JPS641763B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for connecting optical fibers with high strength.

Conventionally, as a method for connecting optical fibers, a fusion splicing method using discharge heating has been generally used.

FIG. 1 shows a conventional fusion splicing process of optical fibers by electrical discharge machining. First, as shown in Figure 1a,
The optical fibers 1 from which the coating has been removed are brought into contact with each other at the midpoint of the discharge electrodes 3 with a very small gap between them, and then, as shown in FIG. 1b, the fibers are pushed in and fused together while being discharged. When the connection is completed, cut off the discharge as shown in Figure 1c,
All work is finished. In FIG. 1a, 2 indicates a coated optical fiber, and 4 indicates a discharge region.

When using such a discharge heating method, the discharge form is determined by the electrode shape, the distance between the electrodes, the applied voltage, the discharge current, the atmosphere of the discharge region, etc.
The temperature distribution within the discharge path is also uniquely determined. Usually, in the discharge heating type fusion device used, the maximum width of the discharge path is about 1 mm;
The center of the mm width is above the melting temperature of glass (usually
(approximately 2000°C), the boundary of the discharge path has a temperature gradient from the temperature to the room temperature. With such a sharp temperature gradient in a very small area, the strength of the connection is reduced to normal fiber strength (6 to 6
7Kg), the strength is lower than that of 7Kg, and the maximum breaking strength is about 1Kg.

As described above, the conventional fusion bonding apparatus using discharge heating has the disadvantage that the strength of the connection portion is significantly deteriorated compared to the strength of a normal fiber. The causes are thought to be (i) generation of fracture sources on the surface due to thermal shock or dirt, dust, etc., and (ii) residual stress due to thermal history inside the material.

The present invention focuses CO ₂ laser light in clean gas with a lens to heat the optical fiber and perform fusion splicing, gradually bringing the focusing lens closer to expand the beam spot diameter and fusion splicing. The purpose of this is to improve the strength of the joint by slowly cooling the subsequent fiber. The present invention will be explained in detail below with reference to the drawings.

FIG. 2 is a diagram showing an embodiment of the present invention. Figure 2a
As shown in FIG. 2, the optical fibers are butted together with a slight distance apart in a clean gas, as in the discharge welding method, and as shown in FIG. Once the optical fibers are fused together, the lens 5 is brought closer to the optical fiber 1, and the laser beam spot on the optical fiber 1 is gradually enlarged, as shown in FIGS. 2c and 2d. As a result, the surface temperature of the optical fiber 1 gradually decreases from about 2000° C., which is the melting point of glass. At the same time, the heating area gradually expands. When the size of the beam spot becomes larger and the surface temperature of the optical fiber 1 falls below the transition temperature of glass, the laser beam 6 is stopped and the connection is completed, as shown in FIG. 2e. Note that 7 is a clean gas shield section.

In the embodiment described above, the spot size on the optical fiber 1 was variably adjusted by bringing the lens 5 closer to the optical fiber 1, but the same effect can be achieved by moving the lens 5 away from the optical fiber 1.

In addition, in the method of the present invention, the laser beam can freely move on the axis of the optical fiber 1,
By enlarging the beam diameter while moving the spot position, the heating temperature of the optical fiber 1 can be slowly cooled to increase its strength.

As explained above, the high-strength optical fiber splicing method according to the present invention involves melting and splicing optical fibers in clean gas, and then slowly cooling the temperature of the optical fiber near the splicing point and relaxing the temperature gradient. Since the material is cooled while being cooled, it is possible to prevent the generation of fracture sources due to thermal shock, dust, etc., and it also has the advantage of alleviating internal stress changes in the material and improving its strength.

[Brief explanation of drawings]

Figures 1a, b, and c are diagrams showing the conventional fusion splicing process of optical fibers using discharge heating; Figures 2a, b, and
3c, d, and e are diagrams showing steps of an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Optical fiber with coating removed, 2... Optical fiber with coating, 3... Discharge electrode, 4... Discharge area, 5... Condensing lens, 6... Laser light, 7
...Clean gas shield section.

Claims (1)

[Claims] 1. Two optical fibers arranged in a straight line facing each other are butted together in a clean gas atmosphere, and the optical fibers are irradiated with carbon dioxide laser light focused by a lens from a direction perpendicular to the optical fibers. After melting and bonding the optical fibers, the lens is attached. Furthermore, by moving the spot closer or further away from the optical fiber, the spot size of the laser beam on the optical fiber is variably adjusted, the heating temperature of the optical fiber is gradually lowered, and the lens or optical fiber is moved in a direction parallel to the optical fiber axis. A high-strength connection method for optical fibers, characterized in that the heating range is moved in the axial direction of the optical fibers by moving the heating range.