JPS61241710A - Method for forming very small lens at end face of optical fiber - Google Patents

Abstract

PURPOSE:To easily form a very small lens at the end face of an optical fiber and, at the same time, to accurately align the optical fiber, by making it sufficient to prepare two optical fiber of the same kind. CONSTITUTION:A wedge-shaped tapered section 3 is formed at the end section of an optical fiber 1 with an end face 2 perpendicular to its axis and then the end section is heated and melted so that a circular cross section can be formed at the end section. Then a manufactured optical fiber 10 having an elliptical cross section at the end part of its core layer and another optical fiber 11 of the same kind is put between electrodes 6 and 7 for electrospark heating, with the optical fibers 10 and 11 being faced to each other, and electrospark heating 12 is performed. As the discharging current is gradually increased, a projected section 13 of the core having a curved shape is obtained at the end face of each optical fiber 10 and 11. Then the optical fibers 10 and 11 are brought closer to each other so that the projected sections 13 can be contacted with each other on the axis 14 of the electrodes 6 and 7, and the electrospark heating 15 is again performed. While the heating 15 is performed, the optical fibers 10 and 11 are separated from each other and, when the core projected parts 16 have cone-like shapes, the electrosparking heating is stopped. When the electrospark heating 17 is again performed and the cone-shaped core part is melted, a very small lens 18 having an elliptical cross section is formed at the end face of the optical fiber 10 by surface tension.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for forming a microlens on an end face of an optical fiber in a coupling device for a semiconductor laser and an optical fiber used for optical signal transmission such as optical communication.

Conventional technology The coupling efficiency of the coupling part between a semiconductor laser and an optical fiber in an optical signal transmission system such as optical communication is one of the biggest factors that determines the transmission distance of a transmission system. High coupling efficiency cannot be obtained simply by placing the fibers in close proximity.

In the case of a single mode optical fiber with a small core diameter, it is approximately 1
Only about 0% can be obtained. Moreover, if the light emitted from the semiconductor laser is partially reflected by the end face of a nearby optical fiber and returns to the semiconductor laser again, this causes instability of the oscillation characteristics of the semiconductor laser and an increase in noise.

In order to solve these problems, generally a lens system is inserted between the semiconductor laser and the optical fiber, and the light beam emitted from the semiconductor laser? In order to achieve high coupling efficiency through control, method A uses a method in which the surface of the lens close to the semiconductor laser is curved to prevent reflected light from returning to the semiconductor laser. Specifically, (1) a method in which a focusing rod lens or a ball lens is used to focus the emitted light from a semiconductor laser and couple it to an optical fiber. (2) A method in which two or more types of lenses are combined, the first stage lens suppresses the spread of the emitted light from the semiconductor laser, and the second stage lens focuses it and couples it to an optical fiber; (3) A method using a microscopic spherical lens or There is a method in which a cylindrical lens is placed close to or integrated with the end face of an optical fiber.

Conventionally, a method as shown in FIG. 2, for example, has been used to form a microlens on the end face of an optical fiber.

That is, an optical fiber 11 is arranged between electrodes 6 and 7 for discharge heating and melting, and a diameter 3
A quartz rod 19 with a diameter of about 0 to 60 μm is prepared, and after aligning the axes of the optical fiber 11 and the quartz rod 19, a part of the quartz rod 19 is heated and melted by electric discharge between the electrodes 6 and 7, so that a part of the quartz rod 19 is attached to the end surface of the optical fiber 11. The microlens is then fused to the glass and subjected to discharge heating again to form a microlens.

Problems to be Solved by the Invention However, in such a method, it is necessary to prepare the quartz rod 4 separately from the optical 7 eyer 3, and furthermore, the diameter of the quartz rod 4 is as small as 30 to 50 μm. Difficult to handle. In addition, when aligning the optical fiber 3 and the quartz rod 4 using monitor light, if the optical fiber 3 has a small core diameter of several μm, such as a single mode optical fiber, a quartz rod with a diameter of 30 to 60 μm may be used. The accuracy of alignment with

Furthermore, the cross section of the microlens produced by such a method is circular, and when coupling the emitted light from the semiconductor laser, which basically has an elliptical emission distribution, to the optical fiber, the coupling efficiency is limited.

Means for Solving the Problems In order to solve the above problems, the present invention applies a wedge-shaped taper process to the end of an optical fiber along the axis of the optical fiber, and then removes the wedge-shaped taper part. The cross section of the core layer at the end of the υA optical fiber is made into an elliptical shape by heating and melting so that the cross section becomes circular, and the end of this optical fiber is made to face the end of another optical fiber of the same type. Taking advantage of the characteristic of fibers, that is, the core layer has a lower melting point than the surrounding cladding layer, the core layers of both optical fibers are heated to a temperature that melts only the core layers, causing them to protrude, and then By bringing the protruding parts of both cores into contact with each other and separating them while heating and melting them again, by heating and melting the protruding part on the optical fiber side whose core layer has an elliptical cross section,
A microlens with an elliptical cross section is formed on the end face of the optical fiber.

Operation According to the present invention, when forming a microlens on the end face of an optical fiber, it is only necessary to prepare two optical fibers of the same type, and a quartz rod is not required. Therefore, it is easy to handle and alignment can be performed with high precision. Further, the cross section of the microlens can be made into an ellipse that is substantially similar to the ellipse of the emission distribution of the light emitted from the semiconductor laser, and the coupling efficiency can be improved.

Embodiment FIG. 1 shows an embodiment of the method of forming a microlens on the end face of an optical fiber according to the present invention. A specific method will be described below according to FIG.

First, as shown in FIG. 1, a wedge-shaped taper 3 is formed along the axis of the optical fiber 1 at the end of the optical fiber 7, which has an end surface 2 perpendicular to the axis of the optical fiber.

Next, as shown in FIG. 1), the end of the optical fiber 1, which has been tapered into a wedge shape, is heated and melted so that the cross section of the optical fiber becomes circular. As a result, a stress 6 is applied to the optical fiber core portion 4 in the direction of the wedge-shaped taper portions on both sides, and the cross section of the optical fiber core portion 4 becomes an ellipse with its long axis in the direction of the wedge-shaped taper portions. .

Next, as shown in FIG. 1 (q), the core layer end elliptical fiber 1o produced in FIGS. Here, a light source is connected to one optical fiber, and an optical power meter is connected to the other.The positions of optical fibers 1o and 11 are adjusted so that the amount of light to the optical power meter is large. Thereafter, when the core layers protrude in the next step, the opposing distance is set so that the core layers of the optical fibers 10 and 11 do not come into contact with each other.

Next, as shown in Figure 1q, in the case of silica-based optical fibers, the cladding layer is generally made of pure silica glass (silica: 510
2), but the core layer is 5l in order to increase the refractive index.
An impurity such as germanium (Go) or silver (P) is added to O2, and the core layer has a lower melting point. For this reason, when discharge heating 12 is performed between the electrodes 6 and 7 and the discharge stream is gradually increased, there is a region of the discharge stream where only the core layer is melted, and this discharge stream melts only the core layer. death,
A core protrusion 13 having a shape having a curvature due to surface tension is obtained.

Next, as shown in FIG.
The core layer protrusion 13 on the end face of the discharge electrode 6, 7
Place them facing each other so that they are touching at the top.

Next, as shown in FIG. 1(G), in the state shown in FIG. 1(2), discharge heating 15 is performed again, and while continuing discharge heating 16, the optical fibers 1o and 11 are separated.

Next, as shown in FIG. 1, the discharge heating is stopped when the core protrusion 16 protrudes into a conical shape.

Next, as shown in FIG. 1(C), the discharge heating 17 is performed again to melt the conically protruding core portion, and due to surface tension, a microlens 18 with an elliptical cross section is formed on the end surface of the optical fiber 1o. be done.

FIG. 1(I) is a schematic diagram of a microlens 18 with an elliptical cross section formed on the end face of the core layer end elliptical optical fiber 10.

Incidentally, by adjusting the discharge current and discharge time during the formation of the lens, it is possible to form a microlens with an arbitrary curvature on the end face of the optical fiber. In addition, in FIG. 1(c), when processing the wedge-shaped taper 3 at the end of the optical fiber, it is possible to form the end of the core layer with an arbitrary ellipticity by adjusting the size of the taper. Accordingly, it is possible to form an elliptical microlens whose cross section has an arbitrary ellipticity.

Effects of the Invention According to the present invention, when forming a microlens on the end face of an optical fiber, it is only necessary to prepare two optical fibers of the same type, and the handling is easy and the axis alignment can be performed with high precision. I can do it. Further, the optimum curvature of the microlens and the ellipticity of the cross-sectional shape can be arbitrarily set based on the emission distribution of the emitted light from the semiconductor laser, and highly efficient coupling between the semiconductor laser and the optical fiber can be realized.

[Brief explanation of drawings]

Figures 1(c) to 1) are process diagrams for explaining the method of forming a microlens on the end face of an optical fiber in an embodiment of the present invention, and Figure 1(I) shows a microlens formed by the method of this embodiment. FIG. 2 is a schematic perspective view for explaining a conventional method for forming a microlens on an end face of an optical fiber. 3... Wedge-shaped taper, 4... Optical fiber core portion, 6.7... Discharge electrode, 10...
...Core layer end elliptical optical fiber, 11...Optical fiber, 12,15°1γ...Discharge heating, 1
3.16...core protrusion, 14...electrode axis, 18...microlens. Name of agent: Patent attorney Toshio Nakao and 1 other person
1yXJ Yoi 1 Figure Ik 2@

Claims (1)

[Claims] At the end of the optical fiber with a plane perpendicular to the axis of the optical fiber,
After performing a wedge-shaped taper process along the axis of the optical fiber, the wedge-shaped taper portion is heated and melted so that the cross section becomes circular, thereby making the cross section of the core layer at the end of the optical fiber elliptical. Then, the end of the optical fiber and the end of another optical fiber of the same type having a plane perpendicular to the axis of the optical fiber are faced, and both the optical fibers are heated at a temperature such that only the core layer of both optical fibers melts. An optical fiber in which the core layer is heated and melted to protrude, both core protrusions are brought into contact with each other, and both core protrusions are separated while being heated and melted again, and the core layer has an elliptical cross section. A method for forming a microlens on an end face of an optical fiber, characterized in that a microlens having an elliptical cross section is formed on the end face of the optical fiber by heating and melting the protrusion.