JPS63257703A - Optical fiber for light guide - Google Patents

Abstract

PURPOSE:To improve light receiving and emitting characteristics of light at an end face and flexibility by using a transparent resin to form a clad enclosing the outside of a core for transmission of light and providing the core having the sectional shape formed of plural pieces of circles which are respectively partly superposed on each other. CONSTITUTION:Parts where the circles are not superposed on each other are supposed to exist in the first quadrant to the fourth quadrant respectively when the sectional shape of the core 1 forming an optical fiber for a light guide is formed of 4 pieces of the circles 11 which are respectively partly superposed on each other. Then, the diameter of the core 1 is maximized at the intermediate of the X-axis and the Y-axis and is minimized in the directions of the X-axis and the Y-axis. The max. diameter of the core 1 in this case is larger than the diameter of the circular core 1 having the same sectional area and the min. diameter of the core 1 is smaller than the diameter of the circular core 1 having the same sectional area. The core 1 having the sectional shape formed by superposing of part of 4 pieces of the circles 11 on each other is, therefore, more bendable in the X-axis direction and the Y-axis direction than the circular core 1 having the same sectional area. The light receiving and emitting characteristics of light at the end face and the flexibility of the optical fiber are thereby simultaneously improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] In optical fibers for light guides, a core with a circular cross section is inferior in flexibility and light/receiving performance at the end face compared to a core with a square cross section having the same cross-sectional area. Therefore, the cross-sectional shape of the core is made close to a rectangular shape to improve flexibility and light-receiving and light-receiving performance at the end face.

[Industrial application field]

The present invention relates to an optical fiber whose core and cladding are made of transparent resin, and particularly to an optical fiber for use as a light guide that transmits light to a remote location.

Optical fibers for light guides are installed, for example, inside the engine room or panel of a car, and are used in applications such as vehicle width indicator lights, direction indicator lights, etc. of a signal light.

It is used as a means to detect when a lamp burns out while the driver is seated. Optical fibers used in such applications are required to have excellent light receiving and emitting properties at their end faces, and also to have excellent flexibility in order to be incorporated into narrow spaces.

[Conventional technology]

FIG. 5 is a perspective view showing a conventional optical fiber.

In the figure, an optical fiber consists of a core 1 that transmits light and a craft 2 that surrounds the outside of the core 1. Optical fibers used for transmitting information in communication systems, etc. are usually made of glass to reduce light loss. However, in order to reduce the cost of optical fibers for light guides, the core 1 and cladding 2 are made of transparent resin. In conventional optical fibers used for light guides, the cross-sectional shape of the core is usually circular, and in fields where particularly excellent flexibility is required, a large number of thin optical fibers are twisted together.

[Problem that the invention seeks to solve]

However, conventional optical fibers that use a core with a circular cross-sectional shape have a thicker cross-sectional area in order to improve the light receiving and emitting properties at the end face (this results in poor flexibility, for example in the engine room or panel of an automobile). It is extremely difficult to use it as a light guide when it is installed in a narrow space such as inside a car.On the other hand, if the diameter of the core is made small to improve flexibility, the light receiving and emitting performance at the end face deteriorates. There was a problem that the difference in brightness could not be detected even if the side of the optical fiber approached an obstacle.In addition, flexibility could be improved by twisting a large number of thin optical fibers together, but the optical fiber manufacturing process In addition, there are gaps between the optical fibers, which limits the ability to receive and emit light, and water can enter through the gaps due to osmotic pressure, causing the lamp to burn out.

[Means for solving problems]

FIG. 1 is a perspective view showing an optical fiber for a light guide according to the present invention. The same objects are represented by the same symbols throughout the plan.

The above-mentioned problem is that the light guide optical fiber has a core 1 that transmits light and a cladding 2 surrounding the core 1 made of transparent resin, and a plurality of circles 11 partially overlap each other. This problem is solved by the optical fiber for light guide of the present invention having a core 1 having a formed cross-sectional shape.

[Effect]

In optical fibers for light guides intended for diffused light, a core with a rectangular cross section has the same cross-sectional area as compared to a core with a circular cross-section because it allows a larger incident and exit angle of light at the end face. This is advantageous in improving the light receiving and emitting properties of the device.

In addition, in FIG. 1, when the cross-sectional shape of the core 1 forming the optical fiber for a light guide is formed by partially overlapping four circles 11, the non-overlapping portions of the circles 11 are from the first quadrant. Assuming there is a fourth quadrant,
The diameter of the core 1 is maximum in the middle between the X-axis and the Y-axis, and is minimum in the X-axis direction and the Y-axis. The maximum diameter of the core 1 in this case is larger than the diameter of a circular core 1 having the same cross-sectional area, and the minimum diameter of the core 1 is smaller than the diameter of a circular core I having the same cross-sectional area. Therefore, the core 1 has a cross-sectional shape formed by partially overlapping each of the four circles 11.
is easier to bend in the X-axis direction and the Y-axis than the circular core 1 having the same cross-sectional area.

In other words, by forming parts of multiple circles overlapping each other, it is possible to change the cross-sectional shape of the core from a circular cross-section to a rectangular cross-section, which improves the light receiving and emitting performance at the end face and the flexibility of the optical fiber. can be improved at the same time.

〔Example〕

Embodiments of the present invention will be described below with reference to the accompanying drawings. Figure 2 is a diagram showing the relationship between cross-sectional shape and bending moment;
The figure shows the relationship between cross-sectional shape and cross-sectional area, and FIG. 4 shows the ratio of bending moment to cross-sectional area.

As shown in FIG. 1, an embodiment of the optical fiber according to the present invention is formed of a core 1 made of polycarbonate resin and a cladding 2 made of a resin whose main component is polymethyl pen-1 or a fluororesin. The cross-sectional shape of 1 is 4
The circles 11 are formed by partially overlapping each other.

When the maximum diameter of the core 1 is D, the diameter of the plurality of circles 11 is d, the bending moment of the core 1 is ■, and the cross-sectional area of the core 1 is S, even if the maximum diameter of the core 1 is constant. When the ratio of the diameter d of the plurality of circles 11 to that changes, the bending moment (2) and the cross-sectional area S of the core 1 also change. These changes can be calculated using mathematical formulas, and FIG. 2 is a diagram showing the relationship between the cross-sectional shape and the bending moment, that is, the change in the bending moment I due to the change in d/D is calculated.

In Fig. 2, the relationship between d/D and bending moment ■ is as follows:
As d/D increases, the bending moment 1 decreases once and reaches a minimum near 0.47. Thereafter, as d/D increases, the bending moment increases again, and reaches its maximum when d/D is 1, that is, when the cross-sectional shape of the core 1 is circular. Note that the region where d/D is 0.5 or less includes both cases where the core 1 is hollow and solid at the center.

Figure 3 is a diagram showing the relationship between cross-sectional shape and cross-sectional area, and shows the relationship between d/
The change in the cross-sectional area S due to the change in D is calculated.

In FIG. 3, the relationship between d/D and cross-sectional area S is such that as d/D increases, cross-sectional area S also increases. However, the rate at which the cross-sectional area S changes is extremely small compared to the rate at which d/D changes.

In order to improve the flexibility of such an optical fiber without reducing the amount of light that can be transmitted, it is necessary to find a cross-sectional shape of the core that minimizes the ratio of bending moment to cross-sectional area S. The diagram showing the ratio of bending moment to cross-sectional area in Figure 4 shows the ratio of bending moment 2 to cross-sectional area S calculated from the change in cross-sectional area S shown in Figure 3 and the change in bending moment ■ shown in Figure 2. When the ratio is minimum,
This is a diagram for determining the ratio of the diameter d of the plurality of circles 11 to the maximum diameter of the core 1, and according to the diagram, d/D is 0.46.
The I/S is minimum in the region of ~0.68.

In this way, the cross-sectional shape of the core 1 is formed by partially overlapping each of the four circles 11, and the ratio of the diameter d of the plurality of circles 11 to the maximum diameter of the core 1 is 0.46 to 0.46.
By selecting a value in the range of 0.68, it is possible to simultaneously improve the light receiving and emitting performance at the end face and the flexibility of the optical fiber, compared to an optical fiber using a core having a circular cross section with a diameter of D. can.

In addition, in optical fibers used for such light guides, by mixing fluorescent dye into the resin constituting the core 1, it is possible to freely select the color tone and improve the brightness at the end face, making it possible to adjust the brightness and darkness of the light in bright places. It is possible to form easily distinguishable optical fibers.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide an optical fiber for a light guide, which has improved light receiving/emitting properties and flexibility at the end face.

[Brief explanation of drawings]

Figure 1 is a perspective view showing the optical fiber for light guide according to the present invention, Figure 2 is a diagram showing the relationship between cross-sectional shape and bending moment, Figure 3 is a diagram showing the relationship between cross-sectional shape and cross-sectional area, and Figure 4 is a diagram showing the relationship between cross-sectional shape and cross-sectional area. The figure is a diagram showing the ratio of bending moment to cross-sectional area, and FIG. 5 is a perspective view showing a conventional optical fiber. In the figure, 1 represents the core, 2 represents the cladding, and 11 represents the circle. cl/D potato 3 same

Claims (1)

[Claims] 1) A light guide optical fiber comprising a core (1) for transmitting light and a cladding (2) surrounding the outside of the core (1) made of transparent resin, comprising: An optical fiber for a light guide, characterized in that the core (1) has a cross-sectional shape formed by partially overlapping circles (11). 2) The optical fiber for a light guide according to claim 1, wherein the ratio of the diameter d of the plurality of circles (11) to the maximum diameter D of the core (1) is 0.46 to 0.68.