JPS6016892Y2 - optical fiber core - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a coated optical fiber, and particularly to a coating structure for coating a central optical fiber.

Although quartz glass optical fibers inherently have high strength, they usually have minute scratches on their surface, which causes a decrease in strength, and when minute scratches occur on the surface, strength decreases.

Therefore, immediately after drawing the optical fiber and before the optical fiber comes into contact with anything else, the optical fiber is coated with a buffering plastic or the like as a primary coat to prevent a decrease in strength and to reduce microbending loss. It meets the requirements for transmission characteristics.

FIG. 1 shows a typical conventional covering structure. In this figure, an optical fiber 11 is coated with a high refractive index silicone layer 12 and a silicone rubber layer 13, and a protective coating layer 14 of nylon 12 or the like is further applied thereon.

However, although this conventional optical fiber core coated only with plastic has excellent transmission characteristics, the plastic cannot block water molecules from entering, so the optical fiber 11 is exposed to water under load. When in contact with molecules, strength deterioration due to water molecules is significant.

In view of the above, the present invention has been developed to block the infiltration of water molecules.
The present invention provides a cored optical fiber in which the optical fiber is coated with an n-metal layer.

This In metal has a low melting point, so it can be easily applied onto an optical fiber, and since it is soft, it does not significantly degrade the transmission characteristics of the optical fiber.

An embodiment of the present invention will be described below with reference to FIG.

In FIG. 2, optical fiber 21 is coated with an In metal layer 22 immediately after drawing and before optical fiber 21 touches anything else.

Further, a rubber or plastic buffer layer 23 such as a silicone rubber layer 23 is coated on the In metal layer 22, and a protective coating layer 24 of thermoplastic plastic such as nylon 12 is further applied.

In this way, according to the present invention, the softness (Prinell hardness:
0.9), the optical fiber 21 immediately after being drawn is coated with the In metal layer 22, which has a low melting point (156.4°C) and good contact with glass, thereby blocking the intrusion of water molecules. In addition to preventing strength deterioration, it is possible to obtain an optical fiber core that does not cause microbending and has transmission loss comparable to that of conventional optical fiber cores with a plastic coating structure. .

That is, when Ag, AI, etc. are used as the metal coating layer,
Since this metal itself is relatively hard, even slight irregularities on the surface in contact with the optical fiber 21 will cause microbending of the optical fiber 21 and increase transmission loss.
This can be avoided.

Further, Ag, AI, etc. have relatively high melting points, and when coating the optical fiber 21 with these metals, a special high temperature device is required, but since In has a low melting point, it is not necessary and can be manufactured easily.

Note that it is of course possible to cover with more plastic layers than shown in FIG.

Next, we will discuss the results of a trial fabrication of a coated optical fiber with the coating structure of the present invention and comparison with a coated optical fiber with a conventional coating structure.

Using optical fibers drawn from the same lot, one side was coated with the structure of the present invention, the optical fiber core thus obtained was referred to as fiber A, and the other side was coated with the conventional structure. The fiber core wire is called fiber B.

Note that in fiber B, methylphenylpolysiloxane with nd = 1.51 was used as the high refractive index silicone layer.

Further, the In metal layer in fiber A was 10 μm thick.

Furthermore, for reference, optical fibers were made that were structurally similar to the present invention, but the material of the metal layer was A1 and wood alloy instead of In, and these were called optical fibers C and D, respectively. I compared them.

The transmission loss and strength deterioration of these four fibers A, B, C, and D in water were investigated.

Transmission loss was measured using light with wavelength λ = 0.84 μm,
An investigation was conducted before and after forming a nylon protective coating layer by extrusion, and the results shown in Table 1 below were obtained.

The underwater strength deterioration test was performed on fibers A and B.

C and D were each wound around a mandrel of a constant diameter, and the time until breakage was measured.

The measurement results are shown in Table 2 below.

In this table, (1) is the mandrel diameter of 3.2rtr.
yi is in water at a temperature of 20C, and (2) is the mandrel diameter of 2.7 m.

It is in water at a temperature of 4 Cf'C.

Fibers C and D were on the same level as fiber A, so they are not listed in this table.

As is clear from Tables 1 and 2, the optical fiber core of the present invention uses soft In metal with a low melting point as the metal layer in contact with the optical fiber, so it is easier to absorb water molecules than in the past. It has high strength because it is not corroded by metal, and compared to the case where other metals are used, there is less increase in microbending loss, making it extremely superior.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a conventional optical fiber, and FIG. 2 is a cross-sectional view of an optical fiber according to an embodiment of the present invention. 11.21...Optical fiber, 12...
High refractive index layer, 13.23... Silicone rubber layer, 14, 24... Protective coating surface, 22...
-In metal layer.

Claims (1)

[Scope of utility model registration request] An optical fiber core wire comprising a central optical fiber coated with an In metal layer in contact with the optical fiber, and a rubber or plastic buffer layer and a thermoplastic plastic layer sequentially coated on the In metal layer.