JPS6410802B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical fiber bundle, particularly an optical fiber bundle for image transmission.

One of the methods for manufacturing optical fiber bundles for image transmission is the so-called acid elution method.

In this acid elution method, a glass material 1 with a relatively high refractive index is used as a core, and 2 glass materials with a relatively low refractive index are placed around it.
A single fiber 4 with a diameter of 200 to 500 μm is coated with a glass material 3 that is soluble in acids such as hydrochloric acid on its outer periphery.
Cut into appropriate lengths (usually 200 to 300 mm), a large number of such single fibers 4 are arranged in an acid-soluble glass tube 5 as shown in FIG. 2, and heated in an electric furnace 7. , the fused fiber bundle 6 is stretched to a suitable thinness.
Further, the fused fiber bundle 6 is cut to an appropriate length, and both ends thereof are coated with an acid-resistant material.
The flexible optical fiber bundle 8 as shown in FIG. 3 is obtained by immersing it in a 1-2N hydrochloric acid solution to elute the soluble glass in the middle portion.

The optical fiber bundle 8 obtained in this way has the acid-resistant material coating removed, and the ends 9 and 9' where each fiber is fixed together, and the soluble glass eluted and the fibers are separated and made into a plastic. The end portions 9, 9' of the optical fiber bundle 8 include a core portion 11 having a high refractive index for transmitting light, and a core portion 11 having a high refractive index for transmitting light, and a core portion 11 having a high refractive index for transmitting light, and A large number of single optical fibers are made up of a low refractive index glad part 12 that covers the core part 11 and a soluble glass 13 that covers the glad part 12 in order to totally reflect the light transmitted through the core part 11. It is in a bundled state.

Generally, in optical fiber bundles used for endoscopes, etc., the thickness of the soluble glass 13 is 0.5~
1μ, the thickness of the glad part 12 is 1~2μ, the thickness of the core part 1
1 has a diameter of about 7 to 10μ, so the area of the core portion 11, which is the part that actually transmits light, is about 40 to 10μ of the total cross-sectional area.
It is about 50%.

Furthermore, even if the diameter of the optical fiber is reduced in order to improve resolution, the thickness of the soluble glass 13 cannot be reduced to less than 0.5 to 1 μm, and the thickness of the glad portion 12 must be optically 1 to 2 μm. In the end, only the diameter of the core part 11 has to be made thinner, and the area ratio of the core part 11 is further reduced, resulting in a dark optical fiber bundle as a whole.

The present invention has been made in view of this problem, and aims to provide a bright optical fiber bundle in which the ratio of the core area to the total cross-sectional area is large.

Hereinafter, the optical fiber bundle according to the present invention will be explained using the drawings and comparing it with a conventional example.

FIG. 5 shows a double-structured single fiber 16 as a material for realizing the optical fiber bundle according to the present invention.
The single fiber 16 is composed of a core part 14 and a glass part ₁₅ coated on the outer periphery of the core part 14. 15 is made of acid-soluble glass whose main components are B ₂ O ₃ and BaO and whose refractive index is around 1.5.

This double-structured single fiber 16 is filled into an acid-soluble glass tube in exactly the same manner as in the method shown in FIG. By cutting it to an appropriate length, coating both ends with an acid-resistant material, and treating it with an acid, a flexible optical fiber bundle having the same appearance as that shown in FIG. 3 can be obtained.

In the conventional flexible optical fiber bundle, each optical fiber in the flexible portion 10 has a double structure of a core portion 11 and a glad portion 12, as shown in FIG. The light transmitted within the core part 11 made of refractive index glass is totally reflected by the glad part 12 made of low refractive index glass, and the light is transmitted from the input end face to the output end face without leaking to the outside.

However, in the flexible optical fiber bundle manufactured using the double-structured single fiber 16 according to the present invention, each optical fiber 19 in the flexible portion is composed of only the core portion 17. Therefore, the light incident from one end mixes with each other at the point where each optical fiber 19 made of the core part 17 contacts, becomes uniform light as a whole, and is emitted from the other end, resulting in an image. It is still unsuitable for transmission.

Therefore, in the present invention, as shown in FIG. 7, optically non-absorbing fine powder such as glass beads 20 having a refractive index of 1.4 to 1.5 and a diameter of about 1 μ to 2 μ is interposed between each of the optical fibers. This prevents contact between the optical fibers 19 and eliminates the above-mentioned disadvantage.

That is, in the structure shown in FIG. 7, since fine powder such as the glass beads 20 is interposed between the optical fibers 19, they do not come into contact with each other and light does not mix.

Further, even in the part where the optical fiber 19 and fine powder such as glass beads 20 are in contact, the refractive index of the fine powder such as glass beads 20 is the same as that of the optical fiber 19.
Since the refractive index of the optical fiber 19 is lower than that of the optical fiber 19, the light transmitted within the optical fiber 19 is totally reflected and no light mixing occurs.

Further, in the fixing part of the flexible optical fiber bundle according to the present invention, as shown in FIG. 6, the core part 17 is covered with a soluble glass 18 having a low refractive index, so that light mixing does not occur here either.

Note that when a fine powder such as glass beads 20 is interposed between the optical fibers 19 by sprinkling, etc., the remaining spaces between the optical fibers 19 where the fine powder such as the glass beads 20 is not interposed become spaces containing air. There is no optical problem, but glass beads 20
In terms of strength, the fine powder such as the glass beads 20 may damage the optical fiber 19 due to bending etc., and the optical fiber 19 may be easily broken. When interposing fine powder such as, the refractive index is 1.4 ~
It is desirable to fill the space between the optical fibers with silicone oil or the like of about 1.5% as a lubricant.

From the above, in the conventional fixed part of the flexible optical fiber bundle, the thickness of the core part 12 and the soluble glass 13 in FIG.
If the diameter of the core part 11 is 6μ, the area of the core part 11 is only 36% of the total cross-sectional area, but in the fixing part of the flexible optical fiber bundle according to the present invention, the thickness of the soluble glass 18 shown in FIG. If we assume 1μ and the pitch is the same as in Figure 4, the core portion 17 will be 8μ and its area ratio will be
It is 64%, and the core part is 17% smaller than the conventional one.
is approximately doubled, resulting in a very bright optical fiber bundle.

As described above, according to the present invention, it has been possible to obtain an optical fiber bundle for image transmission that is extremely bright compared to conventional ones, and when such an optical fiber bundle is used in an endoscope, etc., it is possible to obtain an extremely easy-to-see observation. Its application range is extremely wide, including optical systems.

[Brief explanation of drawings]

Fig. 1 is a perspective view of a single fiber that is the raw material for a conventional optical fiber bundle, Fig. 2 is an explanatory diagram showing a process of manufacturing an optical fiber bundle, and Fig. 3 is a front view of a conventional optical fiber bundle. FIG. 4 is an enlarged sectional view of a fixing part of a conventional optical fiber bundle, FIG. 5 is a perspective view of a single fiber that is the material of the optical fiber bundle according to the present invention, and FIG. 6 is a fixation of the optical fiber bundle according to the present invention. FIG. 7 is an enlarged cross-sectional view of a flexible portion of the optical fiber bundle according to the present invention. 14, 17...Core part, 15...Glass part, 1
6...Single fiber, 18...Soluble glass, 19...
Optical fiber, 20...Fine powder such as glass beads.

Claims (1)

[Claims] 1. Consists of fixed parts at both ends and a flexible part in the middle, in which optical fibers made of a core part and soluble glass covering the core part are bundled. The soluble glass is treated with an acid to be eluted and removed in the intermediate flexible portion, and the optical fibers each consisting of only a core portion are separated in a flexible manner. An optical fiber bundle characterized in that a fine powder with a low refractive index and no optical absorption is interposed between each optical fiber constituting a flexible portion. 2. The optical fiber bundle according to claim 1, wherein the fine powder is interposed between each optical fiber while being filled with a lubricant having a low refractive index.