result of the signal light output level and the monitoring result of the ASE light level are transmitted to the failure determination circuit 20.

When the signal light input level is normal and the amplification gain of the rare earth element-doped optical fiber 4c is also normal, the output signal light level and the ASE level are stable at certain initial levels.

When the input signal light level is lowered due to an abnormality in the input side transmission line fiber, the output signal light level is lower than the initial level, but the ASE light level is higher than the initial level.

When an anomaly occurs in which the gain of the rare earth element-doped optical fiber 4c decreases, the output signal light level becomes lower than the initial level, and the ASE light level also becomes lower than the initial level.

As described above, in the failure determination circuit 20, the normal / abnormal signal light input level and the rare earth element-doped optical fiber 4c are detected based on the signal light output level monitor result and the ASE light level monitor result. It is possible to determine whether the gain is normal or abnormal at the same time.

According to this embodiment, the signal light input level and the gain of the rare earth element-doped optical fiber are judged to be normal / abnormal by monitoring the output signal light level and the ASE level from the rare earth element-doped optical fiber 4c. It is possible to

Further, according to the present embodiment, the optical branching device for monitoring the signal light input level is not required on the input side of the rare earth element-doped optical fiber 4c. Therefore, it is possible to avoid deterioration of the noise figure of about 0.5 dB to 1 dB due to the insertion loss of the optical branching device.

Further, according to the present embodiment, since there is no optical wavelength filter for selecting the transmitted light wavelength in the signal light path, when the optical fiber amplifiers are connected in multiple stages, variations in the transmitted light wavelength of the optical wavelength filter may occur. No signal deterioration occurs.

As described above, according to the present embodiment, the signal light input level and the rare earth element-doped optical fiber 4c are used.
It is possible to obtain an optical fiber amplifier capable of determining normality / abnormality of gain, having low noise, and causing no signal deterioration even when connected in multiple stages.

Although the first optical isolator 5a is connected between the signal light input terminal 1 and the first terminal 31a of the optical multiplexer / demultiplexer 3a in the above embodiment, the second terminal of the optical multiplexer / demultiplexer 3a is connected. The same effect of the present embodiment can be obtained even when it is connected between 32a and the rare earth element-doped optical fiber 4c.

Further, in the above embodiment, the second optical isolator 5b is connected between the first terminal 82b of the optical branching device 8b and the signal light output terminal 6, but the optical branching with the rare earth element-doped optical fiber 4c is performed. The same effect of the present embodiment can be obtained even when connected between the input terminals 81b of the container 8b.

In the above embodiment, the optical multiplexer / demultiplexer 3 is used.
The case where a is connected between the first optical isolator 5a and the rare earth element-doped optical fiber 4c and pumping light is input to the rare earth element-doped optical fiber 4c from the same direction as the signal light traveling direction is shown. 3a is connected between the rare earth element-doped optical fiber 4c and the input terminal 81b of the optical branching device 8b, and pumping light is input to the rare earth element-doped optical fiber 4c from the direction opposite to the signal light traveling direction. The effect of the embodiment can be obtained.

In the above embodiment, the optical multiplexer / demultiplexer 3 is used.
Although a is connected only between the first optical isolator 5a and the rare earth element-doped optical fiber 4c, and the excitation light is input to the rare earth element-doped optical fiber 4c from the same direction as the signal light traveling direction, Is connected between the rare earth element-doped optical fiber 4c and the input terminal 81b of the optical branching device 8b, and the second pumping light source is connected to the second optical multiplexer / demultiplexer.
Even when pumping light is input from both sides of the rare earth element-doped optical fiber 4c, the same effect of this embodiment can be obtained.

[Embodiment 9] FIG. 9 shows the ninth embodiment of the present invention.
An embodiment of is shown. In the figure, 1 is a signal light input terminal, 5a is a first optical isolator, 2 is a pumping light source, 3a
Is an optical multiplexer / demultiplexer, 31a is the first terminal of the optical multiplexer / demultiplexer 3a,
32a is a second terminal of the optical multiplexer / demultiplexer 3a, 33a is a third terminal of the optical multiplexer / demultiplexer 3a, and 34a is a fourth terminal of the optical multiplexer / demultiplexer 3a.
, 4c is a rare earth element-doped optical fiber, 8b is an optical branch, 81b is an input terminal of the optical branch 8b, 82b is a first output terminal of the optical branch 8b, and 84b is a second branch of the optical branch 8b. Output terminal, 5b is a second optical isolator, 6 is a signal light output terminal, 11 is an optical wavelength filter, 115 is an input terminal of the optical wavelength filter 11, 116 is an optical wavelength filter 11
Of the first output terminal 117 of the optical wavelength filter 11
Is an output terminal, 9b is a first light receiver, 9c is a second light receiver, and 20 is a failure determination circuit.

Next, the operation will be described.

The signal light input from the signal light input terminal 1 passes through the first optical isolator 5a, and the optical multiplexer / demultiplexer 3
a between the first terminal 31a and the second terminal 32a,
It is input to the rare earth element-doped optical fiber 4c.

The pumping light output from the pumping light source 2 is transmitted between the third terminal 33a and the second terminal 32a of the optical multiplexer / demultiplexer 3a, and then input to the rare earth element-doped optical fiber 4c to amplify the signal light. Used as energy.

The signal light amplified and output in the rare earth element-doped optical fiber 4c is input to the input terminal 81 of the optical branching device 8b.
b, and most of them are output from the first output terminal 82b and some of them are output from the second output terminal 84b.

The output light from the first output terminal 82b of the optical branching device 8b passes through the second optical isolator 5b, passes through the signal light output terminal 6, and is output. The ASE light component generated in the rare earth element-doped optical fiber 4c is mixed with the output light of the rare earth element-doped optical fiber 4c in addition to the signal light component.

The output light from the second output terminal 84b of the optical branching device 8b is separated by the optical wavelength filter 11 into a signal light wavelength component and a wavelength component other than the signal light wavelength. A signal light wavelength component is output from the first output terminal 116 of the light wavelength filter 11, received by the first light receiver 9b, and used for monitoring the signal light output level.

Second output terminal 11 of optical wavelength filter 11
A wavelength component other than the signal light wavelength is output from 7 and is received by the second light receiver 9c. This is the second light receiver 9c.
Is output from the rare earth element-doped optical fiber 4c.
This means that the SE level is being monitored.

The result of monitoring the signal light output level and the result of monitoring the ASE light level are transmitted to the failure determination circuit 20.

When the signal light input level is normal and the amplification gain of the rare earth element-doped optical fiber 4c is also normal, the output signal light level and the ASE level are stable at certain initial levels.

When the input signal light level is lowered due to an abnormality in the transmission path fiber on the input side, the output signal light level is lower than the initial level, but the ASE light level is higher than the initial level.

When an anomaly occurs in which the gain of the rare earth element-doped optical fiber 4c is lowered, the output signal light level becomes lower than the initial level, and the ASE light level also becomes lower than the initial level.

As described above, in the failure judgment circuit 20, the normal / abnormal signal light input level and the rare earth element-doped optical fiber 4c are detected based on the signal light output level monitor result and the ASE light level monitor result. It is possible to determine whether the gain is normal or abnormal at the same time.

Operating state information such as a monitor PD output is transmitted from the pumping light source 2 to the failure judging circuit 20, and the failure judging circuit 20 can also judge whether the pumping light source 2 is normal or abnormal at the same time.

When an abnormality occurs in the pumping light source 2, measures are taken such as switching to a spare pumping light source.

When the gain of the rare earth element-doped optical fiber 4c is abnormal and the pumping light source 2 is normal, it can be seen that a failure such as a disconnection has occurred in the optical multiplexer / demultiplexer 3a or the rare earth element-doped optical fiber 4c.

According to this embodiment, by monitoring the output signal light level and ASE level from the rare earth element-doped optical fiber 4c and the operating state of the pumping light source, the signal light input level and the gain of the rare earth element-doped optical fiber are monitored. It is possible to simultaneously determine the normality / abnormality of the excitation light source.

Further, according to the present embodiment, the optical branching device for monitoring the signal light input level is not required on the input side of the rare earth element-doped optical fiber 4c. Therefore, it is possible to avoid deterioration of the noise figure of about 0.5 dB to 1 dB due to the insertion loss of the optical branching device.

Further, according to the present embodiment, since there is no optical wavelength filter for selecting the transmitted light wavelength in the signal light path, there is a variation in the transmitted light wavelength of the optical wavelength filter when the optical fiber amplifiers are connected in multiple stages. No signal deterioration occurs.

As described above, according to the present embodiment, the signal light input level and the rare earth element-doped optical fiber 4c are used.
It is possible to obtain an optical fiber amplifier capable of determining normality / abnormality of gain, having low noise, and causing no signal deterioration even when connected in multiple stages.

In the above embodiment, the first optical isolator 5a is connected between the signal light input terminal 1 and the first terminal 31a of the optical multiplexer / demultiplexer 3a, but the second terminal of the optical multiplexer / demultiplexer 3a is connected. The same effect of the present embodiment can be obtained even when it is connected between 32a and the rare earth element-doped optical fiber 4c.

Further, in the above-mentioned embodiment, the second optical isolator 5b is connected between the second terminal 82b of the optical branching device 8b and the signal light output terminal 6, but the optical branching with the rare earth element-doped optical fiber 4c is carried out. The same effect of the present embodiment can be obtained even when connected between the input terminals 81b of the container 8b.

Further, in the above embodiment, the optical multiplexer / demultiplexer 3
The case where a is connected between the first optical isolator 5a and the rare earth element-doped optical fiber 4c and pumping light is input to the rare earth element-doped optical fiber 4c from the same direction as the signal light traveling direction is shown. 3a is connected between the rare earth element-doped optical fiber 4c and the input terminal 81b of the optical branching device 8b, and pumping light is input to the rare earth element-doped optical fiber 4c from the direction opposite to the signal light traveling direction. The effect of the embodiment can be obtained.

In the above embodiment, the optical multiplexer / demultiplexer 3 is used.
Although a is connected only between the first optical isolator 5a and the rare earth element-doped optical fiber 4c, and the excitation light is input to the rare earth element-doped optical fiber 4c from the same direction as the signal light traveling direction, Is connected between the rare earth element-doped optical fiber 4c and the input terminal 81b of the optical branching device 8b, and the second pumping light source is connected to the second optical multiplexer / demultiplexer.
Even when pumping light is input from both sides of the rare earth element-doped optical fiber 4c, the same effect of this embodiment can be obtained.

[Embodiment 10] FIG. 10 shows a tenth embodiment according to the present invention. In the figure, 1 is a signal light input terminal, 5a is a first optical isolator, 8a is an optical branching device,
81a is the first terminal of the optical branching device 8a, 82a is the second terminal of the optical branching device 8a, 83a is the third terminal of the optical branching device 8a, 84a is the fourth terminal of the optical branching device 8a, and 3a is Optical multiplexer / demultiplexer, 31a is a first terminal of the optical multiplexer / demultiplexer 3a, 32a is a second terminal of the optical multiplexer / demultiplexer 3a, and 33a is an optical multiplexer / demultiplexer 3a.
, 3 is a pumping light source, 4c is a rare earth element-doped optical fiber, 5b is a second optical isolator, 6 is a signal light output terminal, 12 is a signal light wavelength elimination filter, and 9a is a first
, 9c is a second light receiver, and 10 is an excitation light source control circuit.

Next, the operation will be described.

The signal light input from the signal light input terminal 1 is transmitted through the first optical isolator 5a, and the optical branching device 8a.
Is input to the first terminal 81a. First of the optical branching device 8a
Most of the signal light input from the terminal 81a is output from the second terminal 82a and part of the signal light is output from the fourth terminal 84a. The ratio of the output from the second terminal 82a and the output from the fourth terminal 84a is usually about 10 dB.

The signal light from the second terminal 82a of the optical branching device 8a is transmitted between the first terminal 31a and the second terminal 32a of the optical multiplexer / demultiplexer 3a, and the rare earth element-doped optical fiber 4c.
Entered in. The pumping light output from the pumping light source 2 is transmitted between the third terminal 33a and the second terminal 32a of the optical multiplexer / demultiplexer 3a, is input to the rare earth element-doped optical fiber 4c, and is used as amplification energy of the signal light. . The signal light amplified and output in the rare earth element-doped optical fiber 4c is
The signal light output terminal 6 is transmitted through the second optical isolator 5b.
Will be output.

The signal light output from the fourth terminal 84a of the optical branching device 8a is received by the first light receiver 9a and used for monitoring the signal light input level.

In the rare earth element-doped optical fiber 4c, ASE light traveling in the direction opposite to the signal light traveling direction is generated,
It is output to the signal light input side. The output light is an optical multiplexer / demultiplexer 3
a between the second terminal 32a and the second terminal 31a,
It is input to the second terminal 82a of the optical branching device 8a. Most of the light input to the second terminal 82a of the optical branching device 8a is output from the first terminal 81a and part of the light is input to the third terminal 83a.
Is output from. The ratio of the output from the first terminal 81a and the output from the third terminal 83a is the ratio of the output from the second terminal 82a and the output from the fourth terminal 84a when input from the first terminal 81a. And is usually about 10 dB.

The output light output from the rare earth element-doped optical fiber 4c to the signal light input side has a weak reflection component of the signal light in addition to the ASE light component. Third of the optical branching device 8a
The output light from the terminal 83a is a wavelength component other than the signal light wavelength from which the signal light wavelength component has been removed by the signal light wavelength component removal filter 12, that is, ASE light is output. A above
The SE light is received by the second light receiver 9c and used for monitoring the ASE light level.

In the rare earth element-doped optical fiber 4c, when the signal light input level is constant, the generated ASE light level is large and the amplification degree is small when the signal light output level is large and the signal light output level is large. When is small, the generated ASE level is also small. Therefore, the first
It is possible to know the signal light output level from the rare earth element-doped optical fiber 4c from the relationship between the signal light input level obtained from the second light receiver 9a and the ASE light level obtained from the second light receiver 9c.

The result of monitoring the signal light input level and the result of monitoring the ASE light level are transmitted to the pumping light source control circuit 10, and the pumping light source is provided so as to obtain an appropriate amplification characteristic according to the signal light input level and the output level. The drive state of 2 is controlled.

According to this embodiment, an optical branching device for monitoring the signal light output level is not required on the output side of the rare earth element-doped optical fiber 4c. Therefore, it is possible to avoid a decrease in the maximum output of about 0.5 dB to 1 dB due to the insertion loss of the optical branching device.

As described above, according to this embodiment, an optical fiber amplifier in which the maximum optical output is not lowered can be obtained.

In the above embodiment, the optical multiplexer / demultiplexer 3a is connected between the optical branching device 8a and the rare earth element-doped optical fiber 4c, and pumping light is input to the rare earth element-doped optical fiber 4c from the same direction as the signal light traveling direction. The optical multiplexer / demultiplexer 3a is connected between the rare earth element-doped optical fiber 4c and the second optical isolator 5b, and pumping light is transmitted from the direction opposite to the signal light traveling direction to the rare earth element-doped optical fiber 4c. Even when input is made, the same effect of this embodiment can be obtained.

In the above embodiment, the optical multiplexer / demultiplexer 3 is used.
The case where a is connected only between the optical branching device 8a and the rare earth element-doped optical fiber 4c and the pumping light is input to the rare earth element-doped optical fiber 4c from the same direction as the signal light traveling direction has been described. A demultiplexer is connected between the rare earth element-doped optical fiber 4c and the second optical isolator 5b, a second pumping light source is connected to the second optical multiplexer / demultiplexer, and pumping light is emitted from both sides of the rare earth element-doped optical fiber 4c. If you type
Similar effects of this embodiment can be obtained.

Further, in the above embodiment, the case where the driving state of the pumping light source 2 is controlled so as to obtain an appropriate amplification characteristic according to the signal light input level and the signal light output level has been described. The same effect can be obtained when the failure determination circuit is used instead of 10 to determine whether the input signal level is normal / abnormal and the gain of the rare earth element-doped optical fiber 4c is normal / abnormal.

Eleventh Embodiment FIG. 11 shows an eleventh embodiment according to the present invention. In the figure, 1 is a signal light input terminal, 8a is an optical branching device, 81a is an input terminal of the optical branching device 8a, 82a is a first output terminal of the optical branching device 8a, and 84a.
Is a second output terminal of the optical branching device 8a, 13 is an optical circulator, 131 is a first terminal of the optical circulator 13, 1
32 is a second terminal of the optical circulator 13, 133 is a third terminal of the optical circulator 13, 3a is an optical multiplexer / demultiplexer,
31a is a first terminal of the optical multiplexer / demultiplexer 3a, 32a is a second terminal of the optical multiplexer / demultiplexer 3a, and 33a is a third terminal of the optical multiplexer / demultiplexer 3a.
, 2 is an excitation light source, 4c is a rare earth element-doped optical fiber, 5c is an optical isolator, 6 is a signal light output terminal, 1
Reference numeral 2 is a signal light wavelength component removal filter, 9a is a first light receiver, 9c is a second light receiver, and 10 is an excitation light source control circuit.

Next, the operation will be described.

The signal light input from the signal light input terminal 1 is input to the optical branching device 8a. Input terminal 8 of optical branching device 8a
Most of the signal light input from 1a is output from the first output terminal 82a, and part is output from the second output terminal 84a. The ratio of the output from the first output terminal 82a and the output from the second output terminal 84a is usually about 10 dB.

The signal light output from the first terminal 82a of the optical branching device 8a is supplied to the first terminal 1 of the optical circulator 13.
It is input to 31. In the optical circulator 13,
The light input to the first terminal 131 is output from the second terminal 132, and the light input to the second terminal 132 is output from the third terminal 133.

Second terminal 132 of optical circulator 13
The signal light output from the optical multiplexer / demultiplexer 3a is transmitted between the first terminal 31a and the second terminal 32a of the optical multiplexer / demultiplexer 3a, and is input to the rare earth element-doped optical fiber 4c. The pumping light output from the pumping light source 2 is transmitted between the third terminal 33a and the second terminal 32a of the optical multiplexer / demultiplexer 3a, is input to the rare earth element-doped optical fiber 4c, and is used as amplification energy of the signal light. . The signal light amplified and output in the rare earth element-doped optical fiber 4c passes through the optical isolator 5c, passes through the signal light output terminal 6, and is output.

The signal light output from the second output terminal 84a of the optical branching device 8a is received by the first light receiver 9a and used for monitoring the signal light input level.

In the rare earth element-doped optical fiber 4c, ASE light traveling in the direction opposite to the signal light traveling direction is generated,
It is output to the signal light input side together with the weak reflected component of the signal light. The output light is transmitted between the second terminal 132 and the third terminal 133 of the optical circulator 13, the signal light wavelength component removal filter 12 removes the signal light wavelength component, and the wavelength component other than the signal light wavelength, that is, the ASE light. Only the light is received by the second light receiver 9c and used as a monitor of the ASE light level.

In the rare earth element-doped optical fiber 4c, when the signal light input level is constant, the generated ASE light level is large when the amplification degree is large and the signal light output level is large, and the signal light output level is small. When is small, the generated ASE level is also small. Therefore, the first
It is possible to know the signal light output level from the rare earth element-doped optical fiber 4c from the relationship between the signal light input level obtained from the second light receiver 9a and the ASE light level obtained from the second light receiver 9c. .

The result of monitoring the signal light input level and the result of monitoring the ASE light level are transmitted to the pump light source control circuit 10, and the pump light source is controlled so as to obtain an appropriate amplification characteristic according to the signal light input level and the output level. The drive state of 2 is controlled.

Further, the optical circulator 13 is provided in the transmission line fiber when the ASE light generated in the rare earth element-doped optical fiber 4c and traveling in the direction opposite to the signal light traveling direction is input to the input side transmission line fiber. It is prevented that the amplification characteristic is deteriorated by being re-inputted to the rare earth element-doped optical fiber 4c due to the reflection due to Rayleigh scattering. Therefore, it is not necessary to connect another optical isolator to the input side of the rare earth element-doped optical fiber 4c.

According to this embodiment, an optical branching device for monitoring the signal light output level is not required on the output side of the rare earth element-doped optical fiber 4c. Therefore, it is possible to avoid the decrease of the maximum output of about 0.5 dB due to the insertion loss of the optical branching device.

As described above, according to this embodiment, it is possible to obtain an optical fiber amplifier in which the maximum optical output is not lowered.

In the above embodiment, the optical multiplexer / demultiplexer 3a is provided with the optical circulator 13 and the rare earth element-doped optical fiber 4c.
A case where the pumping light is input to the rare earth element-doped optical fiber 4c from the same direction as the signal light traveling direction by connecting the optical multiplexer / demultiplexer 3a to the rare earth element-doped optical fiber 4c is shown.
The same effect of the present embodiment can be obtained even when the pumping light is input to the rare-earth element-doped optical fiber 4c from the direction opposite to the signal light traveling direction by connecting the optical fiber to the optical isolator 5c.

[Embodiment 12] FIG. 12 shows a twelfth embodiment of the invention. In the figure, 14 is an optical fiber amplifier to be measured, 15 is an input signal light, 16 is an output light from the optical fiber amplifier under measurement 14, 17 is an output light output from the optical fiber amplifier under test 14 to the input side of the signal light. , 13 is an optical circulator, 131 is a first terminal of the optical circulator 13, 132 is a second terminal of the optical circulator 13, 133 is a third terminal of the optical circulator 13, and 18a is a first wavelength characteristic measuring means. A first optical spectrum analyzer, 18b is a second optical spectrum analyzer which is a second wavelength characteristic measuring means, and 19 is an arithmetic circuit.

Next, the operation will be described.

In the optical circulator 13, the light input to the first terminal 131 is output from the second terminal 132, and the light input to the second terminal 132 is the third terminal 1.
It is output from 33.

The input signal light 15 is the optical circulator 13
Is transmitted from the first terminal 131 to the second terminal 132, and is input to the optical fiber amplifier 14 to be measured. In the measured optical fiber amplifier 14, the signal light is amplified and the AS
E light is generated. The ASE light is output to the signal light output side and the signal light input side. In addition, the optical fiber amplifier under test 14
Due to the weak reflection inside, a small amount of signal light component is also output to the signal light input side.

The output light output from the signal light output side of the measured optical fiber amplifier 14 is input to the first optical spectrum analyzer 18a. The signal light output level is calculated from the measurement result of the first optical spectrum analyzer 18a, and the gain of the measured optical fiber amplifier 14 can be calculated.

In order to calculate the noise figure of the optical fiber amplifier under test 14, the first optical spectrum analyzer 18
It is necessary to calculate the ASE light level from the measurement result of a. However, as described in the above-mentioned third prior art, the first
Since the signal light component and the ASE light component cannot be separated from the measurement result of the optical spectrum analyzer 18a, it is not possible to directly measure the ASE light level at the same wavelength as the signal light wavelength. The estimation error must be calculated from the ASE light level at wavelengths distant by a meter, which causes a large measurement error.

The light output from the signal light input side of the optical fiber amplifier under test 14 passes from the second terminal 132 to the third terminal 133 of the optical circulator 13 and is input to the second optical spectrum analyzer 18b. It Even in the measurement result of the second optical spectrum analyzer 18b, the signal light component and the ASE light component cannot be separated. However, since the signal light component is weak, the ASE light level at a wavelength about 0.2 nm away from the signal light wavelength. From this, the ASE light level at the same wavelength as the signal light wavelength can be estimated, and the measurement error is significantly reduced.

The wavelength characteristics of the ASE light output to the signal light output side and the signal light input side of the measured optical fiber amplifier 14 are the same, but the ASE light level may be different.
The measurement result of the first optical spectrum analyzer 18a and the measurement result of the second optical spectrum analyzer 18b are transmitted to the arithmetic circuit 19, and the ASE light level difference is corrected to be the same as the signal light wavelength output to the signal light output side. Accurately estimate the ASE light level at the wavelength.

As described above, according to the present embodiment, it is possible to obtain an amplification characteristic measuring apparatus for an optical fiber amplifier, which is capable of accurately calculating a noise figure.

Thirteenth Embodiment FIG. 13 shows a thirteenth embodiment according to the present invention. In the figure, 14 is an optical fiber amplifier to be measured, 15 is an input signal light, 16 is an output light from the optical fiber amplifier under measurement 14, 17 is an output light output from the optical fiber amplifier under test 14 to the input side of the signal light. , 8a is an optical splitter, 81a is a first terminal of the optical splitter 8a, 82a is a second terminal of the optical splitter 8a, 83a is a third terminal of the optical splitter 8a, and 18a is a first wavelength characteristic. A first optical spectrum analyzer which is a measuring means, 18b is a second optical spectrum analyzer which is a second wavelength characteristic measuring means, and 19 is an arithmetic circuit.

Next, the operation will be described.

The input signal light 15 passes through the first terminal 81a and the second terminal 82a of the optical branching device 8a and is input to the optical fiber amplifier 14 to be measured. In the optical fiber amplifier under test 14, signal light is amplified and ASE light is generated. The ASE light is output to the signal light output side and the signal light input side. In addition, due to the weak reflection in the optical fiber amplifier under test 14, a small amount of signal light component is output to the signal light input side.

The output light output from the signal light output side of the measured optical fiber amplifier 14 is input to the first optical spectrum analyzer 18a. The signal light output level is calculated from the measurement result of the first optical spectrum analyzer 18a, and the gain of the measured optical fiber amplifier 14 can be calculated.

The light output from the signal light input side of the measured optical fiber amplifier 14 is the second terminal 82a of the optical branching device 8a.
To the first terminal 81a and the third terminal 83a. The output light from the third terminal 83a of the optical branching device 8a is input to the second optical spectrum analyzer 18b.
Even in the measurement result of the second optical spectrum analyzer 18b, the signal light component and the ASE light component cannot be separated. However, since the signal light component is weak, the ASE light level at a wavelength about 0.2 nm away from the signal light wavelength. From this, the ASE light level at the same wavelength as the signal light wavelength can be estimated, and the measurement error is significantly reduced.

The wavelength characteristics of the ASE light output to the signal light output side and the signal light input side of the measured optical fiber amplifier 14 are the same, but the ASE light levels may differ, so
The measurement result of the first optical spectrum analyzer 18a and the measurement result of the second optical spectrum analyzer 18b are transmitted to the arithmetic circuit 19, and the ASE light level difference is corrected to be the same as the signal light wavelength output to the signal light output side. Accurately estimate the ASE light level at the wavelength.

As described above, according to the present embodiment, it is possible to obtain the amplification characteristic measuring device for the optical fiber amplifier, which can calculate the noise figure with high accuracy.

[0256]

As described above, the optical fiber amplifier according to the first aspect of the present invention can monitor the signal light input level without providing an optical branching device on the input side of the rare earth element-doped optical fiber. It is possible and because there is no optical wavelength filter that selects the transmitted light wavelength in the signal light path,
It is possible to prevent signal deterioration even when the noise characteristics are not deteriorated and the connection is made in multiple stages.

Further, as described above, according to the optical fiber amplifier of the second aspect of the present invention, the input side of the rare earth element-doped optical fiber is judged in the failure judgment of the signal light input level lowering and the rare earth element doping optical fiber gain lowering. Since there is no need to provide an optical branching device in the optical path, and there is no optical wavelength filter for selecting the transmitted light wavelength in the signal optical path, the signal optical input level and the rare earth element-doped optical fiber gain normal /
It is possible to determine an abnormality, to prevent deterioration of noise characteristics, and to prevent signal deterioration even when connected in multiple stages.

As described above, according to the optical fiber amplifier of the third aspect of the present invention, the signal light output level can be monitored without providing an optical branching device on the output side of the rare earth element-doped optical fiber. Since this is possible, it is possible to prevent a decrease in the maximum light output.

As described above, according to the optical fiber amplifier of the fourth aspect of the present invention, the signal light output level can be monitored without providing an optical branching device on the output side of the rare earth element-doped optical fiber. Since this is possible, it is possible to prevent a decrease in the maximum light output.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of an optical fiber amplifier according to a first embodiment of the present invention.

FIG. 2 is a block diagram of an optical fiber amplifier according to Embodiment 2 of the present invention.

FIG. 3 is a block diagram of an optical fiber amplifier according to a third embodiment of the present invention.

FIG. 4 is a block configuration diagram of an optical fiber amplifier according to Embodiment 4 of the present invention.

FIG. 5 is a block diagram of an optical fiber amplifier according to a fifth embodiment of the present invention.

FIG. 6 is a block diagram of an optical fiber amplifier according to Embodiment 6 of the present invention.

FIG. 7 is a block diagram of an optical fiber amplifier according to Embodiment 7 of the present invention.

FIG. 8 is a block diagram of an optical fiber amplifier according to an eighth embodiment of the present invention.

FIG. 9 is a block configuration diagram of an optical fiber amplifier according to a ninth embodiment of the present invention.

FIG. 10 is a block configuration diagram of an optical fiber amplifier according to a tenth embodiment of the present invention.

FIG. 11 is a block configuration diagram of an optical fiber amplifier according to an eleventh embodiment of the present invention.

FIG. 12 is a block configuration diagram of an amplification characteristic measuring device for an optical fiber amplifier according to a twelfth embodiment of the present invention.

FIG. 13 is a block configuration diagram of an amplification characteristic measuring device for an optical fiber amplifier according to a thirteenth embodiment of the present invention.

FIG. 14 is a block diagram of an optical fiber amplifier according to a first conventional example.

FIG. 15 is a block diagram of an optical fiber amplifier according to a second conventional example.

FIG. 16 is a block diagram of an optical fiber amplifier according to a third conventional example.

FIG. 17 is a block diagram of an optical fiber amplifier according to a fourth conventional example.

FIG. 18 is a block diagram of an optical fiber amplifier according to a fifth conventional example.

[Explanation of symbols]

1 signal light input terminal, 2, 2a, 2b pumping light source, 3
a, 3b, 3c optical multiplexer / demultiplexer, 4a, 4b, 4c rare earth element-doped optical fiber, 5, 5a, 5b optical isolator, 6 signal light output terminal, 7a, 7b non-reflective termination,
8a, 8b optical branching device, 9a, 9b, 9c light receiving device, 1
0 excitation light source control circuit, 11 optical wavelength filter, 12
Signal light wavelength elimination filter, 13 optical circulator, 1
4 optical fiber amplifier under test, 18a, 18b optical spectrum analyzer, 19 arithmetic circuit, 20 failure judgment circuit.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-6-132905 (JP, A) JP-A-6-268306 (JP, A) JP-A-6-310791 (JP, A) JP-A-5- 283787 (JP, A) JP-A-6-97554 (JP, A) JP-A-4-23625 (JP, A) JP-A-4-333831 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01S 3/00-3/30

Claims (4)

(57) [Claims] 1. A rare earth element-doped optical fiber in which an optical fiber is doped with a rare earth element for amplifying signal light by irradiation with excitation light, and amplification of signal light in the rare earth element-doped optical fiber.
Excitation light source that outputs excitation light used as energy
When the optical splitter for splitting the light output of the rare-earth element doped optical fiber, an optical wavelength filter for splitting the wavelength components other than the optical signal wavelength component branch output optical branching device and the signal light wavelength, the light a first photodetector for receiving the output signal light wavelength components than a wavelength filter, a second light receiver for receiving the wavelength components other than the light wavelength output signal light wavelength of the filter, the first light receiving And output level of the second light receiver
Pump light source control for controlling drive of the pump light source based on
Optical fiber amplifier comprising the a circuit. 2. A rare light that amplifies signal light by irradiation with excitation light.
Rare earth element doped light with earth element doped in optical fiber
Fiber and light that splits the optical output of the rare earth element-doped optical fiber
A branching device and a branching light output from the optical branching device as a signal light wavelength component and a signal light wave.
An optical wavelength filter that splits into a wavelength component other than the length, and a signal light wavelength component output from the optical wavelength filter are received.
A first light receiver that emits light and a wave other than the signal light wavelength output from the optical wavelength filter
A second photoreceiver for receiving a long component, and normal / abnormal of the input level of the signal light and normal / abnormal of the gain of the rare earth element-doped optical fiber are determined from the output levels of the first and second photoreceivers. a circuit for, you, comprising the optical fiber amplifier. 3. A signal light input terminal, a rare earth element-doped optical fiber in which an optical fiber is doped with a rare earth element that amplifies signal light by irradiation of excitation light, and signal light amplification in the rare earth element-doped optical fiber.
Excitation light source that outputs excitation light used as energy
If, inputted from the first terminal for connecting the signal light input terminal
And the light is branched outputs to said rare earth doped optical fiber <br/> second connected terminal and the fourth terminal, also input from the second terminal, the rare earth element doped optical fiber
In the optical branching device for branching and outputting the signal light other than the input signal light generated in 1) to the first terminal and the third terminal, and the input signal light output from the third terminal of the optical branching device.
An optical wavelength filter for removing the input signal light wavelength component from the outside signal light, and a signal light wavelength component output from the fourth terminal of the optical branching device.
Other than the first optical receiver for receiving the light and the input signal light wavelength output from the optical wavelength filter
Second photoreceiver for receiving the wavelength component of , and output levels of the first photoreceiver and the second photoreceiver
Pump light source control for controlling drive of the pump light source based on
Optical fiber amplifier comprising the a circuit. 4. A signal light input terminal, a rare earth element-doped optical fiber in which an optical fiber is doped with a rare earth element that amplifies the signal light by irradiation of excitation light, and signal light amplification in the rare earth element-doped optical fiber.
Excitation light source that outputs excitation light used as energy
When are input from the input terminal to which the signal light input terminal connected
That the signal light optical splitter for splitting the first and second output terminals and said rare earth element doped optical light inputted from the first terminal
Output from the second terminal fiber is connected, and an optical circulator for outputting light input from the second terminal from the third terminal, output from the third terminal of the optical circulator input
An optical wavelength filter for removing a signal light or et input signal light wavelength components other than the signal light, before Symbol optical splitter of the second output signal outputted light waves from the terminal
Other than the first light receiver for receiving the long component and the input signal light wavelength output from the optical wavelength filter
A second optical receiver for receiving the wavelength components, the first photodetector and said second photodetector output level
Pump light source control for controlling drive of the pump light source based on
Optical fiber amplifier comprising the a circuit.