JPH03256013A - Loose tube type optical fiber unit - Google Patents

Abstract

PURPOSE:To prevent a transmission loss from increasing at a low temp. by coating an assembly doubled and twisted with fibers with a 1st waterproof compd. of relatively small consistency and further packing a 2nd waterproof compd. of relatively large consistency between the pipe-shaped coatings. CONSTITUTION:The assembly doubled and twisted with the optical fibers 3 is coated with the 1st waterproof compd. 4 of the relatively small consistency and is housed into the pipe-shaped covering 6 made of plastic. The 2nd waterproof compd. 5 of the relatively large consistency is packed into the gap part between the pipe-shaped covering 6 and the 1st waterproof compd. 4 housed therein to constitute a loose tube type fiber unit 10. The optical fibers are put into a stable state without entangling with each other and the transmission loss is prevented from increasing even at the low temp.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a loose tube type optical fiber unit in which an assembly of optical fiber strands is housed in a pipe-shaped covering, and a waterproof compound is filled in between. .

(Prior art) Since optical fiber wire itself is fragile, in reality, each wire is coated with a protective coating and further formed into various cable structures depending on the purpose of use, and is used as an optical fiber cable. For actual use. When configuring such a cable, it is necessary to configure the optical fiber so that the optical fiber does not experience lateral pressure that increases loss due to microbending or static load that decreases the service life.

There is a loose tube type optical fiber unit as an optical fiber unit that satisfies the above requirements. FIG. 3 is a cross-sectional view of an example of a conventional loose tube type optical fiber unit. As shown in the drawing, optical fiber glass (1
) coated with ultraviolet curing resin, etc. (2) A plurality of shunted optical fibers (cs) are housed in a plastic pipe-shaped covering (8), and a waterproof compound (7) is filled between them. However, the optical fiber strand (3) is configured to be able to move freely in the waterproof compound (7).

In such a loose tube type optical fiber unit, the optical fiber strand (3) does not come into close contact with the pipe-shaped coating (6),
Since it is in a state where it can move freely in the waterproof compound (7), lateral pressure does not act directly on the optical fiber strand (3) when making it into a cable or laying it, and the pipe-shaped coating (8) ) By giving extra length to the optical fiber (3) in advance, even if stress is applied in the axial direction of the coating (6), the effect on the optical fiber (3) is small. It has advantages. In other words, such a loose tube type optical fiber unit has a greater buffering ability against external forces than a conventional solid type optical fiber core in which the optical fiber is directly coated with secondary and secondary coatings. It can be said that there are.

(Problem to be Solved) However, in the conventional loose tube type optical fiber unit described above, when the number of optical fibers housed in the pipe-shaped sheath increases, especially when the number of fibers becomes 6 or more, the loose tube type optical fiber In the manufacturing process of the unit, the optical fibers are intricately intertwined with each other, resulting in an increase in transmission loss.

In order to prevent this, it is known to twist the optical fibers to be stored together. For example, USP4.072.
As shown in No. 398, it is disclosed that after a plurality of optical fiber strands are twisted together, they are housed in a pipe-shaped sheath, and the gap between the optical fiber strands and the pipe-shaped sheath is filled with a waterproof compound. There is.

However, if the consistency of the above-mentioned waterproofing compound is relatively large, the above-mentioned purpose may not be achieved due to untwisting when and after storing the twisted optical fibers in the pipe-shaped sheathing. Also, if the consistency of the waterproofing compound is relatively small, there is a problem in that transmission loss increases at low temperatures.

(Means for Solving the Problems) The present invention provides a loose tube type optical fiber unit that solves the above-mentioned problems. Ori,
The stranded assembly is covered with a first waterproofing compound of relatively low consistency, and furthermore, a second waterproofing compound of relatively high consistency is filled between the pipe-like covering.

(Function) In the above-described loose tube type optical fiber unit of the present invention, since the assembly of optical fiber strands twisted together is covered with a waterproof compound having a relatively low consistency, the formation of the optical fiber unit is Even after the process and formation, the twisting does not unravel. In addition, since the outer periphery of the first waterproof compound is filled with a second waterproof compound having a relatively high consistency, the force that tightens the optical fiber assembly is small even at low temperatures, and no increase in transmission loss occurs. do not have.

(Embodiment) FIG. 1 is a cross-sectional view of an embodiment of a loose tube type optical fiber unit of the present invention.

As shown in the drawing, an assembly of optical fiber glass (1) coated (2) with an ultraviolet curable resin or the like and twisted optical fiber wires (3) is a first waterproof material with a relatively small consistency. It is covered with a compound (4) and housed in a plastic pipe-shaped covering (6). In the gap between the pipe-shaped covering (6) and the aggregate covered with the first waterproofing compound (4) stored therein, a second waterproofing compound (5) having a relatively high consistency is filled. ), forming a loose tube type optical fiber unit (10).

The first and second waterproof compounds include hydrocarbon oil, silica, and styrene block copolymer.
It is preferable to use waterproofing compounds having the same composition but different consistencies by changing the blending ratio of each component. Furthermore, it goes without saying that the waterproof compound mainly contains the above three components, and may also contain small amounts of antioxidants, light stabilizers, heat stabilizers, etc.

The hydrocarbon oil in the above waterproof compound is:
Mineral oil-olefin oil is preferred, and the silica is preferably hydrophobic fumed silica or hydrophilic fumed silica. Furthermore, the styrenic block copolymer has a molecular weight of 10,000 or more, which is more effective than a waterproof compound in preventing oil separation.

FIG. 4 is an explanatory diagram of a method of manufacturing the loose tube type optical fiber unit shown in FIG. 1.

The assembly (21) of twisted optical fibers enters a first coating tank (22), where a relatively small first compound (23) is applied between the optical fibers and the assembly (22).
21). At this time, the first coating tank (22
) may be pressurized to allow the waterproof compound (23) to sufficiently penetrate between the optical fiber strands. Excess waterproofing compound (23) deposited on the assembly (21) is removed by a squeeze (24).

The aggregate (23) coated with the first waterproofing compound (23)
21) is then connected to the crosshead of the loose tube extruder (
25), a plastic pipe-shaped covering (27) is applied thereto, and at the same time, the gap is filled with a second waterproofing compound (2G) having a relatively high consistency, and the compound is cooled and solidified. A loose tube type optical fiber unit (IO) is obtained.

FIG. 2 is a cross-sectional view of a specific example of a waterproof optical fiber cable using the loose tube type optical fiber unit of the present invention.

The optical fiber unit (lO) has an optical fiber glass diameter of 12
It houses 12 single-mode optical fibers of 5 jmφ coated with two layers of ultraviolet curable resin, each with an outer diameter of 250 μ-1.The pipe-shaped coating is made of polybutylene terephthalate and has an inner diameter of 1. 4■■φ
, is formed to have an outer diameter of 2.0■■φ.

This kind of loose tube type optical fiber unit.

) (10) with a plastic coating layer (12)
Appropriate holes are placed around the tensile member (11) that has been
A waterproof optical fiber cable as shown in the figure was constructed by twisting the fibers together with a wire, filling the gap between the twists with a polybutene-based waterproof compound (13), and extruding a plastic outer covering layer (14) thereon.

Table 1 shows the combinations of the presence or absence of twisting when forming a loose tube type optical fiber unit and the waterproofing compound filled into the unit, and Table 2 shows the composition of each sample of the filled waterproofing compound and the consistency at each temperature. This is what is shown.

Table 1's2 Table *1. The average increase amount of 12 optical fibers is shown, assuming that the transmission loss before unit creation is O.

*2. The transmission loss at 25° C. after being made into a cable is O, and the average increase in the 12 optical fibers is shown.

The transmission loss for light with a wavelength of 1.551 m when an optical fiber unit is made with the combinations shown in Table 1, and the transmission loss for light with a wavelength of 1.55 μ■ at -40°C when an optical fiber cable is manufactured using them. The results of measuring transmission loss are shown in Table 1.

In sample 1, no increase in loss was observed during unit creation and at -40'C. An increase in loss was observed in sample 2 at -40"C, and in samples 3 and 4 even during unit fabrication. In addition, the cable of sample 3 was cut out several meters from the terminal, the cable was disassembled, and the state of the bare optical fiber was examined. Upon observation, it was observed that the optical fibers were randomly intertwined with each other.

(Effects of the Invention) As explained above, according to the loose tube type optical fiber unit of the present invention, the optical fiber strands are not entangled with each other and remain in a stable state even during the process of forming the optical fiber unit and after the formation. , no increase in transmission loss occurs even at low temperatures. Therefore, when an optical fiber cable is constructed using such a unit, high density can be achieved, and the cable has great utility as a maintenance-free cable in the field of optical communication.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an embodiment of a loose tube type optical fiber unit of the present invention. FIG. 2 is a cross-sectional view of a specific example of a waterproof optical fiber cable using the loose tube type optical fiber unit of FIG. FIG. 3 is a cross-sectional view of an example of a conventional loose tube type optical fiber unit. FIG. 4 is an explanatory diagram of a method of manufacturing a loose tube type optical fiber unit of the present invention. 3... Optical fiber G-line, 4... First waterproof compound, 5... Second waterproof compound, 6... Pipe-shaped coating, 10... Loose tube type optical fiber uni. ), 11...Tensian member, 12...Plastic coating layer, 13...Waterproof compound, 14...
・External coating layer.

Claims (1)

[Claims] (1) In a loose tube type optical fiber unit in which an assembly of optical fiber strands with a coating layer applied on optical fiber glass is housed in a pipe-shaped coating, and a waterproof compound is filled in between, the assembly is made of optical fibers. The strands are twisted together, and the twisted assembly is covered with a first waterproofing compound of relatively low consistency, and a second waterproofing compound of relatively high consistency is applied between the tubular coatings. A loose tube type optical fiber unit characterized by being filled.