JPH0933745A - Splicing method for heat-resistant optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a splicing part between a metal-coated optical fiber and a polyimide-coated optical fiber which has a diameter nearly equal to the diameters of other parts, has high connection strength, and displays superior heat resistance. SOLUTION: To connect the heat-resistant optical fiber 11 formed by coating an optical fiber 1 with metal to the resin-coated optical fiber 12 formed by coating an optical fiber 2 with resin, the metal coating layer 3 at an end part of the heat-resistant optical fiber 11 is removed with an etchant and the resin coating layer 4 at an end part of the resin-coated optical fiber 12 is removed with acid; and the exposed end tips of the optical fibers 11 and 12 are made to abut against each other and connected by fusion splicing, and the spliced part is coated with a resin layer 5 again.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for connecting a heat-resistant optical fiber, and more particularly to a method for connecting a resin-coated optical fiber and a metal-coated heat-resistant optical fiber.

[0002]

2. Description of the Related Art An optical fiber is a thin glass fiber, and if microscopic defects occur on the surface, it causes destruction, so
From the viewpoint of surface protection and strength, coating with a resin material or the like is applied over several layers. Polyimide is mentioned as one of the coating materials. Since polyimide has excellent heat stress resistance, it is used as a coating material for optical fibers used at relatively high temperatures. However, a polyimide-coated optical fiber obtained by coating an optical fiber with polyimide cannot be used at a high temperature of 300 ° C. or higher.

On the other hand, a metal-coated optical fiber using a metal material as an outer cover has higher heat resistance than a polyimide-coated optical fiber and can be used even at a high temperature of 300 ° C. or higher. However, there is a drawback that long-distance optical transmission is difficult because of large transmission loss. Further, since the metal-coated optical fiber is expensive, there is a problem that the installation cost becomes high when used for long-distance optical transmission.

The metal-coated optical fiber and the polyimide-coated optical fiber are usually used separately, but in order to reduce the amount of expensive metal-coated optical fiber used, the metal-coated optical fiber and the resin-coated optical fiber are connected via a connector. A method has been proposed in which fibers are connected, a metal-coated optical fiber is used in a high temperature region, and a resin-coated optical fiber is used in other regions.

As a method of connecting optical fibers, the resin is swollen with acetone, the coating is removed by a jig or the like, the fusion is spliced by a fusion machine, and a heat-shrink sleeve is put on the spliced portion to heat-shrink it. A method of reinforcing the connection has been proposed.

[0006]

However, the method of selectively using the metal-coated optical fiber and the resin-coated optical fiber depending on the temperature region can realize low loss and low cost.
Since they are connected by a connector, there are problems that the connection portion becomes large and there is no connector that can be used in a high temperature region. In addition, the method of using the above-described heat-shrinkable sleeve as a connection without using a connector also has a problem that the connection portion becomes large as in the case of the connector and that the heat resistance is poor.

Further, when the optical fiber is inserted into a metal tube of 1.4 mm for FIMT (Fiber In Metal Tube), it is necessary to reduce the outer diameter of the connecting portion of the optical fiber in order to insert it into a thin metal tube. There is. For this reason, the connecting part must have the same diameter as the part other than the connecting part, and at the same time, high strength is required.

[0008]

SUMMARY OF THE INVENTION The present invention provides a method for connecting a heat-resistant optical fiber having an optical fiber coated with a metal and a resin-coated optical fiber having an optical fiber coated with a resin. The metal coating layer at the end of the optical fiber is removed by an etching solution, the resin coating layer at the end of the resin coated optical fiber is removed by acid, and the exposed end of each optical fiber is abutted and fusion spliced. Then
The connection portion is recoated with a resin layer.

Further, polyimide is used as a resin layer for recoating the resin and the connection portion of the resin-coated optical fiber,
Sulfuric acid may be used as the acid.

In the present invention, the reason why the metal and resin coatings are removed with an etching solution and sulfuric acid is to prevent deterioration of the strength of the optical fiber.

Further, the connection is made by fusion splicing is as follows.
This is because the connection part has high strength and high heat resistance.
The reason why the resin layer is re-coated on the connecting portion is to make the outer diameter of the connecting portion substantially the same as that of the portion other than the connecting portion.

Further, a polyimide having the same composition as that of the resin-coated optical fiber may be used as the resin of the resin layer, as long as the polyimide has sufficient heat resistance without adversely affecting the strength of the connection portion during recoating. Other compositions may be used.

[0013]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

First, as shown in FIG. 1A, the outer diameter R =
5μm by plating on 125μm optical fiber 1
The end portion (right side from the dotted line) of the metal-coated optical fiber 11 formed by forming the metal coating 3 having the thickness of 1 is immersed in an etching solution for several tens of minutes and removed. Then, the exposed optical fiber 1 is washed with acetone as shown in FIG.

Next, a polyimide-coated optical fiber 1 obtained by applying a polyimide coating 4 to an optical fiber 2 having an outer diameter of 125 μm.
One end of 2 is immersed in sulfuric acid having a predetermined concentration for a few minutes and removed.
In this case, like the metal-coated optical fiber 11, the length of the portion into which the optical fiber is immersed is set to 5 mm or more. afterwards,
The exposed optical fiber 2 is washed with acetone.

After that, as shown in FIG. 1B, the exposed portions of the optical fibers 1 and 2 (right side from the dotted line) are covered with an optical fiber cutter so that the length L of the coating removal portion becomes 5 mm. (FIG. 1 (c)), and as shown in FIG. 1 (d), the cut surfaces of the optical fibers 1 and 2 are abutted against each other,
The fusion splicing is performed using a fusion bonding machine (not shown).

Next, a polyimide having the same composition as that of the polyimide-coated optical fiber is applied to the connecting portion between the metal-coated optical fiber 11 and the polyimide-coated optical fiber 12 at an appropriate thickness, and then cured by heating. This application and re-coating by heat curing are repeated 5 times to obtain
As shown in (1), the polyimide recoat layer 5 was applied to the connecting portion so that the diameter was almost the same as the other portions, and a connecting portion between the metal-coated optical fiber and the polyimide-coated optical fiber was obtained.

Here, the strength and connection loss of the above-mentioned connecting portion were evaluated.

For the connection loss, 30 samples prepared by the above method were prepared and the connection loss was measured. As shown in FIG. 2, the connection loss is shown in a histogram with the number of samples for each 0.01 dB as the vertical axis. The average was 0.046 dB and the dispersion was 0.024 dB.

The strength of the connection portion was evaluated by the tensile strength. The evaluation was performed both before and after recoating. The connection strength before recoating was an average of 3.18 kgf as shown in the Weibull distribution in FIG. 3, and the connection strength after recoating was an average of 3.12 kgf as shown in the Weibull distribution in FIG. That is, the strength of the connection portion is sufficiently high, and there is no influence of recoating.

Therefore, according to the method of the present invention, a connection portion between the metal-coated optical fiber and the polyimide-coated optical fiber having a low connection loss and a high connection strength can be obtained.

Further, although the number of times of coating is 5 in the above-mentioned embodiment, the number of times of coating is one since the outside diameter of the connecting portion is substantially the same as the outside diameter of the connecting portion in the present invention. It may be appropriately changed depending on the thickness of the application.

Further, since the diameter of the connecting portion is almost the same as that of the other portion, it can be inserted into a metal pipe to form a FIMT.

[0024]

In summary, according to the present invention, it is possible to obtain a connection portion between a metal-coated optical fiber and a resin-coated optical fiber which has high connection strength, low loss, and excellent heat resistance. Further, since the resin layer made of polyimide having substantially the same diameter as that of the portion other than the connection portion is recoated on the connection portion, the FIMT
Is possible.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a method for connecting a metal-coated optical fiber and a polyimide-coated optical fiber according to an embodiment of the present invention.

FIG. 2 is a diagram showing a histogram of connection loss in FIG.

FIG. 3 is a diagram showing connection strength before recoating in FIG.

FIG. 4 is a diagram showing connection strength after recoating in FIG.

[Explanation of symbols]

1, 2 optical fiber 3 metal coating layer 4 polyimide coating layer (resin coating layer) 5 polyimide recoat layer (resin layer) 11 metal coating optical fiber 12 polyimide coating optical fiber (resin coating optical fiber

Claims (2)

[Claims] 1. A method of connecting a heat-resistant optical fiber having a metal coated around the optical fiber and a resin-coated optical fiber having a resin coated around the optical fiber, wherein a metal coating layer at an end of the heat-resistant optical fiber is provided. While removing with an etching solution, the resin coating layer at the end of the resin-coated optical fiber is removed with an acid, and the exposed end of each end of the optical fiber is butt-welded and fusion-bonded to the resin. A method for connecting a heat-resistant optical fiber, characterized in that the layers are recoated. 2. The heat-resistant optical fiber connection method according to claim 1, wherein polyimide is used as a resin layer for re-coating the resin and the connection portion of the resin-coated optical fiber, and sulfuric acid is used as the acid.