JPH0279802A - Optical fiber having microlens and its production - Google Patents

Abstract

PURPOSE:To decrease the return of reflected light without increasing coupling efficiency too much by forming a microlens to a circular conical shape of multiple steps and stepwise changing the angles of inclination of the outer side faces of the respective steps according to the height of the lens. CONSTITUTION:The uppermost outer side face 11 is formed to the angle theta1 of inclination, the next outer side face 12 likewise to theta2 and the lowermost outer side face 13 likewise to theta3 when the microlens 10 is formed to the circular conical shape of 3 steps. The microlens is so constituted as to attain the relation. The reflection at the fiber top can be decreased without impairing the coupling efficiency and misalignment tolerance when the optical fiber is constituted in such a manner. The return light to a light emitting element is decreased in this way and contribution can be made to the stable operation of the light emitting element.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical fiber having a microlens for combination with an optical element and a method for manufacturing the same.

(Prior Art) When coupling an optical element to an optical fiber, the method of forming a microlens at the end of the optical fiber has the advantage of obtaining relatively high coupling efficiency with a simple configuration. ) to (e), the shape of the microlens 1 creates a hemispherical shape (Electr-onics Letter
s, Vol, 18. No, 2. pp71), trapezoidal shape.

Conical shape (APPLIED 0PTICS, Vol, 2
1. No, 19. pp3470-3474). Note that 2 is a cladding and 3 is a core.

[Problem to be solved by the invention]

However, in the case of hemispherical or trapezoidal lenses as shown in Figures 5(a) and (b), the tip of the lens is parallel to the aperture surface of the optical element, so the reflected light from this part does not reach the optical element. For example, in the case of coupling with a light-emitting element, problems such as fluctuations in optical output, changes in spectrum, and deterioration of signal-to-noise ratio have occurred, resulting in unstable operation of the light-emitting element.

On the other hand, if the tip is shaped like a cone with a sharp point as shown in Fig. 5(C), the reflected light will not return to the light emitting element and this problem will be solved.
This has the disadvantage that the amount of deviation of the optical axis (defined by the amount of optical axis deviation that decreases) decreases. This problem is particularly noticeable in coupling single mode optical fibers to semiconductor lasers.

The present invention was made in order to solve the above-mentioned problems, and an object of the present invention is to provide an optical fiber having a microlens that reduces the return of reflected light without significantly reducing the coupling efficiency, and a method for manufacturing the same. do.

(Means for Solving the Problems) An optical fiber having a microlens according to the present invention has the microlens formed in a multi-stage conical shape, and the inclination angle of the outer surface of each stage is adjusted in stages according to the height of the lens. It has been changed.

Further, in the method for manufacturing an optical fiber according to the present invention, a multi-stage conical microlens with a stepwise change in inclination angle is formed by immersing an optical fiber in a plurality of etching solutions having different etching rates for a required period of time. This is how it was done.

(Function) According to the optical fiber of the present invention, reflection at the fiber tip can be reduced without impairing coupling efficiency or axis misalignment tolerance. As a result, the amount of light returning to the light emitting element is reduced, contributing to stable operation of the light emitting element.

Furthermore, according to this manufacturing method, since etching liquids having different etching rates are used, it is possible to manufacture multi-stage conical microlenses in which the inclination angle of the outer surface changes stepwise.

〔Example〕

FIG. 1 is a front view showing an embodiment of the present invention. In this figure, numeral 10 is a microlens, which in this embodiment has a three-stage conical shape. That is, the top outer surface 11 has an inclination angle of θ8, the next outer surface 12 has an inclination angle of θ2, and the bottom outer surface 13 has an inclination angle of θ3. The structure is such that the relationship θ1<θ2×θ3 holds. 2.3 is the fifth
As shown in the figure, it has a cladding and a core.

With this configuration, unlike those shown in FIGS. 5(a) and 5(b), the reflected light does not return to the laser side. Moreover, the coupling efficiency does not decrease drastically as in the case of FIG. 5(C).

Next, a method for manufacturing an optical fiber according to the present invention will be explained. This invention applies the principle that when an optical fiber is immersed in a mixed solution of ammonium fluoride NH4F and butic acid (HF), the cladding 2 and the core 3 have different etching rates. In this method, the etching shape is initially trapezoidal;
After a certain amount of time, it becomes a cone shape. The angle of inclination at this time is determined by the capacity ratio of ammonium butyrate NH4F and butyric acid (HF). FIG. 3 shows an example of the change in the angle of inclination of the lens with respect to the mixing ratio of ammonium butyrate (40%) and butyric acid (50%). As can be seen from this figure, a trapezoidal or conical lens can be formed with any angle of inclination. However, since solutions with a volume ratio of ammonium fluoride of 3 or less are unstable, purified water is added.

FIG. 4 shows the change in the inclination angle θ when purified water is added. As shown in this figure, a stable manufacturing method can be obtained over a wide range.

A method of applying this to create a lens whose angle changes stepwise as in the present invention will be described with reference to FIGS. 2(a) and 2(b). Note that, for the sake of simplicity, the embodiment shown in FIG. 2 shows a case of a two-stage conical shape.

First, it is soaked in a solution of NH4F:HF:H20=3:1:3 for 3 hours to form the upper outer surface 11 shown in FIG. 2(a). This etching time can be determined geometrically based on the etching rate of the cladding 2 and the intended inclination angle θ.

Furthermore, in order to create the outer surface 12 with a large inclination angle θ2, N H4F:HF=
After soaking in the 8:1 solution for 30 minutes, the outer surface 12 of the lower stage is formed, resulting in the two-stage conical lens shown in FIG. 2(b). Multi-stage microlenses of three or more stages can also be formed by similar means.

In this invention, the optical fiber can be applied not only to a single mode type but also to a multimode type, and the optical element can be applied not only to a light emitting element but also to other optical elements.

(Effects of the Invention) In the optical fiber having a microlens of the present invention, the microlens is formed into a multi-stage conical shape, and the inclination angle of the outer surface of each stage is changed in stages according to the height of the lens. Reflection at the fiber tip can be reduced without compromising coupling efficiency or misalignment tolerance.As a result, for example, when coupled with a light emitting device, the amount of light returned to the light emitting device is reduced, stabilizing the optical output and improving the signal-to-noise ratio. Further, improvements in characteristics can be expected when coupling with other optical elements for the same reason.

Further, according to the method of manufacturing an optical fiber having a microlens of the present invention, the optical fiber is immersed in a plurality of etching solutions having different etching rates for a required period of time to form a multi-stage cone whose outer surface has a stepwise change in inclination angle. Since shaped microlenses are formed, an optical fiber having a desired microlens can be obtained very easily, and the degree of freedom in designing the microlens can also be improved.

[Brief explanation of the drawing]

FIG. 1 is a front view showing an embodiment of the present invention, and FIG.
), (b) are diagrams showing the steps of the manufacturing method of the present invention, and the third
The figure shows the change in the tilt angle of the lens with respect to the capacity ratio of ammonium fluoride and hydrofluoric acid, Figure 4 shows the change in the tilt angle when water is added, and Figure 5 shows an example of a conventional microlens.
Figure 5(a). is a hemispherical shape, FIG. 5(b) is a trapezoidal shape, and FIG. 5(C) is a conical shape. In the figure, 2 is a cladding, 3 is a core, and 10 is a microlens. Figure 1 Figure 2 Figure 5 Stone 1-1 Leather 05-1ll $[@G)

Claims (2)

[Claims] (1) In an optical fiber having a microlens at the end,
An optical fiber having a microlens, characterized in that the microlens is formed into a multi-stage conical shape, and the inclination angle of the outer surface of each stage is changed stepwise according to the height of the lens. (2) A microlens characterized by forming a multi-stage conical microlens with a stepwise change in the angle of inclination of the outer surface by immersing an optical fiber in a plurality of etching solutions with different etching rates for a required period of time. A method for manufacturing an optical fiber having the following.