JPH0843678A - Optical fiber lens and its production - Google Patents

Abstract

PURPOSE:To provide a method for working an optical fiber having a lens structure having a desired radius of curvature at the end face part of the optical fiber with a simple device constitution, a method for producing a lens by using a curable resin particularly at the optical fiber end face and a structure of the optical fiber end. CONSTITUTION:A recessed part 14 is formed at the center of the end face inclusive of the core 13 of the end face 12 of the optical fiber 11 and thereafter, the curing resin 15 which is optically transparect in a use wavelength region is filled into the recessed part until a projecting surface shape projected from the clad end face of the optical fiber is obtd. at the time of producing the optical fiber having a lens effect at its front end. The resin is then cured to form the lens face 16 at the optical fiber end face.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an end structure of an optical fiber suitable for connecting to a light emitting device such as a semiconductor laser and other optical parts, and a manufacturing method thereof.

[0002]

2. Description of the Related Art The coupling of a light emitting element and an optical fiber is indispensable when constructing an optical circuit component. For example, the coupling between the laser diode (LD) and the optical fiber has the structure shown in FIG. In order to effectively introduce the laser light emitted from the laser diode 1 into the core 3 of the optical fiber 2, the optical fiber tip portion 4 is processed into a convex spherical surface having a minute radius of curvature of several μm to several tens μm. It is used as a fiber lens.

A grinding method is generally adopted as a manufacturing method for obtaining an optical fiber lens having such a tip shape. While rotating the optical fiber around the fiber axis and rotating the disk-shaped grinding tool, apply the outer peripheral surface to the end face of the optical fiber and align the grinding tool with the processed shape of the end face of the optical fiber. By moving it, it is processed into a desired shape. Also, as another method,
There is a method in which a curable resin is added to the core portion at the tip of the optical fiber to form a convex shape to have a lens effect. As a method of forming a lens at the fiber tip using resin, in addition to the method of directly adding resin to the end face of the optical fiber, the tip of the optical fiber is immersed in the ultraviolet curable resin layer to A method is considered in which ultraviolet rays are incident from the core at the other end and only the ultraviolet curable resin in the portion emitted from the core at the tip of the optical fiber is cured and molded. When a shape having a lens effect is produced in the optical fiber by using the cured resin as described above, a large-scale device for processing is not required, and an optical fiber having a lens effect at the tip can be simply produced. Is possible.

[0004]

However, in the conventional processing, in the case of mechanical grinding, 3- or 4-axis control is possible in order to move the grinding tool along the curvature of the optical fiber lens to be processed. Requires a complicated stage configuration and a numerical control device for controlling the stage configuration. For this reason, the device configuration becomes large, and at the same time, the processing device for performing highly accurate processing becomes very expensive.

On the other hand, when an optical fiber lens is manufactured using a curable resin, it has an advantage that the above-mentioned large-scale device configuration is not required. However, there is a drawback that it is difficult to control the processing accuracy. When resin is attached to the end face of the optical fiber and cured to form a lens shape, it is difficult to add the resin precisely to the center of the end face of the optical fiber, and therefore the lens principal point is aligned with the optical axis of the optical fiber core. It was difficult to do. Further, in the case of a method of making a lens by immersing the end face of the optical fiber in an ultraviolet curable resin layer and curing only the core part by irradiation of the optical fiber of ultraviolet rays, the lens made on the end face of the optical fiber is It is possible to make it so that the center is on the optical axis, but it is difficult to freely change the pattern of ultraviolet irradiation from the optical fiber core,
It is difficult to control the curvature of the lens surface.

The present invention is intended to solve the above-mentioned problems in the conventional processing method, and is a method for processing an optical fiber having a lens structure having a required radius of curvature at the end face of the optical fiber with a simple device configuration. In particular, it is an object of the present invention to provide a method for producing a lens by using a curable resin on the end face of an optical fiber.

[0007]

In order to solve the above-mentioned problems of the prior art, the present invention prepares an optical fiber having a lens effect at the tip, as shown in FIG. After forming the concave portion 14 at the center of the end surface including the core 13, the concave portion is filled with the optically transparent cured resin 15 in the wavelength range used until it becomes a convex shape protruding from the clad end surface of the optical fiber. The resin is cured to form the lens surface 16 on the end surface of the optical fiber.

[0008]

According to the above means, the recess 13 formed in the center of the end face of the optical fiber serves as a tray for the resin 14 to be filled,
The cured resin can be positioned and fixed without adjusting the position. Therefore, the lens can be accurately and easily formed at the center of the end face of the optical fiber.

[0009]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 shows an embodiment of an optical fiber end structure according to the present invention. In FIG. 1A, the optical fiber 1
A concave portion 14 is formed at the center of the end face of the first end face 12 including the optical fiber core 13. The method of forming the recess can be performed by mechanical grinding or chemical treatment. For example, when chemical treatment is used, when the end face 12 of the optical fiber 11 is dipped in a hydrofluoric acid (HF) solution, the etching rate of the optical fiber in the solution is different between the core portion and the clad portion due to the difference in glass composition, The part is etched faster. Therefore, a concave portion having a circular cross section is formed in the core portion on the end face of the optical fiber. In the case of a single-mode optical fiber, the shape of the recess in the depth direction is substantially rectangular when viewed in a cross section including the optical axis of the optical fiber because the material composition of the fiber core is substantially uniform in the radial direction. If the etching is continued for a longer time, the etching of the clad portion also progresses, so the etching diameter of the optical fiber end surface becomes larger than the core diameter, and the shape in the depth direction is trapezoidal or mortar-shaped as shown in FIG. 1 (b). Become. The size of the recess etching diameter can be easily adjusted by controlling the time for immersing the optical fiber in the solution. Further, the required etching diameter of the recess does not necessarily have to be equal to the core diameter, and there is no problem even if the recess region extends to the cladding portion outside the core portion. The optical fiber end face 1 in which the end face recess 14 is formed in this manner
2 toward the upper surface, the surface shape of the optically transparent cured resin 15, for example, an ultraviolet curable resin, is projected from the clad end surface of the optical fiber in the end surface recess 14 by using a dispenser in the use wavelength region of the optical fiber. The resin is filled until it becomes convex, and then the resin is cured by irradiating ultraviolet rays to form the lens surface 16 on the end surface of the optical fiber. Since the recess 14 for filling the lens-forming resin is previously formed in the optical fiber end face 12, it is necessary to consider the position of resin addition in order to align the center of the lens with the center of the optical fiber end face. Instead, the position of the lens to be formed can be accurately and easily positioned at the center of the end face of the optical fiber simply by filling the end face recess 14 with resin and curing it. The curvature of the convex surface of the lens can be controlled by adjusting the diameter of the concave end surface and the amount of resin to be filled.

When a lens surface is formed on the end surface of the optical fiber using resin, there is a boundary surface between the optical fiber and the lens. In the structure according to the present invention, a boundary surface 17 between the optical fiber end surface concave portion 14 and the convex lens is formed. However, when the refractive index of the lens and the optical fiber core are different, a loss due to Fresnel reflection occurs at the boundary surface. It causes attenuation of light propagating in the fiber. Therefore, in order to reduce the reflection loss, it is necessary to use a resin having a refractive index that is equal to or close to the refractive index of the cured resin for forming the lens as that of the optical fiber core.

FIG. 2 shows another embodiment of the present invention, in which the optical fiber end face concave portion 21 has a curvature and the lens shape after resin filling and curing of the concave portion is convex on both sides. Further lens effects can be expected compared to the conventional structure shown in FIG.

For example, in a GI type optical fiber, the material composition of the core portion is etched with an HF solution because the dopant for adjusting the refractive index has the largest square in the core center and decreases in the radial direction. Then, the etching rate of the optical fiber core becomes faster in the central part than in the peripheral part,
The formed optical fiber end surface concave portion 21 has a spherical shape having a curvature. A lens formed by filling the concave portion 21 with resin and hardening the resin has a double-sided convex lens shape, and the lens effect is further enhanced.

In this case, in order to obtain the double-sided convex lens effect, it is necessary to make the refractive index of the cured resin higher than the refractive index of the optical fiber core. Therefore, reflection loss occurs at the interface between the optical fiber and the lens.Therefore, before the resin is filled, the antireflection film is coated on the concave portion of the end face of the optical fiber to reduce the reflection loss. The process is performed to obtain an optical fiber end structure having a desired lens effect. FIGS. 3A, 3B and 3C show another embodiment of the present invention, which is an example of a structure in which the cross-sectional shape of the optical fiber end face recess 31 is asymmetric with respect to the center of the optical fiber end face. Optical fiber 11
A concave section 31 having a rectangular cross-section is formed in a region including the core 13 on the end surface.
Is formed and the lens surface 16 is manufactured. In this case, the vertical and horizontal lens surfaces of the lens have different curvatures. For example, it can be used for coupling with a light source in which the shape of the emitting beam differs in the horizontal direction and the vertical direction. As described above, by changing the concave shape of the end face of the optical fiber, it becomes possible to manufacture lens surfaces of various shapes without using a large-scale and expensive device.

[0014]

As described above in detail with reference to the embodiments, according to the present invention, when forming a lens shape using a cured resin at the tip of an optical fiber, the position of the resin to be added is adjusted. Can be positioned and fixed without. Therefore, the lens can be accurately and easily formed at the center of the end face of the optical fiber.

[Brief description of drawings]

FIG. 1 is a structural diagram of an optical fiber end portion showing an embodiment of an optical fiber lens according to the present invention.

FIG. 2 is an optical fiber end structure view showing another embodiment of the present invention.

3A and 3B are structural views of an end portion of an optical fiber showing another embodiment of the present invention, in which FIG. 3A is a front view of the end portion of the optical fiber, FIG. 3B is a longitudinal sectional view of FIG. 3A, and FIG. It is a central cross-sectional view of (a).

FIG. 4 is a structural diagram of an end portion of an optical fiber showing a conventional example of a coupling portion between a light source and an optical fiber.

[Explanation of symbols]

1: Laser diode 2,11: Optical fiber 3,13, Optical fiber core 4, Optical fiber tip part 12: Optical fiber end face 14, 21, 31:
Optical fiber end surface concave part 15: Cured resin 16: Lens surface

Claims (4)

[Claims] 1. A concave portion formed in a part including a core of an end face of an optical fiber is filled with an energy ray curable resin which is optically transparent at a wavelength used, and a convex lens surface is formed on the end face of the optical fiber. An optical fiber lens characterized in that. 2. A concave portion is formed in a part including a core of an end face of an optical fiber, and the concave portion is filled with an energy ray curable resin which is optically transparent at a used wavelength to form a convex lens surface. A method for manufacturing an optical fiber lens, which comprises irradiating an energy ray to cure the resin. 3. A concave part is formed in a part including a core of an end face of an optical fiber, and the concave part is filled with an energy ray curing resin which is optically transparent at a wavelength used, to form a convex lens surface. The optical fiber lens according to claim 2, wherein the refractive index of the energy ray curable resin is substantially equal to the refractive index of the core of the optical fiber in the method for producing an optical fiber lens in which the energy beam is irradiated and cured. Manufacturing method. 4. A concave portion is formed in a part including a core of an end face of an optical fiber, and the concave portion is filled with an optically transparent cured resin at a wavelength used to form a convex lens surface. In the method of manufacturing an optical fiber lens that is cured by irradiating a ray, the concave portion is formed into a spherical surface having a curvature, an antireflection layer is formed in the concave portion, and the refractive index is higher than the refractive index of the core of the optical fiber. The method of manufacturing an optical fiber lens according to claim 2, wherein a line-curing resin is filled to form a convex lens surface, and the lens surface is irradiated with an energy ray to be cured.