JPH07168067A - Optical fiber - Google Patents

Abstract

PURPOSE:To actualize such an optical fiber as being less in double refraction and ease of mounting by adding a specified twist to an optical fiber body or a coated optical fiber body and then applying the coating to it in addition. CONSTITUTION:An optical fiber consists of a core 4 or a part really propagating a light, and a clad being slightly smaller in a refractive index than this core 4. In a single mode fiber, the core and the clad both are widely used with quartz, but since they are breakable if leaving them intact, ultraviolet setting resin is used for protection's sake and primary coating 5 is applied. As this fiber is used after being twisted, further second coating 6 by means of silicone rubber is applied to the fiber added with a required twist rate in advance. This secondary coating 6 performs its role for holding the twist, while it works as absorber to any external force, reducing the extent of double refraction in the fiber. In addition, third coating 7 of metal is applied to this fiber 7 further.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber,
In particular, it relates to an optical fiber having a twist.

[0002]

2. Description of the Related Art Optical fibers are widely used for communication and measurement. A single-mode optical fiber has a chromatic dispersion of 0 when a certain twist is applied, which enables long-distance communication. Further, in a magnetic measuring device using the Faraday effect, birefringence can be reduced by twisting, and it is possible to measure only the Faraday effect. Therefore, twisting a fiber is widely used. The twisting of the twisted fiber is maintained by bonding 3 the connectors 2 on both ends of the fiber 1 and the fiber as shown in FIG.

[0003]

However, the above-mentioned optical fiber has the following problems to be solved. That is, the fiber is twisted to reduce wavelength dispersion and birefringence, but it is necessary to fix the fiber in order to maintain this twist. The fixing of this fiber causes birefringence. Further, the optical fiber is apt to locally bend with a small radius, which also causes birefringence. Further, in mounting, there is a problem that the twisted fiber is entangled and the fiber is broken unless a tensile force is always applied and held.

The present invention has been proposed in order to solve the above-mentioned drawbacks of the prior art, and an object thereof is to realize an optical fiber having a small birefringence and easy to mount.

[0005]

According to the present invention, in an optical fiber in which the optical fiber main body is coated with at least one layer, a predetermined twist is applied to the optical fiber main body or the coated optical fiber main body, and then the optical fiber main body is further coated. It is characterized by

[0006]

According to the optical fiber of the present invention having the above-described structure, since the twist is retained by the coating, the twist is evenly distributed over the entire length of the fiber without applying an excessive force to the connectors attached to both ends of the fiber. Therefore, the birefringence is small. Also, by providing a hard layer of metal or the like on the outside of the fiber, it is possible to remove the local bend having a small radius. Because the twist is retained by the coating, entanglement does not occur without applying tension to the fiber. Therefore, it is possible to realize an optical fiber that has a small birefringence and is easy to mount.

[0007]

FIG. 1 shows an optical fiber according to an embodiment of the present invention. The optical fiber 1 is composed of a core 4 which is a portion that actually propagates light, and a clad 5 having a refractive index slightly smaller than that of the core. In single mode fibers widely used for communication and measurement, quartz is widely used for both the core and the clad. Since it is fragile as it is, the primary coating 5 is applied using a UV effect resin for protection. Although this fiber is used by twisting, a secondary coating 6 of silicone rubber is further applied to the fiber to which a required twist ratio is added in advance. This secondary coating serves to hold the twist and
It acts as an absorber against external force and reduces the birefringence of the fiber. Silicone rubber is optimal as a material that has both softness for absorbing external force and long-term stability. A metallic tertiary fiber 7 is further applied to this fiber. The metal coating should have sufficient hardness to retain the shape of the fiber and flexibility to bend the fiber. This tertiary coating eliminates the risk of local small radius bends in the fiber. In particular, by using a material having a high thermal conductivity such as metal, the temperature distribution of the fiber can be narrowed, and therefore the birefringence caused by the difference in temperature of the fiber part can be reduced.

The optical fiber of another embodiment of the present invention shown in FIG. 2 is coated with two layers. The primary coating 5 is made of a material having a low hardness and the secondary coating 6 is made of a material having a high hardness. It is used. In this way
For example, when a compressive force 8 is applied in the direction of the figure, the secondary coating supports it, and even a slight residual compressive force is not transmitted to the fiber due to the low hardness of the secondary coating, and there is no fear of causing birefringence of the fiber. . This effect is not limited to the two-layer coating, but the hardness of the cladding is a ₀ , and the hardness of the coating is a ₁ , a ₂ , a ₃ from the center of the fiber.
..., a _n , a _m > a _{m + 1} and a _j <a _{j + 1} (j +
If you have layer m), you can get it. That is,
A soft coating layer acting as a cushioning material may be provided on the outer side of the fiber, and a hard coating layer for supporting an external force may be provided further on the outer side thereof.

As described above, the method of using a coating to reduce the amount of birefringent material requires special manufacturing equipment and cannot be easily performed. Therefore, it is also effective to use a heat-shrinkable tube as shown in FIG. After twisting the fiber 1 inserted in the heat-shrinkable tube 10, the heat-shrinkable tube 10
Contract. This alone can hold the twist of the fiber. Further, a plurality of heat-shrinkable tubes having different hardnesses may be prepared to obtain the same effect as in FIG.

[0010]

As described above, according to the present invention, it is possible to assemble a fiber while accurately maintaining the twist, and to realize an optical fiber that reduces birefringence and is easy to mount.

[Brief description of drawings]

FIG. 1 is a cross-sectional configuration diagram of an optical fiber according to an embodiment of the present invention.

FIG. 2 is a sectional configuration diagram of an optical fiber according to another embodiment of the present invention.

FIG. 3 is an exemplary solution diagram of twist formation of an optical fiber according to an embodiment of the present invention.

FIG. 4 is an example solution diagram of conventional twist holding of an optical fiber.

[Explanation of symbols]

 1 ... Optical fiber 2 ... Connector 3 ... Adhesion 4 ... Core 5 ... Clad 6 ... Primary coating 7 ... Secondary coating 8 ... Tertiary coating 9 ... Compressive force 10 ... Heat shrink tube

Claims (4)

[Claims] 1. An optical fiber in which the optical fiber main body is coated with at least one layer or more, and the optical fiber main body or the coated optical fiber main body is further coated after a predetermined twist is applied thereto. 2. The coating comprises two or more layers,
When the hardness of the optical fiber body is a ₀ and the hardness of the coating is a ₁ , a ₂ , ... From the inside in order, a _m > a _{m + 1} and a _j <a _j+1 (j> m) are formed. Claim 1
The described optical fiber. 3. The optical fiber of claim 1, wherein one or more layers of the coating is a flexible metal coating. 4. The optical fiber according to claim 1, wherein the coating is performed using a heat-shrinkable tubular member.