JP3822657B2 - Optical fiber amplifier - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an optical amplifier in an optical transmission apparatus, and more particularly to an optical fiber amplifier that requires high reliability such as a submarine repeater.
[0002]
[Prior art]
An optical amplifier generally used in the 1.55 μm band, which is regarded as a low-loss wavelength region for optical fiber communications, adds 0.98 μm or 1.48 μm excitation light to an optical fiber doped with rare earth erbium. This is an optical amplifier based on the principle that erbium ions in the optical fiber are activated by the pumping light to induce and amplify an optical signal in the 1.55 μm band, and this is called an optical fiber amplifier. This optical fiber amplifier is used as an optical signal relay amplifier in a long-distance optical communication system because it has high efficiency and high gain and the gain hardly depends on the polarization state.
[0003]
The basic configuration of this optical fiber amplifier is shown in FIG. In FIG. 7, 101 and 102 are optical isolators that limit the propagation direction of an optical signal in one direction, 103 is an optical fiber to which erbium is added (hereinafter referred to as “erbium-doped fiber”), 104 is a pumping light source, and 105. Is an optical multiplexer for synthesizing the output of the excitation light source 104 with the erbium-doped fiber 103.
[0004]
The optical signal LIN in the 1.55 μm band input to this optical fiber amplifier is guided to the erbium doped fiber 103 through the optical isolator 101 and the optical multiplexer 105, and when passing through the erbium doped fiber 103, the excitation light source 104 It receives and amplifies the excitation light power from. The amplified optical signal is output as LOUT via the optical isolator 102. As the optical multiplexer 105, a 0.98 μm / 1.55 μm or 1.48 μm / 1.55 μm wavelength multiplexing directional coupler is generally used, and the 0.98 μm or 1.48 μm band excitation light is used. The 1.55 μm band signal light can be efficiently guided to one fiber.
[0005]
Further, in this configuration example, the optical multiplexer 105 is installed between the optical isolator 101 and the erbium-doped fiber 103 so that the excitation light propagates in the same propagation direction as the signal light and gives energy. However, the optical multiplexer 105 is installed between the erbium-doped fiber 103 and the optical isolator 102 so that the excitation light is incident on the erbium-doped fiber 103, and the propagation direction of the signal light and the propagation direction of the excitation light are determined. A similar amplification effect can be obtained even if the arrangement is reversed. The former, that is, the configuration example shown in FIG. 7 is called forward excitation, and the latter is called backward excitation.
[0006]
Since the amplification direction of the erbium doped fiber 103 is reversible, the optical isolator 101 and 102 are used to limit the propagation direction of the optical signal and prevent the optical amplifier from oscillating due to multiple reflection. However, the optical isolator 101 on the input side of the signal light can be omitted if the input side is directly fused and connected to a long optical fiber and a high return loss is maintained.
[0007]
Now, such an optical fiber amplifier does not operate unless 0.98 μm or 1.48 μm pumping light is continuously supplied with a certain power or more. This pumping light is usually oscillated by a semiconductor laser diode. However, in order to realize a highly reliable optical fiber amplifier, it is necessary to make the pumping semiconductor laser diode redundant.
FIGS. 8A and 8B show an example of an optical fiber amplifier in which a pumping light source is made redundant in order to increase the reliability of the amplifier. In FIG. 8A, 106 is a spare excitation light source, and 107 is an optical switch for switching the excitation light output of the excitation light source 104 and the excitation light source 106 with low loss. Since this configuration example has two pumping light sources, even if the pumping light source 104 is normally in a state where the erbium-doped fiber 103 is pumped by the pumping light source 104, the pumping light is switched by the optical switch 107. By switching to the pumping light source 106 side, the amplification function of the optical amplifier is not lost.
However, since this configuration example uses the optical switch 107 for switching the light source, there are movable parts and the switching time is slow, so it is not used much.
[0008]
FIG. 8B shows a solution to the above-mentioned drawback in the configuration example of FIG. In this configuration example, a polarization combiner 108 is provided instead of the optical switch 107. The polarization combiner / combiner 108 is a passive component that efficiently combines and outputs two orthogonal polarization inputs to one port. By inputting the output polarizations of the excitation light source 104 and the excitation light source 106 orthogonally, the respective light components are combined. Is guided to one optical fiber with low loss. Therefore, even when the pumping light source 104 fails in a state where the erbium-doped fiber 103 is pumped by the normal pumping light source 104, the current supply to the pumping light source 104 is stopped and the current supplied to the pumping light source 106 instead. The amplification function of the optical amplifier is not lost by applying.
Further, even if the excitation light source 104 and the excitation light source 106 are set to a normal ½ output and are continuously driven, it is possible to reduce the occurrence of failure of each excitation light source. It is possible to increase.
[0009]
However, using two pumping light sources for one optical fiber amplifier can improve the reliability of the optical amplifier, but raises the problem of increased cost. When an optical fiber amplifier is used as a communication optical repeater, the optical repeater normally uses at least two optical amplifiers for upstream and downstream lines in order to perform bidirectional transmission and reception. Under such circumstances, applying the excitation light source redundancy means as described above is not economically preferable because one excitation circuit requires four excitation light sources. A means for economically solving this problem is proposed by US Pat. No. 5,173,957.
[0010]
FIG. 9 is a block diagram of this proposed method. In FIG. 9, reference numeral 100 denotes an upstream amplification unit, 100 'denotes a downstream amplification unit, and 109 denotes an optical multiplexer / demultiplexer. The inside of the upstream amplification unit 100 and the downstream amplification unit 100 ′ is the same as the optical fiber amplifier described so far, and the downstream amplification unit 100 ′ and the upstream amplification unit 100 have the same functions inside. "'" Is attached to simplify the explanation and avoid complication. In this figure, an optical multiplexer / demultiplexer 109 combines and branches the outputs of two pumping light sources 104 and 106 and supplies them to two optical amplifiers. That is, the light from the pumping light source 104 incident from the port P1 of the optical multiplexer / demultiplexer 109 is bifurcated into the port P3 and the port P4, and the light from the pumping light source 106 incident from the port P2 is bifurcated into the port P4 and the port P3. . Therefore, even if one pumping light source fails and no longer emits pumping light, both optical amplifiers can be operated by the pumping light emitted from the other, improving the reliability as an optical amplifier. Yes. In addition, since two optical amplifiers are excited by two excitation light sources, it is economical.
[0011]
[Problems to be solved by the invention]
In the prior art shown in FIG. 9, since the two excitation lights are combined and branched by the optical multiplexer / demultiplexer 109, the output levels from the two output ports P3 and P4 of the optical multiplexer / demultiplexer 109 are optical multiplexing / demultiplexing. Since it is determined by the branching ratio of the optical multiplexer 109, it is necessary to adjust the branching ratio itself of the optical multiplexer / demultiplexer 109 in order to match the pumping light level supplied to the optical fiber amplifier. However, generally, when an optical multiplexer / demultiplexer 109 is provided with a branching ratio adjusting mechanism, the output level and the branching ratio become unstable, and the operation becomes extremely unstable with respect to the external environment, thereby stabilizing them. For this purpose, advanced technology is required.
[0012]
Further, although the gain of the optical fiber amplifier varies depending on the pumping light power, it is difficult to make the gain of the optical amplifier the same with the same pumping light power. This is because an optical fiber amplifier with exactly the same performance is produced, with the concentration of rare earth ions in the amplification fiber, fiber length, insertion loss of optical components, and connection loss at the connection point with normal fibers being uneven. Is extremely difficult and economically disadvantageous.
Therefore, in order to solve this, it is necessary to adjust the pumping light power supplied to the erbium-doped fibers 103 and 103 ′, respectively, and to adjust the gain and output light level of each optical amplifier to predetermined values. It becomes.
[0013]
Accordingly, an object of the present invention is to provide a highly reliable optical fiber amplifier capable of easily adjusting the gain of the optical fiber amplifier.
[0014]
[Means for Solving the Problems]
To achieve the above object, an optical fiber amplifier according to the present invention comprises an optical fiber doped with rare earth ions for amplifying an optical signal by supplying pumping light, and a light source for generating the pumping light. 2, two optical fibers, a light source that generates three pump lights, and a 3 × 2 coupler that combines and branches the outputs of the three light sources and supplies the two optical fibers with pump light. Is. The 3 × 2 coupler includes one polarization plane maintaining duplexer and two polarization multiplexers, or three using two polarization beam splitters and polarization maintaining optical fibers. An input port and two output ports using optical fibers are provided, and the polarization state of the excitation light at each input port is input in a predetermined state, and the output of the 3 × 2 coupler These two terminals are each provided with an optical isolator.
[0015]
Furthermore, the optical fiber amplifier of the present invention includes an optical fiber doped with rare earth ions that amplifies an optical signal by supplying pumping light, two polarization beam splitters, and three pumping light sources. Each excitation light source is fixed so as to obtain output light in a polarization state, and means for taking out the combined polarization output of the two polarization beam splitters are provided, and the two outputs are respectively pumped into two rare earth ion doped optical fibers. It is something that is made to be done. As a means for obtaining output light in a predetermined polarization state from the excitation light source, a λ / 2 phase plate is installed between the excitation light source and the polarization beam splitter, or between the polarization beam splitter and the polarization beam splitter. Is.
[0016]
[Action]
The optical fiber amplifier of the present invention configured as described above includes three pumping light sources, and almost all of the light generated by the first pumping light source is supplied as pumping light to the upstream amplification unit. Almost all of the light generated by the pumping light source is supplied as pumping light to the downstream amplification unit, and further, the light generated by the third pumping light source is divided into two parts, the upstream amplification unit and the downstream amplification unit, respectively. Therefore, the amplification function of the optical fiber amplifier is not lost even if any one of the pumping light sources fails and the light emission is stopped, and the first or second pumping light source is not lost. By adjusting the emission intensity or adjusting the principal axis angle of the polarization of the light generated by the third excitation light source, the upstream amplification unit and the downstream amplification unit are controlled. In which it is possible to easily adjust the Le.
[0017]
【Example】
FIG. 1 shows a configuration example of an embodiment of the present invention. In this figure, 1, 2 and 3 are excitation light sources, 10 has three input ports I 1, I 2 and I 3 and two output ports O 1 and O 2, and the light input from these three input ports This is a photosynthesis / branching device that synthesizes and branches and outputs the output to the output ports O1 and O2. This is hereinafter referred to as a “3 × 2 coupler”. The optical isolators 101, 101 ′, 102 and 102 ′, the optical multiplexers 105 and 105 ′, and the erbium-doped fibers 103 and 103 ′ in the upstream amplification unit and the downstream amplification unit have all been described so far. The detailed description thereof is omitted.
[0018]
In the optical fiber amplifier configured as described above, the pumping lights generated from the three pumping light sources 1, 2 and 3 are incident on the input ports I1, I2 and I3 of the 3 × 2 coupler 10, respectively. In the 3 × 2 coupler 10, the excitation light incident from each input port is synthesized and branched, and is output to the output ports O1 and O2. That is, almost all of the light incident on the input port I1 from the pumping light source 1 except for the loss is almost output to the output port O1, and almost all of the pumping light incident on the input port I2 from the pumping light source 2 is excluded except for the loss. Is configured to be divided into two and output to the output ports O1 and O2, respectively, into the output port O2 and the pumping light input from the pumping light source 3 to the input port I3.
[0019]
Then, the excitation light output from the output port O1 is applied to the optical multiplexer 105 of the upstream amplification unit and is incident on the erbium-doped fiber 103, whereby the signal that has passed through the optical isolator 101 in the erbium-doped fiber 103. The optical LIN is amplified. Uplink signal light amplified in the erbium-doped fiber 103 is output as an output LOUT via the optical isolator 102.
On the other hand, the excitation light output from the output port O2 of the 3 × 2 coupler 10 is applied to the optical multiplexer 105 ′ of the downstream amplification unit and is incident on the erbium-doped fiber 103 ′. As a result, the downlink signal light LIN ′ that has passed through the optical isolator 101 ′ is optically amplified in the erbium-doped fiber 103 ′ and output as the output LOUT ′ via the optical isolator 102 ′.
[0020]
According to the present invention, since it is configured as described above, by controlling the current supplied to the excitation light source 1, the power of the excitation light output from the output port O1 is changed to the excitation light output from the output port O2. The pumping light power output from the output port O2 can be independently controlled by controlling the current supplied to the pumping light source 2. Therefore, the pumping light power supplied to the erbium doped fibers 103 and 103 ′ can be adjusted independently, and the gains of the upstream optical fiber amplifier and the downstream optical fiber amplifier can be adjusted independently.
[0021]
Moreover, since the required pumping light power is obtained using the three pumping light sources 1 to 3, the pumping light power per pumping light source is 2/3 of the case where two pumping light sources are used. The failure occurrence probability of each excitation light source can be reduced, and the reliability is improved. Furthermore, even if a failure occurs in any one of the pumping light sources, the pumping light power will not become zero, and the amplification function of the optical fiber amplifier will not be lost, improving the reliability of the optical fiber amplifier. Is something that can be done.
[0022]
FIG. 2 shows a first configuration example of the 3 × 2 coupler 10. In FIG. 2, reference numerals 1, 2 and 3 denote excitation light sources composed of semiconductor laser diodes, etc., which are the same as those described above. A polarization maintaining demultiplexer 11 divides the light incident from the input end into two while maintaining the polarization state and outputs it to the two output ends. As such a polarization maintaining demultiplexer, a beam splitter or the like can be used. Reference numerals 12 and 13 denote polarization combiners, for example, polarization beam splitters that have two orthogonal input ends, pass P-polarized light as it is, and reflect 100% of S-polarized light. When P-polarized light is input from one input end and S-polarized light is input from the other input end, the combined output of both is output from a single output end. . In addition, a coupler made of a polarization maintaining optical fiber can also be used as the polarization combining coupler.
[0023]
In the 3 × 2 coupler 10 configured as described above, the excitation light generated by each of the excitation light sources 1 to 3 holds the polarization plane and is 3 through the input ports I1 to I3 of the 3 × 2 coupler 10. X2 Input to the coupler 10. Here, P-polarized light is input from the excitation light source 1 and the excitation light source 2, and S-polarized light is input from the excitation light source 3. The P-polarized pumping light oscillated in the pumping light source 1 enters from one input of the polarization combiner / coupler 12 via the input port I1, and the P-polarized pumping light generated by the pumping light source 2 enters the input port I2. Through one input of the polarization beam combiner 13. Further, the S-polarized excitation light oscillated in the excitation light source 3 is divided into two in the polarization holding demultiplexer 11, and the two outputs of the polarization holding demultiplexer 11 are the polarization synthesis coupler 12 and the polarization synthesis, respectively. The light is incident on the other input of the coupler 13. In addition, the vertical line in a figure represents P polarized light and the circle represents S polarized light.
[0024]
The P-polarized excitation light generated in the excitation light source 1 and the light having half the power of the excitation light generated by the S-polarized excitation light source 3 incident from the polarization holding demultiplexer 11 are combined into the polarization beam combiner. 12, and is output to the output port O <b> 1 of the 3 × 2 coupler 10. This output light is incident on the optical multiplexer 105 of the upstream amplification unit shown in FIG. Similarly, P-polarized excitation light generated in the excitation light source 2 and light having a power half that of the excitation light generated by the S-polarized excitation light source 3 incident from the polarization holding demultiplexer 11. Are combined by the polarization combiner 13 and output to the output port O2 of the 3 × 2 coupler 10. This output light is incident on the optical multiplexer 105 ′ of the downstream amplification unit shown in FIG.
[0025]
In order to make the light oscillated in each of the excitation light sources 1 to 3 enter the polarization maintaining demultiplexer 11 or the polarization combining demultiplexers 12 and 13 while maintaining the polarization, the light generated from each light source May be coupled to the input end by polarization maintaining optical fiber or spatial propagation.
[0026]
FIG. 3 shows a second configuration example of the 3 × 2 coupler 10. In this figure, 1 to 3 are pumping light sources composed of semiconductor laser diodes, and 10 is a 3 × 2 coupler. I1 to I3 are input ports of the 3 × 2 coupler 10, and fiber collimators for converting the light supplied from the respective excitation light sources 1 to 3 through the polarization maintaining optical fibers into parallel light are provided. . O1 and O2 are output ports of the 3 × 2 coupler 10, and a fiber collimator is provided for allowing light output from the 3 × 2 coupler 10 to enter the optical fiber. The lights output from the output ports O1 and O2 to the optical fiber are respectively guided to the optical multiplexer 105 of the upstream amplification unit and the optical multiplexer 105 ′ of the downstream amplification unit in FIG. Reference numerals 14 and 15 denote polarization beam splitters that transmit almost 100% of P-polarized light and reflect almost 100% of S-polarized light.
[0027]
In the 3 × 2 coupler 10 configured as described above, the light generated in the excitation light source 1 is guided to the fiber collimator provided at the input port I1 of the 3 × 2 coupler 10 via the polarization maintaining optical fiber, and is P-polarized light. Is incident on the polarization beam splitter 14. This light passes through the polarizing beam splitter 14 and is coupled to the output port O1. Further, the light oscillated in the excitation light source 2 is inputted with S-polarized light from the input port I2 through the polarization maintaining optical fiber. The S-polarized input light from the input port I2 enters the polarization beam splitter 15, is totally reflected by the polarization beam splitter 15, and is guided to the output port O2.
[0028]
On the other hand, the light oscillated in the excitation light source 3 is incident from the input port I3 through the polarization maintaining optical fiber with the principal axis of the polarization plane being inclined by 45 °. Since this polarization plane is inclined by 45 °, the light is composed of a P-polarized component and an S-polarized component having the same magnitude, and the P-polarized component is transmitted through the polarization beam splitter 15 and guided to the output port O2. . On the other hand, the S-polarized light component is reflected by the polarizing beam splitter 15, is incident on the polarizing beam splitter 14, is totally reflected by the polarizing beam splitter 14, and is guided to the output port O1. That is, the light generated in the excitation light source 3 is divided into two equal parts, one of which is guided to the output port O2, and the other is guided to the output port O1.
[0029]
In this way, light incident from the input port I1 is coupled to the output port O1, and light incident from the input port I2 is coupled to the output port O2 with little loss. The light incident from the input port I3 is branched into two and coupled to the output port O1 and the output port O2. Here, by adjusting the polarization plane of the light input from the input port I3, the level ratio of the P-polarized component and the S-polarized component in the polarization beam splitter 15 can be adjusted, so that the output port O1 and the output port O2 It is possible to adjust the balance of the output levels at and. Further, as in the case of the first configuration example described above, the balance of the output levels of the excitation light output from the two output ports is also adjusted by adjusting the emission intensity of the excitation light source 1 and the excitation light source 2. can do.
[0030]
In the above description, linearly polarized light whose principal axis of polarization plane is inclined by 45 degrees is input from the excitation light source 3 to the input port I3. However, completely circularly polarized light is input from the input port I3. Even if it is made to operate, it operates similarly.
[0031]
FIG. 4 is a diagram illustrating a third configuration example of the 3 × 2 coupler 10. In the configuration example shown in this figure, optical isolators 16 and 17 are provided between the output side of the polarization beam splitter 14 and the output port O1, and between the output side of the polarization beam splitter 15 and the output port O2, respectively. Is different from the second configuration example shown in FIG. Normally, an optical isolator is provided in each of the excitation light sources 1 to 3 to prevent unnecessary oscillation and deterioration of operating characteristics due to reflected light. As shown in FIG. Since it is not necessary to provide each of the pumping light sources 1 to 3 with an optical isolator, the number of optical isolators can be reduced by one compared with the case of providing an optical isolator in each pumping light source. Is.
[0032]
In each of the above-described embodiments, the 3 × 2 coupler and each excitation light source are configured separately, but by providing them integrally, a more compact and stable structure is provided. A source of excitation light having the following can be provided. The embodiment configured as described above will be described with reference to FIGS. 5 and 6.
[0033]
In FIG. 5, reference numeral 20 denotes an excitation light source module having two output ports O1 and O2. Inside the excitation light source module, polarization beam splitters 14 and 15, optical isolators 16 and 17, and semiconductor laser diodes 21, 22, and 23 are provided. The semiconductor laser diode 21 is attached to the excitation light source module 20 so that P-polarized light is incident on the polarization beam splitter 14. The semiconductor laser diode 22 is attached to the excitation light source module 20 so as to be in a position where S-polarized light enters the polarization beam splitter 15. The semiconductor laser diode 23 is attached to the excitation light source module 20 so as to be inclined by 45 ° so that the light incident on the polarization beam splitter 15 has a polarization angle of 45 °. These semiconductor laser diodes are adjusted to have an optimum angle and are attached to the excitation light source module 20 by, for example, YAG welding.
[0034]
In the excitation light source module 20 configured as described above, the P-polarized light oscillated by the semiconductor laser diode 21 is incident on the polarization beam splitter 14, passes through the polarization beam splitter 14, and is output through the optical isolator 16. Output to O1 fiber collimator. The S-polarized light oscillated in the semiconductor laser diode 22 is incident on the polarization beam splitter 15, is totally reflected, and is output to the fiber collimator of the output port O2 via the optical isolator 17.
[0035]
The light having a 45 ° polarization angle oscillated in the semiconductor laser diode 23 is incident on the polarization beam splitter 15. Since this light is decomposed into a P-polarized component and an S-polarized component having the same size, half of the light is transmitted and half is reflected by the polarization beam splitter 15. One half of the light oscillated by the semiconductor laser diode 23 that has passed through the polarization beam splitter 15 is output to the fiber collimator of the output port O 2 via the optical isolator 17. On the other hand, the S-polarized component of the light oscillated by the semiconductor laser diode 23 reflected by the polarization beam splitter 15 is incident on the polarization beam splitter 14, further reflected by the polarization beam splitter 14, and output via the optical isolator 16. Output to O1 fiber collimator.
[0036]
In this way, P-polarized light oscillated in the semiconductor laser diode 21 and ½ of the light oscillated in the semiconductor laser diode 23 are output from the output port O1 of the excitation light source module 20, and erbium shown in FIG. It is introduced into an optical multiplexer 105 for pumping light input of a doped fiber. Further, from the output port O2 of the excitation light source module 20, S-polarized light oscillated in the semiconductor laser diode 22 and ½ of the light oscillated in the semiconductor laser diode 23 are output, and the erbium-doped fiber shown in FIG. It is introduced into the pumping light input optical multiplexer 105 ′.
[0037]
FIG. 6 is a diagram illustrating another configuration example of the excitation light source module. 6, the same components as those in FIG. 5 are denoted by the same reference numerals, and detailed description thereof is omitted. In the configuration example shown in this figure, the semiconductor laser diode 23 is mounted in the same direction as the semiconductor laser diode 21 and the λ / 2 phase is between the semiconductor laser diode 23 and the polarization beam splitter 15. It differs from the configuration example shown in FIG. 5 in that the plate 24 is installed. In the excitation light source module 20 configured as described above, the P-polarized light generated from the semiconductor laser diode 23 is incident on the λ / 2 phase plate 24. In the λ / 2 phase plate 24, the incident light is incident on the polarization beam splitter 15 with the 45 ° polarization plane rotated.
[0038]
That is, in the configuration example shown in FIG. 6, instead of mounting the semiconductor laser diode 23 at an angle of 45 ° as shown in FIG. 5, the mounting direction of the semiconductor laser diode 23 is vertical or horizontal as usual, and λ / By using a two-phase plate, the polarization plane is rotated by 45 °. With this configuration, the semiconductor laser diode can be easily attached, and the amplification degree of both the upstream and downstream optical fiber amplifiers can be easily adjusted by adjusting the rotation angle of the λ / 2 phase plate. It will be able to.
[0039]
【The invention's effect】
Since the present invention is configured as described above, two optical fiber amplifiers can be driven by three pumping light sources, and a redundant configuration of the pumping light sources can be ensured. Accordingly, an economical and highly reliable optical fiber amplifier can be realized. In addition, the output level of each optical fiber amplifier can be individually adjusted.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of an optical fiber amplifier according to the present invention.
FIG. 2 is a diagram showing a configuration example of a 3 × 2 coupler in the optical fiber amplifier of the present invention.
FIG. 3 is a diagram showing another configuration example of the 3 × 2 coupler in the optical fiber amplifier of the present invention.
FIG. 4 is a diagram showing still another configuration example of the 3 × 2 coupler in the optical fiber amplifier of the present invention.
FIG. 5 is a diagram showing a configuration example of a pumping light source module in the optical fiber amplifier of the present invention.
FIG. 6 is a diagram showing another configuration example of the excitation light source module in the optical fiber amplifier of the present invention.
FIG. 7 is a diagram showing a configuration of an optical fiber amplifier.
FIG. 8 is a diagram showing a configuration of a conventional optical fiber amplifier having a redundant configuration.
FIG. 9 is a diagram showing another configuration of a conventional optical fiber amplifier having a redundant configuration.
[Explanation of symbols]
1, 2, 3 Excitation light source
10 3 × 2 coupler
11 Polarization-maintaining demultiplexer
12, 13 Polarization combiner
14, 15 Polarizing beam splitter
16, 17 Optical isolator
20 Excitation light source module
21, 22, 23 Semiconductor laser diode
24 λ / 2 phase plate
100 Up amplification unit
100 'Downward amplification unit
101, 101 ', 102, 102' optical isolator
103, 103 ′ Erbium-doped fiber
104, 106 Excitation light source
105, 105 'optical multiplexer
107 Optical switch
108 Polarization combiner
109 Optical multiplexer / demultiplexer

Claims (1)

In an optical fiber amplifier constituting a pair of optical fiber amplifiers by an optical fiber doped with rare earth ions that amplifies an optical signal by supplying pumping light,
Three light sources for generating excitation light to be supplied to the pair of optical fiber amplifiers;
Branching after combining the outputs of the three light sources, and a 3 × 2 coupler for distributing and supplying the three light sources to the pair of optical fiber amplifiers,
The 3 × 2 coupler includes a first laser beam that outputs a laser beam having a first polarization plane;
A second laser beam that outputs a laser beam having a second polarization plane;
A third laser beam that outputs a laser beam including the first polarization plane and the second polarization plane is input;
The first laser beam is supplied to the first optical fiber amplifier via a first polarization beam splitter that transmits the laser beam having the first polarization plane and reflects the laser beam having the second polarization plane. ,
The second laser beam transmits a laser beam having the second polarization plane and supplies the laser beam to the first polarization beam splitter, and a second beam splitter that reflects the laser beam having the first polarization plane. To the second optical fiber amplifier via
The third laser light passes through the second polarization beam splitter, supplies laser light having a second polarization plane to the second optical fiber amplifier, and laser light having the first polarization plane. Is supplied to the first polarization beam splitter, and is supplied to the first optical fiber amplifier.

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