JPS63301909A - Optical fiber - Google Patents

Abstract

PURPOSE:To scatter and attenuate a light beam of a clad mode so that it is not transmitted nor recurs, by providing a light scattering layer consisting of fine powder of a light scattering material between a first buffer layer and a second buffer layer which have covered the surface of an optical fiber. CONSTITUTION:Between the first buffer layer 2 and the second buffer layer 3 which have covered the surface of an optical fiber 1, a light scattering layer 5 consisting of fine powder of a light scattering material is provided. A clad mode is induced to the first buffer layer, 2 but since the light scattering layer 5 has been formed in a part to be reflected and propagated to the second buffer layer 3, as for this propagation light, the propagation direction scattered in the indiscriminate direction by fine powder comes not to be constant, and as result, said light is attenuated or annihilated. In such a way, even a short size of several meters, an optical fiber of a high quality which can execute an attenuation so that the clad mode can be disregarded is obtained.

Description

[Detailed Description of the Invention] [Summary] An optical fiber core used for optical transmission, in which a light scattering layer made of fine powder of a light scattering material is provided between a first buffer layer and a second buffer layer. Accordingly, the cladding mode light is emitted to the first buffer layer and reflected by the second buffer layer, which is attenuated by scattering, and is prevented from being transmitted and returned.

[Industrial application field]

The present invention relates to a coated optical fiber used for optical transmission, and more particularly to a coating structure for an optical fiber.

The light propagation mode (cladding mode) in the cladding of the optical fiber used for optical transmission and the light propagating in the buffer layer provided on the outer periphery attenuate and disappear while propagating over a long distance and do not pose a problem. For example, in the case of a short optical fiber cable that connects an optical measuring device or the like that is only a few meters away, the attenuation of the cladding mode and the light propagating in the buffer layer is small and does not disappear.

For this reason, there is a demand for high-quality optical fiber cores in which light propagating outside the core can be ignored even in short optical fibers.

[Conventional technology]

Conventionally, as shown in the cross-sectional view of FIG.
In order to prevent damage to the surface of 1 and stabilize the optical transmission characteristics,
A first buffer layer 12 and a second buffer layer 1 are provided on the surface of the optical fiber 11.
3 is applied, and a mantle coating 14 is further applied.

The first buffer layer 12 is made of silicone rubber with a refractive index of 1.5, which is higher than the cladding of the optical fiber 11, the second buffer layer 13 is made of silicone rubber with a refractive index of 1.4, and the outer covering 14 is made of nylon. It is used.

Here, the first buffer layer induces the cladding propagating light to
The second buffer layer is physically stable and protects the first buffer layer, and acts to confine the propagating light within the first buffer layer. This is based on the mutual refractive index difference.

[Problem that the invention seeks to solve]

However, according to the above-mentioned structure, for example, in a short optical fiber core of several meters used in an optical measurement device, the cladding mode is induced to the first buffer layer having a higher refractive index, and the cladding mode propagates. However, the light that is induced into the first buffer layer and propagates is reflected at the interface with the second buffer layer, which has a lower refractive index, and the light propagates inside the first buffer layer. Some of the light propagates and some of the light returns to the cladding.

As described above, at the output end of the optical fiber, the amount of light in the cladding mode changes due to the curvature of the optical fiber, which causes variations in the total amount of light including the core transmitted light, that is, the optical transmission power, making accurate characteristic evaluation difficult. The problem was that it couldn't be done.

The present invention provides a coated optical fiber for solving the above problems.

[Means for solving problems]

The above problems in the conventional structure can be solved by providing a light scattering layer made of fine powder of a light scattering material between the first buffer layer and the second buffer layer coated on the surface of the optical fiber.

[Effect]

The fine powder of the light scattering material provided on the surface of the first buffer layer forms a layer with unevenness, and can scatter and attenuate light propagating within the first buffer layer over a short distance.

〔Example〕

The gist of the present invention will be specifically explained below with reference to an embodiment shown in the drawings.

As shown in the cross-sectional view of Figure 1, the optical fiber core 1
A first coated fiber with an outer diameter of about 200 μm was directly coated on the surface of an optical fiber 1 with a diameter of 50 μm and a cladding lb with a diameter of 125 μm.
A buffer layer 2, that is, a silicon rubber surface with a high refractive index of 1.5, is coated with a fine powder having light scattering properties, such as glass or metal oxide (T+Oz,
On this light scattering layer 5, a second buffer layer 3, that is, a low refractive index 1.
4 is coated with silicone rubber to give an outer diameter of approximately 360 μm, and finally, a mantle coat 4, that is, nylon is coated.

In the optical fiber having the above structure, the cladding mode is induced into the first buffer layer 2 as in the conventional case, but the light scattering layer 5 is formed in the portion where the cladding mode should be reflected and propagated to the J second buffer layer 3. As a result, this propagating light is scattered in indiscriminate directions by the fine powder and the propagation direction is no longer constant, resulting in attenuation or extinction. Furthermore, some light escapes into the second buffer layer.

Due to this rapid attenuation, the propagating light in the cladding is reduced over a short distance.

As a result of measuring the cladding mode of this optical fiber,
It has been confirmed that the cladding mode is attenuated by scattering over a short distance of about 1 m, and there is an effect of attenuating the cladding mode.Moreover, the tensile strength shows a sufficient effect due to the extremely thin light scattering layer, which is comparable to that of conventional optical fiber cores. It was found that there was almost no inferiority compared to the .

In addition, it has been proposed that light-scattering fine powder is added and kneaded into the first buffer layer, but in this case, there is a possibility that the fine powder will come into direct contact with the cladding layer and damage the cladding surface. There is a problem that it is difficult to make the amount of powder mixed in uniform. The present invention is highly reliable in that the light is not directly scattered in the first buffer layer, but instead is guided to the first buffer layer to ensure that the light is scattered and annihilated by the light scattering layer.

Next, a method for forming the light scattering layer will be described.

As shown in the process diagram of FIG. 2, an optical fiber 1 is spun while heating a preform (optical fiber base material) 10 in a spinning furnace 6, and a high refractive index silicone rubber 20 is coated on the surface of the optical fiber 1. Immediately before the surface dries, the light-scattering fine powder 50 and nitrogen gas 51 are blown into the atmosphere of a light-scattering layer coating device 7 that is evacuated 52, and then dried through a drying oven 8 to form the first buffer layer and the light-scattering layer. The optical fiber is coated with a low refractive index silicone rubber 30, passed through a drying oven 9 to form a second buffer layer, and finally coated with nylon (the path shown in the figure) to form a jacket coating. complete.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to obtain a high-quality optical fiber that can attenuate the Talarado mode so that it can be ignored even with a short length of several meters, and the accuracy of optical transmission tests and measurements can be greatly improved. It exhibits extremely useful effects such as increasing the

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of one embodiment of the present invention, and FIG.
FIG. 3 is a process diagram showing a method for forming a light scattering layer of M. FIG. 3 is a cross-sectional view according to a conventional technique. In the figure, 1 is an optical fiber, 1a is a core, 1b is a cladding, 2 is a first buffer layer, 3 is a second buffer layer, 4 is a jacket coating, 5 is a light scattering layer, 6 is a spinning furnace, 7 is a light A scattering layer coating device, 8.9 is a drying oven, 10 is an optical fiber base material, 20 is a high refractive index silicone rubber, 30 is a low refractive index silicone rubber, 50 is a light scattering fine powder, 51 is a nitrogen gas, 52 is a Exhaust, shown.

Claims (1)

[Claims] First buffer layer (2) coated on the surface of the optical fiber (1)
An optical fiber core wire characterized in that a light scattering layer (5) made of fine powder of a light scattering material is provided between the second buffer layer (3) and the second buffer layer (3).