JPH1048456A - Optical fiber coupler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high-performance optical fiber coupler which prevents the generation of reflected return light, is not deteriorated in characteristics even in the use over a long period of time, and has a compact structure. SOLUTION: One or more of optical fibers 1, 2 of the optical fiber coupler 10 constituted by holding fusion tapered parts 11 fused with the plural optical fibers 1, 2 by heating and stretching within a housing case 14 are cut within a housing case 14 and the cut sections 2a thereof are covered with a resin coating layer 16 consisting of a resin material having the refractive index approximate to the refractive index of the cores of the optical fibers or a resin material having light absorptivity. The fibers are covered with a cap 17 via gaps 18 formed between the fibers and this resin coating layer 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an optical communication system,
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fusion-stretched optical fiber coupler in an optical transmission technology, and more particularly to an optical fiber coupler having a number of terminals of M × N (M <N).

[0002]

2. Description of the Related Art In recent years, with the progress of optical communication systems and optical transmission technologies, fusion-stretched optical fiber couplers that are easy to manufacture and have high reliability have been used in various fields.

An optical fiber coupler is used as an optical splitter / coupler for splitting or combining light of a single wavelength or a plurality of wavelengths, or as an optical multiplexer / demultiplexer for multiplexing or splitting light of a plurality of wavelengths for each wavelength.

In such an optical fiber coupler, as shown in FIG. 3, a part of the two optical fibers 1 and 2 is heated and drawn to produce a fusion tapered portion 11. Both ends are fixed to the substrate 12 with an adhesive 13, and this is held in a storage case (not shown).
Further, the number of optical fibers is not limited to two, and the optical fiber coupler 10 can be configured with N (N ≧ 2).

The number of terminals of such an optical fiber coupler 10 is usually N × N (N ≧ 2), that is, the number of terminals is the same on both the input side and the output side. However, an M × N (M <N) type optical fiber coupler 10 having an imbalanced number of terminals on both sides may be used as a method of use in the market.

In such a case, unnecessary one or several optical fibers are cut in the storage case. For example, as shown in FIG. 3, one optical fiber 2 can be cut at the cut surface 2a to form a 1 × 2 optical fiber coupler.

[0007]

However, as described above, M × N (M <N) obtained by cutting one or several optical fibers.
In the N) type optical fiber coupler 10, reflected light is generated at the cut surface 2a of the optical fiber due to the difference in the refractive index between the optical fiber and the air layer, and as a result, the return loss increases in the optical fiber coupler. And the directivity increases.

The directivity is defined by the ratio of the power P2 of the light input from the optical fiber 1 to the power P3 of the light output from the optical fiber 2 by reflection at one terminal, as shown in FIG. , Directivity = 10 × log ₁₀ (P3 / P2).

In general, in the case of a 2 × 2 type optical fiber coupler, the return loss is −50 dB or less and the directivity is −60 dB or less, but the antireflection processing is not performed.
In the case of a × 2 type optical fiber coupler, both the return loss and the directivity are as high as −40 dB or more.

[0010] For this reason, there is a problem that the reflection of the optical fiber coupler itself generates return light to a light source such as a semiconductor laser, thereby causing destruction or unstable generation of the light source.

On the other hand, Japanese Patent Application Laid-Open No. 2-264206 proposes that the cut surface 2a of the optical fiber 2 is inclined to prevent return light as shown in FIG. 3, but in this case, the cut surface 2a Is close to the fusion tapered portion 11, so that the impact at the time of cutting is transmitted to the fusion tapered portion 11, which may cause disconnection or deterioration of characteristics.

On the other hand, as shown in FIG. 4, the cut surface 2a of the optical fiber can be provided outside the storage case 14, but in this case, foreign matter such as dust adheres to the cut surface 2a. As a result, there is a possibility that a difference in the refractive index occurs on the cut surface 2a and reflected return light is generated.

[0013]

SUMMARY OF THE INVENTION Accordingly, the present invention provides an optical fiber coupler comprising a plurality of optical fibers fused and heated and drawn to hold a fusion tapered portion in a storage case. Is cut in the vicinity of the fusion tapered portion, and this cut surface is covered with a resin coating layer made of a resin material having a refractive index close to that of the optical fiber core or a light-absorbing resin material. It is characterized in that it is covered with a lid with an air gap or an antireflection resin interposed therebetween.

[0014]

According to the present invention, the cut surface of the optical fiber in the M × N (M <N) type optical fiber coupler is made of a resin material having a refractive index close to that of the core of the optical fiber or a light absorbing resin material. By forming a resin coating layer, there is no adhesion of dust and the like on the cut surface, and light is not reflected on the cut surface and is emitted from a resin material having an approximate refractive index or light-absorbing resin material The reflected light can be prevented from being generated.

Further, since the resin coating layer is covered with the lid with a gap therebetween, it is possible to prevent reflected light from being generated due to foreign substances adhering to the resin coating layer.

Further, since the cut surface of the optical fiber is covered with the lid and disposed in the storage case, the whole can be made compact.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 and 2 show a 1 × 2 type optical fiber coupler 10. This optical fiber coupler 10 heats and stretches two optical fibers 1 and 2 in a part to form a fusion taper portion 11.
And both ends of the tapered portion 11 are bonded and fixed to a substrate 12 with an adhesive 13.
4 is adhered and fixed.

The optical fiber 2 on one side is cut,
A resin material or a light-absorbing resin material having the same or similar refractive index as the core of the optical fiber 2 is applied to the cut surface 2a, and cured to form a coating resin layer 16. further,
The lid 17 is arranged so as to form a gap 18 between the cover resin layer 16 and a sealing material 19 such as silicon is injected and hardened at both ends of the storage case 14.

The optical fiber coupler 10 functions as a 1 × 2 type coupler, and the fusion tapered portion 11
2 and is held in the storage case 14, so that the structure is firmly protected.

The cut surface 2a of the optical fiber 2 is covered with a resin coating layer 16 made of a resin material having a refractive index close to that of the core of the optical fiber or a light absorbing resin material. No foreign matter adheres to the surface, and the light that has reached the cut surface 2a is emitted or absorbed from the resin coating layer 16, so that the generation of reflected light can be prevented. In addition, since the lid 17 is provided around the resin coating layer 16 via the gap 18 serving as an air layer, it is possible to prevent foreign matter from adhering to the resin coating layer 16 and generating reflected light.

Further, if the cut surface 2a is formed at a position sufficiently distant from the fusion tapered portion 11, there is no adverse effect on the fusion tapered portion 11 during cutting. Further, the cut surface 2a
Can be formed in a slope at any angle.

Further, since the cut surface 2a is covered with the lid 17, unnecessary terminals do not come out of the storage case 14, so that the overall structure can be made compact.

In the resin forming the resin coating layer 16,
As the resin having a refractive index close to that of the core of the optical fiber, an epoxy resin can be used in addition to the visible light curable acrylate resin. Here, the refractive index of the core of the optical fiber is 1.47.
It means that the refractive index is in the range of 1.45 to 1.49. This is because if the refractive index is less than 1.45 or exceeds 1.49, reflected return light is likely to be generated due to the difference in refractive index.

Further, of the resin forming the resin coating layer 16,
Black resin may be used as the light absorbing resin,
Specifically, black polycarbonate or ABS resin, polyethylene, tetrafluoroethylene, polypropylene, or the like, or a resin mixed with carbon particles or the like can be used.

Further, the resin coating layer 16 is applied so as to cover the entire surface of the cut surface 2a.
m. If this is less than 1 mm, if foreign matter adheres to this resin coating layer 16,
This is because a part of the foreign matter may reach the cut surface 2a, whereas if it exceeds 2 mm, it is difficult to cure.

In the above example, the lid 17 made separately was used.
However, by covering with the sealing material 19 through the resin coating layer 16 and the space 18, the sealing material 19 can also serve as a lid.

The space 18 may be filled with an anti-reflection resin. Here, as described above, a resin having a refractive index close to that of an optical fiber or a light-absorbing resin is used as the anti-reflection resin.

Further, in the above example, a 1 × 2 type coupler is shown, but M × N (M
An <N) type optical fiber coupler can be used. In this case as well, the above-mentioned resin coating layer may be provided on the cut surfaces of the plurality of optical fibers, and may be covered with a lid with a gap interposed between the resin coating layers.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical fiber coupler 1 according to the present invention shown in FIGS.
0 was produced. The optical fibers 1 and 2 have a core diameter of 10 μm,
A single-mode fiber with a cladding diameter of 125 μm,
A 1.times.2 type optical fiber coupler was formed so that the light having a wavelength of 1.31 .mu.m had a branching ratio of 50:50.

As a comparative example, as shown in FIG.
An optical fiber coupler not subjected to the anti-reflection treatment was prepared.

Using each coupler, a temperature of 75 ° C.,
A high-temperature and high-humidity test was conducted for 14 days under a condition of 90% humidity, and the directivity before and after the test was compared. Note that the directivity is, as shown in FIG. 5, the power P of the light input from the optical fiber 1 at one terminal.
2 and the ratio of the power P3 of the light output from the optical fiber 2 due to reflection is represented by directivity = 10 × log ₁₀ (P3 / P2).

The results are shown in Table 1. From this result, in the comparative example, the value of the directivity was −53.5 dB as the initial value.
And it became even larger by the high temperature and high humidity test. Therefore, it can be seen that a considerable amount of reflection occurs in the comparative example.

On the other hand, in the example of the present invention, the value of the directivity was as low as about -74 dB, and there was almost no change even after the high temperature and high humidity test. Therefore, according to the present invention, it can be seen that the reflection of light is small and the characteristics are not deteriorated even when used for a long time.

[0035]

[Table 1]

[0036]

As described above, according to the present invention, there is provided an optical fiber coupler comprising a plurality of optical fibers fused and heated and drawn to hold a fusion tapered portion in a storage case.
Cutting a part of the optical fiber near the fusion tapered portion,
The cut surface was covered with a resin coating layer made of a resin material or a light-absorbing resin having a refractive index close to that of the core of the optical fiber, and was covered with a lid with a gap interposed between the resin coating layer and the resin coating layer. As a result, it is possible to prevent the generation of reflected return light, to obtain a high-performance optical fiber coupler having a compact structure without deterioration in characteristics even when used for a long time.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an optical fiber coupler of the present invention.

FIG. 2 is a sectional view taken along line XX in FIG.

FIG. 3 is a perspective view showing a main part of a conventional optical fiber coupler.

FIG. 4 is a perspective view showing a conventional optical fiber coupler.

FIG. 5 is a diagram for explaining the directivity of the optical fiber coupler.

[Explanation of symbols]

 1, 2: Optical fiber 2a: Cut surface 10: Optical fiber coupler 11: Fused taper portion 12: Substrate 13: Adhesive 14: Storage case 16: Resin coating layer 17: Lid 18: Void 19: Sealing material

Claims (1)

[Claims] 1. An optical fiber coupler comprising a plurality of optical fibers fused and heated and drawn to hold a fusion tapered portion in a storage case, wherein a part of the optical fiber is cut in the vicinity of the fusion tapered portion. This cut surface is covered with a coating resin layer made of a resin material or a light-absorbing resin material having a refractive index close to that of the core of the optical fiber, and a gap or an antireflection resin is interposed between the resin layer and the coating resin layer. An optical fiber coupler characterized by being covered with a lid body.