JPS5840162B2 - Manufacturing method of optical fiber cable - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an optical fiber cable that can prevent water from entering and suppress a reduction in transmission loss, and is particularly suitable for use in communications.

Generally, optical fibers have excellent static fatigue properties, but
It is known that especially in the presence of moisture, the fiber will break at a much smaller stress than the maximum breaking stress in a dry state, and this drawback is one of the major problems that must be taken into account when putting optical fiber cables into practical use. They were one.

Therefore, when manufacturing optical fiber cables for communication,
In order to prevent an extreme decrease in the strength of the optical fiber core due to moisture, it is necessary to create a structure that prevents moisture from penetrating into the optical fiber core. An optical fiber cable has been developed in which a viscous liquid is filled in a buffer layer made of a fibrous material formed between a cable and a cable.

By the way, when filling the viscous liquid according to the present invention, if the viscous liquid is heated and softened in order to facilitate its injection and then injected into the buffer layer, the viscous liquid whose temperature drops to room temperature after the injection is finished will solidify. As the optical fiber cable undergoes volumetric contraction, internal stress is generated within the optical fiber cable, and a delicate bending force is applied to the optical fiber core wire.

Normally, microbending occurs when an optical fiber is bent at a curvature below a certain value determined by its outer diameter, core diameter, or refractive index difference between the core and cladding. Although it is known that transmission loss increases, the same phenomenon as this microbending phenomenon occurs in the optical fiber core due to contraction and solidification of the viscous liquid, resulting in an increase in transmission loss.

In view of the fact that conventional optical fiber cables filled with viscous fluid caused a relatively large reduction in transmission loss, the present invention aims to provide a method for manufacturing optical fiber cables that can eliminate this drawback. .

The structure of the method for manufacturing an optical fiber cable according to the present invention, which is distantly related to this object, is to form a buffer layer made of a fibrous material between at least one optical fiber core wire and an outer sheath that covers it. The viscous liquid having a viscosity in the range of 105 centipoise to 108 centipoise is filled into the buffer layer while the temperature of the viscous liquid is maintained near normal temperature or below.

In other words, in order to prevent the viscous liquid from shrinking and solidifying, it is sufficient to maintain the temperature of the viscous liquid as low as possible, near or below room temperature, and inject it into the buffer layer within the optical fiber cable. The viscosity of the liquid at the time of injection is extremely important.

When considering the maintenance of transmission characteristics and the ease of filling work, the lower the viscosity of the viscous liquid, the better.However, from the basic premise of waterproofing (water running), which is the original purpose of viscous liquid filling, there is a lower limit of allowable viscosity. It is desirable that the value is approximately 105 centipoise.

On the other hand, the viscous liquid referred to in the present invention is a non-Newtonian fluid and has a shear rate dependence of viscosity. It is desirable that the upper limit of the viscosity of the viscous liquid that can be easily worked is kept at about 108 centipoise.

In other words, when a viscous liquid with a viscosity in the range of 105 centipoise to 108 centipoise at temperatures near or below room temperature is filled into the buffer layer formed between the optical fiber core and the outer jacket covering it, The purpose of the present invention can be achieved with the highest effect, and examples of viscous liquids that can satisfy these conditions include polybutene, white petrolatum, ACPE, paraffin, microcrystalline wax, and low-molecular hydrocarbons, etc. Alternatively, a combination of multiple types can be mentioned.

Next, as shown in Figure 1, a graded fiber 1 with a core diameter of 50 micrometers and a relative refractive index difference of 1.0% is prepared.
Around the 2-layer silicone resin layer 2 and nylon
FIG. 2 shows an example in which six optical fiber cores 4 coated with 12 layers 3 are combined to form a six-core optical fiber cable.

Six optical fiber cores 4 are arranged at equal intervals around the tension member 5 occupying the center, and are formed between the tension member 5 and an outer sheath 6 made of a thin aluminum film laminated with polyethylene. A plastic yarn (fibrous member) 8 is packed in the buffer layer 7, which has the function of positioning the optical fiber core 4 in the buffer layer 7 and protecting it.

Further, the buffer layer 7 is filled with a viscous liquid 9 having a viscosity of 106 centipoise at room temperature, but the composition of this viscous liquid 9 in this embodiment is 65 centipoise of polybutene (300R). Parts by weight: 3 parts white petrolatum
A mixture consisting of 0 parts by weight, 4 parts by weight of ACPE, and 2 parts by weight of paraffin was used.

Incidentally, the reference numeral 10 in the figure is an overlapping tape for bundling the plastic yarns 78.

The transmission loss ratio of an optical fiber cable obtained by an embodiment of the present invention that employs such a structure is 0.2 dB/km before and after filling with the viscous liquid 9, which is expressed by filling with the viscous liquid 9. The increase in transmission loss is extremely small.

Furthermore, the transmission loss rate when this optical fiber cable is left in a low temperature of -20°C is 0.2 dB/kin, and furthermore, when the optical fiber cable is bent with a curvature several times its outer diameter, the transmission loss rate is 0.2 dB/kin. It has also been confirmed that there is almost no transmission loss, and together with ensuring the waterproofness of the optical fiber, it has an extremely excellent effect.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the internal structure of an optical fiber core used in an embodiment of the present invention, and FIG. 2 is a sectional view showing the internal structure of the optical fiber cable in this embodiment. In the drawing, 4 is an optical fiber core, 6 is a jacket, 7 is a buffer layer,
8 is a plastic yarn and 9 is a viscous liquid.

Claims (1)

[Claims] 1 A buffer layer made of a fibrous material is formed between at least one optical fiber core wire and an outer sheath covering it, and the temperature of a viscous liquid having a viscosity in the range of 105 centipoise to 108 centipoise at the time of filling is kept at room temperature. A method for manufacturing an optical fiber cable, characterized in that the viscous liquid is filled into the buffer layer while maintaining the viscous liquid at a level near or below.