JP2687650B2 - Optical fiber cable stabilized at low temperature - Google Patents

Description

TECHNICAL FIELD The present invention relates to a spacer type optical fiber cable in which an optical fiber is housed in a spacer having a spiral optical fiber housing groove, and particularly when used at low temperatures. The present invention relates to an improved spacer type optical fiber cable that enables stable use without increasing transmission loss.

[Prior Art] As one of typical structures of optical fiber cables, there is a spacer type optical fiber cable as an optical fiber cable which has been put into practical use from an early stage.

Specifically, as shown in FIG. 1, a spacer 2 having spiral optical fiber receiving grooves 3, 3 is extruded and integrated on the outer periphery of a tension member 1 made of a high tensile strength material such as galvanized steel wire, Optical fiber storage grooves 3,3 in which single-core or multiple-core optical fibers 4,4 (strands or cores) are housed, and after a presser winding 5 is applied, a jacket 6 such as plastic is covered. Is.

The optical fiber housing groove 3 is formed in a spiral shape so that the optical fiber 4 housed therein can be provided with a surplus length in the longitudinal direction, and the length of the cable can be expanded by tension or thermal expansion of the cable. This is because the extra length is absorbed by the extra length so that a large tension is not directly applied to the optical fiber 4.

[Problems to be Solved by the Invention] As described above, in the spacer type optical fiber cable, the groove of the spacer is formed in a spiral shape, but the original purpose thereof is that the extension of the cable itself extends to the optical fiber and is weak against tension. This is to prevent the optical fiber from being adversely affected such as disconnection and increase in transmission loss.

However, in recent years, technologies such as information communication and control using optical fibers have been remarkably developed, and the application environment is not limited to use at room temperature or high temperature range, for example, in a freezing warehouse at a low temperature of about −40 ° C. Optical fiber cables have been used for control and management, and for information communication in extreme cold regions, etc., and have come to face new challenges that were not expected at first.

In the spacer type optical fiber cable, when the galvanized steel stranded wire or the single wire is used as the tension member 1 as shown in FIG. 1, the linear expansion coefficient of the cable is a steel wire with a small linear expansion coefficient ( 11.5 × 10 ^-6 / ° C) and a plastic with a large linear expansion coefficient (10 ^-5 / ° C)
It becomes a composite value of the linear expansion coefficient of the cable and can be suppressed so as not to become too large.

However, in recent years, focusing on the fact that optical fibers are not affected by electromagnetic waves, so-called non-metallic materials with high tensile strength such as glass fiber reinforced plastic (hereinafter referred to as FRP) are used without using metal for tension members. In many cases, it has a non-metallic structure.

In particular, in the case of an optical fiber cable used in the state of overhead wire, a structure as shown in FIG. 2 in which the above-mentioned FRP is used for the tension member is also used in order to prevent lightning strikes.

As described above, the plastic material has a large linear expansion coefficient as compared with the metal, and the elongation becomes large at a high temperature, and the shrinkage amount becomes very large at a low temperature.

Therefore, in the case of the spacer type optical fiber cable having the structure as shown in FIG. 2, when the operating temperature becomes lower than −20 ° C., the shrinkage amount of the entire cable including the spacer becomes very large, and as a result, The optical fiber 4 made of glass (5.6 × 10 ⁻⁷ / ° C.) whose coefficient of linear expansion is smaller than those constituent materials is left in the spacer groove 3, and the excess is left in the groove 3 as shown in FIG. When the optical fiber 4 comes into contact with the surrounding presser coil and contracts further than this, the optical fiber 4 becomes a meandering state to absorb the excess length, resulting in small bends at various places, resulting in optical transmission loss. The phenomenon such as a sudden increase is becoming apparent. In such a case, there is a limit in selecting the coating material of the optical fiber to cope with it.

Therefore, a measure has been taken to increase the cross-sectional area of the FRP, which has the smallest linear expansion coefficient among the constituent materials of the optical cable, so that the composite linear expansion coefficient with other plastic materials around it becomes as close as possible to that of FRP. There is.

However, FRP is expensive, and if the cross-sectional area is increased, the cable itself becomes quite expensive, and there is a structural limit to increasing the cross-sectional area. It also goes against the market demand to reduce the overall diameter to reduce costs.

The object of the present invention is to solve the problems of the prior art as described above, and even when used at a considerably low temperature such as a low temperature of −40 ° C. or less, the transmission loss hardly changes, and stable optical transmission is continued. It is an object of the present invention to provide a novel low temperature characteristic-stabilized optical fiber cable that can be retained.

[Means for Solving the Problems] The present invention provides a spacer type optical fiber cable in which an optical fiber element wire or an optical fiber core wire is housed in a spiral optical fiber housing groove formed on the outer periphery of a spacer, The coefficient of linear expansion of the cable is α (℃ ^-1 ), the temperature difference from room temperature to low temperature is ΔT (℃), and the elongation strain due to the tension applied to the optical fiber strand or core wire is given to the ε _f (%) spacer. The elongation strain due to the given back tension is ε _s (%), and the contraction strain of the cable at which transmission loss starts in the optical fiber or the core wire is ε _c (%), α · ΔT × 100- (ε _The tension is applied in advance to the optical fiber element wire or the core wire so as to satisfy the relationship of _f −ε _s ) <ε _c .

[Operation] When the optical fiber is stored in the optical fiber storage groove of the spacer type optical fiber cable, conventionally, tension is not applied to the optical fiber, and the optical fiber is stored without strain. . This has caused the optical fiber in the groove to meander at low temperatures.

In the present invention, the elongation strain calculated in advance is given to the optical fiber. Since this elongation strain does not have to be as large as proof stress, it has little effect on the life of the optical fiber. In particular, when used in a low temperature environment, the elongation strain applied at room temperature in advance is released and relaxed at low temperature. Even if the spacer as a whole contracts, the meandering of the optical fiber does not occur while the elongation strain is released.

[Example] Hereinafter, the present invention will be described with reference to examples.

FIG. 5 is a diagram plotting the temperature-transmission loss increasing characteristics in a comparison experiment of a conventional spacer type optical fiber cable and a spacer type optical fiber cable according to the present invention.

This comparison experiment method does not manufacture the optical fiber cables separately, but as shown in FIG. 4, the four grooves 3, 3 of the non-metallic spacer 2 having the FRP as the core tension member 1 are manufactured. The optical fiber of 0% strain that does not add elongation strain to the two places in the
4B and 4B are stored, optical fibers 4A and 4A to which elongation strain 0.1% is added are stored in the other two places, and the optical fiber cable is configured in this way to make optical fiber 4A at +50 to -45 ° C. This is a measurement of the amount of increase in each 4B transmission loss. By using one spacer 2 in this way, the characteristics can be compared with high accuracy without causing unevenness in the experiment.

The wavelength of the light used is 1.55μ as shown in Fig. 5.
m is the curve A plotted with a circle, and the curve A plotted with a dotted line is a measurement result of the optical fiber 4A according to the present invention to which elongation strain has been previously given at room temperature. It is a measurement result of 4B.

The characteristics at room temperature are not particularly different from each other, but in the case of 4B of the conventional example, the transmission loss remarkably increases at the boundary of -10 ° C.

The shrinkage of the cable when reaching −10 ° C. was ε _c = 0.08%, but the optical fiber 4B of the conventional example has a storage limit in the length when the shrinkage of the cable reaches 0.08%, and the meandering thereafter. As a result, the so-called microbend continues to increase and progresses to a marked increase in transmission loss as shown by the curve B in FIG.

However, the optical fiber 4A according to the present invention, which has been subjected to elongation strain of 0.1% at room temperature, does not show any increase in transmission loss until it reaches a low temperature of -45 ° C.

The shrinkage of the cable at −45 ° C. ε _c = 0.18%. That is, the cable shrinkage is 0.
Until reaching 18%, the optical fiber 4A continues to release its own elongation strain, and the elongation strain of 0.1% given in advance is released, and a difference of 0.08% occurs with the contraction strain of 0.18% of the cable. For the first time, the conventional optical fiber 4B
It started to show the same behavior as that shown at 10 ° C.

Summarizing the results of these experiments, the temperature difference from normal temperature to the critical operating temperature at low temperature is ΔT (° C), the linear expansion coefficient of the cable is α (° C ^-1 ), the tension applied to the optical fiber strand or core wire. Ε _f (%) Elongation strain due to back tension applied to the spacer is ε _s (%) The contraction strain of the cable at which transmission loss starts in the optical fiber or the core wire is ε _c (%) ), It is understood that tension may be applied to the optical fiber element wire or the core wire in advance so as to satisfy the relationship of α · ΔT × 100− (ε _f −ε _s ) <ε _c .

Providing such pretension to the optical fiber is not preferable because it causes so-called static load fatigue when used at room temperature or higher, but when it is used in a frozen warehouse or in a cold region at high latitudes, it is applied. The pretension itself is relaxed to the extent that it does not affect the life of the optical fiber, and it is possible to effectively prevent the meandering in the spacer groove at low temperature and reliably suppress the increase of transmission loss. It becomes.

[Effects of the Invention] As described in detail above, according to the low-temperature characteristic-stabilized optical fiber cable of the present invention, the optical fiber accommodated in the spacer groove simply satisfies a predetermined value without changing the material used. Just by applying such a pre-tension, stable optical signal transmission can be maintained and continued in the expected low temperature environment with almost no increase in transmission loss. There is great industrial significance that the range of use of fiber cables can be expanded.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a specific structure of a conventional spacer type optical fiber cable using a steel wire as a tension member, and FIG.
FIG. 4 is a cross-sectional view of a cable according to the present invention, FIG. 3 is a cross-sectional view showing a state in which it is in a critical state at low temperature, and FIG. 4 is a spacer portion of a cable subjected to a temperature-low temperature loss characteristic experiment. FIG. 5 is an explanatory sectional view, and FIG. 5 is a diagram showing the results of temperature-low temperature loss characteristic experiments. 1: Tension member, 2: Spacer, 3: Optical fiber storage groove, 4: Optical fiber, 5: Presser winding, 6: Outer cover.

Claims (1)

(57) [Claims] 1. A spacer type optical fiber cable in which an optical fiber element wire or an optical fiber core wire is housed in a spiral optical fiber housing groove formed on the outer circumference of a spacer, and the linear expansion coefficient of the cable is ... (℃ ^-1 ) Temperature difference from room temperature to low temperature ... ΔT (℃) Elongation strain due to tension applied to optical fiber or core wire ε _f (%) Elongation strain due to back tension applied to spacer ... ε _s (%) When the contraction strain of the cable in which transmission loss starts in the optical fiber or the core wire is ε _c (%), α · ΔT × 100− (ε _f −ε _s ) <ε _c A low-temperature characteristic-stabilized optical fiber cable in which tension is applied in advance to an optical fiber element wire or a core wire so as to satisfy the following relationship.