JP2634298B2 - Optical fiber amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to an optical fiber amplifier that amplifies an optical signal without converting the optical signal into an electric signal in optical communication.

[Prior art]

Erbium-doped optical fiber with wavelength 1.45 ~
When light near 1.49 μm is injected, erbium atoms are excited to a high energy level to form a population inversion, and when signal light with a wavelength of 1.53 to 1.55 μm enters this optical fiber, stimulated emission occurs. It is known that signal light is amplified. The configuration of this optical fiber amplifier is compared with that of a conventional regenerative repeater that once converts attenuated signal light that has passed through a transmission line into an electric signal, amplifies and processes the signal in the form of an electric signal, and then converts it back to an optical signal. Because of its simplicity, it is promising as a next-generation repeater in an optical communication system and the like, particularly as a transponder for a trans-oceanic submarine system, and is being developed.

[Problems to be solved by the invention]

As a pumping light source for the optical fiber amplifier, a semiconductor laser that can be reduced in size is used, but it has been clarified that this semiconductor laser is deteriorated by long-term use. That is, in order to obtain a large amplification degree in the optical fiber amplifier, an extremely high pumping light of several tens of mW is required, so that an excessive current is supplied to the semiconductor laser serving as the pumping light source, and the pump is relatively short. It is expected that the semiconductor laser will deteriorate in the period. Therefore, when an optical fiber amplifier is applied to an optical communication system requiring high reliability such as a submarine system, it is considered essential to provide a spare pumping semiconductor laser light source. SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical fiber amplifier with improved reliability that can be easily switched to a spare light source when the pumping semiconductor laser light source deteriorates in order to improve the reliability of the optical fiber amplifier. is there.

[Means for Solving the Problems]

The most important aspect of the present invention is that the emission of a plurality of pumping semiconductor lasers is supplied to the end of an erbium-doped optical fiber via a wavelength multiplexer or a polarization multiplexer. A feature is that the plurality of excitation semiconductor lasers are selectively driven so that the other excitation semiconductor lasers are used as spare excitation semiconductor laser light sources.

[Action]

With the above configuration, the excitation light from the driven excitation laser light source can be guided to one end of the optical fiber and multiplexed to the signal light via the wavelength multiplexer or the polarization multiplexer. .

【Example】

Before describing the embodiments of the present invention in detail, first, examples of a polarization multiplexer and a wavelength multiplexer, which are optical components used in the optical circuit of the present invention, are shown in FIGS. 1 and 2, respectively. Will be described and the outline thereof will be described. The polarization multiplexer reflects light polarized perpendicular to the plane of FIG. 1 (hereinafter referred to as S-wave) and transmits light polarized parallel to the plane of FIG. 1 (hereinafter referred to as P-wave). Dielectric multilayer film 1
In contrast, the S-wave coming from below is reflected by the dielectric multilayer film 1 and the P-wave coming from the left side is reflected by the dielectric multilayer film 1 as shown in FIG. To Penetrate. When both the S-wave and the P-wave enter, they are combined and propagate to the right. The wavelength multiplexer reflects light having a wavelength equal to or less than a certain wavelength λc and makes the light incident on the dielectric multilayer film 2 that transmits light having a wavelength equal to or more than the wavelength λc as shown in FIG. Light coming from below (λ ₁ <λc) is reflected by the dielectric multilayer film 2 and light coming from the left (λ ₂ > λc)
Is transmitted through the dielectric multilayer film 2. When the light enters from below and from the left, both lights are combined and propagate to the right. FIG. 3 shows a first reference example of an optical fiber amplifier based on the above principle. In this reference example, the output light of the first excitation semiconductor laser 3 emitting in the vicinity of 1.45 to 1.46 μm and the output light of the second excitation semiconductor laser 4 emitting in the vicinity of 1.48 to 1.49 μm are combined into a first wavelength multiplexer. 5, the pump light exiting the multiplexer 5 is multiplexed with the signal light propagating through the input fiber 7 by the second wavelength multiplexer 6, and is incident on the erbium-doped optical fiber 8. I do. The pumping light thus incident propagates through the optical fiber 8 in which erbium is doped in the same direction as the signal light, excites erbium atoms to a high energy level, generates stimulated emission, and amplifies the signal light. I do.
At the other end of the optical fiber 8 doped with erbium, a dielectric multilayer film 9 is coordinated. Excitation light is reflected by the dielectric multilayer film 9 and only signal light passes through the dielectric multilayer film 9, A part of the signal light is split by the optical splitter 10, and most of the signal light enters the output fiber 11 and propagates through the output fiber 11. Further, a part of the signal light branched by the optical branching device 10 is incident on the photodetector 12, and the light amount is measured. If any of the pumping semiconductor lasers that are energized here deteriorates, the amount of pumping light in the erbium-doped optical fiber 8 decreases and the amplification factor of the signal light falls below a required value. The deterioration of the pumping semiconductor laser can be sensed by measuring the light quantity in the detector 12. With such a configuration, when the first pumping semiconductor laser 3 is used in the initial state and the deterioration occurs, the level decrease due to the deterioration is detected by the photodetector 12, and the deterioration is detected. When the power from the power supply 13 is switched from the first pumping semiconductor laser 3 to the second pumping semiconductor laser 4 on the condition that is detected, the amplification factor of the erbium-doped optical fiber 8 becomes the required amplification. It is possible to return to the rate. FIG. 4 shows a second reference example based on the above principle. In this reference example, the output light of the first pumping semiconductor laser
Is multiplexed with the signal light propagating through the input fiber 7 and enters the optical fiber 8 into which erbium has been doped. The pumping light thus incident propagates through the optical fiber 8 in which erbium is doped in the same direction as the signal light, and excites erbium atoms to a high energy level to generate stimulated emission to amplify the signal light. . The output light of the second pumping semiconductor laser 16 is reflected by the dielectric multilayer film in the second wavelength multiplexer 17 and is incident on the erbium-doped optical fiber 8. The pumping light from the second pumping semiconductor laser 16 is an optical fiber 8 doped with erbium.
Propagates in the opposite direction to the signal light, excites erbium atoms to a high energy level, generates stimulated emission, and amplifies the signal light. On the other hand, the signal light that has propagated through the optical fiber 8 doped with erbium and has undergone amplification passes through the dielectric multilayer film in the second wavelength multiplexer 17, and a part of the signal light is branched by the optical branching device 10. The majority enters the output fiber 11 and
Propagate 11 The light amount of a part of the signal light branched by the optical branching device 10 is measured by the photodetector 12. The configuration and operation of the photodetector 12 and the power supply 13 used for switching the pumping semiconductor lasers 14 and 16 are the same as those in the first embodiment shown in FIG. The excitation semiconductor lasers 14, 16 are selectively driven based on the detection of the drop. FIG. 5 is a third reference example based on the above principle. In this reference example, the emission light of the semiconductor laser used as the excitation light source is polarized in the direction parallel to the active layer, so that the output light of the first semiconductor laser 20 can be transmitted through the polarization maintaining fibers 18 and 19. Is incident on the polarization multiplexer 21 as an S-wave, and the output light of the second semiconductor laser 22 is incident on the polarization multiplexer 21 as a P-wave. Therefore, as described above, the pump lights from the two semiconductor lasers 20 and 22 for pumping the optical fiber amplifier are multiplexed by the polarization multiplexer 21. The pump light multiplexed by the polarization multiplexer 21 is multiplexed with the signal light propagating through the input fiber 7 by the wavelength multiplexer 23, and is incident on the optical fiber 8 into which erbium is doped. The pumping light thus incident propagates through the optical fiber 8 doped with erbium in the same direction as the signal light, excites erbium atoms to a high energy level, generates stimulated emission, and amplifies the signal light. I do. At the other end of the optical fiber 8 doped with erbium, a dielectric multilayer film 9 is disposed. Excitation light is reflected by the dielectric multilayer film 9 and only signal light passes through the dielectric multilayer film 9.
A part of the signal light is split by the optical splitter 10, and most of the signal light enters the output fiber 11 and propagates through the output fiber 11. Optical splitter
The light amount of a part of the signal light branched at 10 is measured by the photodetector 12. The configuration and operating method of the photodetector 12 and the power supply 13 used for selectively switching the semiconductor lasers 20 and 22 for excitation are the same as those of the first embodiment shown in FIG.
The pump light of any of the semiconductor lasers 20 and 21 is combined with the signal light. FIG. 6 shows a first embodiment corresponding to claim 1 of the present invention. In this embodiment, the output light of the first excitation semiconductor laser 24 emitting near 1.45-1.46 μm and the output light of the second excitation semiconductor laser 25 emitting near 1.48-1.49 μm are combined with the first wavelength multiplexer 26. The multiplexed pump light is multiplexed with the signal light propagating through the input fiber 7 by the second wavelength multiplexer 27, and is incident on the optical fiber 8 into which erbium is doped. The pumping light thus incident propagates through the optical fiber 8 in which erbium is doped in the same direction as the signal light, and excites erbium atoms to a high energy level to generate stimulated emission to amplify the signal light. . Third excitation semiconductor laser 28 emitting light in the vicinity of 1.45 to 1.46 μm and 1.48 to 1.49
The output light of the fourth pumping semiconductor laser 29 which emits light in the vicinity of μm is multiplexed by the third wavelength multiplexer 30, and the multiplexed pumping light is applied to the dielectric material in the fourth wavelength multiplexer 31. Reflected by the multilayer film,
Erbium is incident on the doped optical fiber 8.
The pumping light from the third and fourth pumping semiconductor lasers 28 and 29 synthesized by the third wavelength multiplexer 30 propagates through the erbium-doped optical fiber 8 in the opposite direction to the signal light. The erbium atoms are excited to a high energy level to generate stimulated emission and amplify the signal light. On the other hand, the signal light that has propagated through the optical fiber 8 doped with erbium and has been amplified
Through the dielectric multilayer film in the wavelength multiplexer 31
, A part of the signal light is branched, and most of the light enters the output fiber 11 and propagates through the output fiber 11. In the optical circuit configuration of this embodiment, the first and second pumping semiconductor lasers 24, 25
Pump light from the optical fiber 8 with erbium doped
After being propagated, the light is reflected by the dielectric multilayer film in the fourth wavelength multiplexer 31 and enters the third and fourth pumping semiconductor lasers 28 and 29. Semiconductor lasers 24, 25
The third and fourth pumping semiconductor lasers 28 and 29 are preferably provided with isolators in order to eliminate the influence of the pumping light. First and second pumping semiconductor lasers 24,2
The same applies to 5 and it is desirable to provide an isolator to eliminate the influence of the excitation light from the third and fourth semiconductor lasers for excitation 28 and 29. The light amount of a part of the signal light branched by the optical branching device 10 is measured by the photodetector 12. The configuration and operation of the photodetector 12 and the power supply 13 used for selectively switching the semiconductor lasers 24, 25, 28 and 29 for excitation are the same as those of the first embodiment of the present invention shown in FIG. By switching, one of the pumping semiconductor lasers
The 24, 25, 28, and 29 pump lights are multiplexed with the signal light. FIG. 7 shows a second embodiment corresponding to claim 2 of the present invention. In this embodiment, as described above, the emitted light of the semiconductor laser used as the excitation light source is polarized in a direction parallel to the active layer. The output light of the semiconductor laser 34 is a first polarization multiplexer.
Since the output light of the second semiconductor laser 36 is incident on the first polarization multiplexer 35 as a P-wave as an S-wave, and as described above, the two Excitation lights from the semiconductor lasers 34 and 36 are multiplexed by the first polarization multiplexer 35. The pump light multiplexed by the first polarization multiplexer 35 is multiplexed with the signal light propagating through the input fiber 7 by the first wavelength multiplexer 37, and is incident on the optical fiber 8 into which erbium is doped. Is done. The pumping light thus incident propagates through the optical fiber 8 in which erbium is doped in the same direction as the signal light, and excites erbium atoms to a high energy level to generate stimulated emission to amplify the signal light. . As in the case of the first and second pumping semiconductor lasers 34 and 36, the output lights of the third and fourth pumping semiconductor lasers 38 and 39 are multiplexed by a second polarization multiplexer 40. The waved excitation light is reflected by the dielectric multilayer film in the second wavelength multiplexer 41, and is incident on the optical fiber 8 into which erbium is doped. Third and fourth pumping semiconductor lasers multiplexed by the second polarization multiplexer 40
The pumping light from 38 and 39 propagates through the erbium-doped optical fiber 8 in the opposite direction to the signal light, and excites erbium atoms to a high energy level to generate stimulated emission and amplify the signal light. On the other hand, the signal light propagated through the erbium-doped optical fiber 8 and amplified passes through the dielectric multilayer film in the second wavelength multiplexer 41, and a part of the signal light is branched by the optical branching device 10. Most of the light enters the output fiber 11 and propagates through the output fiber 11. As described in the first embodiment of FIG. 6, the pumping semiconductor lasers 34, 36, 38, and 39 may include an isolator to eliminate the influence of pumping light from other semiconductor lasers. desirable. The light amount of a part of the signal light branched by the optical branching device 10 is measured by the photodetector 12. The configuration and operation of the photodetector 12 and the power supply 13 used for selectively switching the semiconductor lasers for excitation 34, 36, 38 and 39 are different from those of the first embodiment of the present invention shown in FIG. The same is true, and the pumping light of any of the pumping semiconductor lasers 34, 36, 38, and 39 is multiplexed with the signal. FIG. 8 shows a third embodiment corresponding to claim 3 of the present invention. In the third embodiment, first and second pumping semiconductor lasers 44 and 45, which emit light in the vicinity of 1.45 to 1.46 μm, through polarization maintaining fibers 42 and 43 are multiplexed by a first polarization multiplexer 46. Further, the third and fourth pumping semiconductor lasers 49 and 50 that emit light in the vicinity of 1.48 to 1.49 μm via the polarization maintaining fibers 47 and 48 are multiplexed by the second polarization multiplexer 51. The pump light emitted near 1.45 to 1.46 μm, which is multiplexed by the first polarization multiplexer 46, and the second
The pump light emitted near 1.48 to 1.49 μm, which has been multiplexed by the polarization multiplexer 51, is multiplexed by the first wavelength multiplexer 52. First
The pump light multiplexed by the wavelength multiplexer 52 is multiplexed with the signal light propagating through the input fiber 7 by the second wavelength multiplexer 53, and is incident on the optical fiber 8 doped with embium. You. The pumping light thus incident propagates through the optical fiber 8 doped with embium in the same direction as the signal light, and excites embium atoms to a high energy level to generate stimulated emission to amplify the signal light. . At the other end of the optical fiber 8 doped with embium, a dielectric multilayer film 9 is coordinated. Excitation light is reflected by the dielectric multilayer film 9 and only signal light passes through the dielectric multilayer film 9. A part of the signal light is split by the splitter 10, and most of the signal light enters the output fiber 11 and propagates through the output fiber 11. The light amount of a part of the signal light branched by the optical branching device 10 is measured by the photodetector 12. The configuration and operation of the photodetector 12 and the power supply 13 used for selectively switching the semiconductor lasers for excitation 44, 45, 49, and 50 are the same as those of the first reference example shown in FIG. The pumping light of any of the pumping semiconductor lasers 44, 45, 49, 50 is multiplexed with the signal.

【The invention's effect】

As described above, in the optical fiber amplifier of the present invention, a spare pumping semiconductor laser that can be switched with the current pumping semiconductor laser by extremely simple means of turning on / off the current for driving the semiconductor laser. Therefore, in an optical fiber amplifier in which it is essential to increase the output of the semiconductor laser, it is possible to switch to a spare pumping semiconductor laser in accordance with the deterioration of the pumping semiconductor laser due to the high output. There is an advantage that the reliability can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a simplified configuration of a polarization multiplexer used in the optical circuit of the optical fiber amplifier according to the present invention, and FIG. 2 is a diagram showing the wavelength combination used in the optical circuit of the optical fiber amplifier according to the present invention. FIG. 3 is a diagram showing a simplified configuration of a wave filter, and FIG.
FIG. 4 shows a second embodiment of the present invention, FIG. 5 shows a third embodiment of the present invention, and FIG. 6 shows a first embodiment of the present invention. FIG. 7 is a view showing a second embodiment of the present invention, and FIG. 8 is a view showing a third embodiment of the present invention. 1,2,9 …… Dielectric multilayer film, 18,19,32,33,42,43,47,48 ……
Polarization-maintaining fiber, 3, 4, 14, 16, 20, 22, 24, 25, 28, 29, 34, 3
6,38,39,44,45,49,50 …… Semiconductor laser, 21,35,40,46,5
1 ... Polarization multiplexer, 6,15,17,23,26,27,30,31,37,41,52,5
3 wavelength combiner, 7 input fiber, 8 erbium-doped optical fiber, 10 optical splitter, 11
... Output fiber, 12 ... Photodetector, 13 ... Power supply.

Claims (3)

(57) [Claims] An output light of a first pumping semiconductor laser and a second pumping semiconductor laser are incident on a first wavelength multiplexer,
The pump light is multiplexed with the signal light by the second wavelength multiplexer,
A third pumping semiconductor laser that emits at the same wavelength as the first pumping semiconductor laser, by causing signal light and pumping light to enter from one end of the erbium-doped optical fiber so as to travel in the same direction; The output light of the fourth pumping semiconductor laser emitting at the same wavelength as that of the second pumping semiconductor laser is incident on a third wavelength multiplexer, and the pumping light is passed through a fourth wavelength multiplexer. And an optical circuit in which the signal light and the pumping light are made to enter from the other end of the erbium-doped optical fiber so as to travel in opposite directions. The four pumping semiconductor lasers are alternatively used. An optical fiber amplifier driven by conduction. A first pumping semiconductor laser, a second pumping semiconductor laser, and a first pumping semiconductor laser;
The output light emitted from the pumping semiconductor laser is input to the first polarization multiplexer via the polarization maintaining fiber, and the pump light is multiplexed with the signal light by the first wavelength multiplexer, A third semiconductor laser emitting light at the same wavelength as the first pumping semiconductor laser, wherein the signal light and the pumping light are incident from one end of the erbium-doped optical fiber so as to travel in the same direction; The output light of the fourth semiconductor laser emitting at the same wavelength as the second pumping semiconductor laser is incident on the second polarization multiplexer via the polarization maintaining fiber, and the pumping light is transmitted to the second polarization multiplexer. An optical circuit that uses a wavelength multiplexer to cause the signal light and the pump light to enter from the other end of the erbium-doped optical fiber so as to travel in opposite directions;
An optical fiber amplifier, wherein one of the semiconductor lasers for excitation is selectively driven by conduction. 3. The output light of the first and second pumping semiconductor lasers is incident on a first polarization multiplexer via a polarization maintaining fiber,
The output light of the third and fourth pumping semiconductor lasers, which emits light at a wavelength different from that of the first and second pumping semiconductor lasers, is incident on the second polarization multiplexer via the polarization maintaining fiber.
The light emitted from the polarization multiplexers is incident on a first wavelength multiplexer, and the pump light is multiplexed with the signal light by a second wavelength multiplexer to form one of the erbium-doped optical fibers. It is composed of an optical circuit that makes it enter with the signal light from the end of
An optical fiber amplifier, wherein the four semiconductor lasers for excitation are selectively driven by conduction.