JPH07140422A - Bi-directional optical amplifying circuit - Google Patents

Abstract

PURPOSE:To provide an optical amplifying circuit which can amplify light signals irrelevantly to whether signal lights which are propagated in both directions are different or equal in wavelength by combining two optical amplifiers and one 4-terminal optical circulator. CONSTITUTION:The 1st and 3rd terminals 401 and 403 of the 4-terminal optical circulator are used as input/output terminals 405 and 406 for signal lights respectively, and the 2nd and 4th terminals 402 and 404 are connected to the optical amplifiers A1 and A2. Here, all the terminals of the optical circulator are input/ output terminals which serve also for input and output, so the optical amplifiers A1 and A2 which are connected to the 2nd and 4th terminals 402 and 404 are necessitated that the input terminal is the same as the output terminal. A normal optical amplifier has an input and an output terminal separated and can not be applied, which is solved by using the reflection type optical amplifiers A1 and A2 where the signal lights are reflected at terminals and return to input terminals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplifying circuit for increasing the distance between repeaters in an optical communication system, in which two optical waves propagating in both directions are provided with one optical circulator and two optical waves. The present invention relates to a bidirectional optical amplification system that amplifies by an optical amplifier.

[0002]

Description of the Related Art When bidirectional optical communication is performed using one optical line, and optical amplification is performed in the middle of a transmission line,
An outline of a communication system configuration according to a conventional technique is as shown in FIG. In FIG. 1, 101 is one optical transmitter, 10
2 is an optical receiver corresponding to 101, 103 is the other optical transmitter, 104 is an optical receiver corresponding to 103, 105 and 106 are optical amplifiers, 107, 108, 109 and 11
0 is an optical element for separating an optical signal according to the traveling direction of light, 1
11 and 112 are optical fibers. 107-110
An optical circulator can be used as the optical element.

An optical circulator has, for example, three terminals, light input from the first terminal is output from the second terminal, light input from the second terminal is output from the third terminal, and input from the third terminal. The emitted light is output from the first terminal,
An optical component in which the input and output are contradictory. Optical transmitter 10
When the wavelengths of 1 and 103 are different, an optical multiplexer / demultiplexer can be used. The optical multiplexer has a function of combining two light waves of different wavelengths propagating in different optical fibers so as to propagate in one optical fiber, and conversely, a function of different wavelengths propagating in one optical fiber. An optical component that also has the function of separating a light wave so that it propagates through two separate optical fibers.

The system configuration of FIG. 1 requires two optical circulators and two optical amplifiers, but it is also possible to amplify bidirectional signal light with one optical amplifier. The optical amplifier circuit shown is proposed. This optical amplifier circuit can be applied when the wavelengths of the signal light are different in both directions. For example, the two wavelengths of the signal light are 1.53 μm each.
m and 1.55 μm. 201 is an erbium-doped optical fiber, and 202 and 203 have a wavelength of 1.48 μm.
A semiconductor laser light source for pumping, 204 and 205 are optical multiplexers / demultiplexers for multiplexing the signal light and the subcutaneous excitation, 206 and 207 are optical isolators for the pumping light, 208,
209, 210, and 211 are multiplexers / demultiplexers for light having wavelengths of 1.55 μm and 1.53 μm, 212 and 213 are isolators for signal light, and 214 is a center wavelength of 1.5.
A 3 μm optical filter, 215 is an optical filter having a center wavelength of 1.55 μm, and 216 and 217 are input and output ends of the amplifier.

The optical multiplexers / demultiplexers 208, 209, 210 and 211 have the same function and have a function of multiplexing or demultiplexing a light wave having a wavelength of 1.55 μm and a light wave having a wavelength of 1.53 μm.

Symbols A to C in FIG. 2 are symbols of terminals of the multiplexer / demultiplexer, and also correspond to connection points of parts of the optical multiplexer / demultiplexer, optical isolator, and optical filter. A, mosquito, ki and shi have a wavelength of 1.55 μm and a wavelength of 1.53 μm
The terminals through which the light waves of (a), (e), (c) and (c) are terminals through which the light waves with a wavelength of 1.55 μm propagate, and (c), (o), (c) and (a) are the terminals through which the light waves with a wavelength of 1.53 μm propagate.
Terminals through which light waves of two types of wavelengths propagate, such as a, mosquito, ki, and shi, are called multiplexing terminals, and terminals through which long-wavelength light waves propagate, such as a, d, ku, and ko, have long wavelengths. Terminals are called terminals, and terminals such as C, OH, KE, and SA through which light waves on the short wavelength side propagate are called short wavelength terminals. I and D and K and S are connected with negligible connection loss. Also, 214 and U, 2
12 and E, 213, KU, 215 and C are also connected with negligible connection loss. By the optical multiplexers / demultiplexers 210 and 208, the light waves with the wavelength of 1.55 μm are
A light wave having a wavelength of 1.53 μm that propagates through the optical circuit of
Propagate through the optical circuits of O, U, and A. Since the optical isolators are inserted in the optical circuits of K, O, U, and A, the light waves having the wavelength of 1.53 μm that have propagated through the optical circuits of A, C do not reach E.

With the optical multiplexers / demultiplexers 209 and 211, a light wave with a wavelength of 1.55 μm propagates through the optical circuits of KI, KU, KO, and SH, and a light wave with a wavelength of 1.53 μm is Propagate through optical circuits. Since the optical isolators are inserted in the optical circuits of K, K, K, and S, the light waves having the wavelength of 1.55 μm propagating through the K, K, and C optical circuits do not reach K.

The amplifier circuit shown in FIG. 2 has a signal light input / output terminal 2
16 between 217 and 217 are unidirectional for the light wave having the wavelength of 1.55 μm and the light wave having the wavelengths of 1.53 and μm, respectively, but the erbium-doped optical fiber in which the signal light and the pump light interact with each other. Since each light propagates in both directions, it has a structure capable of amplifying bidirectional signal light.

An optical amplifier having the configuration shown in FIG. 3 has been proposed as a bidirectional optical amplifier circuit that can be used when the wavelengths of signal light in both directions are different. Reference numerals 301, 302, 303, and 304 are four optical multiplexers / demultiplexers. The terminals S, T, TE and D are multiplexing terminals. Terminals S, J, N and N are short wavelength terminals. Terminals T, G, N and C are long wavelength terminals. Reference numeral 305 is an optical amplifier. No. is an input terminal of the optical amplifier, and C is an output terminal of the optical amplifier. 306, 307,
Reference numerals 308, 309, 310, and 311 are optical cords for connection.

The optical amplifier is an erbium-doped optical fiber amplifier having a wavelength of 1.52 μm or more and 1.59.
A light wave of less than μm can be amplified.

A light wave having a wavelength of 1.528 μm or more and 1.54 μm or less can propagate between the multiplexing terminal and the short wavelength terminal of the optical multiplexer / demultiplexer, and the wavelength between the multiplexing terminal and the long wavelength terminal is 1. A light wave of 545 μm or more can propagate. The two wavelengths of the signal light are 1.535 μm and 1.55 μm, respectively.
Is.

When a light wave having a wavelength of 1.535 μm enters the optical multiplexer / demultiplexer 301 from the terminal S, it is output from the terminal S by the action of 301 and enters the optical multiplexer / demultiplexer 302 through the optical cord 306 and the terminal H. This light wave is output from the terminal by the action of 302, passes through the optical code 310 and the terminal, and enters the optical amplifier 305. Wavelength amplified by optical amplifier 1.
The light wave of 535 μm enters the optical multiplexer / demultiplexer 304 through the terminal C, the optical cord 311, and the terminal D. This light wave is 304
Is output from the terminal N and enters the optical multiplexer / demultiplexer 303 through the optical cord 308 and the terminal N. By the action of this optical multiplexer / demultiplexer 303, it is output from the terminal TE.

When a light wave having a wavelength of 1.55 μm enters the optical multiplexer / demultiplexer 303 from the terminal T, it is output from the terminal T by the action of 303, passes through the optical cord 307 and the terminal T, and the optical multiplexer / demultiplexer 3
Enter 02. This light wave is output from the terminal by the action of 302, passes through the optical code 310 and the terminal, and enters the optical amplifier 305. Wavelength 1.5 amplified by optical amplifier
The 5 μm light wave enters the optical multiplexer / demultiplexer 304 through the terminal C, the optical cord 311, and the terminal D. This light wave is output from the terminal N by the action of 304, passes through the optical cord 309 and the terminal S, and enters the optical multiplexer / demultiplexer 301. This light wave is output from the terminal by the action of 301.

The midpoint of the optical cord 306 and the optical cord 308
Insert a 1.535 μm optical filter at the midpoint of
Inserting a 1.55 μm optical film at the midpoint of the optical cord 307 or the midpoint of the optical cord 309 is effective in preventing leakage of each light wave.

In the embodiment shown in FIG. 3, the wavelength of the signal light is 1.5.
35 μm and 1.55 μm, but a plurality of signal lights in respective wavelength ranges of the optical multiplexer / demultiplexer may be used.

[0016]

The optical amplifier circuit shown in FIG.
It can be applied only when the wavelengths of propagating light in both directions are different enough to be combined or demultiplexed by an optical multiplexer / demultiplexer. The optical amplifier circuit of FIG. 2 is also a circuit suitable when the wavelengths of propagating light in both directions are different. If the optical amplifier circuit of FIG. 2 is applied to the case where the wavelengths in both directions are the same, 210, 208, 20
The optical elements 9 and 211 must be a three-terminal optical circulator, resulting in an expensive circuit configuration. The system configuration of FIG. 1 operates even if the wavelengths of propagating light in both directions are the same, but requires two three-terminal optical circulators.

Therefore, in the present invention, an optical signal can be amplified by combining two optical amplifiers and one 4-terminal optical circulator regardless of whether the wavelengths of the signal light propagating in both directions are different or the same. An object is to provide an optical amplifier circuit.

[0018]

In order to solve the above problems, the first and third terminals of a four-terminal optical circulator are
The signal light input / output terminals are respectively provided, and the second and fourth terminals are respectively connected to optical amplifiers. However, since all terminals of the optical circulator are input / output terminals that also serve as input and output, the optical amplifier connected to the second and fourth terminals must have the same input terminal and output terminal. This problem was solved by using a reflection type optical amplifier in which the signal is reflected at the terminal and returned to the input because the input and output ends of the ordinary optical amplifier are separated and cannot be applied.

[0019]

As a result, the lights propagating bidirectionally through one optical transmission line are input to different optical amplifiers, so that a bidirectional optical amplifier circuit is formed.

[0020]

FIG. 4 is a schematic diagram of the configuration of an embodiment of the present invention.
C indicates the range of the main body of the optical circulator,
A1 indicates the range of the first optical amplifier, and A2 indicates the range of the second optical amplifier.
Shows the range of the optical amplifier of. 401, 402, 40
Reference numerals 3 and 404 are the first, second, third, and fourth input / output fibers of the optical circulator, respectively.
Reference numeral 405 is an optical connector attached to 401, and 406 is an optical connector attached to 403. 407 is 4
02 and the input / output terminal of the first optical amplifier, 408
Is a connection point between 404 and the input / output terminal of the second optical amplifier. 409 and 410 are excitation light sources, 411 and 41
2 is an optical fiber doped with a rare earth element, 413 and 414 are optical multiplexers for multiplexing pumping light and signal light, 4
15 and 416 are narrow band optical filters, 417 and 4
Reference numeral 18 indicates a light reflection end. Reference numeral 419 denotes an enclosure of the optical circulator, and the arrow inside 419 is an arrow for indicating the rule of light propagation inside the optical circulator.

The function of the optical circulator inside the area C will be described below. The light input from the input / output optical fiber 401 is output from the input / output optical fiber 402, and the light input from the input / output optical fiber 402 is input / output optical fiber 4
The light output from the input / output optical fiber 403 and input from the input / output optical fiber 403 is output from the input / output optical fiber 404, and the light input from the input / output optical fiber 404 is output from the input / output optical fiber 401. It is known that such a function can be obtained by combining a polarization separation element and an optical Faraday element, and a 4-terminal optical circulator having a performance of transmitted light loss of about 1 dB is commercially available.

The function of the first optical amplifier is as follows. The signal light input from the connection point of 407 passes through the optical filter 415, is multiplexed with the excitation light by the multiplexer 413, and propagates through the optical fiber 411 doped with the rare earth element.
The signal light propagating through 411 is amplified by the interaction with the pumping light, reaches 417, and is reflected. Excitation light source 40
The excitation light emitted from 9 is combined with the signal light at 413,
Propagate through the optical fiber 411 doped with rare earth element
Reach 17 The intensity distribution of the excitation light along the optical fiber 411 is strong on the side of 413 and is attenuated so that it does not function as excitation light at 417. The signal light reflected by 417 propagates in the optical fiber 411 doped with the rare earth element in the direction of 407, is further amplified by the interaction with the excitation light, passes through 413, 415, and reaches the connection point 407. . Thus, the first optical amplifier inside A1 is a reflection type optical amplifier in which the amplified signal light returns to the input end.

The function of the second optical amplifier inside A2 is the same as the function of the first optical amplifier inside A1.

With the above-mentioned configuration, the signal light entering the optical circulator from 405 is 402 and 40.
After passing through No. 7, it enters the first optical amplifier and is amplified to 407
And propagate through 402 and 403 to 406
Reach The signal light entering the optical circulator from 406 passes through 404 and 408, enters the second optical amplifier, is amplified and returns to 408, and 404 and 4
Propagate 01 and reach 405. In this way, the light propagating from 405 to 406 and the light propagating from 406 to 405 pass through different optical amplifiers, and thus are amplified without affecting each other. That is, in the optical communication system in which the transmission lines are connected to 405 and 406, bidirectional propagation light is amplified.

The narrow band optical filters 415 and 416 are for removing the noise generated in the optical amplifier, but when the input to the optical amplifier is relatively large, the generation of noise is small and can be omitted. However, if a reflection point of light exists on the transmission line connected to 405 and the transmission line connected to 406, the reflected wave propagates through the closed loop including the first optical amplifier and the second optical amplifier, and the oscillation state is generated. Narrow band optical filters 415 and 4 having different transmission wavelengths.
This can be prevented by inserting 16.

[0026]

As described above, in the bidirectional optical amplifier circuit of the present invention, one optical circulator and two optical amplifiers can bidirectionally propagate and amplify two signal lights. There is an economical and highly reliable effect in proportion to the method using two optical circulators. It seems that using two optical amplifiers is not economical as compared with the known bidirectional amplification method using one optical amplifier, but when an optical amplifier with high output is required due to wavelength multiplexing or the like. ,
Since it is difficult to use one optical amplifier, this is not a drawback.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an optical communication system according to a conventional technique when bidirectional communication is performed by one optical line and optical amplification is performed in the middle of a transmission line.

FIG. 2 is a schematic configuration diagram of an existing bidirectional optical amplifier circuit.

FIG. 3 is a schematic diagram of the configuration of another existing bidirectional optical amplifier circuit.

FIG. 4 is a schematic configuration diagram of a bidirectional optical amplifier circuit of the present invention.

[Explanation of symbols]

101, 103 Optical transmitter 102, 104 Optical receiver 105, 106 Optical amplifier 107, 108, 109, 110 Optical element 111, 112 Optical fiber 201 Erbium-doped optical fiber 202, 203 Excitation semiconductor laser light source 204, 205, 208, 209, 210, 211,
Optical multiplexer / demultiplexer 206, 207, 212, 213 Optical isolator 214, 215 Optical filter 216, 217 Signal light input / output terminal a, a, u, d, o, mosquito, ki, ku, ke, co, sa, si terminal 301, 302, 303, 304 Optical multiplexer / demultiplexer 305 Optical amplifier 306, 307, 308, 309, 310, 311 Optical cord, Se, So, Ta, Chi, Tsu, Te, To, Na, Ni, Nu, Ne ,
No. C Terminal C Symbol for indicating range of main body of optical circulator A1 Symbol for indicating range of first optical amplifier A2 Symbol for indicating range of second optical amplifier 401 First input / output optical fiber of optical circulator 402 Optical Second input / output optical fiber of circulator 403 Third input / output optical fiber of optical circulator 404 Fourth input / output optical fiber of optical circulator 405,406 Optical connector 407,408 Connection point 409,410 Excitation light source 411,412 Noble Optical fiber 413,414 Optical multiplexer 415,416 Narrow band optical filter 417,418 Light reflecting end 419 Optical circulator enclosure

Claims (1)

[Claims] 1. An optical circulator having first, second, third, and fourth four input / output optical fibers, wherein a first input / output optical fiber end inputs and outputs signal light. A signal light input / output optical connector is attached, a first optical amplifier is connected to a second input / output optical fiber end of the 4-terminal optical circulator, and a third input / output of the 4-terminal optical circulator. A second signal light input / output optical connector for inputting and outputting signal light is connected to the optical fiber end, and a second optical amplifier is connected to the fourth input / output optical fiber end of the 4-terminal optical circulator. In the optical amplification circuit, the light input / output sequence of the optical circulator is such that the light input from the first input / output optical fiber end is output from the second input / output optical fiber end and the second input / output light is output from the second input / output optical fiber end. Light input from the output optical fiber end Is output from the third input / output optical fiber end, and the light input from the third input / output optical fiber end is
A four-terminal type optical circulator in which light output from the input / output optical fiber end and light input from the fourth input / output optical fiber end is output from the first input / output optical fiber end; And the second optical amplifier are reflection type amplifiers in which the optical input end and the output end of the amplified light are the same.