JPH01284806A - Erasing method for flaw on surface of optical fiber - Google Patents

Abstract

PURPOSE:To erase a flaw on the surface of an optical fiber without using an acid liquid by allowing an arc discharge to generate between electrodes provided so as to be opposed to each other and melting a surface layer of the optical fiber by its discharge heating. CONSTITUTION:End faces of optical fibers 14, 16 whose covering 13 has been eliminated partially are butted, an arc discharge is allowed to generate between electrodes 11, 12 which have positioned the center line on its butted surface, and the fusion splicing is executed by moving the optical fiber 16 in the direction as indicated with an arrow. In its fusion splicing part 19, the surface of the optical fiber is also heated to a temperature exceeding a melting temperature, therefore, a surface flaw of its part is erased. In that case, as for surface flaws 17', 18' which remain behind on both sides in the longitudinal direction of the connecting part 19, an arc discharge is executed by moving relatively the optical fiber in the longitudinal direction against the electrodes 11, 12, and by melting only the surface layer, the surface flaw is erased. In this case, it is also possible that the erasion of the surface flaw is executed before the fusion splicing.

Description

[Detailed Description of the Invention] Summary This invention relates to an optical fiber surface layer erasing method suitable for erasing the surface layer generated during end face polishing prior to fusion splicing of optical fibers, which erases the optical fiber surface layer without using an acid solution. The present invention aims to provide a method for erasing the surface layer of an optical fiber by melting the surface layer of the optical fiber by an arc discharge generated between electrodes provided facing each other.

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for erasing an optical fiber surface layer, which is suitable for erasing a surface layer generated during end face polishing prior to fusion splicing of an optical fiber.

In the field of optical communication or optical transmission that uses optical fibers as optical transmission lines, it is necessary to optically and mechanically connect optical fibers to each other in order to install optical transmission lines over long distances. The most common practical connection method is fusion, in which optical fibers are coaxially fused, cooled, and integrated to achieve optical and mechanical connections. be done. A fusion splice between optical fibers is required to have as high mechanical strength as possible, provided that optical power loss does not increase there. For example, with regard to tensile strength, the current situation is that the tensile strength of a single mode fiber in the unspliced part (for example, 5 kg) is reduced to, for example, 1 kg in the fusion spliced part, and there is a need for a significant improvement. It is something.

When fusion splicing optical fibers, even if the cut surfaces are fused together as they are, the cut surfaces are brittle fracture surfaces and are not necessarily flat, so bubbles and bends are likely to occur in the fusion splice, making it difficult to maintain good properties. can't get it. For this reason, in the past, the end faces were polished as shown below before fusion splicing.

FIG. 4 is a diagram showing a cross-sectional configuration of a general optical fiber core wire. Optical fiber 3 consisting of core 31 and cladding 32
3 is coated with a primary coating 34, and a secondary coating 35 of nylon or the like is further applied thereon to form an optical fiber having a diameter of, for example, 0.9 mm. The primary coating 34 is formed by applying a polyimide resin with a thickness of 2 to 3 μm or a UV coating with a thickness of 100 to 150 μm immediately after spinning the optical fiber 33. With this configuration, the primary coating 34 is Except when removing the coating 34,
There is almost no possibility that the surface of the optical fiber 33 will be damaged.

When polishing the end face of the optical fiber having the above-mentioned cross-sectional configuration, the following procedure is performed, for example. First, as shown in FIG. 5(a), two coats y! are applied from the end face of the optical fiber 33 to an appropriate length. Remove 35. Next, as shown in FIG. Uniform end face polishing can be performed.

Figure 6 shows the primary coating 3 of the optical fiber core wire whose end face has been polished.
FIG. 4 is a diagram showing a state in which 4 has been removed. A plurality of fine scratches 51 are generated near the polished end surface of the outer peripheral surface of the optical fiber 33. Such scratches occur because polishing powder such as diamond or quartz powder generated during polishing enters between the optical fiber 33 and the primary coating 34 and directly damages the optical fiber 33, or the powder is caused by the chuck member 41.
This is because they enter between the primary coating 34 and the primary coating 34 and damage the optical fiber 33 by penetrating the primary coating 34. Note that a surface layer may be formed not only when polishing the end face but also when removing the coating. When optical fibers with surface layers formed in this way are fusion spliced, some, if not all, of the surface layer remains after the fusion splicing, resulting in a decrease in mechanical strength. There is a need for a method of erasing the surface layer. Recently, there is a belief that the decrease in tensile strength of fusion splices is due to thermal stress.
Although countermeasures seem to have been taken, there is a pressing need to establish a method for erasing the above-mentioned surface layer.

BACKGROUND OF THE INVENTION A conventional method for erasing an optical fiber surface layer is to immerse the portion of the optical fiber where the surface layer is formed in hydrogen fluoride, which is capable of dissolving quartz. The surface layer of the optical fiber is melted, the surface layer becomes less sharp, and stress concentration on the surface layer is alleviated.

Problems to be Solved by the Invention However, the above conventional methods have the following drawbacks.

(b) Hydrogen fluoride is dangerous and therefore requires complicated handling to ensure safety.

(b) In order to completely erase the surface layer, it is necessary to melt the surface layer of the optical fiber deeper than the depth of the scratch, which inevitably reduces the strength due to the decrease in diameter.

The present invention was created in view of these circumstances, and aims to provide a method for erasing the surface layer of an optical fiber without using an acid solution such as hydrogen fluoride.

Means for Solving the Problems FIG. 1 is a diagram showing the principle of the present invention, which was made to solve the above problems.

The first method is to erase the surface layer of the optical fiber 3 by melting the surface layer of the optical fiber 3 by means of an arc discharge generated between the electrodes 1 and 2 provided facing each other.

The second method is to move the optical fiber 3 in its axial direction 4 relative to the electrodes 1 and 2 during an arc discharge that occurs between the electrodes 1 and 2 that are disposed opposite each other. This is a method of erasing the surface layer of the optical fiber 3 by melting the surface layer of the optical fiber 3.

Function: The reason why arc discharge is employed in the method of the present invention is as follows. In other words, arc discharge can obtain a temperature that is sufficiently higher than the melting temperature of the optical fiber, and heating of the optical fiber by arc discharge is due to the inflow of heat at the interface between the gas phase and the optical fiber. Therefore, when the optical fiber is being heated, a temperature gradient occurs in which the temperature decreases from the surface of the optical fiber toward the center of the optical fiber. Therefore, by setting an appropriate discharge time, This is because only the surface layer of the optical fiber can be melted to a desired depth. When the surface layer of the optical fiber is melted, surface tension acts on the melted portion, so that the surface layer is almost completely erased. The reason why only the surface layer of the optical fiber is melted is because if the center of the optical fiber is melted, the entire fiber will be significantly deformed and cannot be used as an optical transmission line.

The reason why the optical fiber is moved relative to the electrode in the second method is as follows. In other words, when the optical fiber is fixed to the electrode, the range in which the surface layer can be erased is limited by the spatial size of the arc discharge, but the optical fiber can be moved at an appropriate speed. This is because by doing so, only the surface layer of the optical fiber can be sequentially melted to a desired depth over a wide range. Comparing the second method of the present invention with the case where arc discharge is performed multiple times in the longitudinal direction of the optical fiber in order to eliminate the limitation on the range in which the surface layer can be erased due to the spatial size of the arc discharge, it is found that heating and cooling The latter is superior in that it can be performed uniformly.

In the second method of the present invention, the optical fiber is moved relative to the electrode in its axial direction. This is because there are cases where it is moved.

Example Embodiments of the present invention will be described below based on the drawings.

FIG. 2 is a process diagram showing a method for erasing the surface layer remaining during fusion splicing of optical fibers after fusion splicing.

First, as shown in FIG. 3A, the end face of the optical fiber 14 from which the coating (primary coating and secondary coating) 13 has been partially removed is placed on the center line of the electrodes 11 and 12 arranged coaxially. This optical fiber 14 is fixedly held at the center between the electrodes 11 and 12 so that Then, the optical fiber 16 from which the coating 15 has been removed and which is to be fusion spliced is supported so as to be movable coaxially with the optical fiber 14. At this time, since the end face of the optical fiber 14.16 has already been polished, the surface layer 17.18 is approximately 1.5 mm thick in the longitudinal direction of the fiber near the end face.
It occurs in the range of mm. In addition, optical fiber 14.16
If the thermal properties (for example, melting temperature) of the fibers are different, the fiber end face on the fixed side is offset from the center line of the electrode 11, 12 and held fixed, so that each fiber is subjected to a different thermal stress. Also good.

Next, as shown in FIG.
6 in the direction of the arrow and polish the end surface of the optical fiber 14.
Perform fusion splicing by bringing it into contact with the polished end surface of the The same figure (C) shows the state after fusion splicing, and since the surface of the optical fiber is also heated to a temperature higher than the melting temperature at the fusion splicing part 19, the surface layer of that part has been erased. It is.

At this time, since the range heated to a temperature higher than the melting temperature of the optical fiber is about 1 mm in the longitudinal direction of the fiber, a surface layer of about 0.5 cm long on both sides of the fusion splice 19 is placed at 17°. , 18' remain.

FIG. 6(6) shows the state when the remaining surface layer 18' is erased. The tips of the electrodes 11 and 12 are connected to the surface layer 18
Either move the electrodes 11.12' in the longitudinal direction of the fiber or move the optical fiber to the electrodes 11.12' so that they are opposite to each other.
After moving in the same direction as the optical fiber 16, an arc discharge is applied to the surface layer 18° to melt only the surface layer of the optical fiber 16 and erase this surface layer. In this case, since the range melted by the arc discharge is longer than the length of the surface layer 18', the surface layer 18'' can be erased with - times of discharge. Can be erased.

For setting discharge conditions such as discharge time and discharge current,
In view of the fact that the depth of the surface layer produced by polishing the end face of an optical fiber is generally about several micrometers, any material that can melt the surface layer at that depth may be used.

FIG. 3 is another embodiment of the present invention, showing a method of scanning the arc discharge in the longitudinal direction of the fiber. Electrode 1
1.12 is fixed and the optical fiber is moved in the direction of the arrow, or the optical fiber is fixed and the electrode 11.1 is moved in the direction of the arrow.
2 in the direction opposite to the arrow, the surface layers 17' and 18' are sequentially and continuously erased. According to this method, even if the surface layer remains over a wide area, it can be easily dealt with by expanding the scanning range of arc discharge. In addition, heating and cooling are not uneven as is the case when arc discharge is performed multiple times, so
There is no risk of mechanical strength decreasing due to residual distortion. Note that the discharge conditions such as the discharge current and the moving speed can be set so that only the surface layer of the optical fiber is melted, as in the previous embodiment.

In the above explanation, the surface layer is erased after fusion splicing the optical fibers, but it is of course possible to perform the surface layer erasing method shown in FIGS. 2 and 3 before fusion splicing. be.

Note that in view of the fact that the melting point of quartz, etc., which is the material of optical fibers, is generally not clear, the term "melting" in this specification includes "softening."

Effects of the Invention As detailed above, according to the present invention, it is possible to provide a method for erasing an optical fiber surface layer without using an acid solution. Furthermore, erasing the surface layer of the optical fiber has the effect of improving the mechanical strength of the fusion spliced portion of the optical fiber.

[Brief explanation of the drawing]

Fig. 1 is a diagram of the principle of the present invention, Fig. 2 is a process diagram of fusion splicing and surface layer erasure showing an embodiment of the present invention, and Fig. 3 is a diagram illustrating another embodiment of the present invention. , Figure 4 is a cross-sectional view of a typical optical fiber core wire, Figure 5 is a diagram for explaining the end face polishing prior to fusion splicing of the optical fiber, and Figure 6 is the surface of the optical fiber produced by end face polishing. FIG. 3 is a diagram for explaining layers. 1.2.11.12... Electrode, 3.14.16... Optical fiber, 17, ITo, 18.18°... Surface layer.

Claims (2)

[Claims] (1) A method of erasing the surface layer of the optical fiber (3) by melting the surface layer of the optical fiber (3) by an arc discharge generated between electrodes (1, 2) provided facing each other. (2) The optical fiber (3) is moved in its axial direction (4
), the surface layer of the optical fiber (3) is melted by moving the surface layer of the optical fiber (3) relative to the electrodes (1, 2), thereby erasing the surface layer of the optical fiber (3).