JPS6150285B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an optical fiber cable for communication. FIG. 1 is a sectional view showing an example of a conventional self-supporting optical fiber cable, in which 1 is a cable support wire, 2 is a cable sheath, and 3 is a cable core. In the first place, self-supporting fiber optic cables are
The cable support line 1 is fixed to a telephone pole while applying tension, and the cable core 3 is held by the cable sheath 2 while being fixed so as not to cause excessive slack as a whole. In conventional self-supporting fiber optic cables, the cable support wire 1, cable sheath 2, and cable core 3 are all mechanically integrated, so the tension applied to the cable support wire 1 during spanning is There was a drawback that the cable core 3 was transmitted through the sheath 2 to the cable core 3, and the cable core 3 was stretched during the span. FIG. 2 is a diagram showing the results of calculations of the temperature-elongation characteristics of a conventional self-supporting optical fiber cable when it is strung. However, the calculation conditions are that the product (E x A) of the Young's modulus (E) of the cable and the cross-sectional area (A) of the cable is 3.34 x 10 ⁵ Kg, the coefficient of thermal expansion of the cable is 1.45 x 10 ^-5 /℃, and the weight of the cable. teeth
Assuming 300g/m, the distance between utility poles is 40m. As can be seen from Fig. 2, since the cable support wire 1, cable sheath 2, and cable core 3 are integrated, the cable can be maintained at room temperature, i.e., 20
There is also an elongation of 0.05% at ℃ degrees, and if the cable becomes hot due to direct sunlight, that is, 60℃, it will elongate by nearly 0.1%. For glass fibers, constant elongation is extremely dangerous from the viewpoint of reliability, and it is essential to suppress elongation to the smallest possible extent. The present invention solves the disadvantages of conventional self-supporting optical fiber cables by separating the cable support wire, cable sheath, and cable core, or by separating the cable support wire and cable sheath from the cable core, in order to suppress the elongation of the fiber during installation.
Alternatively, the cable core and cable sheath have approximately the same coefficient of thermal expansion. The present invention will be explained in detail below with reference to the drawings. FIG. 3 is a sectional view of a self-supporting optical fiber cable according to an embodiment of the present invention, in which 1 is a cable support wire, 2 is a cable sheath, 3 is a cable core,
4 is a void. The cable support line 1 and the cable sheath 2 are mechanically integrated, and when the cable is strung across a utility pole, the cable support line 1 and the cable sheath 2 extend in the same way, but the cable core 3 extends through the gap 4. Since the cable support line 1 and the cable sheath 2 are mechanically independent, the elongation of 1 and 2 is not transmitted to the cable core 3. Therefore, even when the cable is strung, the cable core 3 does not stretch and can maintain a free state, and the optical fiber core 3 housed inside the cable core 3 also does not stretch. Furthermore, the coefficient of thermal expansion of the combined cable support wire 1 and cable sheath 2 and the coefficient of thermal expansion of the cable core 3 are approximately equal. That is, the Young's modulus, cross-sectional area, and coefficient of thermal expansion of the N types of materials constituting the cable support wire 1 and the cable sheath 2 are E _i , A _{i ,} and α _{i ,} respectively, and the M types of materials constituting the cable core 3 are Young's modulus, cross-sectional area and coefficient of thermal expansion are each E
_j , A _j and α _j , satisfies the following conditions. The left side of the above equation shows the thermal expansion coefficient of the combined cable support wire 1 and cable sheath 2, and the right side shows the thermal expansion coefficient of the cable core. Therefore, if we consider the case where a temperature change of t°C occurs, the thermal expansion of the combined cable support wire 1 and cable sheath 2 is:

[Formula], and The thermal expansion of Bullcore is

[Formula], so the two are almost equivalent. Therefore, there is no protrusion or retraction of the cable core. An example of a self-supporting optical fiber cable in which the coefficients of thermal expansion of No. 1, No. 2, and No. 3 are approximately the same will be described below. FIG. 4a is a cross-sectional view of a self-supporting optical fiber cable showing an embodiment of the present invention, in which 1 is a cable support wire, 2 is a cable sheath, 3 is a cable core, 4 is a gap, and 5 is a protective layer. It is. FIG. 4b is a detailed enlarged sectional view of the cable core 3 of FIG. 4a, in which 6 is a steel wire, 7 is a polyethylene coating, 8 is an optical fiber core, and 9 is a tape wrapping layer. Figure 4c
is a detailed enlarged sectional view of the optical fiber core wire 8 in FIG. 4b, 10 is an optical fiber strand, 11 is a buffer layer,
12 is a coating. Cable support wire 1 has an outer diameter of 1.8
The cable sheath 2 is made of polyethylene, and the protective layer 5 is made of soft aluminum. On the other hand, in the cable core, as shown in FIG. 4b, a polyethylene coating 7 is coated around a steel wire 6, and 12 optical fiber cores 8 are arranged around the steel wire 6, and 6, 7, and 8 are covered with tape. It has an integrated structure by the winding layer 9. Also, optical fiber core 8
As shown in FIG. 4c, the optical fiber wire 10 is surrounded by a buffer layer 11 and a coating 12 in two layers. If the cable support wire 1, cable sheath 2, and protective layer 5 are configured with material constants and cross-sectional areas as shown in Table 1, the thermal expansion coefficient of the combined cable support wire and cable sheath is 1.33×10 ^-5 /℃
becomes. On the other hand, the steel wire 6, polyethylene coating 7, optical fiber wire 10, and buffer layer 11 constituting the cable core
If the coating 12 is configured with material constants and cross-sectional areas as shown in Table 2, the coefficient of thermal expansion of the entire cable core will be 1.31×10 ^-5 /°C. Since the cable support wire, cable sheath, and cable core have almost the same coefficient of thermal expansion,
Even if the two are separated from each other, expansion and contraction due to temperature changes are approximately the same, so there is no protrusion or retraction of the cable core at the cable connection portion. The self-supporting optical fiber cable according to the above embodiment has no distortion at room temperature (20°C) even when being strung, and even when the temperature of the cable reaches 60°C due to direct sunlight, the distortion is suppressed to about 0.05%. be able to.

【table】

[Table] FIG. 5 is a cross-sectional view of a self-supporting optical fiber cable showing another embodiment of the present invention, in which 1 is a cable support wire, 2 is a cable sheath, 3 is a cable core, and 13 is a jewelry. . The self-supporting fiber optic cable according to this embodiment includes a cable support line 1, a cable sheath 2, and a cable core 3.
and are mechanically independent from each other by the gear 13, so that they function similarly to the embodiment shown in FIG. As explained above, the self-supporting optical fiber cable according to the present invention has the effect of being able to reduce the strain that occurs in the optical fiber even during installation, and improving the flexibility of the optical cable. Furthermore, since the coefficients of thermal expansion of the cable support wire and cable sheath are approximately the same as those of the cable core, there is an advantage that the cable core does not protrude or retract due to temperature changes.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an example of a conventional self-supporting optical fiber cable, and FIG. 2 is a diagram showing the relationship between temperature and elongation of a conventional self-supporting optical fiber cable.
FIG. 3 is a sectional view of a self-supporting optical fiber cable showing one embodiment of the present invention, FIG. 4a is a sectional view of a self-supporting optical fiber cable showing another embodiment of the invention, and FIG. 4b 4 is a detailed enlarged sectional view of the cable core of the embodiment of FIG. 4a, FIG. 4c is a detailed enlarged sectional view of the optical fiber core of the embodiment of FIG. 4b, and FIG. 5 is another embodiment of the present invention. 1 is a cross-sectional view of an exemplary self-supporting fiber optic cable; FIG. DESCRIPTION OF SYMBOLS 1... Cable support wire, 2... Cable sheath, 3... Cable core, 4... Gap, 5... Protective layer, 6... Steel wire, 7... Polyethylene coating, 8
... Optical fiber core wire, 9 ... Tape winding layer, 10
... Optical fiber wire, 11 ... Buffer layer, 12 ...
Covering, 13...Jiely.

Claims (1)

[Claims] 1. The cable support line made of stranded steel wire and the cable sheath made of plastic etc. are mechanically integrated against changes in temperature and tension, and
A polyethylene coating is applied around the steel wire, a plurality of optical fiber cores are provided around the outer periphery, and a tape is further wrapped on top of the polyethylene coating, so that the cable core installed inside the cable sheath is protected against temperature changes and tension changes. , the cable support line and cable sheath are separated from the cable core, or a jelly is filled between them, and the cable support line and cable sheath are combined. 1. A self-supporting optical fiber cable, wherein a coefficient of thermal expansion of the cable core is approximately equal to a coefficient of thermal expansion of the cable core.