JPH07244220A - Plastic optical fiber - Google Patents

Abstract

PURPOSE:To improve the bending and lateral-pressure characteristics of a GI- type plastic optical fiber obtd. by preform drawing by specifying the breaking elongation and the hardness due to lateral thrust to be a certain value or higher. CONSTITUTION:When an optical fiber 4 is wound on a mandrel 8, the elastically deformed region is transferred to a plastically deformed region by the stress of bending and a microscopic abnormal structure is formed, hence a light transmitting in the core infiltrates into the clad, and loss is increased. Accordingly, the breaking elongation of the fiber 4 is controlled above a specified value, especially to 20%, hence the elastically deformed region is windened and hardly transferred to a plastically deformed region even by increase in bending stress, and the loss is not increased by the bending. Besides, the hardness of the film 4 due to the lateral thrust is controlled above a specified value, especially to >=15g/mum<2>, hence the fiber 4 is hardly deformed by the lateral pressure since the outside (clad) is hard, and the loss is not increased.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to plastic optical fibers. In particular, it is improved so as to suppress an increase in loss due to bending and winding.

[0002]

2. Description of the Related Art An optical fiber whose core and clad are both plastic is used as a short-distance optical transmission line between electronic devices for transmitting and receiving optical communication, as compared with glass fiber, in which transmission loss is not a problem. Since it is easy and low-priced, it is diversified and particularly important in the concept of next-generation communication networks such as LAN and ISDN.

As a plastic optical fiber, a step index (SI) having a refractive index distribution shown in FIG.
Type fiber has been put to practical use, but this fiber has a small transmission capacity and is not suitable for communication. In order to use it for communication, it is necessary to use a graded index (GI) type fiber having a large transmission capacity and having a refractive index distribution shown in FIG.

Conventionally, as a method of manufacturing a plastic optical fiber, for example, as disclosed in Japanese Patent Laid-Open No. 4-124602, a method of spinning a core material to a predetermined diameter and coating a clad material thereon is known. Although used, in order to manufacture a GI type plastic optical fiber by this method, coating must be performed in multiple steps, and the process is complicated.

[0005]

Therefore, it is possible to reduce the number of steps by synthesizing a GI type preform, heating it, melting it, and making it into a fiber, and it is possible to produce various fibers having different outer diameters. It is possible.

As disclosed in Japanese Patent Laid-Open No. 4-366903, there is an example in which the increase in loss due to bending and winding is improved by defining the physical properties of a plastic optical fiber. However, the cladding coating method using a die is used. However, the GI type plastic optical fiber obtained by the preform drawing method cannot be bent and the lateral pressure characteristics cannot be improved.

The present invention has been made in view of the above prior art, and is obtained by the preform drawing method.
The purpose is to improve the bending and lateral pressure characteristics of the plastic optical fiber. That is, the purpose is to improve the bending and lateral pressure characteristics by defining the elongation and hardness of the GI type plastic optical fiber.

[0008]

The structure of the present invention for attaining such an object is a plastic optical fiber having a core and a clad having a predetermined refractive index and made of plastic, and the elongation at break is a certain value or more. It is characterized in that the hardness due to pressing down is above a certain value. Particularly, the plastic optical fiber has a breaking elongation of 20%.
Above, and the hardness by pressing from the side is 15
It is preferably g / μm ² or more, and is preferably applied to a graded index fiber.

[0009]

When the stress due to bending of the optical fiber increases, the elastic deformation region shifts to the plastic deformation region, and microscopic structural irregularities occur, so that the light transmitted through the core leaks into the clad and the loss increases. In the conventional optical fiber having a small breaking elongation, since the elastic deformation region is narrow, the stress increases due to bending, so that the region easily shifts to the plastic deformation region, and the increase in loss due to bending is relatively large. In the plastic optical fiber of the present invention, when the breaking elongation is a certain value or more, particularly 20% or more, the elastic deformation region is wide, and it is difficult to shift to the plastic deformation region even when the stress due to bending increases.
It is possible to suppress an increase in loss due to bending.

When the lateral pressure is increased with respect to the optical fiber, the clad is deformed, so that the light transmitted through the core oozes out into the clad and the loss is increased. In the conventional optical fiber having a small hardness due to lateral pressing, the cladding is easily deformed by the lateral pressure, so that the loss increase by the lateral pressure is relatively large. The plastic optical fiber of the present invention has a hardness of not less than a certain value when pressed down from the side, especially 15
By setting g / μm ² or more, the outer side (clad) is hard, so that the fiber is not easily deformed even when subjected to lateral pressure, and an increase in loss can be suppressed.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the embodiments shown in the drawings. The bending test of the plastic optical fiber is shown in FIG.

First, the power meter 9 is connected to one end of the 5 m optical fiber 4 and the spectroscope 7 is connected to the other end, and the loss of the optical fiber 4 is measured without bending. Next, the optical fiber 4 is placed 2 m from the spectroscope 7.
Is wound around the mandrel 8 by 90 °, and the loss of the optical fiber 4 is measured. Here, the mandrel 8 has a diameter of 10
Various types of 0 mm, 90 mm, 80 mm, ... 10 mm are used.

After that, the difference between the first measured value (infinite bending diameter) and the value when the mandrel 8 is fixed next is calculated. When the optical fiber 4 is wound around the mandrel 8, it is subjected to stress due to bending and moves from an elastic deformation region to a plastic deformation region, causing microscopic structural irregularities, so that light transmitted through the core seeps into the clad, Loss increases. In the conventional optical fiber having a small breaking elongation, since the elastic deformation region is narrow, the stress increases due to bending, so that the region easily shifts to the plastic deformation region, and the increase in loss due to bending is relatively large.

On the other hand, the optical fiber 4 of this embodiment is
By setting the breaking elongation to be a certain value or more, particularly 20% or more, the elastic deformation region is wide, and it is difficult to shift to the plastic deformation region even when the stress due to bending increases, and therefore, the loss increase due to bending can be suppressed. . The elongation at break defined in the present invention is a concept including an elastic deformation region and a plastic deformation region, as in a commonly used term, but the elastically effective region is important in terms of action and effect. That is, when the elongation at break is equal to or greater than a certain value, it should be rephrased that the elastic deformation region is equal to or greater than a certain value.

The flat plate lateral pressure test is shown in FIG. First, the power meter 9 is connected to one end of the 5 m optical fiber 4, and the spectroscope 7 is connected to the other end. Next, on the side pressure table 10, a stainless plate with a side of 10 cm (weight: 260 g)
The optical fiber 4 is sandwiched between 11 and the maximum load 1 is 50 kg.
Multiply by 2 and measure the loss increase. Then, the weight is removed by 10 Kg each, and the loss measurement is continuously performed. Furthermore, assuming that the loss when sandwiched by the stainless steel plate 11 is 0, the wavelength is 650μ.
Calculate the difference in m.

In the optical fiber 4, when lateral pressure is applied by the load 12, the clad deforms, so that the light transmitted through the core leaks into the clad and the loss increases. In the conventional optical fiber having a small hardness due to lateral pressing, the cladding is easily deformed by the lateral pressure, so that the loss increase by the lateral pressure is relatively large. On the other hand, in the plastic optical fiber of the present invention, when the hardness due to lateral pressing is set to a certain value or more, particularly 15 g / μm ² or more, the outside (clad) is hard, so that the fiber is not affected by lateral pressure. Is difficult to deform, and loss increase can be suppressed.

The hardness (hereinafter, simply referred to as "hardness") due to lateral pressing is referred to here as shown in FIG.
It is the hardness calculated from the load and the depth of diving when the indenter 3 (made of diamond) of the triangular pyramid is pressed from above and fixed. Next, specific examples of the present invention will be described in comparison with comparative examples.

[Example 1] A plastic optical fiber preform having a GI type refractive index distribution was prepared, the furnace core tube temperature was 240 ° C, the outer diameter center was 650 µm, and the linear velocity was 2
Drawing was performed at m / min. At this time, the fiber elongation at break was 40% and the hardness was 25 g / μm ² . When the bending test and the flat plate lateral pressure test of the produced fiber were performed, the maximum values of loss increase were 0.1 dB and 0.
It was 15 dB.

[Example 2] A plastic optical fiber preform having a GI type refractive index distribution was prepared, the furnace core tube temperature was 240 ° C, the outer diameter center was 750 µm, and the linear velocity was 2
Drawing was performed at m / min. At this time, the fiber elongation at break was 30% and the hardness was 25 g / μm ² . When the bending test and the flat plate lateral pressure test of the produced fiber were performed, the maximum values of the increase in loss were 0.15 dB and 0.1 dB, respectively.

[Embodiment 3] A plastic optical fiber preform having a GI type refractive index distribution was prepared, the furnace core tube temperature was 240 ° C, the outer diameter center was 500 µm, and the linear velocity was 2
Drawing was performed at m / min. At this time, the fiber elongation at break was 50% and the hardness was 18 g / μm ² . When the bending test and the flat plate lateral pressure test of the produced fiber were performed, the maximum values of loss increase were 0.08 dB and 0.2 dB, respectively.

[Comparative Example 1] A plastic optical fiber preform having a GI type refractive index distribution was prepared, the temperature inside the furnace core tube was 220 ° C, the outer diameter center was 650 µm, and the linear velocity was 2
Drawing was performed at m / min. At this time, the fiber elongation at break was 10% and the hardness was 25 g / μm ² . When the bending test and the flat plate lateral pressure test of the produced fiber were carried out, the maximum values of loss increase were 5.0 dB and 0.
It was 1 dB, and the flat plate lateral pressure characteristics were excellent, but the bending characteristics were poor.

[Comparative Example 2] A plastic optical fiber preform having a GI type refractive index distribution was prepared, the furnace core tube temperature was 260 ° C, the outer diameter center was 750 µm, and the linear velocity was 2
Drawing was performed at m / min. At this time, the fiber breaking elongation was 40% and the hardness was 10 g / μm ² . When the bending test and the flat plate lateral pressure test of the produced fiber were carried out, the maximum values of loss increase were 0.1 dB and 1.
It was 0 dB, and the flat plate lateral pressure characteristics were excellent, but the bending characteristics were poor.

[0023]

As described above in detail with reference to the embodiments, the present invention provides a plastic optical fiber having a breaking elongation of a certain value or more and a hardness by pressing from a lateral pressure to a certain value. It is possible to improve the bending and lateral pressure characteristics of the. As a result, handling of the GI type plastic optical fiber becomes easier, and it is possible to suppress an increase in loss when installed.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a 90 ° bending test.

FIG. 2 is an explanatory diagram of a flat plate side pressure test.

FIG. 3 is an explanatory diagram of a method of measuring hardness by pressing the optical fiber from the side.

FIG. 4 is a refractive index profile of an SI type fiber.

FIG. 5 is a refractive index profile of a GI type fiber.

[Explanation of symbols]

 1 clad 2 core 3 indenter 4 plastic optical fiber 5 adhesive 6 substrate 7 spectroscope 8 mandrel 9 power meter 10 side pressure table 11 stainless steel plate 12 load

Claims (4)

[Claims] 1. A plastic optical fiber having a core and a clad having a predetermined refractive index and made of plastic, wherein the breaking elongation is not less than a certain value and the hardness by lateral pressing is not less than a certain value. Plastic optical fiber. 2. The plastic optical fiber according to claim 1, wherein the breaking elongation of the plastic optical fiber is 20% or more. 3. The plastic optical fiber according to claim 1, wherein the plastic optical fiber has a hardness of 15 g / μm ² or more when pressed from the side. 4. The plastic optical fiber according to claim 1, wherein the plastic optical fiber is a graded index fiber.