JPH0219766Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cored optical fiber in which a coating layer is provided around the optical fiber.

FIG. 1 is a cross-sectional view of a conventional optical fiber core wire, in which 1 is an optical fiber, 2 is a modified silicone rubber, and 3 is a sectional view of a conventional optical fiber core wire.
is silicone rubber, and 4 is plastic.

A conventional optical fiber core wire is constructed as shown in Fig. 1, and in order to prevent deterioration of the breaking strength of the optical fiber 1, the periphery of the optical fiber 1 is first coated with a modified silicone rubber 2, and at the same time, a silicone rubber 3 is also coated. It is then wound onto a bobbin. Thereafter, a plastic 4 such as nylon or polyethylene is coated. Modified silicone rubber 2 and silicone rubber 3
has a function as a buffer layer.

The reason why modified silicone rubber 2 and silicone rubber 3 are used in this structure is because modified silicone rubber 2 is more expensive than silicone rubber 3, and because it is impossible to thicken the layer of modified silicone rubber 2 in one process. Because it is possible.

The elastic modulus of modified silicone rubber 2 and silicone rubber 3 is almost the same, and modified silicone rubber 2
The refractive index of the silicone rubber 3 is larger than that of the silicone rubber 3.

When such an optical fiber core is placed under high water pressure, the elastic modulus of the outer layer plastic 4 is larger than that of the inner layer modified silicone rubber 2 and silicone rubber 3, and the Since the adhesion is poor and there are many voids at the interface, an increase in the optical loss of the optical fiber 1 can be prevented until the water pressure reaches the point where the plastic 4 functions as a shell, but once the water pressure exceeds that water pressure, the plastic 4 will sit This has the drawback of causing a significant increase in optical loss.

Another drawback is that when the optical fiber is cut and water pressure is applied to the cut surface, water runs through the gap between the plastic 4 and the silicone rubber 3, degrading the characteristics of the optical fiber 1. Ta.

In order to eliminate these drawbacks, the present invention provides a plurality of coating layers having successively smaller elastic modulus around the optical fiber. The present invention will be explained in detail below with reference to the drawings.

FIG. 2 is a sectional view of an embodiment of the present invention,
Reference numeral 5 denotes a rubber elastic body, and other symbols that are the same as those in FIG. 1 are designated by the same symbols.

In this structure, instead of the plastic 4 shown in FIG. 1, a rubber elastic body 5 having an elastic modulus equal to or lower than that of the silicone rubber 3 is provided.

When such an optical fiber core wire is placed under a certain hydrostatic pressure, as mentioned above, the elastic modulus of the modified silicone rubber 2 and the silicone rubber 3 are almost the same, and the elastic modulus of the rubber elastic body 5 is the same as that of the silicone rubber. 3
, the rubber elastic body 5 does not have the function of a shell, that is, the function of not allowing pressure to propagate to the inner layer silicone rubber 3 up to a certain pressure. Therefore, a uniform pressure commensurate with the hydrostatic pressure will always act on the optical fiber 1, and no increase in loss in the optical fiber will occur against such uniformly applied external pressure. Note that it is possible to manufacture the silicone rubber 3 and the rubber elastic body 5 so that no voids exist between them, but even if some voids remain, the elastic modulus of the rubber elastic body 5 is small, so it is not possible to create a static The absolute value of the non-uniform stress acting on the optical fiber 1 under water pressure is very small, and does not cause any increase in optical loss to the optical fiber 1.

FIG. 3 is a sectional view of another embodiment of the present invention.
In this structure, a rubber elastic body 5 having a smaller elastic modulus than the modified silicone rubber 2 is provided on the outer layer of the modified silicone rubber 2. Since such a cored optical fiber can be considered to have essentially the same structure as the cored optical fiber shown in FIG. 2, it has excellent characteristics without increased optical loss even under hydrostatic pressure.

In addition, in the above embodiment, a structure having three or two coating layers around the optical fiber 1 is exemplified, but four or more coating layers may be used so that the elastic modulus decreases sequentially from the optical fiber 1 toward the outer layer. A similar effect can be obtained by providing a coating layer of. Further, it goes without saying that the rubber elastic body 5 is not limited to a rubber material as long as it is a member having elasticity.

As explained above, since the optical fiber core wire having the above-described structure has coating layers having a smaller elastic modulus in order toward the outer layer, no increase in optical loss occurs under hydrostatic pressure. Therefore, if the optical fiber core of the present invention is employed in a submarine optical cable, reliability can be significantly improved.

Furthermore, under hydrostatic pressure, the radial stress is theoretically greater in the inner layer, so the self-sealing effect improves the airtightness between the members constituting the main wire, allowing it to be used in submarine optical cables.

Furthermore, if an optical cable is constructed by twisting together the required number of optical fiber units made up of a plurality of optical fiber cores of the present invention, the frictional force between the optical fiber cores and between the cable core and the jacket can be greatly increased. As a result, creep resistance performance is dramatically improved.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a conventional optical fiber, Figure 2 is a cross-sectional view of a conventional optical fiber core wire.
The figure is a sectional view of one embodiment of the optical fiber core according to the present invention, and FIG. 3 is a sectional view of another embodiment of the optical fiber core according to the present invention. 1... Optical fiber, 2... Modified silicone rubber,
3...Silicone rubber, 4...Plastic, 5...
...Rubber elastic body.

Claims (1)

[Scope of utility model registration request] An optical fiber core wire characterized in that a coating layer made of a plurality of rubber elastic bodies is provided around the optical fiber so that the elastic modulus becomes gradually smaller toward the outer layer.