JPH11243369A - Optical fiber amplifier - Google Patents

Abstract

(57) [Problem] To provide a highly reliable optical fiber amplifier which can cope with a case where different gains are required. SOLUTION: Since pumping lights from a plurality of pumping light sources 3-1 to 3-N are supplied to a plurality of optical fiber amplifiers 9-1 to 9-N via an optical star coupler 8, pumps having different wavelengths are provided. By using the light sources 3-1 to 3-N, it is possible to cope with a case where different gains are needed, and to use the pump light sources 3-1 to 3-
By using a plurality of N, even if one of the pumping light sources 3-1 fails, the other pumping light sources 2-2 to 3-N can compensate for the failure, so that a highly reliable optical fiber amplifier can be provided. Can be.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an optical fiber amplifier.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram of a conventional optical fiber amplifier.

[0003] In this method, excitation light is input from a pumping light source to a rare earth-doped optical fiber via an optical multiplexer / demultiplexer, and light in a part of the wavelength band of the light amplified by the rare earth-doped optical fiber is selectively added to the rare earth. It returns to the optical fiber cyclically.

The signal light input from one end (left end in the figure) of the optical fiber passes through the optical isolator 1 and is multiplexed with the pump light input from the pump light source 3 by the optical multiplexer 2.
The light passes through the optical fiber grating filter 4 and enters the rare earth-doped optical fiber 5.

Here, the optical grating filter 4 has a diffraction grating formed in the optical fiber by irradiating an optical fiber containing a high concentration of Ge with high-power short-wavelength laser light. This optical grating filter 4 can reflect only an optical signal of a desired wavelength and bandwidth by changing the period and the number of gratings of the diffraction grating, and is a fiber type. There is an advantage that the connection loss is small as compared with.

The excitation light has a wavelength corresponding to the excitation level of the added rare earth ion, and the excitation light forms a population inversion of the energy level of the rare earth ion in the rare earth doped optical fiber 5. When signal light is input to the rare earth-doped optical fiber 5 in which the population inversion is formed, a stimulated emission phenomenon occurs, and the signal light is amplified. At the same time as the signal light is amplified, spontaneous emission light is emitted from the rare-earth-doped optical fiber 5.
Part of the spontaneous emission light is reflected at the wavelengths of the optical fiber grating filters 4 and 6, oscillates in the rare-earth-doped optical fiber 5, and the rare-earth-doped optical fiber 5 is saturated, and the signal gain is fixed. The magnitude of the signal gain is determined by the reflectance of each optical fiber grating filter. The signal light amplified by the rare earth-doped optical fiber 5 passes through the optical isolator 7 and is output. The optical isolator 7 is for preventing the reflected light from the output end of the signal light from returning into the amplifier again and falling into an unstable state such as oscillation.

[0007]

However, when a plurality of optical fiber amplifiers are operated collectively from the same pumping light source, it is not possible to cope with a case where each optical fiber amplifier requires a different gain. In addition, in the case where the number of pumping light sources is one for one rare-earth-doped optical fiber, if the pumping light source does not operate for any reason, amplification becomes impossible and reliability is lacking. there were.

It is an object of the present invention to solve the above-mentioned problems and to provide an optical fiber amplifier which can cope with a case where different gains are required and which has high reliability.

[0009]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a rare earth-doped optical fiber, an optical multiplexer / demultiplexer for inputting pumping light to the rare earth-doped optical fiber, and a rare earth-doped optical fiber. A plurality of optical fiber amplifiers having cyclic feedback means for selectively cyclically returning light of a specific wavelength band in the light to the rare earth-doped optical fiber, and a plurality of optical fiber amplifiers for supplying pump light to each optical fiber amplifier. An excitation light source;
An optical star coupler for supplying pumping light from each pumping light source to each optical fiber amplifier.

In addition to the above configuration, the present invention provides an optical fiber amplifier in which pump light from different pump light sources is input to a plurality of input ports of an optical star coupler and output light from a plurality of output ports of the optical star coupler is different from each other. May also be supplied.

In addition to the above configuration, the cyclic feedback means of the optical fiber amplifier according to the present invention may be constituted by optical fiber grating filters provided at both ends of the rare earth doped optical fiber.

In addition to the above configuration, the cyclic feedback means of the optical fiber amplifier of the present invention includes an optical coupler provided at both ends of the rare-earth-doped optical fiber and an optical bandpass filter connected between the two optical couplers. It may be configured.

In addition to the above configuration, the cyclic feedback means of the optical fiber amplifier of the present invention comprises an optical circulator provided at both ends of the rare-earth-doped optical fiber and an optical band-pass filter provided between the two optical circulators. It may be configured.

In addition to the above configuration, the cyclic feedback means of the optical fiber amplifier according to the present invention includes a multi-port optical circulator in which both ends of the rare-earth-doped optical fiber are connected to respective ports, and a multi-port optical circulator connected to other ports. It may be composed of a light reflector or a wavelength-selective light reflector.

According to the above configuration, the pumping light from the plurality of pumping light sources is supplied to the plurality of optical fiber amplifiers via the optical star coupler. Therefore, when different gains are required by using pumping light sources having different wavelengths. By using a plurality of pumping light sources of the same wavelength, even if one of the pumping light sources fails, the other pumping light source can make up for it, so that a highly reliable optical fiber amplifier can be provided.

[0016]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. Note that common members are used for members similar to those in the conventional example.

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

The optical fiber amplifier includes a plurality (N) of pump light sources 3-1 to 3-N, a plurality (N) of optical fiber amplifiers 9-1 to 9-N, and each of the pump light sources 3-1. And optical star couplers 8 for supplying the pumping lights from .about.3-N to the respective optical fiber amplifiers 9-1 to 9-N.

The optical fiber amplifiers 9-1 to 9-N include an optical isolator 1 for transmitting signal light only in one direction, an optical multiplexer 2 for multiplexing pump light, and an output of the optical multiplexer 2. Optical fiber grating filters 4 and 6 as cyclic feedback means for selectively cyclically returning light in the wavelength band on the side;
It comprises a rare earth-doped optical fiber 5 for amplifying signal light and an optical isolator 7 for preventing return light.

In the optical fiber amplifier 10 having such a configuration, the pumping light from the plurality of pumping light sources 3-1 to 3-N is supplied to the plurality of optical fiber amplifiers 9-1 to 9-N. By using the pump light sources 3-1 to 3-N having different wavelengths, it is possible to cope with a case where a different gain is required. Even if -1 fails, another excitation light source 3-
Since it can be compensated by 2 to 3-N, it is possible to provide the optical fiber amplifier 10 with high reliability.

Here, the rare-earth-doped optical fiber 5 is an optical fiber having a core doped with a rare-earth element, and includes Er (erbium), Nd (neodymium),
Yb (yttrium), Pr (praseodymium), C
It contains at least one kind of e (cerium), Sm (samarium), Tm (thulium), La (lanthanum) and the like.

The wavelength of the signal light is the same as that of the rare-earth-doped optical fiber 5.
The wavelength of the excitation light is about 0.98 μm or about 1.48 μm when Er is used, for example.

In this embodiment, the optical amplifiers 9-1 to 9-1 are used.
As the 9-N pumping method, a forward pumping method (a method in which the traveling direction of the signal light and the traveling direction of the pumping light are the same in the rare-earth-doped optical fiber) has been described.
The present invention is not limited to this, and other systems such as a backward pumping system and a bidirectional pumping system may be used.

FIG. 2 is a block diagram showing another embodiment of the optical fiber amplifier of the present invention.

The difference from the optical fiber amplifier shown in FIG. 1 is that the cyclic feedback means includes an optical coupler provided at both ends of the rare-earth-doped optical fiber and an optical bandpass connected between the two optical couplers. This is a point composed of filters.

The optical fiber amplifiers 11-1 to 11-N are:
A rare earth-doped optical fiber 5 for amplifying signal light, an optical multiplexer 2 for inputting pump light to the rare earth-doped optical fiber, optical isolators 1 and 7, and a part of the amplified output light is branched. An optical coupler 12-1, an optical bandpass filter 13 for passing only light of a specific wavelength, an optical coupler 12-2 for inputting the light passing through the optical bandpass filter 13 to the rare-earth-doped optical fiber 5 again, An optical band reject filter 14 for preventing output of an internally oscillated optical signal is provided.

The pumping light from the pumping light sources 3-1 to 3-N is inputted to the optical multiplexer 2 via the optical star coupler 8, the signal light is inputted to the optical coupler 12-2, and the amplified light is light. It is output from the band reject filter 14.

The optical fiber amplifier 15 has the same effect as that of the optical fiber amplifier shown in FIG.

FIG. 3 is a block diagram showing another embodiment of the optical fiber amplifier of the present invention.

The difference from the optical fiber amplifier shown in FIG. 1 is that the cyclic feedback means includes an optical circulator provided at both ends of the rare-earth-doped optical fiber and an optical band-pass provided between both optical circulators. This is a point composed of filters.

The optical fiber amplifiers 16-1 to 16-N are:
An optical circulator 17 having forward characteristics from port A to port B and from port B to port C; an optical circulator 18 having forward characteristics from port D to port E and from port E to port F; The optical multiplexer / demultiplexer 2 and the rare-earth-doped optical fiber 5 connected between the port B and the port E of the optical circulator 18, the port C of the optical circulator 17, and the optical circulator 18
And an optical attenuator 19 and an optical bandpass filter 20 connected in series with the port D.

The pumping light from the pumping light sources 3-1 to 3-N is input to the optical multiplexer 2 via the optical star coupler 8, the signal light is input to the port A of the optical circulator 17, and the amplified light is Output from the port F of the optical circulator 18.

With such an optical fiber amplifier 21, the same effects as those of the optical fiber amplifier shown in FIG. 1 can be obtained.

FIG. 4 is a block diagram showing another embodiment of the optical fiber amplifier of the present invention.

The difference from the optical fiber amplifier shown in FIG. 1 is that the cyclic feedback means is connected to a multiport optical circulator in which both ends of a rare-earth-doped optical fiber are connected to each port, and to another port of the multiport optical circulator. And a wavelength selective light reflector connected thereto.

The optical fiber amplifiers 22-1 to 22-N are:
An optical circulator 23 having a forward characteristic from port A to port B, port B to port C, port C to port D, port D to port E, and an optical circulator 2
3, an optical multiplexer 2 and a rare earth-doped optical fiber 5 connected in series between a port B and a port D, and a wavelength-selective optical reflector connected to a port C of an optical circulator 23 via an optical attenuator 24. And an optical fiber grating filter 25 and an optical non-reflection terminator 26.
Note that a light reflector may be used instead of the wavelength-selective light reflector.

The pump light from the pump light sources 3-1 to 3-N is input to the optical multiplexer 2 via the optical star coupler 8, the signal light is input to the port A of the optical circulator 23, and the amplified light is It is output from the port E of the optical circulator 23.

With such an optical fiber amplifier 27, the same effect as that of the optical fiber amplifier shown in FIG. 1 can be obtained.

The above optical fiber amplifier has the following features. (1) The pump light is input to the rare earth-doped optical fiber via the optical multiplexer / demultiplexer, and the light of a specific wavelength band in the light amplified by the rare earth-doped optical fiber is In the optical fiber amplifier that selectively circulates the light back to the rare earth-doped optical fiber, the pump light supplied from the pump light source is distributed to the rare earth-doped optical fibers of the plurality of optical fiber amplifiers by the optical star coupler. The fiber amplifier can be operated to amplify using the same excitation light source.

(2) In an optical fiber amplifier, by using an optical star coupler having two or more input ports and two or more output ports, pump light is supplied from a plurality of pump light sources to a plurality of optical fiber amplifiers. Since the supply can be performed, and even if a problem occurs in the excitation light source, it is possible to cope with the problem, so that the reliability is improved.

[0041]

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

It is possible to provide a highly reliable optical fiber amplifier which can cope with a case where different gains are required.

[Brief description of the drawings]

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

FIG. 2 is a block diagram showing another embodiment of the optical fiber amplifier of the present invention.

FIG. 3 is a block diagram showing another embodiment of the optical fiber amplifier of the present invention.

FIG. 4 is a block diagram showing another embodiment of the optical fiber amplifier of the present invention.

FIG. 5 is a block diagram of a conventional optical fiber amplifier.

[Explanation of symbols]

 3-1 to 3-N Excitation light source 8 Optical star coupler 9-1 to 9-N Optical fiber amplifier 10 Optical fiber amplifier

Claims (6)

[Claims] 1. A rare-earth-doped optical fiber, an optical multiplexer / demultiplexer for inputting pumping light to the rare-earth-doped optical fiber, and a light in a specific wavelength band selected from light amplified by the rare-earth-doped optical fiber. A plurality of optical fiber amplifiers having cyclic feedback means for cyclically feeding back the rare earth-doped optical fiber, a plurality of excitation light sources for supplying excitation light to each optical fiber amplification unit, and excitation light from each excitation light source. An optical fiber amplifier comprising: an optical star coupler for supplying each optical fiber amplifier. 2. An excitation light from a different excitation light source is input to each of a plurality of input ports of the optical star coupler, and output lights from a plurality of output ports of the optical star coupler are respectively supplied to different optical fiber amplifiers. The optical fiber amplifier according to claim 1. 3. The optical fiber amplifier according to claim 1, wherein said cyclic feedback means comprises optical fiber grating filters provided at both ends of said rare earth-doped optical fiber. 4. The recirculating feedback means comprises an optical coupler provided at both ends of the rare-earth-doped optical fiber, and an optical bandpass filter connected between the two optical couplers. 3. The optical fiber amplifier according to 2. 5. The recirculating feedback means comprises an optical circulator provided at both ends of the rare-earth-doped optical fiber, and an optical bandpass filter provided between the two optical circulators. 3. The optical fiber amplifier according to 2. 6. The multi-port optical circulator, wherein both ends of the rare-earth-doped optical fiber are connected to respective ports, and an optical reflector or wavelength selector connected to another port of the multi-port optical circulator. The optical fiber amplifier according to claim 1, wherein the optical fiber amplifier is configured to include a reflective light reflector.