JPS6322564B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for forming a microlens at the end face of an optical fiber in a semiconductor laser and optical fiber coupling module used for optical signal transmission in optical communications and the like.

Conventional configurations and their problems The coupling efficiency of the coupling part between the semiconductor laser and the optical fiber in optical signal transmission systems such as optical communications is one of the most important factors that determines the transmission distance of the transmission system. High coupling efficiency cannot be obtained simply by placing the semiconductor laser and the optical fiber close to each other. In particular, in the case of a single mode optical fiber with a small core diameter, it is only about 10%. Furthermore, if the emitted light from the semiconductor laser is partially reflected by the end face of a nearby optical fiber and returns to the semiconductor laser again, this will cause instability in the oscillation characteristics of the semiconductor laser and an increase in noise.

In order to solve these problems, a lens system is generally inserted between the semiconductor laser and the optical fiber to control the light beam emitted from the semiconductor laser and achieve high coupling efficiency. A method is used in which the surface close to the lens is made a curved surface to prevent reflected light returning to the semiconductor laser as much as possible. Specifically, (1) a method that uses a concentrating Rondo lens or a ball lens 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, and the first stage lens suppresses the spread of the emitted light from the semiconductor laser, and the second stage lens concentrates it and couples it to the 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 the optical fiber.

Conventionally, as shown in FIG. 1, a method for forming a microlens on the end face of an optical fiber involves placing an optical fiber 3 between electrodes 1 and 2 for discharge heating and melting. A quartz rod 4 of about 30 to 50μ is prepared, and after aligning the axes of the optical fiber 3 and the quartz rod 4, a part of the quartz rod 4 is heated and melted by electric discharge between the electrodes 1 and 2, and a part of the quartz rod 4 is attached to the optical fiber 3. It is fused to the end face and subjected to discharge heating again to form a microlens. However, in this method, it is necessary to prepare the quartz rod 4 separately from the optical fiber 3, and in addition, the diameter of the quartz rod 4 is
It is difficult to handle because it is minute, measuring 30 to 50 μm.
Also, when aligning the optical axes of the optical fiber 3 and the quartz rod 4 using the monitor light, it is important to note that when the optical fiber 3 is a single mode fiber, the cosa diameter is approximately 6 to 10 μm.
If the diameter is small, the accuracy of alignment with the quartz rod 4 having a diameter of 30 to 50 μm will decrease.

Purpose of the Invention The present invention provides a semiconductor laser and optical fiber coupling module used for optical signal transmission such as optical communication.
Another object of the present invention is to easily form a microlens at the end face of an optical fiber with good precision and reproducibility in order to improve the coupling efficiency and to minimize the amount of reflection at the end face of the optical fiber returning to the semiconductor laser.

Structure of the Invention The method for forming a microlens on the end face of an optical fiber of the present invention uses the same type of optical fiber as the optical fiber forming the microlens on the end face, and has a structure in which both are opposed between electrodes for electric discharge heating and melting. It is characterized by taking advantage of the characteristic of the fiber, that is, the core layer has a lower melting point than the cladding layer.

DESCRIPTION OF EMBODIMENTS FIG. 2 shows an embodiment of the fiber end face microlens forming method of the present invention. The specific method is shown in Figure 2 and described below.

Figure 2 A; Optical fiber 1 with the end face cut vertically
3 and 14 are opposed between the discharge heating electrode and 2. Here, a light source is attached to one optical fiber,
An optical power meter is connected to the other end, and the positions of the optical fibers 13 and 14 are adjusted so that the amount of light to the optical power meter is maximized. Thereafter, in the next step, when the core layers protrude, a spacing between them is established so that the core layers of the optical fibers 13 and 14 do not come into contact with each other.

Figure 2B: In the case of silica-based optical fibers, the cladding layer is generally made of pure silica glass (silica:
SiO ₂ ), but impurities such as germanium (Ge) or phosphorus (P) are added to SiO ₂ to increase the refractive index of the core layer, and the core layer has a lower melting point. For this reason, discharge heating 15 is performed between the electrodes 1 and 2. When the discharge current is gradually increased, only the core layer melts, and a shape 16 having curvature is obtained due to surface tension.

FIG. 2C: The core layers 16 having the curvature of the end surfaces of the optical fibers 13 and 14 are opposed to each other so as to be in contact with each other on the axis 0 of the discharge electrodes 1 and 2.

FIG. 2D: Discharge heating 17 is performed again with the core layers 16 in contact with each other, and while continuing the discharge heating 17, the optical fibers 13 and 14 are separated.

FIG. 2E: Discharge is stopped when the core layer protrudes like a conical shape 18.

FIG. 2F: When the discharge heating 19 is performed again to melt the conical protruding core portion, a microlens 20 is formed on the end surface of the optical fiber 14 due to surface tension.
is formed. At this time, by adjusting the discharge current and discharge time, a microlens 20 having an arbitrary curvature can be formed on the end face of the optical fiber.

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 fibers of the same type, and since the two fibers are of the same type,
They are easy to handle, have the same core diameter, and can be accurately aligned before melting by electric discharge heating. Further, by controlling the discharge flow and the discharge time, a microlens with an arbitrary curvature can be formed with good reproducibility.

[Brief explanation of the drawing]

FIG. 1 is a front view of a conventional optical fiber end face microlens forming method, and FIGS. 2A to 2F are process front views of an embodiment of the optical fiber end face microlens forming method of the present invention. DESCRIPTION OF SYMBOLS 1, 2... Electrode for discharge heating, 13, 14... Optical fiber, 15... Discharge heating, 16... Core layer protrusion due to discharge heating melting, 18... Conical protrusion of core layer, 208... A microlens formed on the end face of an optical fiber.

Claims (1)

[Claims] 1. Two optical fibers are placed facing each other, and both core layers of the optical fibers are heated and melted using a discharge flow that melts only the core layers of the optical fibers, thereby causing the core protrusions of both fibers to protrude. A method for forming a microlens on an end face of an optical fiber, the method comprising: bringing the two core protrusions into contact with each other, separating the two core protrusions while melting them again with discharge heat, and then melting the protrusions with discharge heat to form a microlens.