JPH04295834A - Fiber coupler for optical amplifier - Google Patents

Abstract

PURPOSE:To provide the fiber coupler for optical amplifiers which is suitable for use as the optical amplifier of an optical communication system, has an excellent amplification gain and decreases insertion losses. CONSTITUTION:A fiber 1 for transmission light and a glass optical fiber 2 for pumping light are arranged in parallel and a part 3 thereof is stretched and fused. Erbium is incorporated into the core glass 2a of the glass optical fiber 2 for pumping light. Both of the glass optical fiber 1 for transmission light and the glass optical fiber 2 for pumping light are single-mode fibers and the mode field diameters of the two optical fibers 1 and 2 are preferably the same. The transmission laser beam is amplified in the fused part 3 if the pumping light varying in the wavelength different from the transmission laser beam is made incident on the glass optical fiber 2 for pumping light while the transmission laser beam is made incident on the glass optical fiber 1 for transmission light. The erbium is incorporated into the core glass 2a of the glass optical fiber 2 for pumping light and the fused part 3 at this time and, therefore, the amplification gain increases.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fiber coupler for an optical amplifier in an optical communication system.

0002

[Prior Art] Optical signals propagated through optical fibers in optical communication systems are attenuated due to transmission losses inherent in the fibers.
The S/N ratio is decreasing. Therefore, in order to perform long-distance transmission, it is necessary to amplify the transmitted light using a repeater.

Conventionally, transmission light has been amplified by first converting an optical signal into an electrical signal, amplifying it using an electrical circuit, and then converting it back into an optical signal.

However, this method has its own limitations in relaying multiplex communications that require high speed;
There were problems such as the complexity of the system. As is conventionally known, if an optical amplifier using a fiber laser is used, it is possible to directly amplify the transmitted light without converting it into an electrical signal, thereby solving the above problem. Such an optical amplifier is, for example, two optical fibers that are heated and fused in the middle, one of which is used as an optical fiber for transmission light, and the other one is used as a fiber for pumping light.

[0005] Optical couplers and optical splitters used for combining and distributing laser beams in optical communication systems are disclosed in, for example, Japanese Patent Publication No. 59-26006 and Japanese Patent Publication No. 6.
It is disclosed in Japanese Patent No. 0-51685. These optical couplers and optical splitters are made by heating and fusing multiple optical fibers of the same type, and the optical couplers and optical splitters disclosed therein are
The method for manufacturing an optical splitter can also be applied to fiber couplers for optical amplifiers.

On the other hand, an optical fiber containing a rare earth element, especially erbium, in the core glass and a manufacturing method are disclosed in Japanese Patent Application Laid-Open No. 2-299.
It is disclosed in Japanese Patent No. 3332.

[0007]

SUMMARY OF THE INVENTION In view of the above-mentioned conventional technology, the present invention provides a fiber coupler for an optical amplifier, which is suitable for use as an optical amplifier in an optical communication system, has excellent amplification gain, and has low insertion loss. The purpose is to

[0008]

[Means for Solving the Problems] In order to achieve the above object, the present inventor has focused on the structure of an optical fiber used in a fiber coupler for an optical amplifier, and has conducted various studies. As a result, we found out the following. In order to increase the amplification gain of a fiber coupler for an optical amplifier, it is desirable that the mode field diameter of the glass optical fiber for pumping light be smaller than that of the glass optical fiber for transmission light. However, even if such a structure achieves a large amplification gain, the connection loss increases and the amplification characteristics cannot be fully utilized. Therefore, we conducted further research and studied the elements contained in optical fibers. As a result, when the optical fiber containing erbium in the core glass disclosed in JP-A-2-293332 is used as a fiber for pumping light, the mode field diameter of the optical fiber for transmission light and the optical fiber for pumping light is It was found that the amplification gain can be increased even if the values are the same.

[0009] The optical amplifier fiber to which the present invention, which was made based on the above knowledge, is applied includes a glass optical fiber 1 for transmission light and a glass optical fiber 2 for pumping light, as shown in FIG. 1(C). This is a fiber coupler for an optical amplifier, in which the fibers are arranged in parallel and a portion 3 thereof is stretched and fused, and is characterized in that the core glass 2a of the glass optical fiber 2 for pumping light contains erbium.

It is preferable that both the glass optical fiber 1 for transmission light and the glass optical fiber 2 for pumping light be single mode fibers, and that the mode field diameters of both optical fibers 1 and 2 are the same.

[0011]

[Operation] While inputting the transmission laser light into the glass optical fiber 1 for transmission light of this optical amplifier fiber coupler,
When pump light having a wavelength different from that of the transmitted laser light is input into the glass optical fiber 2 for pumping light, the transmitted laser light is amplified at the fused portion 3 . At this time, since the core glass 2a and the fused portion 3 of the glass optical fiber 2 for pumping light contain erbium, the amplification gain becomes large.

0012

Embodiments Hereinafter, embodiments of the present invention will be explained in detail with reference to the drawings.

FIGS. 1A to 1C are schematic diagrams showing the manufacturing process of a fiber coupler for an optical amplifier according to the present invention.

Glass optical fiber 1 for transmission light shown in FIG.
is a single mode fiber consisting of a core 1a and a cladding 1b. The core 1a is made of Ge-doped quartz glass, has a relative refractive index difference of 0.6%, and has a diameter of 6.2 μm. The cladding 1b is made of quartz glass and has an outer diameter of 125 μm. The glass optical fiber 2 for pumping is also a single mode fiber consisting of a core 2a and a cladding 2b.
The diameters of the core 1a and the cladding 2b are the same as those of the core 1a and the cladding 1b of the glass optical fiber 1 for transmission light. The material of the cladding 2b is the same as the cladding 1b, but the material of the core 2a is basically Ge-doped quartz glass, which is the material of the core 1a, doped with 1000 ppm of erbium, and the relative refractive index difference is 0.8%. be.

As shown in FIG. 1(a), a glass optical fiber 1 for transmission light and a glass optical fiber 2 for pumping are arranged in parallel and in contact with each other, and a clamp 4 is placed at a distance in the center. and fixed at 5.

As shown in (b), a laser light source 7 with a wavelength λ=1.55 μm is placed on one end side of the glass optical fiber 1 for transmission light, and a light amount measuring device 8 is placed on the opposite side. Ru. A light quantity measuring device 9 is also arranged on the glass optical fiber 2 for pumping. Therefore, the laser light emitted from the laser light source 7 passes through the glass optical fiber 1 for transmission light and is measured by the light amount measuring device 8, and also leaks from the glass optical fiber 1 for transmission light to the glass optical fiber 2 for pumping. The light amount is measured by a light amount measuring device 9. In this state, when the central parts of the glass optical fiber 1 for transmission light and the glass optical fiber 2 for pumping which are in contact with each other are heated with flame 6 and the clamps 4 and 5 are pulled in opposite directions, both glass fibers are heated. Optical fibers 1 and 2 are stretched while being fused. Initially, the laser light from the laser light source 7 does not leak from the transmission light glass optical fiber 1 to the pumping glass optical fiber 2, so the light amount measuring device 9 indicates 0. As the fusion stretching progresses, the amount of light detected by the light amount measuring device 8 decreases, and the amount of light detected by the light amount measuring device 9 increases. When the amounts of light detected by both become equal, the pulling by the clamps 4 and 5 is stopped, and the heating by the flame 6 is also stopped, thereby stopping the fusion and stretching.

As shown in (c), the fiber coupler for an optical amplifier can be made in the above-mentioned one step by cutting it with a diamond cutter 10 at the central fused portion 3 and then optically polishing the end face. You get two.

A schematic diagram of the actual use of this optical amplifier fiber coupler is shown in FIG.

As shown in FIG. 2, an optical fiber 11 having the same structure is fusion-spliced to a glass optical fiber 1 for transmission light of a fiber coupler for an optical amplifier, and a glass optical fiber 2 for pumping light is fusion-spliced. Glass optical fiber 1 with the same structure (containing erbium in the core glass)
2 are fusion spliced. In addition, a glass optical fiber 2 for pumping light is attached to the fused part 3 of the optical amplifier fiber coupler.
One end of an intermediate optical fiber 13 (about 100 m long), which has the same structure as above and whose core glass contains erbium, is fusion spliced. Further, at another end of this intermediate optical fiber 13, a fusion spliced portion 3 of another optical amplifier fiber coupler is fusion spliced, and the glass optical fiber 1 for transmission light of the optical amplifier fiber coupler is fusion spliced. An optical fiber 14 having the same structure is fusion spliced to the optical fiber 14.

With the above configuration, while 10 mW of pumping light with a wavelength λ = 1.46 μm is input from the glass optical fiber 12 , transmission light with a wavelength λ = 1.55 μm is input from the optical fiber 11 and output from the optical fiber 14 . The intensity of the transmitted light was measured. As a result, the amplification gain of the transmitted light is 28
It was dB. At this time, the insertion loss due to the optical amplifier fiber coupler is 0, including the loss due to fusion splicing at both ends.
．． The loss was as low as 15 dB.

FIG. 3 shows the structure of another embodiment.

The configuration of this embodiment is such that an optical amplifier fiber coupler and an intermediate optical fiber are integrated. In this configuration, the transmitted light is transmitted to the intermediate portion 16 near the end of the glass optical fiber 15 (same structure as the glass optical fiber 2 for pumping light) containing erbium, which has a length of approximately 100 m including the length of the intermediate portion. The end portions of the glass optical fibers 1 are arranged in parallel so as to be in contact with each other, and the glass optical fibers 1 are fused and drawn in the same manner as in FIG. 1(b). The other configurations are the same as those in FIG.

With the above configuration, while 10 mW of pumping light with a wavelength λ = 1.46 μm is input from the glass optical fiber 12 , transmission light with a wavelength λ = 1.55 μm is input from the optical fiber 11 and output from the optical fiber 14 . The intensity of the transmitted light was measured. As a result, the amplification gain of the transmitted light is 30
It was dB. Since this configuration has fewer connections, the insertion loss due to the fiber coupler for optical amplifiers is further reduced.
It was 0.12 dB.

For comparison, the following experiment was conducted.

An optical fiber coupler was manufactured in the same manner as in the example shown in FIG. 2, except that both optical fiber 1 and optical fiber 2 were single mode optical fibers having the same structure as the communication optical fiber. When optical amplification characteristics similar to those described above were measured using this optical fiber coupler, the amplification was 19 dB with 10 mW of pump light. Insertion loss due to optical fiber couplers includes fusion splicing loss due to increased number of connection points,
It was a large value of 0.45 dB.

[0026]

As described above in detail, the optical amplifier fiber coupler to which the present invention is applied can increase the amplification gain because erbium is contained in the core glass of the glass optical fiber for pumping light. Therefore, even if the mode field diameter of the glass optical fiber for pumping light and the mode field diameter of the glass optical fiber for transmission light are made equal, sufficient amplification can be obtained, and connection loss due to the size of the diameter can be suppressed.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the manufacturing process of a fiber coupler for an optical amplifier to which the present invention is applied.

FIG. 2 is a schematic diagram of an embodiment showing the usage state of a fiber coupler for an optical amplifier to which the present invention is applied.

FIG. 3 is a schematic diagram of another embodiment showing the usage state of a fiber coupler for an optical amplifier to which the present invention is applied.

[Explanation of symbols]

1, 11, and 14 are glass optical fibers for transmission light, 2.1
2, 13, 15 are glass optical fibers for pumping, 3
1 is a fusion part, 4 and 5 are clamps, 6 is a flame, 7 is a laser light source, 8 and 9 are light amount measuring devices, 10 is a diamond cutter, 1a and 2a are cores, and 1b and 2b are claddings.

Claims (2)

[Claims] 1. A fiber coupler for an optical amplifier, in which a glass optical fiber for transmission light and a glass optical fiber for pumping light are arranged in parallel and a part of the fibers are stretched and fused, wherein the glass optical fiber for pumping light is A fiber coupler for an optical amplifier, characterized in that the core glass of the optical fiber contains erbium. 2. The transmission light glass optical fiber and the pumping light glass optical fiber are both single mode fibers, and the mode field diameters of both optical fibers are the same. The fiber coupler for optical amplifiers according to item 1.