JPH0425825A - Optical fiber amplifier - Google Patents

Abstract

PURPOSE:To easily switch a semiconductor laser light source which deteriorates to a stand-by light source by supplying light beams which are emitted by plural semiconductor lasers for excitation to an end part of an Er-doped optical fiber through a wavelength multiplexer or polarized wave multiplexer. CONSTITUTION:The output light of a 1st semiconductor laser 3 for excitation which emits light of about 1.45 - 1.46 mum and a 2nd semiconductor laser 4 for excitation which emits light of about 1.48 - 1.49 mum are made incident on a 1st wavelength multiplexer 5, whose excitation light output is multiplexed by a 2nd wavelength multiplexer 6 with signal light propagated in an input fiber 7 and made incident on the Er-doped optical fiber 8. This exciting light is propa gated in the optical fiber 8 in the same direction with the signal light to excite Er atoms to a high energy potential and signal light which is induced and emit ted is amplified. A dielectric multi-layered film 9 is arranged at the other end of the optical fiber 8 and the exciting light is reflected by the multi-layered film 9; and only the signal light is transmitted through the multi-layered film 9 and branched partially by an optical branching device 10, the majority enters an output fiber 11, and part of the light is made incident on a photodetector 12, which measures the quantity of the light.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an optical fiber amplifier that amplifies optical signals as they are without converting them into electrical signals in optical communications.

[Conventional technology]

The wavelength of erbium-doped optical fiber is 1.45.
When light in the vicinity of ~1.49 μm is input, erbium atoms are excited to a high energy level and a population inversion is formed, and when signal light with an It length of 1.53 to 1.55 μm enters this optical fiber. It is known that signal light is amplified by stimulated emission. This optical fiber amplifier has a structure compared to a conventional regenerative repeater, which converts the signal light that has passed through a transmission path and attenuated into an electrical signal, amplifies and processes the electrical signal, and then converts it back into an optical signal. Because it is extremely simple, it is viewed as a promising next-generation repeater for optical communication systems, especially for transoceanic submarine systems, and development is progressing. [Problem to be Solved by the Invention] A semiconductor laser, which can be made compact, is used as a pumping light source for the optical fiber amplifier, but it has been revealed that this semiconductor laser deteriorates after long-term use. ing. In other words, in order to obtain a large degree of amplification, the above-mentioned optical fiber amplifier requires extremely high pumping light of several tens of mW, which means that an excessive current is passed through the semiconductor laser serving as the pumping light source, making it relatively expensive. It is expected that semiconductor lasers will deteriorate in a short period of time. Therefore, when applying an optical fiber amplifier to an optical communication system that requires high reliability, such as a submarine system, it is considered essential to provide a backup semiconductor laser light source for pumping. SUMMARY OF THE INVENTION An object of the present invention is to provide an optical fiber amplifier with improved reliability by easily switching to a spare light source when a pumping semiconductor laser light source deteriorates. be. 1. Means for Solving the Problems The present invention supplies the light emitted from a plurality of pumping semiconductor lasers to the end of an erbium-doped optical fiber via a wavelength multiplexer or a polarization multiplexer. The most important feature is that by selectively driving the plurality of excitation semiconductor lasers, the other excitation semiconductor lasers can be used as backup excitation semiconductor laser light sources.

[Effect]

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 into the signal light via the wavelength multiplexer or 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. The outline will be explained below. The polarization multiplexer generates light (
As shown in Figure 1, light is incident on a dielectric multilayer film 1 that reflects light (hereinafter referred to as S waves) and transmits light polarized parallel to the plane of the paper in Figure 1 (hereinafter referred to as P waves). The S wave coming from below is reflected by the dielectric multilayer film 1, and the P wave coming from the left is transmitted through the dielectric multilayer film 1. Furthermore, when both an S wave and a P wave are incident, they are combined and propagated to the right. The wavelength multiplexer has a certain wavelength λ. Reflects light with a wavelength of less than or equal to the wavelength λ. As shown in Figure 2, light is incident on the dielectric multilayer film 2 that transmits light of the wavelengths above, and the light (λ1<λC) coming from below is reflected by the dielectric multilayer film 2. Furthermore, the light (λ, >λC) coming from the left is transmitted through the dielectric multilayer film 2. Furthermore, when the light enters from below and from the left, both lights are combined and propagate to the right. FIG. 3 shows a first embodiment of the present invention. In this embodiment, the first excitation semiconductor laser 3 emits light in the vicinity of 1.45 to 146 μm and the
The output light from the second pumping semiconductor laser 4 emitting light in the vicinity is input to the first wavelength multiplexer 5, and the pumping light exiting from the multiplexer 5 is transmitted to the second wavelength multiplexer 6. It is combined with the signal light that has propagated through the input fiber buffer, and enters the optical fiber 8 doped with erbium. The pumping light thus incident propagates through the erbium-doped optical fiber 8 in the same direction as the signal light, excites the erbium atoms to a high energy level, and amplifies the signal light that generates stimulated emission. do. A dielectric multilayer film 9 is arranged at the other end of the optical fiber 8 doped with erbium, the excitation light is reflected by the dielectric multilayer film 9, and only the signal light is transmitted through the dielectric multilayer film 9.
A part of the signal light is branched by the optical splitter 10, and most of the signal light enters the output fiber 11 and propagates through the output fiber 1. Further, a part of the signal light branched by the optical splitter 10 is incident on a photodetector 12, and the amount of light is measured. If any of the excitation semiconductor lasers used here deteriorates, the amount of excitation light in the erbium-doped optical fiber 8 will decrease, and the amplification factor of the signal light will fall below the required value, resulting in photodetection. Deterioration of the excitation semiconductor laser can be detected by measuring the amount of light in the device 12. With this configuration, when the first excitation semiconductor laser 3 is used in the initial state and its deterioration occurs, the photodetector 12 senses the level drop due to this deterioration, and the deterioration is detected. If energization 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 the erbium-doped optical fiber 8 is sensed, the amplification factor of the erbium-doped optical fiber 8 can be increased to the required amplification. It is possible to restore the rate. FIG. 4 shows a second embodiment of the invention. In this example,
The pressure light from the first excitation semiconductor laser 14 is multiplexed by the first wavelength multiplexer 15 with the signal light propagating through the input fiber, and enters the optical fiber 8 doped with erbium. The thus incident excitation light propagates through the erbium-doped optical fiber 8 in the same direction as the signal light, excites erbium atoms to a high energy level, generates stimulated emission, and amplifies the signal light. . The output light from the second excitation semiconductor laser 16 is reflected by the dielectric multilayer film in the second wavelength multiplexer 17 and is input to the erbium-doped optical fiber 8 . The excitation light from the second excitation semiconductor laser 16 is transmitted through an optical fiber 8 doped with erbium.
propagates in the opposite direction to the signal light, excites the erbium atoms to a high energy level, generates stimulated emission, and amplifies 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 17, and a part of the signal light is split by the optical splitter 10. Most of it enters the output fiber 11 and propagates through the output fiber 11. A portion of the signal light branched by the optical splitter 10 is measured for its light intensity by a photodetector 2. Note that the configuration and operation method of the photodetector 12 and power supply 13 used to switch the excitation semiconductor lasers 14 and 16 are the same as in the first embodiment corresponding to claim 1 of the present invention shown in FIG. Based on the detection of the level drop by the photodetector 12, the excitation semiconductor lasers 14 and 16 are selectively driven. FIG. 5 shows a third embodiment corresponding to claim 3 of the present invention. In this example, the light emitted from the semiconductor laser used as the excitation light source is polarized in a direction parallel to the active layer.
Through the polarization maintaining fibers 18 and 19, the output light of the first semiconductor laser 20 is sent to the polarization multiplexer 21 as an S wave, and the output light of the second semiconductor laser 22 is sent to the polarization multiplexer 21. It is incident as a P wave. Therefore, as explained above, two semiconductor lasers 20 for pumping the optical fiber amplifier are used.
．． The excitation light from 22 is multiplexed by a polarization multiplexer 21. The pump light multiplexed by the polarization multiplexer 21 is multiplexed by the wavelength multiplexer 23 with the signal light propagating through the input fiber, and is input into the optical fiber 8 doped with erbium. The excitation light thus incident propagates through the erbium-doped optical fiber 8 in the same direction as the signal light, excites the erbium atoms to a high energy level, generates stimulated emission, and increases the signal light. I do. A dielectric multilayer film 9 is arranged at the other end of the erbium-doped optical fiber 8, and the excitation light is reflected by the dielectric multilayer film 9, and only the signal light is transmitted through the dielectric multilayer film 9, and the light is branched. A part of the signal light is branched by the device 10, and most of the signal light enters the output fiber 11 and propagates through the output fiber 11. A portion of the signal light branched by the optical splitter 10 is sent to a photodetector 12 to measure its light weight. The configuration and operation method of the photodetector 12 and power supply 13 used to selectively switch the excitation semiconductor lasers 20 and 22 are the same as in the first embodiment shown in FIG. The pump light of 20.21 is combined with the signal light. FIG. 6 shows a fourth embodiment corresponding to claim 4 of the present invention. In this embodiment, the first excitation semiconductor laser 24 emits light in the vicinity of 145 to 146 μm, and 1,48 to 49 μm.
The output light of the second pumping semiconductor laser 25 emitting light in the vicinity of m is multiplexed by the first wavelength multiplexer 26, and the combined pumping light is sent to the input fiber fiber by the second wavelength multiplexer 27. It is combined with the signal light propagated through the erbium-doped optical fiber 8 and enters the erbium-doped optical fiber 8. The thus incident excitation light propagates through the erbium-doped optical fiber 8 in the same direction as the signal light, excites the erbium atoms to a high energy level, generates stimulated emission, and amplifies the signal light. . A third wavelength multiplexer 30 outputs the output light from the third pumping semiconductor laser 28 that emits light in the vicinity of 145 to 1.46 μm and the fourth pumping semiconductor laser 29 that emits light in the vicinity of 1,48 to 1.49 μm. The combined excitation light is reflected by the dielectric multilayer film in the fourth wavelength multiplexer 31, and is input to the erbium-doped optical fiber 8. The excitation light from the third and fourth excitation semiconductor lasers 2g and 29 combined by the third wavelength multiplexer 30 propagates through the erbium-doped optical fiber 8 in the opposite direction to the signal light. It excites erbium atoms to a high energy level, generates stimulated emission, and amplifies 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 fourth wavelength multiplexer 31, and then passes through the optical splitter 1.
At 0, part of the signal light is branched and most of it is sent to the output fiber 11.
The signal enters and propagates through the output fiber 11. Note that in the optical circuit configuration of this embodiment, the excitation light from the first and second excitation semiconductor lasers 24 and 25 propagates through the erbium-doped optical fiber 8 and then passes through the fourth wavelength multiplexer 31. Since the light is reflected by the dielectric multilayer film inside and incident on the third and fourth excitation semiconductor lasers 28 and 29, the influence of the excitation light from the first and second excitation semiconductor lasers 24 and 25 is eliminated. Therefore, it is desirable that the third and fourth excitation semiconductor lasers 2g and 29 are provided with an isolator. The first and second excitation semiconductor lasers 24.25 are also similar to this, and are equipped with isolators to eliminate the influence of excitation light from the third and fourth excitation semiconductor lasers 28.29. It is desirable to be present. A portion of the signal light branched by the optical splitter 1o is measured for its light intensity by a photodetector 12. Photodetector 12 and power supply 13 used to alternatively switch the excitation semiconductor laser 24, 25, 28, 29
The structure and operation method of claim 1 of the present invention are shown in FIG.
This is the same as the first embodiment corresponding to
Either excitation semiconductor laser 24°25, 28.29
The excitation light is combined with the signal light. FIG. 7 shows a fifth embodiment corresponding to claim 5 of the present invention. In this embodiment, as explained above, the emitted light of the semiconductor laser used as the excitation light source is polarized in the direction parallel to the active layer, so if it passes through the polarization maintaining fibers 32 and 33, the first The output light of the semiconductor laser 34 enters the first polarization multiplexer 35 as an S wave, and the output light of the second semiconductor laser 36 enters the first polarization multiplexer 35 as a P wave. As explained above, the pumping lights from the two semiconductor lasers for pumping the optical fiber amplifier: (4, 36) are combined by the first polarization multiplexer 35. The waved excitation light is multiplexed by the first wavelength multiplexer 37 with the signal light that has propagated through the input fiber buffer, and is input to the erbium-doped optical fiber 8. The light propagates through the optical fiber doped with erbium in the same direction as the signal light, excites the erbium atoms to a high energy level, generates stimulated emission, and amplifies the signal light. As in the case of the pumping semiconductor lasers 34 and 36, the output lights of the third and fourth pumping semiconductor lasers 3839 are combined by the second polarization multiplexer 40, and this combined pumping light is It is reflected by the dielectric multilayer film in the wavelength multiplexer 41 and is input to the erbium-doped optical fiber 8.The third and fourth excitation wavelengths are multiplexed by the second polarization multiplexer 40. The excitation light from the semiconductor laser 3839 propagates through the erbium-doped optical fiber 8 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 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 at the optical splitter 10. Most of it enters the output fiber 11 and enters the output fiber 11.
will be propagated. As explained in the fourth embodiment of FIG. 6, the excitation semiconductor lasers 34, 36, 38, and 39 are equipped with an isolator to reduce the influence of excitation light from other semiconductor lasers by υF. or desirable. A part of the signal light branched by the optical splitter 10 is transmitted to the photodetector 12
The amount of light is measured. Excitation semiconductor laser 34, 3
The configuration and operating method of the photodetector 12 and the power supply 13 used for selectively switching the 6.38.39 are the same as in the first embodiment corresponding to claim 1 of the present invention shown in FIG. The excitation light from either of the excitation semiconductor lasers 3436, 38, 39 is combined into a signal. FIG. 8 shows a sixth embodiment corresponding to claim 6 of the present invention. In this sixth embodiment, first and second excitation semiconductor lasers 44,45 that emit light in the vicinity of 1.45 to 1.46 μm are connected to a first polarization multiplexer 46 via polarization-maintaining fibers 42 and 43.
The third and fourth excitation semiconductor lasers 49.50, which emit light in the vicinity of 1.48 to 1.49 μm, are combined via a polarization-maintaining fiber 47.48 to a second polarization multiplexer 5I. and combine the waves. 1, 45 multiplexed by the first polarization multiplexer 46
The excitation light emitted in the vicinity of ~1.46 μm and the excitation light emitted in the vicinity of 148 to 1.49 μm, which are combined by the second polarization multiplexer 51, are combined in the first wavelength multiplexer 52. . 1st
The pump light multiplexed by the wavelength multiplexer 52 is multiplexed by the second wavelength multiplexer 53 with the signal light propagating through the input fiber, and is input into the enbium-doped optical fiber 8. . The excitation light thus incident propagates through the embium-doped optical fiber 8 in the same direction as the signal light, excites the erbium atoms to a high energy level, generates stimulated emission, and amplifies the signal light. . A dielectric multilayer film 9 is arranged at the other end of the enbium-doped optical fiber 8. The excitation light is reflected by the dielectric multilayer film 9, and only the signal light is transmitted through the dielectric multilayer film 9, and the light is A part of the signal light is branched by the splitter IO, and most of the signal light enters the output fiber 11 and propagates through the output fiber 11. A portion of the signal light branched by the optical splitter 10 is measured for its light intensity by a photodetector 12. The configuration and operation method of the photodetector 12 and power supply 13 used to selectively switch the excitation semiconductor lasers 44, 45, 49, 50 are the same as in the first embodiment shown in FIG. Li, excitation semiconductor laser 44.45.49.
One of the 50 pump lights is multiplexed into a signal.

【Effect of the invention】

As explained above, in the optical fiber amplifier of the present invention, a spare pumping semiconductor laser that can be switched with the currently used pumping semiconductor laser is created by an extremely simple method of ON10 FF switching the current that drives the semiconductor laser. Therefore, in an optical fiber amplifier where it is essential to increase the output of the semiconductor laser, it is possible to switch to a spare pumping semiconductor laser in response to deterioration of the pumping semiconductor laser due to high output, and therefore, This has the advantage of increasing its reliability.

[Brief explanation of drawings]

FIG. 1 shows a simplified configuration of a polarization multiplexer used in the optical circuit of the optical fiber amplifier of the present invention, and FIG. 2 shows a wavelength multiplexer used in the optical circuit of the optical fiber amplifier of the present invention. FIG. 3 is a diagram showing a simplified configuration of the wave generator, and FIG.
4 is a diagram showing a second embodiment of the present invention, FIG. 5 is a diagram showing a third embodiment of the present invention, and FIG. 6 is a diagram showing a fourth embodiment of the present invention. , FIG. 7 shows a fifth embodiment of the invention, and FIG. 8 shows a sixth embodiment of the invention. 1.2.9...Dielectric multilayer film, 1.8.19.
32.33.42.4347.48...Polarization maintaining fiber 3, 4, 14.16.20.22゜24, 2
5.28.29.34.36.38.39.44.45
．． 49.50...Semiconductor laser, 21.35.40
．． 46.51...Polarization multiplexer, 615, 17.2
3.26.27.30.31.37.41.52.53
... Wavelength multiplexer, 7 ... Input fiber 8
...Erbium-doped optical fiber, 10
... Optical splitter, 11... Output fiber, 12...
...Photodetector, 13...Power supply.

Claims (6)

[Claims] (1) A first semiconductor laser for excitation, a second semiconductor laser for excitation, and an erbium-doped output light emitted from the first semiconductor laser for excitation and the second semiconductor laser for excitation. It comprises means for coupling to at least one end of a fiber, and means for inputting signal light into the optical fiber, and the first and second excitation semiconductor lasers are selectively driven with electricity. optical fiber amplifier. (2) The first excitation semiconductor laser has a diameter of 1.45 to 1.
The second excitation semiconductor laser emits light at around 46 μm, the second excitation semiconductor laser emits light at 1.48 to 1.49 μm, and the second excitation semiconductor laser combines the outputs of the first excitation semiconductor laser and the second excitation semiconductor laser. 2. The optical fiber amplifier according to claim 1, comprising one wavelength multiplexer and a second wavelength multiplexer that multiplexes the multiplexed output light and the signal light. (3) The output light of the first pumping semiconductor laser and the second pumping semiconductor laser is input to the polarization multiplexer via a polarization-maintaining optical fiber. fiber optic amplifier. (4) The output lights of the first pumping semiconductor laser and the second pumping semiconductor laser are input into the first wavelength multiplexer, and this pumping light is combined with the signal light by the second wavelength multiplexer. A third excitation semiconductor laser emitting light at the same wavelength as the first excitation semiconductor laser, in which signal light and excitation light are made to travel in the same direction from one end of an erbium-doped optical fiber. The output light of the semiconductor laser and the fourth semiconductor laser for excitation that emits light at the same wavelength as the second semiconductor laser for excitation is
A fourth wavelength multiplexer is used to pass this pump light into a fourth wavelength multiplexer so that the signal light and the pump light travel in opposite directions from the other end of the erbium-doped optical fiber. What is claimed is: 1. An optical fiber amplifier comprising an optical circuit for inputting light, and wherein the four pumping semiconductor lasers are selectively energized and driven. (5) A first semiconductor laser for excitation, a second semiconductor laser for excitation, and output light emitted from the first semiconductor laser for excitation and the second semiconductor laser for excitation through a polarization maintaining fiber. The pump light enters the first polarization multiplexer through the erbium-doped optical fiber, and the pump light is multiplexed with the signal light by the first wavelength multiplexer. a third semiconductor laser that emits light at the same wavelength as the first semiconductor laser for excitation; and a fourth semiconductor laser that emits light at the same wavelength as the second semiconductor laser for excitation; The output light of the semiconductor laser is input to the second polarization multiplexer via the polarization maintaining fiber, and this pump light is input to the second polarization multiplexer.
It consists of an optical circuit that uses a wavelength multiplexer to input signal light and excitation light from the other end of an erbium-doped optical fiber so that they travel in opposite directions, and connects the four excitation semiconductor lasers. An optical fiber amplifier characterized in that it is selectively energized and driven. (6) The output light of the first and second pumping semiconductor lasers is input to the first polarization multiplexer via the polarization maintaining fiber, and emits light at a wavelength different from that of the first and second pumping semiconductor lasers. The output light from the third and fourth pumping semiconductor lasers is input to the second polarization multiplexer via the polarization maintaining fiber, and the light output from the two polarization multiplexers is combined into the first wavelength multiplexer. It is composed of an optical circuit that inputs the pump light into a wavelength multiplexer, combines the pump light with a signal light by a second wavelength multiplexer, and inputs the pump light together with the signal light from one end of an erbium-doped optical fiber. An optical fiber amplifier characterized in that the four pumping semiconductor lasers are selectively energized and driven.