JPS6045210A - Optical fiber core wire - Google Patents

Abstract

PURPOSE:To soften clamping by contraction of the time of a low temperature, and to obtain a good optical fiber core wire by enlarging gradually toward the outside a Young's modulus of at least a secondary coating layer, in a buffer layer and the secondary coating layer. CONSTITUTION:A primary coating layer 2, a buffer layer 4-1, and secondary coating layers 3-1, 3-2 are provided on a glass fiber 1. Also, a material whose Young's modulus is high is placed on the outermost layer 3-2 of the secondary coating, a material whose Young's modulus is comparatively low is placed on its inside, and a double layer structure of the secondary coating is formed. The optical fiber is a multi-graded type fiber by a CVD method and has 50mum core diameter, 125mum outside diameter and 1.0% specific refractive index difference, and immediately after spinning, a silicone resin of 1.52 refractive index and 0.2kg/mm.<2> Young's modulus is applied and hardened to thickness of about 50mum.

Description

[Detailed description of the invention] The present invention relates to a coating structure for a glass fiber for optical transmission.

Various methods have been proposed for coating optical fibers, but most of the methods that have been put into practical use or have a high possibility of being put into practical use are basically those described in Japanese Patent Application Laid-Open No. 51
-100734 is a typical example. That is, it is a method in which a film of a resin composition is formed immediately after melt-spinning an optical fiber and before the optical fiber comes into contact with other solid materials, and then a thermoplastic resin composition is melt-extruded to coat the film. . This maintains the virgin strength of the glass by forming a coating of a resin composition (hereinafter referred to as secondary coating) immediately after melt-spinning the optical fiber, and extrusion coating (hereinafter referred to as secondary coating) a thermoplastic resin on top of the virgin strength of the glass. The purpose of this coating is to further increase mechanical strength and protect the optical fiber from subsequent mechanical stress, moisture in the air, ultraviolet rays, etc.

In addition, in order to prevent changes in transmission characteristics due to microbending phenomena, there is a method in which a buffer layer made of a material with a small Young's modulus capable of absorbing external stress is interposed between the secondary coating layer and the secondary coating layer. However, this structure has advantages and disadvantages depending on the selection of the Young's modulus of the 4A material used in the secondary coating layer.

That is, when a material with a high Young's modulus is selected for the secondary coating,
Although it is very effective in preventing microbends due to lateral pressure, on the other hand, if a large constriction force is applied due to contraction due to the coefficient of thermal expansion at low temperatures, a force exceeding the buffer layer's relaxation ability will be generated, and the transmission due to microbends. Increased losses will occur.

On the other hand, if a material with a low Young's modulus is selected for the secondary coating, the phenomenon that micro-bends occur due to compaction at low temperatures and increase transmission loss will disappear, but on the other hand, micro-bends will occur due to external stress such as lateral pressure, increasing loss. This will cause

The secondary coating layer originally has the role of protecting the internal glass, primary coating layer, and buffer layer, and requires a material with a high Young's modulus. In other words, as mentioned above, materials with a high Young's modulus prevent the influence of external pressure on the inside of the core wire, and have strong mechanical strength and abrasion resistance.
Although it is possible to protect the internal fiber from the effects of various processes such as cable production and external pressure after cable installation, conversely, at low temperatures, the secondary coating material itself shrinks and generates a larger sealing force, which reduces transmission. It has drawbacks that worsen losses. Various studies were carried out to improve this drawback.

■Further increase the stress absorption capacity of the buffer layer. Specifically, a material with a smaller Young's modulus is used. Or make the buffer layer thicker. ■ Two methods of reducing the tightening force of the secondary coating layer are effective.

If the Young's modulus of the buffer layer is unnecessarily reduced, the buffer layer may peel off due to mechanical contact during the extrusion process, or
Since many buffer layers are made by coating and baking thermosetting resins, making the buffer layer even thicker reduces the manufacturing line speed and requires large manufacturing equipment (1iii), which is not practical.

In addition, the Young's modulus (longitudinal elastic modulus) of the secondary coating layer is 2000
It has been proposed that by using a polyamide in the range of K9/1yn2-8000 Ky/cm2, an optical fiber core with good low temperature properties can be provided.

However, in this case, the Young's modulus is relatively low, so the low-temperature characteristics are good;
It was insufficient to prevent an increase in transmission loss against external pressure (in the cable manufacturing process or the environment after installation) at a temperature of 0 to 80°C. The present invention has been made in view of these points, and its gist is to provide an optical fiber in which a buffer layer is provided on an optical fiber strand in which a glass fiber is provided with a primary coating, and a secondary coating layer is applied on the outer side of the buffer layer. The optical fiber core wire is characterized in that the Young's modulus of at least the secondary coating layer of the buffer layer and the secondary coating layer increases stepwise or continuously toward the outside.

A detailed explanation will be given below with reference to the drawings.

FIG. 1 shows an example of a conventional optical fiber core wire, where (a) is a cross-sectional view of the core wire, (b) is a Young's modulus of the cross section, and
FIG. 3 shows an embodiment of the present invention. Here, a primary coating layer (2) is provided on the glass fiber (1) and a buffer layer (
4), (4-1), (4-2), secondary coating layer (3), (
3-1) and (3-2) have been applied.

FIG. 2 shows a two-layer structure of the secondary coating, in which a material having a high Young's modulus is placed in the outermost layer of the secondary coating, and a material having a relatively low Young's modulus is placed inside.

Of course, the number of layers is not limited to two, but may be two or more layers.

Further, as shown in FIG. 3, the secondary coating layer and the buffer layer may have a gradient in Young's modulus.

By adopting this structure, that is, by arranging a high Young's modulus material in the outermost layer, its excellent mechanical strength and abrasion resistance prevent the influence of external pressure on the fiber and the influence during cable processing. (2) Therefore, by arranging a material with a low Young's modulus, tightness due to shrinkage at low temperatures can be alleviated, and a good optical fiber core can be obtained.

This will be explained below using Examples and Comparative Examples.

The optical fiber used in the examples is a multi-mode graded fiber made by CVD, with a core diameter of 50 μm.
It has an outer diameter of 125 μm and a relative refractive index difference of 0%, and is made by applying and hardening silicone resin with a refractive index of 1.52 and a tongue modulus of Q of 2 Kg/[2 to a thickness of about 50 μm immediately after spinning. .

Comparative Example 1) The above wire had a tongue rate of about 0.2 Kg/myr.
Buffer layer made of silicone resin of t2 (outer diameter 400/, tm
) and coated with a polyamide resin (Nylon-12) having a Young's modulus of 120K17mm2 by extrusion using a 3oφ extruder, and having an outer diameter of 900/jm.

2) A core wire using a polyamide resin (Nylon-12) with a Young's modulus of 4·Q Kg/si2 in Comparative Example υ.

Example 1) A buffer layer (outer diameter 400 μm) of silicone resin with a Young's modulus of 0.2 Kg/m2 was formed on the above wire, and a first secondary coating layer was formed of polyamide (Nylon 12) with a Young's modulus of 4 oKy/B2. A core wire having an outer diameter of 700 μm coated with polyamide (Nylon-12) having a Young's modulus of 12QK5+/M2 and having an outer diameter of 900 μm.

2) A buffer layer (outer diameter 400 μm) of silicone resin with a Young's modulus Q of 3 K97B2 is formed on the above wire, and a first secondary coating layer is formed on the buffer layer with a Young's modulus 50i<g/B2
+7) A core wire coated with polyester elastomer to an outer diameter of 700 μm and further coated with polyamide (Nylon-12) having a Young's modulus of 100 K5+/np2 to an outer diameter of 900 μm.

200 m of each of the above-mentioned various core wires were placed in a low temperature of -40°C to investigate changes in transmission loss. In addition, lateral pressure (10 kg/30 crn) was applied to various core wires in an atmosphere of 80"C, and changes in transmission loss were investigated.

The results are shown in Table-1.

*An LED (wavelength -0.85 μm) light source was used to measure the loss.

As is clear from Table 1, the structures of Examples 1) and 2) have superior properties against lateral pressure both at low temperatures and at relatively high temperatures, compared to Comparative Examples 1) and 2). There is.

Although this structure has been described for a single-fiber wire, the same structure can be used for a multi-fiber wire.

[Brief explanation of drawings]

Figures 1 (a) and (b) are cross-sectional views of conventional optical fiber cores, Young's modulus within the cross section, Figures 2 (a) and Φ, and Figures 3 (a) and (b).
) shows the cross-sectional view and Young's modulus according to the present invention. Here, l...glass fiber, 2...-secondary coating layer,
3... Secondary coating layer, 4... Buffer layer. Procedures Amendment 1 Indication of the case 1982 Patent Application No. 1.53424 No. 2 Name of the invention Optical fiber core wire 3, person making the amendment Relationship to the case Special n'l - Applicant Address Kitahama, Higashi-ku, Osaka City 5-15 Name (213) Sumitomo Electric Industries Co., Ltd. Address 1-1-3 Shimaya, Konohana-ku, Osaka City Sumitomo Electric Industrial Forest Type 9 Company Internal drawing subject to 6 corrections Surface 7, contents of corrections Clear with dark ink Correct the figures 1 to 3 drawn in Figures 1 to 3 as shown in the attached sheet.

Claims (1)

[Claims] In an optical fiber core wire in which a buffer layer is provided on the optical fiber strand and a secondary coating layer is applied on the outside thereof, the Young's modulus of at least the secondary coating layer of the buffer layer and the secondary coating layer is such that the Young's modulus of the secondary coating layer is directed outward. An optical fiber core wire characterized by increasing its size stepwise or continuously.