JPH05224098A - Optical coupling circuit and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain an optical coupling circuit in which a coupling of a semicon ductor light emitting element and an optical fiber is high efficient and at a low cost. CONSTITUTION:Fiber 2 with a sphere at the tip in which the core part is projected at a hemisphere form on an optical axis of light beam with 1.55mum wavelength outputted from the semiconductor laser 1, is arranged in close vicinity to a semiconductor laser 1. The fiber with a sphere at the tip is a single mode fiber with a 10mum core diameter and a 125mum outer diameter, and the projected length of the hemisphere core is 10mum and the curvature is about 5mum. A dopant concentration in the core decreases in a nearly square distribution against a distance from the center by thermal diffusion during manufacturing of the fiber. Thus when a flat fiber end face is etched with an etching solution whose etching speed is slower, as the dopant concentration is higher, the fiber 2 with a sphere at the tip in which the core part is projected in a hemisphere form is produced at a lower cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical coupling circuit for optical communication for coupling the output light of a semiconductor optical device to an optical fiber and a method for manufacturing the same.

[0002]

2. Description of the Related Art An optical coupling circuit in which an output light of a semiconductor light emitting element which is a signal light source in an optical communication system is coupled to an optical fiber which is an optical transmission line is one of important devices in constructing an optical communication system. Is.

Conventionally, as a high performance coupling circuit, for example, Applied Optics (Applied Optix) is used.
cs) 1980, Volume 19, p2578, using a spherical fiber described in a paper by Mr. Kuwahara. In this optical coupling circuit, a single mode fiber whose incident end is processed into a hemispherical shape is brought close to the emitting end of a semiconductor laser, and the output light from the semiconductor laser is coupled to the single mode fiber.

[0004]

Generally, polishing is used to form the hemispherical portion of the incident end of the front spherical fiber. In this polishing step, since a small incident end portion of the optical fiber is polished, more man-hours are required than in the ordinary flat polishing step. As a result, there is a drawback that the price of the spherical fiber becomes high. Furthermore, in the case of an array-shaped optical coupling circuit that couples a plurality of semiconductor light emitting elements and optical fibers, each of the front spherical fibers is hemispherical in order to make the optical coupling efficiency of each fiber comparable. It is necessary to align the incident ends on the same line. For this reason, in order to manufacture an arrayed front spherical fiber, an arraying process for aligning the incident ends is required in addition to a polishing process for forming a hemisphere, which makes it difficult to price the arrayed front spherical fiber end. There was a big problem.

[0005]

The optical coupling circuit of the present invention comprises:
It is characterized by including a semiconductor optical element and an optical fiber having a hemispherical core on the end face on the side facing the semiconductor optical element. The higher the core dopant concentration of the optical fiber is, the slower the etching rate is. The optical fiber end face is etched with an etching solution, and the core is formed into a hemispherical shape by heating and melting the surface of the etched optical fiber end face.
This simplifies the hemispherical process without requiring a complicated polishing process. In addition, a plurality of end faces of optical fibers that are integrated in parallel are etched with the etching solution, and the plurality of cores are collectively packaged by heating and melting the surface of the end faces of the etched optical fibers. It can be formed in a hemispherical shape, and the step of arranging the incident ends can be eliminated.

[0006]

In general, the refractive index distribution of the core of a single-mode fiber is ideally a step type, so the core dopant concentration is designed to be substantially constant within the core. However, in reality, the dopant in the core is thermally diffused due to thermal diffusion during fiber production, and the dopant concentration distribution has a distribution that decreases as a square distribution with respect to the distance from the center. Therefore, by etching the flat end face of the fiber with an etching solution having a slower etching rate as the dopant concentration is higher, it is possible to manufacture a front spherical fiber in which the core portion protrudes in a hemispherical shape and the other portions are flat. After that, by heating and melting the surface of the etched fiber end face, the roughness on the core surface can be reduced and the aberration of the hemispherical core can be improved. As a result, the efficiency of optical coupling can be improved.
According to the present invention, since the core is hemispherical by etching and only heat treatment is performed, the process is not complicated as in the conventional polishing process, and the cost of the front spherical fiber can be easily reduced. Further, in the case of manufacturing a plurality of front spherical fibers arranged in an array, after arranging the end faces of the optical fibers in an array, the optical fiber incident end faces are collectively polished flat, and then the above-mentioned etching solution is used. By etching the end face of the optical fiber and subjecting it to heat treatment, a plurality of cores can be collectively formed into a hemispherical shape. As described above, the arrayed front-end fibers having uniform tips can be easily manufactured without requiring the step of arranging the incident ends as in the prior art.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing a first embodiment of the present invention. A front spherical fiber 2 having a core portion protruding in a hemisphere on the optical axis of a light beam having a wavelength of 1.55 μm output from the semiconductor laser 1 is arranged close to the semiconductor laser 1. Here, the spherical fiber 2 has a core diameter of 10 μm and an outer diameter of 125 μm.
It is a single mode fiber of m, and the protrusion amount of the hemispherical core is 10 μm, and the radius of curvature of the tip is about 5 μm. The distance between the semiconductor laser 1 and the front spherical fiber 2 is about 10 μm. The semiconductor laser 1 is fixed on the heat sink 3 to emit heat. The etching solution for hemispherically etching the core of the single mode fiber entrance end is 49% hydrofluoric acid (HF) and 40% ammonium fluoride (NH ₄ F) in a weight ratio of 1:10. It is a mixture of so-called warm shock hydrofluoric acid. The etching time for obtaining the core protrusion amount of 10 μm in this embodiment is about 3 hours at room temperature. (Fig. 2
reference). In the present invention, since the method of etching is used as the method of forming the core hemisphere, the core hemisphere can be easily formed without being complicated as in the conventional polishing process. Since the etching time can be shortened by increasing the temperature of the etching solution, it is easy to shorten the above etching time and further increase the work efficiency. Also, the etching solution is not limited to the above-mentioned one, and an etching solution having a slower etching rate as the dopant concentration is higher may be used. For example, the weight ratio of HF and NH ₄ F is changed to 2:10 or 3:10, or nitric acid is added to add nitric acid, HF and N.
For example, the weight ratio of H ₄ F may be 1: 1: 10.
When nitric acid is added, the etched surface becomes smoother.

Next, the etched end surface of the optical fiber is heated and melted by discharging.

The light beam output from the semiconductor laser 1 having the above-mentioned structure is coupled to the hemispherical core. In this embodiment, an optical coupling circuit having a coupling loss of 3 dB and a coupling efficiency as high as the conventional one was obtained.

FIG. 3 is a plan view of a 4-channel array optical coupling circuit showing a second embodiment of this embodiment. The four semiconductor lasers 1a to 1d are fixed in parallel on the heat sink 3 at a pitch of 250 μm and integrated. Further, four spherical fibers 2a to 2d are fixed and integrated in a V groove formed on the surface of the silicon (Si) substrate 4 with a pitch of 250 μm. The V groove is formed by anisotropic etching. The shape and dimensions of the spherical fibers 2a to 2d are the same as those in the first embodiment. In the method of producing the above-mentioned arrayed front spherical fibers 2a to 2d, first, four single-mode fibers are respectively formed on the surface of the silicon substrate by V.
It is arranged and fixed in the groove, and then the incident end face of the single mode fiber is collectively polished flat. After that, the flat incident end face is etched with the etching solution used in the first embodiment,
The core is collectively formed into a hemispherical shape.

Then, the etched end surface of the optical fiber is heated and melted by discharging. In this way, since it is possible to collectively form a plurality of cores on a flat surface with aligned tips into a hemispherical shape, the step of arranging the incident ends unlike the conventional case is required,
It becomes easy to reduce the cost of arrayed spherical fibers.

Now, with the above-mentioned structure, the semiconductor lasers 1a-1a
The light beams output from d are respectively coupled to hemispherical cores. In this embodiment, an array optical coupling circuit having a coupling loss of 3 dB for all four channels and a high efficiency coupling similar to the conventional one was obtained.

As described above, the single mode fiber is used as the front spherical fiber in the two embodiments, but the present invention is not limited to this, and a similar effect can be obtained even with a focused multimode fiber having a focused distribution of core dopant concentration.

Although the heat generated by the discharge is used as the means for heating and melting, the present invention is not limited to this, and it goes without saying that it may be heated and melted in an electric furnace.

Further, in order to improve the light reflection characteristics, a non-reflective coating may be applied on the surface of the hemispherical core.

A semiconductor laser 1 is used as a semiconductor optical device.
However, other semiconductor light emitting elements such as LEDs or semiconductor optical amplifier elements may be used. In this case, the front spherical fiber 2 may be arranged on the input / output side of the semiconductor optical amplifier element.

In the second embodiment, the number of channels is 4
However, the present invention is not limited to this and may be used for four or more channels.

[0018]

As described above, it is possible to obtain an optical coupling circuit in which the semiconductor light emitting element and the optical fiber are highly efficiently coupled and the manufacturing cost is extremely low.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a first embodiment of the present invention.

FIG. 2 is a relationship diagram showing a relationship between an etching time and a core protrusion amount.

FIG. 3 is a plan view showing a second embodiment of the present invention.

[Explanation of symbols]

 1, 1a to 1d Semiconductor laser 2, 2a to 2d Front spherical fiber 3 Heat sink 4 Silicon substrate

Claims (4)

[Claims] 1. An optical coupling circuit comprising: a semiconductor optical element; and an optical fiber having a hemispherical core on the end face facing the semiconductor optical element. 2. A step of etching the end face of the optical fiber with an etching solution having a slower etching rate as the core dopant concentration of the optical fiber is higher, and a step of heating and melting the surface of the end face of the optical fiber etched. Method for manufacturing optical coupling circuit. 3. The array optical coupling circuit according to claim 1, wherein a plurality of semiconductor optical devices and a plurality of the optical fibers are integrated in parallel. 4. An end face of a plurality of optical fibers integrated in parallel is etched with an etching solution having a slower etching rate as the core dopant concentration is higher, and the surface of the etched end face of the optical fiber is heated and melted. A method of manufacturing an array optical coupling circuit, wherein the plurality of cores are collectively formed into a hemispherical shape.