JPH04267209A - Optical fiber core - Google Patents

Abstract

PURPOSE:To restrain an optical fiber from being broken or from increasing the loss of transmission even though an optical fiber core is distorted, by covering an optical fiber having beforehand a curvature in the longitudinal direction thereof CONSTITUTION:By changing the condition for drawing work for and the structure of an optical fiber 2, a curvature in a longitudinal direction may be given to the optical fiber 2 in a free condition. For example, the optical fiber 2 is drawn in a drawing furnace with a uniform temperature distribution around the periphery thereof, or a peripheral composition distribution is given to a clad. Thus, obtained optical fiber 2 is formed thereover with a cover 1 by use of a normal method in order to form an optical fiber core. That is, the optical fiber 2 having beforehand a curvature in the longitudinal direction thereof so as to form the optical fiber core which is a straight line like while it is distorted 2 within the cover 1.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated optical fiber formed by coating an optical fiber having a core and a cladding.

0002

2. Description of the Related Art When optical fibers are manufactured, they are usually manufactured with a core portion and a cladding portion that propagate light in a straight state (having no curvature in the longitudinal direction). By the way, some optical fiber cables have bends, such as curled cords. If such a bent cable is manufactured using a coated optical fiber that is straight in its free state, the coated material will cause the optical fiber to have a curvature. In this case, the optical fiber is always in a strained state. On the other hand, as an optical fiber core wire in which an optical fiber is bent, there is one described in Japanese Patent Laid-Open No. 51-20840. The content is to manufacture a coated optical fiber while bending the optical fiber by an external force during the process of applying a coating to a straight optical fiber.

0003

[Problems to be Solved by the Invention] However, conventional bent optical fibers have the following problems. That is, 1) An optical fiber coated wire in which the optical fiber is given a curvature by a coating material and is constantly strained is more likely to break than an optical fiber coated wire without distortion in the optical fiber. 2) Optical fiber core wires manufactured while applying bending to the optical fiber by an external force in the coating process are difficult to manufacture and also have the problem that they are likely to break when bending is applied.

0004

SUMMARY OF THE INVENTION The present invention provides a coated optical fiber that solves the above-mentioned problems, and is characterized by coating an optical fiber that has a pre-curvature in the longitudinal direction.

[0005]

[Operation] By changing the drawing conditions and structure of the optical fiber, it is possible to impart curvature to the free optical fiber along its longitudinal direction. For example, the optical fiber may be drawn in a drawing furnace with a temperature distribution in the circumferential direction, or the cladding may be structured to have a composition distribution in the circumferential direction. The optical fiber thus obtained is coated by a conventional (known) method to produce a coated optical fiber. In this optical fiber core wire, as shown in FIG. 1, the optical fiber 2 is straight in the coating 1 while being distorted. For example, when a curl cord is manufactured using the above-mentioned optical fiber core wire, the strain for forming the curl cord is alleviated by the strain that the optical fiber already has, and the optical fiber becomes difficult to break. Needless to say, in this case, it is desirable that the optical fiber be bent in the same direction and with the same curvature as the curl cord.

[0006]

EXAMPLES The present invention will be explained in detail below based on examples. Example 1. As the optical fiber core wire of this example, an optical fiber manufactured from a preform as shown in FIG. 2 was used. This preform has double cladding layers surrounding a core 11, including an inner cladding layer 12 made of synthetic quartz and an outer cladding layer 13 made of natural quartz, and the inner cladding layer 12 is eccentric from the center. An optical fiber having an outer diameter of 125 μm drawn from this preform was coated with two layers of UV acrylate as a coating layer to obtain an optical fiber core. When the coating layer was removed from the optical fiber core wire produced in this way, the uncoated optical fiber was approximately 1.0 m long.
The radius of curvature was shown. This optical fiber core wire is 20m in diameter.
When the wire was wound into a coil of 500 mm and left for one month, it was inspected for breakage, and the result was 0/10, with no breakage observed. On the other hand, when we similarly examined the presence or absence of breakage for ordinary optical fiber cores whose cladding layer is not eccentric (the radius of curvature of the optical fiber with the cladding layer removed is infinite), the results showed that breakage occurred at a rate of 6/10. was recognized. The optical fiber of this embodiment is suitable for a loose type curled cord. The reason for this is that when the loose type is used, the optical fiber core can be bent in the direction in which it is bent, and the bending stress applied to the optical fiber core is reduced. Example 2. As an optical fiber, a plastic fiber (cladding diameter 1.0 mm) consisting of a core made of polymethyl methacrylate and a cladding layer made of fluoropolymer was produced by spinning. The spinning die was given a curvature, and the plastic fiber was given a curvature with a radius of 60 mm in a free state. This plastic fiber is coated with PVC and has a diameter of 2.2 m.
The optical fiber core wire was made of m. When the optical fiber is stretched in a straight line, the inside of the optical fiber becomes as shown in FIG. This optical fiber was slightly curled due to the preexisting distortion of the optical fiber. This optical fiber core wire was subjected to a bending test and compared with a conventional example in which a straight optical fiber was coated in a free state. For the bending test, a round bar with a diameter of 2.5 mm was used, and the bending radius was 1.25.
The optical fiber was repeatedly bent at a bending angle of 60° in the direction of the curl, and the relationship between the number of bends and the light intensity retention rate (ratio of the amount of light output to the amount of incident light, based on the number of bends of 0) was investigated. The results are shown in Table 1. As can be seen from Table 1, in this example, the light intensity retention rate was
There is almost no decrease in the number of times. Therefore, in this example,
It can be seen that it has superior bending properties compared to the conventional example. The optical fiber core of the present invention can be used not only for optical fiber curl cords, but also for various sensors,
Needless to say, it can also be used for parts.

[0007]

[Table 1]

[0008]

As explained above, according to the present invention, since a coated optical fiber is manufactured by coating an optical fiber that has a curvature in advance in the longitudinal direction, even if the coated optical fiber is strained, This has the excellent effect that the optical fiber is less likely to break and an increase in transmission loss can be suppressed.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a coated optical fiber according to the present invention.

FIG. 2 is a cross-sectional view of one embodiment of an optical fiber used in the optical fiber core according to the present invention.

[Explanation of symbols]

1 Coating 2 Optical fiber 11 Core 12 Inner cladding layer 13 External cladding layer

Claims (1)

[Claims] 1. An optical fiber core wire characterized in that an optical fiber having a curvature in the longitudinal direction is coated.