JPH06268306A - Optical amplifier - Google Patents

Abstract

(57) [Summary] (Correction) [Purpose] To provide an optical amplifying device having a simple configuration with no loss of input signal light, constant amplification gain. [Structure] An optical amplifier 21 for amplifying input signal light,
In the optical amplifier device including the control circuit 26 for controlling the amplification gain of the optical amplifier 21, from the port P ₁ to which the signal light Sigi is input to the port P ₂ connected to the input side of the optical amplifier 21, to the port P ₂ From the optical circulator 20 having a forward characteristic from the port P ₃ to the port P ₃ , and detecting the light intensity of the spontaneous emission light Pase− from the optical amplifier 21, which is connected to the port P ₃ , and outputs the detected light intensity value to the control circuit 26. And a light intensity detector 25 for outputting.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplifier, and more particularly to an optical amplifier device that keeps the amplification gain constant.

[0002]

2. Description of the Related Art The following method has been proposed as a method for keeping the amplification gain of an optical amplifier device constant. 8 to 11 are block diagrams of conventional optical amplifiers.

(1) Feedback control method As shown in FIG. 8, the optical amplification apparatus uses the input signal light Sig.
An input side optical branching device 1 for branching i in two directions and one of the branched signal lights Sig connected to the input side optical branching device 1.
An optical amplifier 4 including an optical amplification medium 2 for amplifying i ₁ and a pumping device 3 for providing pumping light to the optical amplification medium 2, and a pumping power control circuit 5 for controlling an amplification gain of the optical amplifier 4 are branched. The input side light intensity detection circuit 6 that detects the light intensity of the other signal light Sigi ₂ and outputs the detected light intensity to the excitation power control circuit 5, and the output signal light Sigo amplified by the optical amplifier 4 in two directions. To the output side optical branching device 7 and one of the output signal lights Sigo ₁ branched by the output side optical branching device 7.
And an output-side light intensity detection circuit 8 which detects the light intensity and outputs the detected light intensity to the excitation power control circuit 5.

This amplifying apparatus uses the input signal light Sigi
And a part of the input signal light and a part of the amplified signal light Sigo are detected, and the light intensity ratio of the two lights is constant, that is, the amplification gain of the optical amplifier 4 is constant. Control the device 3.

(2) Feedforward control method As shown in FIG. 9, the optical amplifying device uses the input signal light Sig.
An input side optical branching device 1 for branching i in two directions, and an optical amplification medium 2 for amplifying one of the branched signal lights Sigi _1.
And the pumping power control circuit 9 for controlling the amplification gain of the optical amplifier 4, and the optical power of the other branched signal light Sigi ₂ are detected. And an input side light intensity detection circuit 6 for outputting the detected light intensity value to the excitation power control circuit 9.

[0006] This optical amplifying device uses the input signal light Sig.
i is amplified, the light intensity of the signal light Sigi is detected, and the pumping device 3 is controlled so that the amplification gain of the optical amplification medium becomes constant.

(3) Method of controlling amplification gain based on spontaneous emission light emitted from the side surface of a rare earth-doped optical fiber as an optical amplification medium In FIG. 10, a pumping light source 10 as a pumping device and an optical amplification medium are used. The rare earth-doped optical fiber 11 and the optical multiplexer 12 that multiplexes the input signal light Sigi and the pumping light from the pumping light source 10 and inputs the multiplexed light to the rare earth-doped optical fiber 11.
And an optical isolator 13 that is connected to the output side of the rare earth-doped optical fiber 11 and prevents reflected return light. Based on this optical amplifier, a light intensity detector 14 provided in the vicinity of the rare earth-doped optical fiber 11 for detecting spontaneous emission light emitted from the side surface of the optical fiber 11, and a light intensity detection value from the light intensity detector 14. Excitation light source 1
An optical amplifier is configured with a pump power control circuit that controls the light intensity of zero.

This optical amplifying device amplifies the input Sigi and controls the pumping light based on the light intensity of the spontaneous emission light from the optical fiber 11 so that the amplification gain becomes constant.

The rare earth-doped optical fiber is provided with a coating (for example, a UV coating) that allows spontaneous emission light to be extracted from the side surface of the optical fiber. Prevents unstable operation.

(4) Method for controlling the amplification gain based on the spontaneous emission light emitted from the side surface of the rare earth-doped optical fiber as the optical amplification medium, and for preventing the excessive input and excessive output of the pumping light source as shown in FIG. The optical amplifying device is basically the same as the method (3), except that a light intensity detector 15 for detecting the light intensity of the pumping light is provided in the vicinity of the pumping light source 10, and this light intensity detector is used. The point is that the pump power limiting circuit 16 that outputs a signal for limiting the light intensity of the pump light to the pump power control circuit 9 when the detected light intensity value detected by 15 exceeds a preset reference value is provided. . By providing the pumping power limiting circuit 16, it is possible to prevent the pumping light source 10 from excessive input and output.

In addition, although not shown in the figure, a bidirectional pumping method (a pumping light source is provided before and after the rare earth-doped optical fiber, and pumping light is supplied to the optical fiber from both directions to pump signal light. There is a method of amplifying the signal light).

[0012]

However, the above-mentioned method has the following problems.

In the method (1), the input light cannot be detected when the signal light Sigi is not input, so that the amplification gain cannot be controlled. In addition, since the output light includes the spontaneous emission light as well as the amplified signal light Sigo, a control error occurs. Further input signal light S
Since the light intensity is detected after the igi is branched, the loss of the signal system is large.

Since the method (2) controls the amplification gain according to the light intensity of the input signal light Sigi, it is necessary to accurately grasp the relationship between the amplification gain and the signal light and the pump light in advance, and the control system also. It gets complicated.

In the methods (3) and (4), the light intensity of the spontaneous emission light that can be extracted from the side surface of the optical fiber changes as the coating material ages. That is, even if the light intensity of the spontaneous emission light generated in the optical fiber is constant, the light intensity of the spontaneous emission light that can be extracted changes. Therefore, it is necessary to control the change in the light intensity, which makes the control difficult. When the excitation light source 10 and the light intensity detector 15 are housed in the same package 17 as shown in FIG. 11, the output of the excitation light source 10 is large and the temperature of the package 17 greatly fluctuates. Since the excitation light source 10 and the light intensity detector 15 are spatially coupled to each other, the coupling efficiency varies due to this temperature variation, and accurate monitoring cannot be performed. On the other hand, when the pumping light source 10 and the light intensity detector 15 are not housed in the same package, a part of the pumping light is branched by using a branching device or the like, so that the pumping efficiency is lowered.

Further, in the bidirectional pumping method, the information used for control is only the light intensity of the spontaneous emission light, but since the two pumping light sources are controlled, the relationship between the operating characteristics and the like of both pumping light sources is accurately grasped. If this is not done, stable control cannot be performed, the number of parts will increase, and the cost will increase.

Therefore, an object of the present invention is to solve the above-mentioned problems, to eliminate the loss of input signal light, to maintain a constant amplification gain,
Moreover, it is to provide an optical amplifier having a simple structure.

[0018]

In order to achieve the above object, the present invention provides an optical amplifier device comprising an optical amplifier for amplifying input signal light, and a control circuit for controlling the amplification gain of the optical amplifier, An optical circulator having forward characteristics from port 1 to which signal light is input to port 2 connected to the input side of the optical amplifier, and from port 2 to port 3, and spontaneous emission from the optical amplifier connected to port 3. A light intensity detector that detects the light intensity of light and outputs the detected light intensity value to a control circuit.

Further, the present invention controls an amplification gain of the optical amplifier, which comprises an optical amplification medium for amplifying the input signal light and a pumping device for providing pumping light for pumping the optical amplification medium. In an optical amplifying device equipped with a control circuit and a limiting circuit connected to the control circuit for limiting the light intensity of pumping light of a pumping device to a reference value or less, an input side of an optical amplifying medium from a port 1 to which signal light is input. Port 2 connected to
An optical circulator having a forward characteristic from the port 2 to the port 3, an optical demultiplexer connected to the port 3 for demultiplexing spontaneous emission light and excitation light from the optical amplification medium, and an optical demultiplexer. The first light intensity detector that detects the light intensity of the demultiplexed spontaneous emission light and outputs the light intensity detection value to the control circuit, and the intensity detection value of the excitation light demultiplexed by the optical demultiplexer And a second light intensity detector for outputting to the limiting circuit.

Further, according to the present invention, an optical amplifying medium for amplifying the input signal light and a forward pumping device for giving pumping light from the input side to the optical amplifying medium for exciting the optical amplifying medium and an output side for the optical amplifying medium are provided. An optical amplifier including a backward pumping device that supplies pumping light from the pump, a control circuit that controls the amplification gain of the optical amplifier, and a limiting circuit that is connected to the control circuit and limits the intensity of the pumping light of each pumping device to a reference value or less. In the provided optical amplification device, a first optical circulator having forward characteristics from port 1 to which signal light and pumping light are input to port 2 connected to the input side of an optical amplification medium and from port 2 to port 3. And a first optical demultiplexer connected to the port 3 for demultiplexing the spontaneous emission light and the excitation light from the optical amplification medium, and the light intensity of the spontaneous emission light demultiplexed by the first optical demultiplexer Detected and control the light intensity detection value The first light intensity detector for outputting to the optical path, the second light intensity detector for outputting the excitation light demultiplexed by the first optical demultiplexer to the limiting circuit, and the excitation light from the backward excitation device A second optical circulator having forward characteristics from another input port 1 to another port 2 connected to the output side of the optical amplification medium, and from another port 2 to another port 3, and another port A second optical demultiplexer connected to 3 for demultiplexing the signal light amplified by the optical amplifier and the excitation light, and the light intensity of the excitation light demultiplexed by the second optical demultiplexer is detected, And a third light intensity detector for outputting the light intensity detection value to the limiting circuit.

Furthermore, according to the present invention, an optical amplifying medium for amplifying the input signal light and a forward pumping device for giving pumping light from the input side to the optical amplifying medium for exciting the optical amplifying medium and outputting to the optical amplifying medium. From the side, an optical amplifier consisting of a backward pumping device that gives pumping light of a wavelength different from that of the forward pumping device, a control circuit that controls the amplification gain of the optical amplifier, and the pumping light intensity of each pumping device that is connected to the control circuit as a reference In a light amplification device having a limiting circuit for limiting the value to a value or less, a forward characteristic from port 1 to which signal light is input to port 2 connected to the input side of an optical amplification medium and from port 2 to port 3 is shown. An optical circulator having the above, a first optical demultiplexer connected to the port 3 for demultiplexing spontaneous emission light and excitation light from the optical amplification medium, and spontaneous emission light demultiplexed by the first optical demultiplexer Detects the light intensity of A first light intensity detector that outputs a detection value to a control circuit, a second light intensity detector that outputs the excitation light demultiplexed by the first optical demultiplexer to a limiting circuit, and an optical amplification medium A second optical demultiplexer connected to the output side for demultiplexing the signal light amplified by the optical amplifier and the pumping light, and the light intensity of the pumping light demultiplexed by the second optical demultiplexer are detected. And a third light intensity detector for outputting the light intensity detection value to the limiting circuit.

The present invention also relates to an optical amplifier comprising a rare earth-doped optical fiber and a pumping light source, an optical isolator connected to the input side of the rare earth-doped optical fiber for blocking reflected return light to the optical amplifier, and port 1 to port. 2 to port 2
To a port 3 and having an optical circulator in which a pumping light source is connected to the port 1, an output side of a rare earth-doped optical fiber is connected to the port 2, and an output terminal is connected to the port 3. Is.

[0023]

According to the above structure, the optical circulator having the forward characteristic from the port 1 to which the signal light is input to the port 2 connected to the input side of the optical amplifier, and the optical circulator having the port 2 to the port 3 are provided. It has a light intensity detector that is connected and detects the light intensity of the spontaneous emission light from the optical amplifier, and outputs the detected light intensity value to the control circuit. Since the signal light is input, there is no loss of signal light, and since only spontaneous emission light is input to the light intensity detector, the amplification gain can be accurately controlled.

Further, an optical circulator having forward characteristics from the port 1 to which the signal light is input to the port 2 connected to the input side of the optical amplification medium and from the port 2 to the port 3 and the optical circulator connected to the port 3 are provided. An optical demultiplexer that demultiplexes the spontaneous emission light and the excitation light from the amplification medium, and the light intensity of the spontaneous emission light demultiplexed by the optical demultiplexer is detected, and the detected light intensity value is output to the control circuit. The second light intensity detector, which includes the first light intensity detector and the second light intensity detector that outputs the intensity detection value of the excitation light demultiplexed by the optical demultiplexer to the limiting circuit, Since the pump is inputted with the pumping light without being affected by the temperature change by the pumping device and the signal light is not lost, the light intensity of the pumping light can be accurately controlled.

Further, since the optical circulator is used, the number of parts is reduced, and since the optical isolator is used, there is no reflected return light to the rare earth-doped optical fiber, and the amplification operation becomes stable.

[0026]

An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a block diagram of an embodiment of the optical amplifying device of the present invention.

In the figure, reference numeral 20 denotes an optical circulator having forward characteristics from the port 1P ₁ to the port 2P ₂ and from the port 2P ₂ to the port 3P ₃ . Port 1
P ₁ is connected to the input terminal Pi for inputting the signal light Sigi, and the port 2P ₂ is connected to the input side of the optical amplifier 21.

The optical amplifier 21 receives the input signal light Sig.
optical amplification medium 22 for amplifying i, and optical amplification medium 22
And a pumping device 23 for supplying pumping light for pumping the light. The output side is connected to an output terminal Po, and the amplified signal light Sigo is output to the output terminal Po.

The port 3P ₃ is connected to the input side of the optical filter 24.

When excitation light is applied to the optical amplification medium 22 from the excitation device 23, spontaneous emission light is generated. The spontaneous emission light includes a component propagating in the same direction as the signal light Sigi (hereinafter spontaneous emission light Pase +) and a component propagating in the opposite direction to the signal light Sigi (hereinafter spontaneous emission light Pase−). Spontaneous emission light Pase- propagating in the opposite direction
Is from port 2P ₂ to port 3 of the optical circulator 20.
It is incident on the optical filter 24 via P ₃ . Optical filter 2
4 is used to remove light in the excitation light wavelength band. The spontaneous emission light exists over the entire wavelength band, and the light intensity thereof is strongest in the amplification wavelength band of the optical amplifier 21. Since the pumping light wavelength band and the amplification wavelength band are different from each other, the optical filter 24 is a band pass filter that passes only the light of the amplification wavelength band or a band elimination filter that removes only the light of the pumping wavelength band.

A light intensity detector 25 is connected to the output side of the optical filter 24. The light intensity detector 25 converts the spontaneous emission light Pase- that has passed through the optical filter 24 into an electric signal to generate excitation power. Output to the control circuit 26. The excitation power control circuit 26 controls the excitation power applied to the excitation device 23 based on the detection result of the light intensity detector 25 so that the amplification gain becomes constant. This depends on the intensity of the excitation power applied to the excitation device 23.
This is because the gain and the spontaneous emission light intensity are determined, and the amplification gain of the optical amplifier 21 can be obtained by detecting the spontaneous emission light intensity.

FIG. 2 is a block diagram for explaining the optical amplifying device shown in FIG. 1 in more detail.

In the figure, the optical amplifier is connected to a rare earth-doped optical fiber 22a as an optical amplifying medium, a pumping light source 23a as a pumping device, and an output side of the pumping light source 23a and an output side of the rare earth-doped optical fiber 22a. The pumping light Pump from the pumping light source 23a is supplied to the rare-earth-doped optical fiber 2
2a, an optical amplifier comprising an optical multiplexer 27,
The optical circulator 20 having the above-mentioned forward characteristic and having the port 1P ₁ connected to the input terminal Pi and the port 2P ₂ connected to the input side of the optical amplifier (the input side of the rare earth-doped optical fiber 22a) (3-terminal type). And the spontaneous emission light Pa connected to the port 3P ₃ of the optical circulator 20.
an optical filter 24 that passes SE-, and an optical filter 24
Light intensity detector 2 connected to the output side of the detector 2 for detecting the light intensity of the spontaneous emission light Pase- and outputting it to the excitation power control circuit 26.
5a, a pump power control circuit 26 that controls the light intensity of the pump light Pump emitted from the pump light source 23a based on the light intensity detection value of the light intensity detector 25a, and an optical multiplexer 27.
Of the optical isolator 28 connected to the output side of the optical isolator 28 for preventing reflected return light, and an output terminal Po connected to the output side of the optical isolator 28. At signal light Si
The method in which the traveling direction of gi and the traveling direction of the excitation light are opposite) is used.

The rare earth-doped optical fiber 22a is one in which a rare earth element is added to the core of the optical fiber. Examples of rare earth elements include Er (erbium), Nd (neodymium), Yb (ytterbium), Pr (praseodymium), Ce (cerium), Sm (samarium), and Tm.
(Thulium), La (lanthanum), or the like is used. The core of the rare earth-doped optical fiber 22a contains at least one kind of these rare earth elements.

Excitation light Pu emitted from the excitation light source 23a
The wavelength of mp corresponds to the rare earth element added to the rare earth optical fiber 22a. For example, Er is used as the rare earth element.
The wavelength of the pumping light Pump when using is about 0.8 μm,
It is either about 0.98 μm or about 1.48 μm.
The optical isolator 28 prevents the operation of the optical amplifier from becoming unstable due to the reflected return light as described above.

At the port 2P ₂ of the optical circulator 20, of the spontaneous emission light Pase− and the excitation light Pump, the excitation light P which is not absorbed by the rare earth-doped optical fiber 22a.
ump 'is incident. The optical filter 24 uses the excitation light Pu.
The spontaneous emission light Pase− from which the wavelength band of mp ′ has been removed passes through and is incident on the light intensity detector 25a. The light intensity of the spontaneous emission light Pase- is detected by the light intensity detector 25a. The pump power control circuit 26 controls the pump power of the pump light source 23a, that is, the light intensity of the pump light Pump, based on the intensity detection result of the light intensity detector 25a.

Next, the operation of the embodiment will be described.

When the signal light Sigi is inputted to the input terminal Pi, the signal light Sigi is inputted to the port 1P ₁ of the optical circulator 20 and directly inputted to the rare earth-doped optical fiber 22a from the port 2P _2, so that it is the same as the conventional one. The branch loss of the signal light Sigi almost disappears (only a small insertion loss of the optical circulator 20), and the loss can be reduced. When the pumping light Pump is supplied from the pumping light source 23 a to the optical multiplexer 27, the input signal light Sigi is amplified and output to the output terminal Po via the multiplexer 27 and the optical isolator 28. Along with this, the pumping light Pump ′ that was not absorbed by the rare earth-doped optical fiber 22a
And the spontaneous emission light Pase− are transmitted from the optical circulator 20 through the port 2P ₂ to the port 3P ₃ to the optical filter 24.
Is incident on. Light spontaneously emitted from the optical filter 24 Pase
Only − passes and enters the light intensity detector 25a, and the detection result is input to the excitation power control circuit 26, so that the amplification gain of the optical amplifier is constant without being affected by the signal light Sigi as in the conventional case. Is precisely controlled to be.

FIG. 3 is a block diagram of another embodiment of the optical amplifying device of the present invention. In addition, common reference numerals are used for members common to the amplifying apparatus shown in FIG.

In the figure, the difference from the embodiment shown in FIG. 2 is that the backward pumping method (method in which the traveling direction of the signal light and the traveling direction of the pumping light are the same in the rare earth-doped optical fiber) is used. That is the point.

The port 2P ₂ of the optical circulator 20 is connected to one input side of the optical multiplexer 29, and the pump light source 23a is connected to the other input side of the optical multiplexer 29 so that the optical multiplexer 29 has Rare earth doped optical fiber 2 on the output side
The input side of 2a is connected. An optical isolator 28 is connected to the output side of the rare earth-doped optical fiber 22a. The port 3P ₃ of the optical circulator 20 is connected to a light intensity detector 30 that detects the light intensity of the spontaneous emission light from the rare earth-doped optical fiber 22a. Light intensity detector 30
The output value of is input to the pump power control circuit 31 that controls the pump light source 23a.

The signal light Sigi from the port 1P _{1 of the} circulator 20 and the pump light from the pump light source 23a are incident on the rare earth-doped optical fiber 22a, and the amplified signal light S is input.
Igo is output from the optical isolator 28.

Since this optical amplifying apparatus uses the forward pumping method, the pumping light is not incident on the port 2P ₂ of the optical circulator 20. Therefore, the pumping light is transmitted between the optical circulator 20 and the light intensity detector 30. No optical filter to remove is needed. Therefore, the configuration is simpler than that of the optical amplifying device shown in FIG.

FIG. 4 is a block diagram of another embodiment of the optical amplifying device of the present invention.

The difference from the embodiment shown in FIG. 2 is to prevent the excessive input of pumping light to the rare earth-doped optical fiber by limiting the pumping power by using the pumping light not absorbed by the rare earth-doped optical fiber. It is a point.

In FIG. 4, the rare earth-doped optical fiber 22
A, the optical multiplexer 27, and the pumping light source 23a constitute a backward pumping type optical amplifier. This optical amplifier and a pump power control circuit 3 for controlling the light intensity of the pump light Pb of the pump light source 2.
2, a pump power control circuit 32 connected to the pump power control circuit 32 to limit the light intensity of the pump light to a preset reference value or less, and a port 1P ₁ connected to the input terminal Pi, a port 2P ₂ Is a rare earth-doped optical fiber 22a
Of the optical circulator 20 connected to the input side of the optical circulator 20 and the port 3P ₃ of the optical circulator 20, and the spontaneous emission light Pase− from the rare earth-doped optical fiber 22a and the excitation light P not absorbed by the rare earth-doped optical fiber 22a.
The optical demultiplexer 34 for demultiplexing b ′ and the optical intensity of the spontaneous emission light Pase− demultiplexed by the optical demultiplexer 34 are detected, and the optical intensity detection value is output to the excitation power control circuit 32. No. 1 light intensity detector 35 and the excitation light Pb ′ demultiplexed by the optical demultiplexer 34
The optical amplification device includes a second optical intensity detector 36 that detects the optical intensity of the light and outputs the detected optical intensity to the excitation power limiting circuit 33, and an optical isolator 28 that is connected to the output side of the optical multiplexer 27. Is configured.

In this optical amplifier, the signal light Sigi incident from the port 1P ₁ of the optical circulator 20 enters the rare earth-doped optical fiber 22a via the port 2P ₂ of the optical circulator 20. The pumping light Pb from the pumping light source 23a is supplied to the rare-earth doped optical fiber 2 by the optical multiplexer 27.
It is incident on 2a. The rare earth-doped optical fiber 22a amplifies the incident signal light Sigi. At this time, spontaneous emission light Pase +, Pase from the rare earth-doped optical fiber 22a
-Is generated, but the port 2P _{2 of the} optical circulator 20
The spontaneously incident light Pase− and the excitation light P are
Of b, there is the excitation light Pb ′ that has not been absorbed by the rare earth-doped optical fiber 22a. Spontaneous emission light Pase-,
The pumping light Pb ′ is incident on the optical demultiplexer 34 via the port 3P ₃ of the optical circulator 20. The optical demultiplexer 34 demultiplexes into an excitation wavelength band and a signal wavelength band. The light intensity detector 35 detects the spontaneous emission light Pase− in the signal wavelength band. The light intensity detector 36 detects the light intensity of the excitation light Pb 'in the excitation wavelength band. The pump power control circuit 32 controls the pump power of the pump light source 23a based on the detection result of the light intensity detector 35 so that the amplification gain becomes constant. When the detection result of the light intensity detector 36 exceeds a preset reference value, the excitation power limiting circuit 33 gives a control signal to the excitation power control circuit 32 to limit the input current of the excitation light source 23a.

This optical amplifying device keeps the amplification gain constant and monitors the pumping light Pb 'which is not absorbed by the rare earth-doped optical fiber 22a, thereby pumping from the pumping power control circuit 32 without lowering the pumping efficiency. Light source 2
The excitation light source 23a can be protected by preventing excessive excitation power (current) from being input to 3a.

FIG. 5 is a block diagram of another embodiment of the optical amplifying device of the present invention.

The difference from the embodiment shown in FIG. 2 is that the bidirectional pumping method is used, the amplification gain is kept constant, and the light intensity of the pumping light from the pumping device is limited.

In the figure, the first optical circulator 4 is constructed by using two three-terminal type optical circulators 40 and 41.
0 port 2P ₁₂ of connecting a rare earth doped optical fiber 22a between the port 2P ₂₂ of the second optical circulator 41, the port 1 of the respective optical circulators 40 and 41
The excitation lights Pb and Pf are made to enter from P ₁₁ and P ₂₁ .

The forward pumping light Pf from the pumping light source 42 as the forward pumping device and the signal light S incident from the input terminal P ₁
The igi is multiplexed by the optical multiplexer 43, is incident on the port 1P ₁₁ of the optical circulator 40, and is incident on the rare earth-doped optical fiber 22a via the port 2P ₁₂ .

The backward pumping light Pb from the pumping light source 44 as the backward pumping device is supplied to the port 1P of the optical circulator 41.
Incident on _21, port 2P ₂₂ of the optical circulator 41
And enters the rare earth-doped optical fiber 22a.

The spontaneous emission light Pase− and the backward pumping light Pb ′ that has not been absorbed by the rare earth-doped optical fiber enter the port 2P ₁₂ of the optical circulator 40 and the port 3P ₁₃ thereof.
Is incident on the first demultiplexer 45.

A first light intensity detector 46 for detecting the light intensity of the spontaneous emission light Pase− is provided on one output side of the demultiplexer 45.
Are connected. The light intensity detector 46 is connected to a pump power control circuit 47 that controls the light intensity of the pump light of the pump light source 42 based on the detected value.

A second light intensity detector 48 for detecting the light intensity of the backward pumping light Pb 'is connected to the other output side of the demultiplexer 45. When the light intensity of the pumping light of the pumping light source 42 exceeds a reference value set in advance based on the detected value, the light intensity detector 48 detects the pumping power control circuit 47.
Is connected to a pump power control circuit 49 which gives a signal for limiting the input current of both pump light sources 42 and 44.

Of the signal light Sigo amplified by the rare earth-doped optical fiber 22a and the forward pumping light Pf, the pumping light Pf 'which is not absorbed by the rare earth-doped optical fiber 22a.
Enters the port 2P ₂₂ of the optical circulator 41 and enters the second optical demultiplexer 50 via the port 3P ₂₃ of the optical circulator 41. The optical demultiplexer 50 demultiplexes the incident light into a signal wavelength band and an excitation wavelength band. One output side of the optical demultiplexer 50 is connected to the output terminal Po, and the other output side is connected to the third light intensity detector 51.

The light intensity detector 51 detects the light intensity of the forward pumping light Pf ′ and outputs the detection result to the pumping power limiting circuit 49. As a result, both the amplification light sources 42 and 44 can be protected while keeping the amplification gain constant.

The result of the light intensity detector in the same figure may be used for controlling the amplification gain. For example, there is a method in which the front or rear pumping light intensity is controlled to be kept constant and then the gain is kept constant from the detection result of the light intensity detector. This method simplifies the control of the amplification gain.

FIG. 6 is a block diagram of another embodiment of the optical amplifying device of the present invention.

The difference from the embodiment shown in FIG. 2 is that the bidirectional pumping method using pumping light of different wavelengths is used, the amplification gain is kept constant, and the light intensity of the pumping light from both pumping devices is changed. The point is to limit.

In FIG. 6, the rare earth-doped optical fiber 22
a, a forward pumping device 53 that gives pumping light Pf from the input side through the forward optical multiplexer 52 to pump the rare earth-doped optical fiber 22a, and a pumping light Pf emitted from the forward pumping device 53 with different wavelengths. An optical amplifier is configured with the backward pumping device 55 that supplies the pumping light Pb of 1 to the rare earth-doped optical fiber 22a from the output side via the backward optical multiplexer 54.

This optical amplifier, a pump power control circuit 56 for controlling the amplification gain of the optical amplifier, and a pump power control circuit 56.
A pumping power limiting circuit 57 which is connected to the pumping device 53, 55 and limits the intensity of the pumping light Pf, Pb of each pumping device 53, 55 to a reference value or less,
A port 2P connected to the input side of the rare earth-doped optical fiber 22a from the port 1P ₁ into which the signal light Sigi enters
₂ , the optical circulator 20 having a forward characteristic from the port 2P ₂ to the port 3P ₃ , and the spontaneous emission light Pas from the rare earth-doped optical fiber 22a connected to the port 3P _3.
The light intensity of the first optical demultiplexer 58 that demultiplexes e− and the excitation light Pb ′ that has not been absorbed by the rare earth-doped optical fiber 22a and the spontaneous emission light Pase− that is demultiplexed by the optical demultiplexer 58. Of the detected light intensity and outputs the detected light intensity to the excitation power control circuit 57, and outputs the excitation light Pb ′ demultiplexed by the optical demultiplexer 58 to the excitation power limiting circuit 56. The second light intensity detector 60 and the rare earth-doped optical fiber 22
Signal light Si connected to the output side of a and amplified by an optical amplifier
The second optical demultiplexer 61 that demultiplexes go and the excitation light Pf ′ that has not been absorbed by the rare earth-doped optical fiber 22a, and the light intensity of the excitation light Pf ′ that is demultiplexed by the optical demultiplexer 61 is detected. Then
The third optical intensity detector 62 that outputs the detected optical intensity to the excitation power limiting circuit 57 and the optical isolator 28 that is provided on the output side of the optical demultiplexer 61 and outputs the amplified signal light Sigo An amplification device is configured.

This optical amplifying device has both pumping light sources 53 and 55.
Pumping lights Pf and Pb are incident on the rare earth-doped optical fiber 22a from both front and rear directions to be excited. Both excitation light sources 5
Since the pump wavelength bands of 3 and 55 are different, each pump light Pf,
Pb passes through without being demultiplexed (separated) by the optical multiplexers 52 and 54. The backward excitation light Pb ′ and the spontaneous emission light Pase which are not absorbed by the rare earth-doped optical fiber 22a.
-Is incident on the port 2P ₂ of the optical circulator 20, and is incident on the optical demultiplexer 58 via the port 3P ₃ . The optical demultiplexer 58 demultiplexes the spontaneous emission light Pase− and the backward excitation light Pb ′, and the photodetectors 59 and 60 respectively demultiplex the two lights Pase.
-, The light intensity of Pb 'is detected. Excitation power control circuit 56
Is based on the detection result of the light intensity detector 59.
Control 3, 55. The forward pumping light Pf ′ that has not been absorbed by the rare earth-doped optical fiber 22 a is demultiplexed with the signal light Sigo amplified by the optical demultiplexer 61, and detected by the light intensity detector 62. The excitation power limiting circuit 57 sends a control signal to the excitation power control circuit 56 when the detection results of the light intensity detectors 60 and 62 exceed a preset reference value to limit the input currents of both the excitation light sources 53 and 55. However, the excitation light sources 53 and 55 are prevented from being destroyed by the overcurrent.

In the above, an optical circulator having forward characteristics from port 1 to which signal light is input to port 2 connected to the input side of the optical amplifier, and port 2 to port 3 are connected to port 3, Since the light intensity detector detects the light intensity of the spontaneous emission light from the optical amplifier and outputs the detected light intensity value to the control circuit, the signal light is directly input to the optical amplifier without being branched. Therefore, there is no loss of signal light, and since only spontaneous emission light is input to the light intensity detector, the amplification gain can be accurately controlled.

Further, an optical circulator having forward characteristics from the port 1 to which the signal light is input to the port 2 connected to the input side of the optical amplification medium and from the port 2 to the port 3 and the optical circulator connected to the port 3 are provided. An optical demultiplexer that demultiplexes the spontaneous emission light and the excitation light from the amplification medium, and the light intensity of the spontaneous emission light demultiplexed by the optical demultiplexer is detected, and the detected light intensity value is output to the control circuit. The second light intensity detector, which includes the first light intensity detector and the second light intensity detector that outputs the intensity detection value of the excitation light demultiplexed by the optical demultiplexer to the limiting circuit, The pump is not affected by the temperature change by the pump, and the pump light is input without loss of the signal light, so that the pump light can be accurately limited and the pump light source is protected.

In each of the above-described embodiments, the rare-earth medium is a rare-earth-doped optical fiber as the optical amplification medium, but the present invention is not limited to this, and a semiconductor amplifier may be used.

FIG. 7 is a block diagram of another embodiment of the optical amplifying device of the present invention. In order to simplify the explanation, a detector,
A limiting circuit and a control circuit are omitted.

The difference from the embodiment shown in FIG. 2 is that an optical amplifier consisting of a rare earth-doped optical fiber and a pumping light source, and a light connected to the input side of the rare earth-doped optical fiber to block the reflected return light to the optical amplifier. Has an isolator and forward characteristics from port 1 to port 2, port 2 to port 3,
An excitation light source is connected to the port 1, an output side of the rare earth-doped optical fiber is connected to the port 2, and an optical circulator having an output terminal connected to the port 3 is provided.

In FIG. 7, the pumping light Pb emitted from the pumping light source 23a is the port 1P _{1 of the} optical circulator 20.
To the rare earth-doped optical fiber 22a through the port 2P ₂ of the optical circulator 20. The signal light Sigi input from the input end Pi of the optical isolator 28 is amplified by passing through the rare earth-doped optical fiber 22a pumped by the pumping light source 23a, and the optical circulator 2
It is incident on the 0 port 2P ₂ . The amplified signal light incident on the port 2P ₂ of the optical circulator 20 is output from the output terminal P ₀ via the port 3P ₃ of the optical circulator 20.

The pumping light loss of this optical amplifier is only the insertion loss of the optical circulator 20, and the gain of the optical amplifier is increased as compared with the case where the optical isolator and the multiplexer are used.
Higher output is possible. Further, by using the optical circulator 20, the isolator in the output stage, the pumping light source, and the optical isolator in the optical multiplexer are unnecessary, and the number of parts can be reduced. As a result, the cost can be reduced.

[0073]

In summary, according to the present invention, the following excellent effects are exhibited.

Since the optical circulator is used, it is possible to control the amplification gain of the optical amplifier to be constant without loss of the input signal light with a simple structure.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of an optical amplifier of the present invention.

FIG. 2 is a block diagram for explaining the optical amplification device shown in FIG. 1 in more detail.

FIG. 3 is a block diagram of another embodiment of the optical amplifying device of the present invention.

FIG. 4 is a block diagram of another embodiment of the optical amplifying device of the present invention.

FIG. 5 is a block diagram of another embodiment of the optical amplifying device of the present invention.

FIG. 6 is a block diagram of another embodiment of the optical amplifying device of the present invention.

FIG. 7 is a block diagram of another embodiment of the optical amplifying device of the present invention.

FIG. 8 is a block diagram of a conventional optical amplifier.

FIG. 9 is a block diagram of a conventional optical amplifier.

FIG. 10 is a block diagram of a conventional optical amplifier.

FIG. 11 is a block diagram of a conventional optical amplifier.

[Explanation of symbols]

 20 optical circulator 21 optical amplifier 25 light intensity detector 26 control circuit (excitation power control circuit)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location // G02B 27/28 A 9120-2K

Claims (7)

[Claims] 1. An optical amplifier for amplifying input signal light,
In an optical amplifying device including a control circuit for controlling the amplification gain of the optical amplifier, from port 1 to which signal light is input to port 2 connected to the input side of the optical amplifier, and from port 2 to port 3. And an optical intensity detector connected to the port 3 for detecting the light intensity of the spontaneous emission light from the optical amplifier and outputting the detected light intensity value to the control circuit. An optical amplifying device characterized by being provided. 2. The optical filter for removing excitation light and passing spontaneous emission light is provided between the port 3 of the optical circulator and the light intensity detector. Optical amplifier. 3. An optical amplifier comprising an optical amplification medium for amplifying input signal light and a pumping device for providing pumping light for pumping the optical amplification medium, and a control circuit for controlling an amplification gain of the optical amplifier. And a limiting circuit which is connected to the control circuit and limits the light intensity of the pumping light of the pumping device to a reference value or less, in the optical amplifying device, the input of the optical amplifying medium from the port 1 to which the signal light is input. Port 2 connected to the side
An optical circulator having forward characteristics from the port 2 to the port 3, an optical demultiplexer connected to the port 3 for demultiplexing spontaneous emission light and excitation light from the optical amplification medium, and the optical demultiplexer A first light intensity detector for detecting the light intensity of the spontaneous emission light demultiplexed by the demultiplexer and outputting the detected light intensity value to the control circuit, and the excitation demultiplexed by the optical demultiplexer An optical amplification device comprising: a second light intensity detector that outputs a light intensity detection value to the limiting circuit. 4. An optical amplification medium for amplifying input signal light, a forward pumping device for supplying pumping light from the input side to the optical amplification medium for exciting the optical amplification medium, and an output side to the optical amplification medium. An optical amplifier including a backward pumping device for giving pumping light, a control circuit for controlling an amplification gain of the optical amplifier, and a limiting circuit connected to the control circuit for limiting the intensity of the pumping light of each of the pumping devices to a reference value or less. In a light amplification device including: a signal light and a pump light, a port 1 having a forward characteristic from a port 1 to a port 2 connected to an input side of the light amplification medium, and a port 2 to a port 3 having a forward characteristic. No. 1 optical circulator, a first optical demultiplexer connected to the port 3 for demultiplexing spontaneous emission light and excitation light from the optical amplification medium, and demultiplexed by the first optical demultiplexer. Detected the intensity of the spontaneous emission light, A first light intensity detector that outputs a degree detection value to the control circuit, and a second light intensity detector that outputs the excitation light demultiplexed by the first optical demultiplexer to the limiting circuit, Forward characteristics from another port 1 to which the pumping light from the backward pumping device is input to another port 2 connected to the output side of the optical amplification medium and from another port 2 to another port 3 are shown. A second optical circulator having the same, a second optical demultiplexer connected to the other port 3 for demultiplexing the signal light amplified by the optical amplifier and the pumping light, and the second optical demultiplexer And a third light intensity detector for detecting the light intensity of the excitation light demultiplexed in step (3) and outputting the detected light intensity value to the limiting circuit. 5. An optical amplification medium for amplifying input signal light, a forward pumping device for supplying pumping light from the input side to the optical amplification medium to excite the optical amplification medium, and an output side to the optical amplification medium. An optical amplifier including a backward pumping device that gives pumping light of a wavelength different from that of the forward pumping device, a control circuit that controls the amplification gain of the optical amplifier, and the intensity of the pumping light of each pumping device that is connected to the control circuit. And a limiting circuit for limiting the signal to a reference value or less, from a port 1 to which signal light is input to a port 2 connected to the input side of the optical amplification medium, and from the port 2 to a port 3. An optical circulator having a forward characteristic, a first optical demultiplexer connected to the port 3 for demultiplexing spontaneous emission light and excitation light from the optical amplification medium, and the first optical demultiplexer The intensity of the demultiplexed spontaneous emission light A first light intensity detector for detecting and outputting the light intensity detection value to the control circuit, and a second light for outputting the excitation light demultiplexed by the first optical demultiplexer to the limiting circuit. An intensity detector, a second optical demultiplexer connected to the output side of the optical amplification medium and demultiplexing the signal light amplified by the optical amplifier and the pumping light, and the second optical demultiplexer An optical amplification device comprising: a third light intensity detector that detects the light intensity of the demultiplexed excitation light and outputs the detected light intensity value to the limiting circuit. 6. The optical amplifying device according to claim 3, wherein a rare earth optical fiber is used as the optical amplifying medium. 7. An optical amplifier comprising a rare-earth-doped optical fiber and a pumping light source, an optical isolator connected to the input side of the rare-earth-doped optical fiber to block reflected return light to the optical amplifier, and from port 1 to port 2. A forward characteristic from the port 2 to the port 3, the pump light source is connected to the port 1, the output side of the rare earth-doped optical fiber is connected to the port 2, and the output terminal is connected to the port 3. Optical circulator and an optical amplifier.