JP2862040B2 - Optical fiber amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber amplifier, and more particularly to a bidirectional pumping optical fiber amplifier for introducing pump light from both directions of a signal light input side and a signal light output side of an optical amplification fiber.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 2, an optical fiber amplifier of this type is provided with a pump light generated by one or a plurality of pump light sources 22 and a signal of an optical transmission line on a signal light input side of an optical amplifier fiber 21. A multiplexer / demultiplexer (or multiplexer) for multiplexing light with light 2
3 and a multiplexer / demultiplexer (or multiplexer) for introducing pump light generated by one or more pump light sources 24 from the signal light output side of the optical amplification fiber 21 to the signal light output side of the optical amplification fiber 21. 25 was connected.

In such a conventional optical fiber amplifier,
The excitation light source 2 is passed through the multiplexers / demultiplexers 23 and 25 located on the signal light input side and the signal light output side of the optical amplification fiber 21.
By introducing the pumping light (having a different wavelength band from the signal light) generated by 2 and 24 into the optical amplifying fiber 21, the optical amplifying fiber 21 is brought into an excited state. In this state, when the signal light is input from the signal light input side, the signal light is amplified by stimulated emission while propagating through the inside of the optical amplification fiber 21, and is emitted from the signal light output side.

[0004]

In the conventional optical fiber amplifier, the spontaneous emission light (having the same wavelength band as the signal light) generated by the optical amplification fiber 21 is located at the input / output end of the optical amplification fiber 21. When the gain of the optical fiber amplifier is increased because the light is reflected by the optical component, spontaneous emission light is amplified one after another, which causes a problem that the noise characteristic is deteriorated and the small signal gain is reduced.

SUMMARY OF THE INVENTION In view of the foregoing, it is an object of the present invention to constitute an optical amplification fiber section by connecting an optical circuit in series between two or more sets of optical amplification fibers, and to input signal light by the optical circuit. So that low noise is realized by passing only from the side to the signal light output side, and high gain is obtained by passing the pump light in both directions between the signal light input side and the signal light output side. To provide an improved optical fiber amplifier.

[0006]

SUMMARY OF THE INVENTION An optical fiber amplifier according to the present invention combines a pump light and a signal light generated by a pump light source at a signal light input side of an optical amplification fiber that absorbs the pump light and amplifies the signal light. And a multiplexer for introducing the pump light generated by the pump light source from the signal light output side of the optical amplification fiber to the signal light output side of the optical amplification fiber. In a bidirectionally pumped optical fiber amplifier to be connected, an optical amplifying fiber section passes signal light only in one direction from an input port to an output port in the middle of each of two or more sets of optical amplifying fibers, and in the opposite direction. The optical circuit is characterized in that it has a configuration in which optical circuits having a characteristic of passing in both directions from the input port to the output port and from the output port to the input port are connected in series.

[0007]

In the optical fiber amplifier according to the present invention, when the pumping light generated by the pumping light source is introduced into the optical amplifying fiber section through the multiplexers located on the signal light input side and the signal light output side of the optical amplifying fiber section, Pass through the optical circuit in both directions of the signal light input side and the signal light output side to excite the optical amplification fiber. In this excited state, when signal light is input from the signal light input side, the signal light is amplified by stimulated emission while propagating inside the optical amplification fiber on the signal light input side,
Further, the light is further amplified by stimulated emission while propagating inside the optical amplification fiber on the signal light output side via the optical circuit. On the other hand, spontaneous emission light generated by the optical amplification fiber on the signal light input side propagates through the optical circuit to the optical amplification fiber on the signal light output side and is amplified and output together with the signal light. The spontaneous emission light generated by the optical amplification fiber is blocked by the optical circuit and does not propagate to the optical amplification fiber on the signal light input side, thereby preventing an increase in noise in the optical amplification fiber on the signal light input side.

[0008]

Next, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing a configuration of an optical fiber amplifier according to one embodiment of the present invention. The optical fiber amplifier of the present embodiment combines the pump light generated by the pump light source 2 and the signal light of the optical transmission line on the signal light input side of the optical amplification fiber unit 1 and introduces the combined light into the optical amplification fiber 6. A multiplexer (or multiplexer) 3 is connected, and the pump light generated by the pump light source 4 is supplied to the signal light output side of the optical amplification fiber unit 1.
Multiplexer / demultiplexer (or multiplexer) introduced from the signal light output side of the
5 is a bidirectional pumped optical fiber amplifier.

The optical amplification fiber section 1 is constituted by connecting an optical circuit 8 in series between two sets of optical amplification fibers 6 and 7 for absorbing pump light and amplifying signal light.

In the optical circuit 8, the signal light passes only in one direction from the input port to the output port and does not pass in the reverse direction. The pumping light passes in both directions from the input port to the output port and from the output port to the input port. This is an optical circuit having the characteristic of passing through the optical circuit. In this embodiment, the optical circuit 8 is configured such that multiplexers / demultiplexers 9 and 10 are connected in series to an input / output end of an optical isolator 11, and further, the excitation light ports of the multiplexers / demultiplexers 9 and 10 are connected to each other via an optical fiber 12. Has been realized.

Next, the operation of the thus configured optical fiber amplifier of this embodiment will be described.

The pump light (having a wavelength band different from that of the signal light) generated by the pump light sources 2 and 4 is supplied to the optical amplifying fiber unit 1.
When the light is introduced into the optical amplification fiber unit 1 through the multiplexers / demultiplexers 3 and 5 located on the signal light input side and the signal light output side,
The pumping light generated by the pumping light source 2 puts the optical amplification fiber 6 on the signal light input side into an excited state, and outputs the light on the signal light output side via the multiplexer / demultiplexer 9, the optical fiber 12 and the multiplexer / demultiplexer 10. The amplification fiber 7 is also set to the excited state. The pumping light generated by the pumping light source 4 puts the optical amplification fiber 7 on the signal light output side into an excited state, and outputs the signal light on the signal light input side via the multiplexer / demultiplexer 10, the optical fiber 12 and the multiplexer / demultiplexer 9. The optical amplification fiber 6 is also in an excited state.

When signal light is input from the signal light input side in such an excited state of the optical amplification fibers 6 and 7, the excitation light and the signal light are multiplexed by the multiplexer / demultiplexer 3. The signal light is amplified by stimulated emission while propagating inside, and is input to the multiplexer / demultiplexer 9.

The multiplexer / demultiplexer 9 branches the signal light and the pumping light of the input signal light and the pumping light toward the optical isolator 11 and the pumping light toward the optical fiber 12.

The signal light split in the direction of the optical isolator 11 passes through the optical isolator 11 and the multiplexer / demultiplexer 10, is introduced into the optical amplifier fiber 7 on the signal light output side, and propagates inside the optical amplifier fiber 7. In the meantime, the light is further amplified by stimulated emission and output to the signal light output side via the multiplexer / demultiplexer 5.

Since the spontaneous emission light generated by the optical amplification fiber 6 on the signal light input side has the same wavelength band as the signal light, the signal light is transmitted via the multiplexer / demultiplexer 9, the optical isolator 11 and the multiplexer / demultiplexer 10. The spontaneous emission light generated by the optical amplification fiber 7 on the output side of the signal light is propagated to the optical amplification fiber 7 on the output side and amplified and output together with the signal light. The light passes through the wave filter 10 and is cut off by the optical isolator 11, and does not propagate to the optical amplification fiber 6 on the signal light input side.

In the optical fiber amplifier of this embodiment, amplification is performed in two stages, namely, amplification by the optical amplification fiber 6 on the signal light input side and amplification by the optical amplification fiber 7 on the signal light output side. Preventing the spontaneous emission light generated by the optical amplification fiber 7 on the signal light output side from propagating to the optical amplification fiber 6 on the signal light input side, which has a large degree of determining the exponent, plays a significant role in reducing the overall noise figure. Fulfill.

FIGS. 3 and 4 are diagrams comparing the gain-light output characteristics and the noise figure-gain characteristics of the optical fiber amplifier of this embodiment and the conventional optical fiber amplifier. The characteristics (b) of the optical fiber amplifier according to the present embodiment and the characteristics (a) of the conventional optical fiber amplifier are shown in comparison. The optical fiber amplifier according to the present embodiment allows the pump light to pass in both directions between the signal light input side and the signal light output side when performing two-stage amplification by the two sets of optical amplification fibers 6 and 7. Because it is used effectively, compared to conventional optical fiber amplifiers,
The gain is high in the non-saturation region of the light output (see FIG. 3). In addition, for example, after the excitation light generated from the excitation light source 2 is optimally adjusted to minimize the noise figure of the spontaneous emission light generated in the optical amplification fiber 6, the intensity of the excitation light generated from the excitation light source 4 is changed. If the gain is adjusted in this way, the noise figure becomes almost constant regardless of the gain (see FIG. 4).

In the above embodiment, the optical amplification fiber section 1 is composed of two sets of optical amplification fibers 6 and 7 and one optical circuit 8.
However, it is needless to say that the present invention can be implemented in the same manner as long as the optical amplifier fiber section is configured such that an optical circuit is connected in series between two or more sets of optical amplifier fibers. Absent.

[0021]

As described above, the present invention provides a bidirectionally pumped optical fiber amplifier in which an optical amplifier fiber section has a configuration in which an optical circuit is connected in series between two or more sets of optical amplifier fibers, and a signal optical signal. Is transmitted only from the signal light input side to the signal light output side so that spontaneous emission light generated in the signal light output side optical amplification fiber is not propagated to the signal light input side optical amplification fiber, thereby realizing low noise, and By bypassing the pumping light and passing it in both directions between the signal light input side and the signal light output side, there is an effect that the pump light can be effectively used and a high gain can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a block diagram illustrating an example of a conventional optical fiber amplifier.

FIG. 3 is a diagram comparing gain-optical output characteristics between the optical fiber amplifier of the present embodiment and a conventional optical fiber amplifier.

FIG. 4 is a diagram comparing noise figure-gain characteristics between the optical fiber amplifier of the present embodiment and a conventional optical fiber amplifier.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical amplification fiber part 2, 4 Excitation light source 3, 5 Multiplexer / demultiplexer (multiplexer) 6, 7 Optical amplification fiber 8 Optical circuit 9, 10, Multiplexer / demultiplexer 11 Optical isolator 12 Optical fiber

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Claims (1)

(57) [Claims] 1. A multiplexer for multiplexing pump light generated by a pump light source and signal light on the signal light input side of an optical amplification fiber that absorbs pump light and amplifies signal light, and introduces the multiplexed light into the optical amplification fiber. A bidirectional pumping optical fiber amplifier for connecting a multiplexer for introducing pumping light generated by a pumping light source from the signal light output side of the optical amplification fiber to the signal light output side of the optical amplification fiber. The amplification fiber section is located between the two or more sets of optical amplification fibers, and the signal light passes only in one direction from the input port to the output port and does not pass in the opposite direction, and the pump light passes from the input port to the output port. An optical fiber amplifier having a configuration in which optical circuits having characteristics of passing in both directions from an output port to an input port are connected in series.