JPH095806A - Optical amplifier - Google Patents

Abstract

PURPOSE: To decrease the number of parts of an optical amplifier and to lessen the loss of the optical amplifier which executes bidirectional transmission. CONSTITUTION: This optical amplifier has an optical circulator 66 which has forward direction transmission characteristics toward a first terminal A, a second terminal B and a third terminal C and is respectively connected with a rare earth-added optical fiber 62 to the second terminal B and a signal light output terminal to the third terminal C. Exciting light is supplied via the optical circulator 66 to the rare earth-added optical fiber 62. The signal light amplified by the rare earth-added optical fiber 62 is outputted from the signal light output terminal via the optical circulator 66.

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 for amplifying signal light transmitted through an optical fiber by passing it through a rare earth-doped optical fiber supplied with pumping light.

[0002]

2. Description of the Related Art FIG. 5 shows the configuration of a conventional optical amplifier. This optical amplifier is connected to an optical isolator 10 to which an input signal light input Pi is supplied, a rare earth-doped optical fiber 12 connected to the output end of the optical isolator 10, a pumping light source 14, and an output end of the pumping light source 14. Optical isolator 16, an optical multiplexer 18 connected to the output of the rare earth-doped optical fiber 12 and the output of the optical isolator 16, and an optical isolator 20 connected to the output of the optical multiplexer 18.

In the optical amplifier configured as described above, the input signal light Pi enters the rare earth-doped optical fiber 12 through the optical isolator 10. On the other hand, the excitation light source 14
The excitation light emitted from the laser beam enters the rare earth-doped optical fiber 12 via the optical isolator 16 and the optical multiplexer 18. The excitation light has a wavelength corresponding to the excitation level of the added rare earth ion, and in the rare earth-doped optical fiber 12, the incident signal is generated by the stimulated emission phenomenon caused by the population inversion of the energy level of the rare earth ion formed by the excitation light. To amplify. The amplified signal light is output as a signal light output Po via the optical isolator 20. Here, the optical isolators 10 and 20 provided at the input and output ends prevent signal light and spontaneous emission light from returning to the inside of the amplifier again due to reflection from the outside and falling into an unstable state such as oscillation. Further, the optical isolator 16 provided at the output end of the pumping light source 14 prevents the pumping light source 14 from being adversely affected by the amplified signal light or spontaneous emission light entering the pumping light source 14. An optical filter that blocks a pair of signal light wavelengths may be used instead of the optical isolator 16.

In addition to the method of exciting the rare earth-doped optical fiber 12 from the rear side as described above, the rare earth-doped optical fiber 1 is also used.
There is also a method of exciting from the front of No. 2 or both front and back as shown in FIG. The conventional optical amplifier of FIG. 6 has a signal light input P
Optical isolator 22 for inputting i and first pumping light source 2
4, an optical multiplexer 26 connected to the optical isolator 22 and the first pumping light source 24, a rare earth-doped optical fiber 28 connected to the optical multiplexer 26, a second pumping light source 30, and a rare earth-doped optical fiber An optical multiplexer 32 connected to the output of 28 and the output end of the second pumping light source 30 and an optical isolator 34 connected to the optical multiplexer 32. As described above, according to the method of pumping from both the front side (signal light incident side) and the rear side (signal light emitting side) of the rare earth-doped optical fiber, noise, gain characteristics and saturated output characteristics can be enhanced.

Generally, in an optical transmission system, in order to improve the reliability of the transmission system, the transmission line is duplicated, and when the failure occurs due to the disconnection of the transmission line or the like, the transmission line is switched to the standby system. When optical amplifiers are used in such a duplicated system, both systems must be equipped with optical amplifiers. As shown in FIG. 7, in a normal state, the signal light transmitted from the optical fiber 36 is amplified by the amplifier 40, and when an abnormality occurs in the system of the optical fiber 36, the system is switched to the optical fiber 38 side and the amplifier 42 The signal light is amplified by.

However, in the conventional system as shown in FIG. 7, it is necessary to provide two systems in parallel,
Since two amplifiers are required, there is a problem that the cost becomes high. Therefore, as shown in FIG.
The two transmission lines 44 and 46 are connected by, a part of the signal light inputs Pi and Pi ′ is input to the optical amplifier 50, and the output of the amplifier 50 is branched by the optical coupler 52 and output. With such a configuration, one amplifier can be shared by two transmission lines.

[0007]

However, in the conventional optical amplifier shown in FIG. 5, the number of optical components used such as an optical isolator and an optical multiplexer is large, which is disadvantageous in terms of cost, and the optical components are different from each other. However, there is a problem in that an excessive loss is caused when the connection is made. Further, according to the configuration of the optical amplifier shown in FIG. 8, since the transmission line is connected via the optical coupler, a huge loss occurs in the input / output of the optical signal.
Such an excessive loss causes a deterioration in signal quality and leads to a reduction in relay distance, which is a disadvantage.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above conventional problems, and an object thereof is to reduce the number of parts of an optical amplifier. Another object is to reduce the loss of the optical amplifier that performs bidirectional transmission.

[0009]

In order to achieve the above object, in the present invention, an optical circulator is used in place of the conventionally used optical isolator and optical multiplexer. That is, in the first invention of the present application, in the optical amplifier configured to amplify the signal light input from the signal light input terminal by passing through the rare earth-doped optical fiber and output the signal light from the signal light output terminal. An optical circulator having forward transfer characteristics in the directions of the first terminal, the second terminal, and the third terminal, in which a rare earth-doped optical fiber is connected to the second terminal and a signal light output terminal is connected to the third terminal. A pumping light source for inputting pumping light to the first terminal of the optical circulator, the pumping light is supplied to the rare earth-doped optical fiber through the optical circulator, and the signal light amplified by the rare earth-doped optical fiber is passed through the optical circulator. And is output from the signal light output terminal.

In another invention of the present application, the first aspect
And the first and second signal lights respectively inputted from the first and second signal light input terminals are amplified by passing through the rare earth-doped optical fiber, and outputted from the first and second signal light output terminals, respectively. In the configured optical amplifier, the optical amplifier has forward transfer characteristics in the directions of the first terminal, the second terminal, and the third terminal, the first signal light input terminal is connected to the first terminal, and the second terminal Is connected to one end of a rare earth-doped optical fiber, and a third terminal is connected to a second signal light output terminal, a first optical circulator, a first terminal, a second terminal, and a third optical circulator.
Has a forward transfer characteristic in the direction of the terminal, the second signal light input terminal is connected to the first terminal, the other end of the rare earth-doped optical fiber is connected to the second terminal, and the third terminal is First
A second optical circulator connected to the signal light output terminal, a first pumping light source for inputting the first pumping light from one end of the rare earth-doped optical fiber, and a second pumping light for the rare earth-doped optical fiber. A second pumping light source input from the end;
The first signal light input from the first signal light input terminal is
Output from the first signal light output terminal via the first terminal of the first optical circulator, the second terminal, the rare earth-doped optical fiber, the second terminal of the second optical circulator, and the third terminal, The second signal light input from the second signal light input terminal is the first terminal of the second optical circulator, the second terminal, the rare earth-doped optical fiber, the second terminal of the first optical circulator, The signal light is output from the second signal light output terminal via the third terminal.

[0011]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 shows the configuration of an optical amplifier according to the first embodiment of the present invention. This optical amplifier
The optical isolator 60 to which the input signal light Pi is input, the rare earth-doped optical fiber 62 connected to one end of the optical isolator 60, the optical circulator 66 connected to the other end of the rare earth-doped optical fiber 62, and the optical circulator 66
And a pumping light source 64 connected to one terminal (A). The optical circulator 66 includes three terminals A, B, and C, and has forward characteristics in the ABC direction. That is, it has a non-reciprocal characteristic that light incident from the terminal A is output only from the terminal B with low loss and is not output from other terminals. The same applies to the light incident on the terminals B and C.

In the optical amplifier configured as described above, the input signal light Pi is input to the rare earth-doped optical fiber 62 via the optical isolator 60. On the other hand, the excitation light emitted from the excitation light source 64 enters the terminal A of the optical circulator 66, and enters the rare earth-doped optical fiber 62 via the terminal B. After that, the signal light amplified in the rare earth-doped optical fiber 62 enters the terminal B of the optical circulator 66 and is output from the terminal C as output signal light Po.

The optical circulator has a limited range of wavelengths that can operate correctly, and it is difficult to operate at both wavelengths when the wavelengths of the signal light and the pumping light are significantly different. For example, Er (Erbium) is used as a rare earth additive. In the case of the added optical fiber, the amplification wavelength band is 1.55 μm, whereas the excitation wavelength band closest to this is 1.48 μm, and when both wavelengths are close to each other, The optical circulator works normally at both wavelengths. Here, description will be given under such a premise.

The signal light and spontaneous emission light amplified in the rare earth-doped optical fiber 62 are blocked by the optical circulator 66 and do not reach the excitation light source 64. Therefore, it is necessary to provide an optical isolator and an optical filter in front of the excitation light source 64. Absent. Further, unnecessary reflected light returning from the output end side of the optical amplifier is also blocked by the optical circulator 66 and does not reach the rare earth-doped optical fiber 62 or the pumping light source 64, so that it is not necessary to provide an optical isolator at the output end.
That is, the optical circulator 66 shown in FIG. 1 corresponds to the optical multiplexer 18 and the optical isolator 1 of the conventional optical amplifier shown in FIG.
It can be seen that they also have the functions of the three optical elements 6 and 20.

FIG. 2 shows the configuration of an optical amplifier according to the second embodiment of the present invention. In this optical amplifier, a pumping light source is connected also behind the rare earth-doped optical fiber of the amplifier according to the first embodiment shown in FIG. 1, and an optical isolator 68 to which the input signal light Pi is input and a pumping light source. 70
And the isolator 7 connected to the output end of the pumping light source 70.
2 and the optical multiplexer 7 connected to the isolators 68 and 72
4, a rare earth-doped optical fiber 76 connected to the optical multiplexer 74, an optical circulator 80 connected to the rare earth-doped optical fiber 76, and an excitation light source 78 connected to one terminal (A) of the optical circulator 80. Is equipped with. The optical circulator 66 has three terminals A, B and C,
It has a forward characteristic in the direction of -BC. That is, the light incident from the terminal A is output only from the terminal B with low loss,
It has a non-reciprocal characteristic that it is not output from other terminals. The same applies to the light incident on the terminals B and C.

In the optical amplifier configured as described above, the input signal light Pi is the optical isolator 68 and the optical multiplexer 7.
Then, it is input to the rare earth-doped optical fiber 76 via 4. on the other hand,
The excitation light emitted from the excitation light source 70 is supplied to the isolator 7
2. It is incident on the rare earth-doped optical fiber 76 via the optical multiplexer 74. Further, the excitation light from the excitation light source 78 enters the terminal A of the optical circulator 80, and enters the rare earth-doped optical fiber 76 via the terminal B. After that, the signal light amplified in the rare earth-doped optical fiber 76 enters the terminal B of the optical circulator 80, and passes through the terminal C to output the signal light P.
Output as o.

FIG. 3 shows the configuration of an optical amplifier according to the third embodiment of the present invention. This optical amplifier includes optical fibers 82 and 89 for transmitting the first and second input signal lights Pi and Pi ′, optical circulators 83 and 90 connected to the optical fibers 82 and 89, and an optical circulator 83, respectively. Optical multiplexers 85 and 88 connected to 90, and pumping light sources 84 and 87 for supplying pumping light to the optical multiplexers 85 and 88, respectively.
And a rare earth-doped optical fiber 86 connected between the optical multiplexers 85 and 88. Optical circulator 83
Has three terminals A, B, and C and has a forward characteristic in the direction of ABC. That is, it has a non-reciprocal characteristic that light incident from the terminal A is output only from the terminal B with low loss and is not output from other terminals. The same applies to the light incident on the terminals B and C. The optical fiber 82 is connected to the terminal A, the optical multiplexer 85 is connected to the terminal B, and the optical fiber 92 for output is connected to the terminal C. The optical circulator 90 has three terminals A ′, B ′,
C ', has forward characteristics in the direction of A'-B'-C', an optical fiber 89 is connected to the terminal A ', an optical multiplexer 88 is connected to the terminal B', and a terminal C'is connected. An output optical fiber 91 is connected.

In the optical amplifier configured as described above, the input signal light Pi is incident on the terminal A of the optical circulator 83 and from the terminal B through the optical multiplexer 85 to the rare earth-doped optical fiber 86. Excitation light from the excitation light source 84 enters the rare earth-doped optical fiber 86 via the optical multiplexer 85. The signal light amplified in the rare earth-doped optical fiber 86 passes through the optical multiplexer 88, and the optical circulator 9
It is incident on the terminal B ′ of 0, the terminal C ′, the output optical fiber 9
It is output as the output signal light Po after passing through 1. On the other hand, the input signal light Pi ′ enters the terminal A ′ of the optical circulator 90 and enters the rare earth-doped optical fiber 86 from the terminal B ′ via the optical multiplexer 88. The excitation light from the excitation light source 87 enters the rare earth-doped optical fiber 86 via the optical multiplexer 88. The signal light amplified in the rare earth-doped optical fiber 86 passes through the optical multiplexer 85, and the optical circulator 8
3 is incident on the terminal B, the terminal C, and the output optical fiber 9
It is output as output signal light Po ′ after passing through 2.

As described above, in the optical amplifier shown in FIG. 3, there are two paths: a path from the input signal light Pi to the signal light output Po and a path from the input signal light Pi 'to the signal light output Po'. In contrast, a single rare earth-doped optical fiber 86
Will give an amplification effect in common.

FIG. 4 shows the configuration of an optical amplifier according to the fourth embodiment of the present invention. This optical amplifier is an improvement of the optical amplifier shown in FIG. 3, and here, only the difference will be described in detail. That is, the terminals D and D ′ are added to the above-mentioned optical circulators 83 and 90, and these terminals D and D ′ are connected by the optical fiber 94. As a result, the output optical fiber 9
The backward signal light Pi-r input from 1 is incident on the terminal C ′ of the optical circulator 90, and is input to the optical fiber 94 via the terminal D ′. The light that has passed through the optical fiber 94 is
The optical fiber 8 passes through the terminals D and A of the optical circulator 83.
It is output as a signal light output Po-r via 2. The backward signal light Pi-r ′ input from the output optical fiber 92 enters the terminal C of the optical circulator 83, and enters the optical fiber 94 via the terminal D. The light from the optical fiber 94 is supplied to the terminal D ′ of the optical circulator 90,
Signal light output Po− via A ′ through the optical fiber 89
It is output as r '.

As described above, in the optical amplifier shown in FIG. 4, in addition to the advantages of the optical amplifier shown in FIG. 3, there is an effect that signal transmission in the reverse direction is possible. The optical amplifiers shown in FIGS. 3 and 4 employ a bidirectional pumping method in which the rare earth-doped optical fiber 86 is pumped from both ends.
As a result, the signal light amplified through the two paths is amplified in a well-balanced manner, but it is also possible to adopt a method of exciting the rare earth-doped optical fiber from one side.

[0022]

As described above, the optical amplifier according to the present invention can reduce the number of parts of the optical amplifier. Further, there is an effect that the loss of the optical amplifier that performs bidirectional transmission can be reduced.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing a configuration of an optical amplifier according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a configuration of an optical amplifier according to a third embodiment of the present invention.

FIG. 4 is a circuit diagram showing a configuration of an optical amplifier according to a fourth embodiment of the present invention.

FIG. 5 is a circuit diagram showing a configuration of an optical amplifier according to a conventional technique.

FIG. 6 is a circuit diagram showing a configuration of another optical amplifier according to the related art.

FIG. 7 is a schematic diagram for explaining a conventional technique.

FIG. 8 is a schematic diagram for explaining a conventional technique.

[Explanation of symbols]

 60, 68, 72 ... Optical isolator 62, 76, 86 ... Rare earth doped optical fiber 64, 78, 84, 87 ... Excitation light source 66, 80, 83, 90 ... Optical circulator 74, 85, 88 ... Optical multiplexer 82, 89, 91, 92, 94 ... Optical fiber

Claims (4)

[Claims] 1. An optical amplifier configured to amplify a signal light input from a signal light input terminal by passing through a rare earth-doped optical fiber and output the amplified signal light from a signal light output terminal. A forward transfer characteristic in the direction of the terminal and the third terminal, and the rare earth-doped optical fiber is attached to the second terminal,
An optical circulator having the third terminal connected to each of the signal light output terminals, and an excitation light source for inputting excitation light to the first terminal of the optical circulator, wherein the excitation light is added to the rare earth element via the optical circulator. An optical amplifier, characterized in that the signal light supplied to an optical fiber and amplified by a rare earth-doped optical fiber is output from the signal light output terminal via the optical circulator. 2. An optical amplifier configured to amplify a signal light input from a signal light input terminal by passing through a rare earth-doped optical fiber and output the amplified signal light from a signal light output terminal. An optical circulator having forward transfer characteristics in the direction of a terminal and a third terminal, wherein the output terminal of the rare earth-doped optical fiber is connected to the second terminal and the signal light output terminal is connected to the third terminal. A first pumping light source for inputting a first pumping light to a first terminal of the optical circulator; an optical multiplexer connected between the signal light input terminal and an input end of the rare earth-doped optical fiber; A second pumping light source for generating second pumping light supplied to the rare earth-doped optical fiber via an optical multiplexer, wherein the first and second pumping lights are the optical circulator and the optical multiplexer, respectively. Through the vessel The fed to the rare earth doped optical fiber, an optical amplifier, characterized in that the signal light amplified by the rare-earth doped optical fiber is configured to be outputted from the signal light output terminal through the optical circulator Te. 3. The first and second signal lights respectively input from the first and second signal light input terminals are amplified by passing through the rare earth-doped optical fiber, and the first and second signal lights are respectively amplified. An optical amplifier configured to output from an output terminal has forward transfer characteristics in the directions of a first terminal, a second terminal, and a third terminal, and the first signal optical input terminal is provided at the first terminal. A first optical circulator having a second terminal connected to one end of the rare earth-doped optical fiber and a third terminal connected to the second signal light output terminal; and a first terminal and a second terminal , A forward transfer characteristic in the direction of the third terminal, the second signal light input terminal is connected to the first terminal, and the other end of the rare earth-doped optical fiber is connected to the second terminal, A second terminal whose third terminal is connected to the first signal light output terminal An optical circulator, a first pumping light source for inputting the first pumping light from one end of the rare earth-doped optical fiber via the first optical multiplexer, and a second pumping light for passing through the second optical multiplexer. And a second pumping light source input from the other end of the rare earth-doped optical fiber, and the first signal light input from the first signal light input terminal is the first signal light of the first optical circulator. The first terminal through the terminal, the second terminal, the first optical multiplexer, the rare-earth doped optical fiber, the second optical multiplexer, the second terminal of the second optical circulator, and the third terminal. Of the second optical signal output from the second optical signal input terminal and the second optical signal input from the second optical signal input terminal of the second optical circulator. Wave device, the rare earth-doped optical fiber, the first optical multiplexer, the first light The second terminal of the over Curator, through said third terminal second
An optical amplifier configured to be output from the signal light output terminal of. 4. A first, a second, a third, and a fourth signal light input / output terminal for inputting first, second, third, and fourth signal lights, respectively, and said first and second signals. A rare earth-doped optical fiber that amplifies light, and forward transfer characteristics in the directions of the first terminal, the second terminal, the third terminal, and the fourth terminal, and the first signal light input / output terminal at the first terminal. A first optical circulator having a second terminal connected to one end of the rare earth-doped optical fiber and a third terminal connected to the fourth signal light input / output terminal; It has forward transfer characteristics in the directions of two terminals, a third terminal, and a fourth terminal, the second signal light input / output terminal is connected to the first terminal, and the rare earth-doped optical fiber is connected to the second terminal. The other end is connected, the third terminal is connected to the third signal light input / output terminal, and the fourth terminal is connected to the first optical server. A second optical circulator connected to the fourth terminal of the curator; a first pumping light source for inputting the first pumping light from one end of the rare earth-doped optical fiber via a first optical multiplexer; A second pumping light source for inputting two pumping lights from the other end of the rare earth-doped optical fiber through a second optical multiplexer, and a first pumping light input from the first signal light input / output terminal. The signal light is a first terminal, a second terminal of the first optical circulator, the first optical multiplexer, the rare earth-doped optical fiber,
It is output from the third signal light input / output terminal and is input from the second signal light input / output terminal via the second terminal and the third terminal of the second optical multiplexer and the second optical circulator. The second signal light is emitted from the first terminal of the second optical circulator, the second terminal, the second optical multiplexer, the rare earth-doped optical fiber, the first optical multiplexer, and the first optical circulator. The third signal light output from the fourth signal light input / output terminal via the second terminal and the third terminal and input from the third signal light input / output terminal is output from the second optical circulator. Output from the first signal light input / output terminal through the third terminal, the fourth terminal, the fourth terminal of the first optical circulator, and the first terminal, and input from the fourth signal light input / output terminal. The fourth signal light is transmitted to the third terminal of the first optical circulator and the fourth signal light. Child, the second fourth terminal of the optical circulator, an optical amplifier, characterized by being configured so as to be outputted from the through the first terminal and the second signal light output terminal.