JPH02216113A - Optical cable for cryogenic service - Google Patents

Abstract

PURPOSE:To allow stable light transmission with a lens transmission loss even at an extremely low temp. by constituting the cable by using optical fibers formed by loosely housing coated fibers coated with a UV curing type resin into metallic tubes. CONSTITUTION:The coated optical fibers 3 of the optical cable to be used for LNG storage facilities, etc., are constituted by loosely housing the optical fibers 1 primarily coated with the UV curing type resin having a good low-temp. charactersitic into the metallic tubes 2 having a low coefft. of expansion. The optical cable 8 for cryogenic service is formed by using such coated optical fibers 3. Since the shrinkage of the metallic tubes 2 is thereby lessened even under the extremely low temp., bending and side pressures are not applied on the fibers 1 and the increase in the transmission loss is prevented. Since the construction is of a loose type, the fibers 1 are kept free from the side pressures even when subjected to abrupt external forces, such as bending, at the time of cabling.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a cryogenic optical cable that is suitably used under cryogenic conditions such as in LNG storage facilities, and is particularly aimed at reducing increases in transmission loss. .

[Conventional technology]

One type of optical fiber that has been conventionally used for optical cables is an optical fiber that is made by primarily coating the outer periphery of an ordinary quartz-based fiber with silicone resin, ultraviolet curable resin, or the like. Among these optical fibers, those in which the primary coating layer is made of silicone resin have poor low-temperature properties and show a very large increase in transmission loss at extremely low temperatures. It is known that coated optical fibers have good low-temperature properties and are capable of stable optical transmission even at extremely low temperatures. For this reason, it was thought that it would be better to use strands coated with ultraviolet-curable resin for cryogenic optical cables, but stranded fibers have poor mechanical properties such as lateral pressure and are difficult to make into cables. Because of these disadvantages, it is considered necessary to form an optical fiber coated wire in which a secondary coating layer is further formed on the outer periphery of the wire.

Such optical fiber cores include tight optical fiber cores in which a secondary coating layer made of nylon, UV-curable resin, polyester, etc. is provided on the outer periphery of the above-mentioned UV-curable resin-coated optical fiber wire. There is a line. However, with this tight optical fiber core, lateral pressure occurs due to bending during the cable production process, which not only causes an increase in transmission loss, but also
At low temperatures, the resin forming the secondary coating layer shrinks, resulting in disadvantages such as increased lateral pressure on the strands.

Therefore, in order to avoid the above-mentioned lateral pressure problem, loose optical fiber cores have been proposed and used. This is made by housing the optical fiber loosely in a resin tube or resin pipe, and creating a gap between the fiber and the resin tube or resin pipe, or by filling this gap with sherry, etc. It is.

[Problem to be solved by the invention]

However, because of the loose structure of such loose optical fiber cores, the problem of lateral pressure caused by bending during the cable production process has been resolved, but since a resin tube or pipe is used, When the temperature becomes low, the resin that makes up the tube or pipe contracts, and if it is filled with sherry, it also contracts, eventually adding bending to the strands, resulting in an increase in transmission loss of 1B. There was a problem.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned problems and provide a stable cryogenic optical cable with little increase in transmission loss even under low temperature conditions.

[Means for solving problems].

The present invention uses a coated optical fiber in which an optical fiber primarily coated with an ultraviolet curable resin is loosely accommodated in a metal tube or metal pipe.

[For production]

The above-mentioned optical fiber core has a structure in which the optical fiber is housed in a metal tube or pipe with a low coefficient of linear expansion, so even if it is placed under extremely low temperature conditions, the metal Since the shrinkage of the optical fiber is small, bending and lateral pressure are not applied to the optical fiber.

In addition, since it has a loose structure, even if it is subjected to sudden external force such as bending when being made into a cable, lateral pressure due to bending etc. is not easily applied to the tip fiber strand.

Therefore, an optical cable using such an optical fiber core does not have the disadvantage of increased transmission loss due to lateral pressure, not only under normal environments but also under extremely low temperature conditions.

Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 shows an example of a cross section of a coated optical fiber used in the optical cable of the present invention.

Reference numeral 1 in FIG. 1 is a bare optical fiber. This optical fiber strand 1 is composed of an optical fiber Ia at the center and a primary coating layer 1b provided on the outer periphery of the optical fiber Ia. Here, the central optical fiber 1a is a normal silica-based glass fiber, and the -order Wm layer 1b is
Ultraviolet curing resin is used. As this ultraviolet curable resin, ordinary urethane acrylate and epoxy acrylate resins are suitably used.
The above-mentioned primary coating layer 1b is formed by coating to a thickness of about 140 μl.

One or more of these optical fibers 1 are loosely accommodated in a metal tube or metal pipe 2 to form a loose optical fiber core 3. Here, the metal tube or metal pipe 2 is made of metal such as stainless steel, copper, or aluminum and has an inner diameter of 0.
．． 8-1. A tube or pipe with an outer diameter of about 1.2 to 1.8 cm is preferably used.

These coated optical fibers 3 are suitably used as coated optical fibers for the following cryogenic optical cables. Specifically, as shown in FIG. 2, for example, one loose optical fiber core 3 is twisted around a tensile strength member (tension member) 5, and the outer periphery is further pressed with a rolling tape 6. Although it is used as a cryogenic optical cable 8 which is wound and further provided with an outer covering layer 7, the structure of this cryogenic optical cable 8 is not particularly limited to this.

Here, the tensile strength member 5 has a diameter of 1. Approximately 2xm steel wire is preferably used, and the wrapping tape 6 is preferably inorganic wrapping such as glass mica tape, glass cloth, carbon cloth, or protective tape such as aluminum tape or corrugated iron tape. be done.

In addition, the outer covering layer 7 is made of polyethylene, polyvinyl chloride, P
Diameter 70mx made of fluororesin such as FA, FEP, etc.
A sheath of approximately 100 mm is preferably used.

As described above, in this optical cable 8 for cryogenic use, the optical fiber core 1i13 is a loose type in which the optical fiber 1, which is primarily coated with an ultraviolet curable resin, is loosely accommodated in the metal tube or pipe 2. , the increase in transmission loss can be kept to a minimum not only under normal environments but also under extremely low temperature conditions. That is, by using the metal tube or pipe 2 with a low coefficient of linear expansion, the metal shrinks little even under extremely low temperature conditions, so that the optical fiber element vA1 is not bent or subjected to lateral pressure.

Furthermore, by forming the optical fiber core 3 into a loose structure, there is an advantage that no lateral pressure is applied to the tip fiber strand l even if it is subjected to a sudden external force such as bending during cable formation. Therefore, the disadvantage of increasing transmission loss due to lateral pressure during cable formation, which is the case with conventional tight optical fiber cores, is eliminated.

〔Example〕

Core diameter 50μ! A primary limb covering layer made of an ultraviolet curable resin was provided on the outer periphery of a quartz-based optical fiber having a fiber diameter of 125U+ to form an optical fiber strand having an outer diameter of 0.25IIJI. Two of these optical fibers have inner diameters of 0 and 8 z.
A loose optical fiber core wire having a cross-sectional structure as shown in FIG.

Six optical fibers thus obtained were closely wound in a spiral on the outer periphery of a steel tension member with an inner diameter of 7. A cryogenic optical cable having a cross-sectional structure as shown in FIG. 2 was manufactured by inserting the cable into a polyethylene sheath of Ou.

(Comparative Example 1) A tight coated optical fiber was prepared by forming a secondary coating layer made of nylon on the outer periphery of the same optical fiber as used in the example. Using this optical fiber core wire, a cable was formed in the same manner as in the example to create an optical cable, which was used as Comparative Example 1.

(Comparative Example 2) The outer periphery of the quartz-based optical fiber used in the example was coated with silicone resin to form a tip fiber strand with an outer diameter of 0.2531 JI, and two of these strands were formed, with an inner diameter of 0.8zx and an outer diameter of 1.21
An optical cable was prepared in the same manner as in Example 1 except that it was housed in the stainless steel pipe of Comparative Example 2.
And so.

(Test Example 1) Using each of the optical cables of Example and Comparative Example 1, changes in transmission loss due to cable formation were investigated, and the results are summarized in FIG. 3. The transmission loss was measured by guiding skin light with a wavelength of 0.85μ, and the number of measurements was 10 for each cable.

From FIG. 3, it is clear that in the optical cable of the example, the increase in transmission loss during the cable forming process is smaller than that of the optical cable of Comparative Example 1.

(Test Example 2) Using each of the optical cables of Example and Comparative Example 2, the low-temperature characteristics of each were investigated, and the results are summarized in FIG. 4. The measurement was carried out by measuring the transmission loss when light with a wavelength of 0.85 μm was guided at a low temperature of −196° C., and the measurement length was 300 m.

From Figure 4, the optical cable of Comparative Example 2 has a temperature of -196°C.
However, in the optical cable of the example, the transmission loss increases by about 0.0% even under the same conditions. 6
It became clear that the low-temperature characteristics were as small as dB/km, and that the low-temperature characteristics were good.

(Test Example 3) Using the optical cable of the example, its temperature characteristics were investigated and are shown in FIG. The measurement was performed by guiding light with a wavelength of 0.85 μm and measuring the transmission loss due to temperature changes from +60'C to -40°C.
It was set as m.

From FIG. 5, in the optical cable of the example, the increase in transmission loss due to temperature change is Q, even after 4 days have passed.
It was found that the temperature characteristics were extremely small, 1 dB/k11 or less, and that the temperature characteristics were good.

〔Effect of the invention〕

As explained above, the cryogenic cable of the present invention is
Since we use an optical fiber core consisting of an optical fiber primarily coated with ultraviolet curable resin that is loosely housed inside a metal tube or pipe, it can be used not only under normal conditions but also under extremely low-grade conditions. Stable optical transmission can be performed with little increase in transmission loss. In other words, it goes without saying that a primary coating layer made of an ultraviolet curable resin with good low-temperature properties is provided on the optical fiber, and a metal tube or pipe with a low coefficient of linear expansion is used for the optical fiber core. Therefore, it does not shrink even at low temperatures, and therefore does not cause lateral pressure.

Further, since the optical fiber core wire has a loose structure as described above, lateral pressure is not applied due to bending or the like during the cable forming process.

Moreover, since the optical fiber is not used as it is, but is made into a core structure, the optical cable has sufficient strength and can be made into a cable.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a schematic cross-sectional view showing an example of the optical fiber core used in the present invention, and FIG. 2 is a schematic cross-sectional view showing an example of the cryogenic optical cable of the present invention. FIG. 3 is a graph showing the transmission loss characteristics of the optical cables of the embodiment of the present invention and the comparative example, respectively. FIG. 5 is a graph showing the temperature characteristics of the optical cable according to the embodiment of the present invention. ■...Optical fiber wire, 2...Metal tube or pipe, 3...
...Optical fiber core, 8...Cryogenic optical cable.

Claims (1)

[Claims] 1. An optical cable for cryogenic use, characterized in that it is constructed using a cored optical fiber in which an optical fiber primarily coated with an ultraviolet curable resin is loosely accommodated in a metal tube or metal pipe.