JPH0325985A - Optical fiber amplifier - Google Patents

Abstract

PURPOSE:To effectively utilize a pumping light from a pumping light source of an amplifier and to improve amplifying efficiency by passing the pumping light plural times through an optical fiber doped with a rare earth element. CONSTITUTION:A pumping light emitted from a pumping LD 38 is incident to an optical fiber 10 doped with erbium (Er). On the other hand, a signal light is incident through an incident side optical fiber 12. The signal light is incident to the fiber 10 through a reflection film 40. Er atoms of excited state by the introduction of a pumping light are transited to a low energy state by the introduction of the signal light, and a light is inductively emitter. Thus, the signal light is amplified, and introduced into an emitting side optical fiber 14. On the other hand, the pumping light passed through the fiber 10 is reflected by the film 40, and sent back to the fiber 10, thereby performing further amplifying action.

Description

[Detailed description of the invention] Table of contents Overview Industrial field of application Prior art Problems to be solved by the invention Means for solving the problems Implementation Examples Summary of effects of the invention Doped optical fiber doped with rare earth elements Regarding optical fiber amplifiers that directly amplify signal light by inputting signal light and pumping light, we aim to provide an optical fiber amplifier that makes effective use of pumping light, and we have developed a doped optical fiber doped with rare earth elements. In an optical fiber amplifier that directly amplifies signal light by simultaneously inputting pumping light from a pumping light source and simultaneously inputting signal light, a first multiplexer/demultiplexer in the signal light propagation path, one end of which is connected to the pumping light source. A pumping light that is introduced into the doped optical fiber through the first multiplexer/demultiplexer and passes through part or all of the doped optical fiber,
A pumping light reflecting means is provided for returning the pumping light to the doped optical fiber.

Industrial Field of Application The present invention is capable of achieving
This invention relates to an optical fiber amplifier that directly amplifies signal light.

In optical fiber communication systems currently in practical use, repeaters are inserted at regular intervals to compensate for optical signal attenuation due to optical fiber loss. The repeater uses a structure in which the optical signal is converted into an electrical signal by a photodiode, the signal is amplified by an electronic amplifier, the signal is converted into an optical signal by a semiconductor laser, etc., and the signal is sent out again to the optical fiber transmission line. . If this optical signal can be directly amplified as an optical signal with low noise, the optical repeater can be made smaller and more economical.

Therefore, research into optical amplifiers that can directly amplify optical signals is actively underway, and the optical amplifiers that are the subject of research can be roughly divided into optical fibers doped with rare earth elements (ErNb, Yb, etc.) and optical fibers doped with rare earth elements (ErNb, Yb, etc.); A combination of light,
■Using a semiconductor laser doped with rare earth elements, ■
There are three types of amplifiers: stimulated Raman amplifiers that utilize nonlinear effects in optical fibers, and stimulated IJ and IJ Yuan amplifiers.

Among these, the optical amplifier that combines rare earth doped optical fiber (hereinafter referred to as doped optical fiber) and pumping light is characterized by its lack of polarization dependence, low noise, and low coupling loss with the transmission line. It has excellent characteristics,
It is expected that this technology will dramatically increase the transmission relay distance in optical fiber transmission systems and enable the distribution of optical signals to a large number of users.

BACKGROUND OF THE INVENTION FIG. 12 shows the principle of optical amplification using a doped optical fiber. 2 is an optical fiber composed of a core 4 and a cladding 6, and the core 4 is doped with erbium (Er). When pumping light (excitation light) is incident on such an Er-doped optical fiber 2, Er atoms are excited to a high energy level. When the signal light enters the Er atoms in the optical fiber 2 that are excited to a high energy level in this way, the Er atoms transition to a lower energy level, but
At this time, stimulated emission of light occurs, the power of the signal light gradually increases along the optical fiber, and the signal light is amplified.

A schematic diagram of a conventional optical fiber amplifier using such a principle is shown in FIG. The optical fiber amplifier is generally designated by the numeral 8. 10 is a doped optical fiber doped with Er, 12 is an input side optical fiber, and l4 is an output side optical fiber. The input side optical fiber 12 and the doped optical fiber IO are optically coupled using two lenses 16.16, and the doped optical fiber 10 and the output side optical fiber l4 are also optically coupled using two lenses 16.16. combined.

18 is a pumping light source (excitation light source) such as a semiconductor laser (LD) that emits pumping light (excitation light) with a wavelength of 1.48 μm, and the pumping light emitted from the pumping light source 18 is optically coupled via a lens 20. It is coupled to the signal light from the input optical fiber 12 by the optical fiber 12 . By increasing the optical power of the pumping light sufficiently, Er atoms in the doped optical fiber 10 are brought into an excited state, and are stimulated to be emitted by the input of the signal light. Therefore, the optical power of the signal light gradually increases along the doped optical fiber IO, that is, the signal light is amplified and input to the output side optical fiber 14.

In order to perform sufficient optical amplification, a high output power (for example, several hundred meters) is required.
'vV) is required, but if it is difficult to obtain a large output with one pumping light source 18, two pumping light sources 18.'vV) are required, as shown in FIG.
I am trying to use 24.

That is, the pumping light from the pumping light source 24 is transmitted to the pumping light source 18 by the optical coupler 28 via the lens 26.
The pumping light thus coupled is further coupled to the signal light from the input side optical fiber 12 by the optical coupler 22, and the pumping light is coupled to the signal light from the input side optical fiber 12 to the doped optical fiber 10.
It is designed to be incident on .

Problems to be Solved by the Invention As mentioned above, when optical amplification is conventionally performed using a doped optical fiber doped with a rare earth element such as Er, for example, several hundred mW is required.
A pumping light source with a relatively high output is required, and in order to compensate for the lack of output, a plurality of pumping light sources are usually used to input pumping light into the doped optical fiber. For this reason, since the pumping light source such as the LD is made to have a high output, the driving current becomes large, which may impair the reliability of the device. Furthermore, since a plurality of pumping light sources are used, the pumping light incidence mechanism becomes complicated, which is extremely uneconomical. Furthermore, if the output of the pumping light source is small, the length of the doped optical fiber must be increased, for example, to several tens of meters, which poses problems such as the inability to downsize the optical amplifier.

The present invention has been made in view of these points, and an object of the present invention is to provide an optical fiber amplifier that makes effective use of pumping light.

Means for Solving the Problem In an optical fiber amplifier that directly amplifies the signal light by inputting pumping light from a pumping light source and also inputting signal light into a doped optical fiber doped with a rare earth element,
Means for passing a pumping light source or lano pumping light through the doped optical fiber multiple times is provided to achieve this objective.

According to the second aspect of the invention, by inputting pumping light from a pumping light source and simultaneously inputting signal light into a doped optical fiber doped with a rare earth element,
In an optical fiber amplifier that directly amplifies signal light, a first multiplexer/demultiplexer whose one end is connected to the pumping light source is provided in a signal light propagation path including a doped optical fiber. and,
A pumping light reflecting means is provided for returning the pumping light that has been introduced into the doped optical fiber via the first multiplexer/demultiplexer and passed through part or all of the doped optical fiber back to the doped optical fiber.

According to the invention set forth in claim 4, a second multiplexer/demultiplexer for separating the signal light and the pumping light is provided in the signal light propagation path on the opposite side of the first multiplexer/demultiplexer to the doped optical fiber; Second
A pumping light reflecting means is provided on the pumping light output side of the multiplexer/demultiplexer.

According to the invention set forth in claim 6, first and second multiplexers and demultiplexers for multiplexing and demultiplexing the signal light and the pumping light are provided in the signal light propagation path with a doped optical fiber sandwiched between them, and the first and second The multiplexer/demultiplexer is connected with a connecting fiber to form a fiber loop, and a pumping light source is connected to the fiber loop to construct an optical fiber amplifier.

According to the invention as set forth in claim 8, a plurality of signal light propagation paths each including a doped optical fiber are provided, and adjacent signal light propagation paths are connected with a connecting fiber to form a fiber loop. Means for transmitting the signal light and circulating the pumping light within the fiber loop is provided at the connection point between each signal light propagation path and the connecting fiber, and the pumping light source is connected to the fiber loop.

According to the invention described in claim 1, by providing a means for passing the pumping light from the pumping light source through the doped optical fiber once ffl, the pumping light can be used efficiently, and the amplification of the optical fiber amplifier is improved. Increased efficiency.

Further, according to the invention according to claims 2 and 4, in which the pumping light reflection means is provided, the pumping light that has passed once through the doped optical fiber is reflected by the pumping light reflection means and is incident on the doped optical fiber again. Pumping light can be used efficiently, and the amplification efficiency of the optical fiber amplifier is improved.

Furthermore, according to the invention according to claims 6 and 8, in which a fiber loop through which the pumping light circulates is provided in place of the pumping light reflecting means, the pumping light that has passed through the doped optical fiber is incident on the doped optical fiber again by the fiber loop. This allows efficient use of pumping light and improves the amplification efficiency of the optical fiber amplifier.

Improved amplification efficiency makes it possible to lower the output of the pumping light source, improving the economic efficiency and reliability of optical fiber amplifiers. Furthermore, since the amplification efficiency is improved, the length of the doped optical fiber used can be shortened, and the optical fiber amplifier can be made smaller.

Embodiments Hereinafter, embodiments of the present invention will be described in detail based on the drawings. In the description of the embodiments, substantially the same structures or parts will be described with the same reference numerals in all embodiments, and substantially the same structures or parts as the conventional optical fiber amplifier shown in FIGS. 12 and 13. will be explained using the same reference numerals.

FIG. 1 shows a schematic structural diagram of an optical fiber amplifier 30a of a first embodiment. 10 is a doped optical fiber whose core is doped with a rare earth element such as erbium (Er),
Reference numeral 12 denotes an input side optical fiber 14 is an output side optical fiber. The doped optical fiber IO and the output side optical fiber 14 are connected by a connecting portion 32 such as a fusion splice. The input side optical fiber 12 and the doped optical fiber 10 are connected via a reflective film 40.

The connection of the reflective film portion is configured as shown in the enlarged sectional view of FIG. 2, and the reflective film 40 is provided in the ferrule 42 as shown in FIG. are inserted into the ferrule 42 from both sides to connect the input side optical fiber 12 and the doped optical fiber 10 via the reflective film 40, as shown in FIG. The inner diameter of the ferrule 42 is formed to be slightly larger than the outer diameter of the optical fiber, and by inserting the input optical fiber 12 and the doped optical fiber 10, the ferrule 42 aligns both optical fibers 10 and 12 accurately. I try to fix it. The ferrule 42 is made of a material such as ceramic.

The reflective film 44 reflects the wavelength of the pumping light, and the l. 55μ
It has a property of transmitting m-band signal light, and is made of, for example, a dielectric multilayer film.

A fiber fusion type multiplexer/demultiplexer 3 is provided on the output side optical fiber 14.
4 is provided, and one optical fiber 36 of the multiplexer/demultiplexer 34 is connected to a pumping LD 38. An optical isolator 37 is provided on one of the optical fibers 36 of the multiplexer/demultiplexer 34, and the reflected feedback light of the Bonhing light is used as the pumping L D 3 8 1. : Prevents light from entering.

Therefore, the pumping light emitted from the pumping LD 38 (for example, the wavelength of 0.67 μm, 0.98 μm, or 1.5 μm)
48 μm> is incident on the doped optical fiber 10 whose core is doped with Er via the multiplexer/demultiplexer 34. On the other hand, signal light (for example, wavelength 1.55 μm) is transmitted through the input optical fiber 1.
2. The reflective film 40 is ■. Since it has a characteristic of transmitting signal light in the 55 μm band, the signal light passes through the reflective film 40 and enters the doped optical fiber 10.

Er atoms that are in an excited state due to the incidence of the pumping light transition to a lower energy state due to the incidence of the signal light,
At this time, light is stimulated to be emitted.

Therefore, the optical power of the signal light gradually increases along the doped optical fiber 10, that is, the signal light is amplified and input to the output side optical fiber 14. On the other hand, the pumping light that has passed through the doped optical fiber 10 is reflected by the reflective film 40 and sent back into the doped optical fiber 10, thereby achieving further amplification.

FIG. 4 shows an optical fiber amplifier 3 according to a second embodiment of the present invention.
0b shows a schematic diagram of the structure. In the figure, the input side optical fiber 12 and the doped optical fiber 10 are connected by a connecting portion 44 such as a fusion splice. A fiber fusion type multiplexer/demultiplexer 46 similar to the multiplexer/demultiplexer 34 is provided on the input side optical fiber 12.
is provided, and one optical fiber 4 of the multiplexer/demultiplexer 46
A reflective film 50 is provided on the end surface of 8. Reflective film 50
may be a reflective film that reflects only the wavelength of the pumping light, or a total reflective film that reflects all wavelengths.

The rest of the structure of this embodiment is the same as that of the first embodiment shown in FIG.

However, the radiation is emitted from the pumping LD 38 and the multiplexer/demultiplexer 3
The pumping light incident on the doped optical fiber 10 via the input optical fiber 12 is separated from the signal light by the multiplexer/demultiplexer 46 provided near the output end of the input side optical fiber 12.
The light is incident on one optical fiber 48. Since a reflective film 50 is provided at the end of the optical fiber 48, the pumping light is reflected by the reflective film 50 and enters the doped optical fiber 10 via the multiplexer/demultiplexer 46 again. On the other hand, the signal light is
The light enters the input optical fiber 12, passes through the multiplexer/demultiplexer 46, enters the doped optical fiber 1o, is amplified by stimulated emission, and then enters the output optical fiber 14 and propagates through the transmission line.

In FIGS. 1 and 4, the multiplexer/demultiplexer 34 and 46 are placed at the output side optical fiber 14 and the input side optical fiber l2, respectively, but they may also be placed at both ends of the doped optical fiber 10. good.

The embodiments shown in FIGS. 1 and 4 show examples of backward pumping in which the direction of incidence of the pumping light is different from the direction of incidence of the signal light, but forward pumping in which the pumping light enters from the same direction as the signal light The same applies to pumping, which is shown in FIGS. 5 and 6.

Further, the input side optical fiber 12 and the doped optical fiber 10 may be connected using lenses 16 and 16 as shown in FIG. The connection between the output side optical fiber 14 and the doped optical fiber 10 can be similarly configured. Reflective film 5
2 is formed on the end face of the doped optical fiber IO by vapor deposition or the like.

Referring to FIG. 8, a schematic diagram of an optical fiber amplifier 60a according to a sixth embodiment of the present invention is shown. In this embodiment, fiber fusion type multiplexer/demultiplexers 34 and 46 are connected by a connecting optical fiber 62 to form a fiber loop. Pumping light emitted from the pumping LD 38 is coupled to the fiber loop by the optical coupler 64.

To explain the operation of this embodiment, the pumping LD3
The pumping light emitted from the doped optical fiber 10 passes through a fiber fusion type optical coupler 64 and a multiplexer/demultiplexer 34 . On the other hand, the signal light is transmitted through the input side optical fiber 1.
2, passes through the multiplexer/demultiplexer 46, and enters the doped optical fiber 10. Er atoms excited to a higher energy level by the pumping light transition to a lower energy level by the incidence of the signal light, and at this time, light is stimulated to be emitted. Therefore, the optical power of the signal light is
0, it gradually increases in size (is amplified) and enters the output side optical fiber 14.

On the other hand, the pumping light that has passed through the doped optical fiber 10 is separated from the signal light by the multiplexer/demultiplexer 46, propagates through the connecting optical fiber 62, and is transmitted to the pumping LD by the optical coupler 64.
It is combined with the pumping light from 38 and guided to the doped optical fiber IO via the multiplexer/demultiplexer 34. In this way, the pumping light that has been used once is input into the doped optical fiber 10 again through the fiber loop, thereby making it possible to improve the amplification efficiency.

Next, referring to FIG. 9, there is shown a schematic configuration diagram of an optical fiber amplifier 60b according to a seventh embodiment of the present invention. A fiber fusion type multiplexer/demultiplexer 66 is provided on the output side optical fiber 14, and pumping and demultiplexing are performed via the multiplexer/demultiplexer 66. LD38
The pumping light is directly input to the output optical fiber 14. This embodiment is similar to the sixth embodiment shown in FIG. 8 in that the connecting optical fiber 62 forms a fiber loop for pumping light.

With this structure, the backscattered light generated when the pumping light from the pumping LD 3g is input to the doped optical fiber 10 is transferred to the multiplexer/demultiplexer 3 provided in the output side optical fiber l4.
4, and this backscattered light can be carried in the opposite direction by the fiber loop formed by the connecting optical fiber 62 and made to enter the doped optical fiber 10 again.

Referring to FIG. 10, a schematic structural diagram of an optical fiber amplifier 60c according to an eighth embodiment of the present invention is shown. In this embodiment, there are other signal light propagation paths for transmitting signal light in the opposite direction to the signal light propagation path composed of the input side optical fiber 12, the doped optical fiber 10, and the output side optical fiber 14. A structural element is indicated with a (') on the right shoulder. The multiplexer/demultiplexer 46 and the multiplexer/demultiplexer 34' are connected by a first connecting optical fiber 68, and the multiplexer/demultiplexer 34 and the multiplexer/demultiplexer 4
6' are connected by a second connecting optical fiber 70 to form a fiber loop.

The pumping light emitted from the pumping LD 38 is input to the second connecting optical fiber 70 by the optical coupler 64.

In this embodiment, two optical amplification sections each constituted by doped optical fibers 10 and 10' are provided in the fiber loop. Since the pumping light gradually attenuates as it propagates through the fiber loop, in order to make the amplification factors of both amplification sections approximately the same, it is necessary to
It is desirable that the length of the doped optical fiber 10 is longer than the length of the doped optical fiber 10. This embodiment has the advantage that a single pumping LD 38 can perform a plurality of optical amplifications simultaneously by using a fiber loop.

Referring to FIG. 11, a schematic structural diagram of an optical fiber amplifier according to a ninth embodiment of the present invention is shown. In this embodiment, a plurality of signal light propagation paths (five in this embodiment) each consisting of an input optical fiber 12, a doped optical fiber IO, and an output optical fiber 14 are provided, and each signal light propagation path is The optical fibers in the structure are distinguished by symbols ae. Each signal light propagation path is connected by a connecting fiber 72, and a fiber fusion type multiplexer/demultiplexer 74 is provided at each connecting portion. With this configuration, it is possible to construct an optical fiber amplifier in which a plurality of optical amplifying sections are provided in the fiber loop. Pumping light from the pumping LD 38 is input into the fiber loop via the optical coupler 64 and circulates around the fiber loop in the forward direction. Similar to the eighth embodiment described above, the pumping light is gradually attenuated as it propagates through the fiber loop, so in order to make the amplification factors of each amplification section approximately the same, it is necessary to use the doped optical fibers 10a to 10.
It is desirable that the length of e be increased in stages.

Although each of the embodiments described above uses a fiber fusion type multiplexer/demultiplexer, the present invention is not limited to this.
For example, a multiplexer/demultiplexer using a dielectric multilayer film, a wavelength separation coupler, etc. can also be used. Further, in order to input the signal light into the doped optical fiber, it is not necessary to pass through the input-side optical fiber, and the signal light may be input directly from a light source such as an LD module.

Each of the embodiments shown in FIGS. 8 to 10 is an example of backward pumping in which the direction of incidence of the pumping light and the signal light are different. Forward matching the incident direction.
It goes without saying that a similar effect can be obtained in the case of pumping.

Effects of the Invention As described in detail above, the present invention can effectively utilize pumping light, and therefore has the effect of improving amplification efficiency. Improved amplification efficiency makes it possible to lower the output of the pumping light source, and optical amplification is possible with one low-output pumping light source, improving the reliability and economic efficiency of the optical fiber amplifier.

Furthermore, due to the improvement in amplification efficiency, the length of the doped optical fiber used can be shortened as long as the output of the pumping light source is the same, so the size of the optical fiber amplifier can be reduced.

The use of a reflective film and multiplexer/demultiplexer prevents pumping light from leaking into the transmission path, which also has the secondary effect of enabling high-quality optical communications.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the first embodiment of the present invention, and FIG. 2 is a schematic diagram of the first embodiment of the present invention.
FIG. 3 is a perspective view of the ferrule, FIG. 4 is a schematic structure of the second embodiment, FIG. 5 is a schematic structure of the third embodiment, and FIG. 6 is a schematic diagram of the fourth embodiment. FIG. 7 is a schematic diagram of the fifth embodiment; FIG. 8 is a schematic diagram of the sixth embodiment; FIG. 9 is a schematic diagram of the seventh embodiment; FIG. 10 is a schematic diagram of the seventh embodiment. 11 is a schematic diagram of the ninth embodiment; FIG. 12 is a schematic diagram showing the principle of optical amplification using a doped optical fiber; FIG. 13 is a schematic diagram of the conventional example. FIG. 14 is a schematic diagram of another conventional example. 0... Doped optical fiber, 2... Input side optical fiber, 4... Output side optical fiber, 4.34', 46.46'... Multiplexer/demultiplexer, 7... Optical isolator, 8...Pumping LD, 0,50.52...Reflection film, 2...Connection optical fiber, 4...Optical coupler.

Claims (8)

[Claims] (1) Doped optical fiber doped with rare earth elements (10
), the pumping light from the pumping light source (38) is input into the doped optical fiber (10), and the optical fiber amplifier directly amplifies the signal light by inputting the pumping light from the pumping light source (38) and the signal light. An optical fiber amplifier characterized in that it is provided with means for passing the fiber multiple times. (2) Doped optical fiber doped with rare earth elements (10
In an optical fiber amplifier that directly amplifies signal light by inputting pumping light from a pumping light source (38) and signal light into A first multiplexer/demultiplexer (34) connected to the pumping light source (38) is provided, and a doped optical fiber (1) is provided via the first multiplexer/demultiplexer (34).
The pumping light that was introduced into the doped optical fiber (0) and passed through part or all of the doped optical fiber is transferred to the doped optical fiber (1
pumping light reflecting means (40, 50,
52). (3) The pumping light reflecting means (40, 50, 52)
3. The optical fiber amplifier according to claim 2, wherein is a reflective film (40, 52) provided in the signal light propagation path that transmits the signal light and reflects the pumping light. (4) A second multiplexer/demultiplexer (46) that separates the signal light and the pumping light in the signal light propagation path on the opposite side of the first multiplexer/demultiplexer (34) with respect to the doped optical fiber (10). 3. The optical fiber amplifier according to claim 2, further comprising a pumping light reflecting means (50) on the pumping light output side of the second multiplexer/demultiplexer (46). (5) The optical fiber amplifier according to claim 4, wherein the pumping light reflecting means (50) is a reflective film (50) that reflects at least the pumping light. (6) Doped optical fiber doped with rare earth elements (10
) is an optical fiber amplifier that directly amplifies signal light by inputting pumping light from a pumping light source (38) and inputting signal light into the doped optical fiber (10). First and second multiplexers/demultiplexers (34, 46) are provided that multiplex and demultiplex signal light and pumping light with an optical fiber (10) interposed between them, and the first and second multiplexers/demultiplexers (34, 46) are provided. 46) are connected by a connecting fiber (62) to form a fiber loop, and the pumping light source (38) is connected to the fiber loop. (7) A second signal light propagation path including a second doped optical fiber (10') is provided, and a third and third signal light propagation path is provided with the second doped optical fiber (10') interposed therebetween. 4
A multiplexer/demultiplexer (34', 46') is provided, and the second and third multiplexer/demultiplexer (46, 34') is provided instead of directly connecting the first and second multiplexer/demultiplexer (34, 46). First connection fiber (68
), and the first and fourth multiplexer/demultiplexers (34, 46') are connected by a second connecting fiber (70) to form a fiber loop. . (8) In an optical fiber amplifier that directly amplifies signal light by inputting pumping light from a pumping light source (38) and signal light into a doped optical fiber doped with a rare earth element, each of the doped optical fibers (
A plurality of signal light propagation paths including 10a to 10e) are provided, and adjacent signal light propagation paths are connected with a connecting fiber (72) to form a fiber loop, and each signal light propagation path and the connecting fiber (72) are connected. A means (7) for transmitting the signal light to the connection point of the fiber loop and circulating the pumping light within the fiber loop.
4), wherein the pumping light source (38) is connected to a fiber loop.