JPS58223636A - Preparation of core wire of optical fiber - Google Patents

Abstract

PURPOSE:To prepare an optical fiber wire capable of assuring the safety against the static fatigue, by drawing a coating material extruded into the form of a tube under reheating, applying an extension strain to the coating by reducing the diameter thereof, closely adhering the coating material to the optical fiber, and reheating the optical fiber to give a shrinkage strain to the coating. CONSTITUTION:An element wire 1 of an optical fiber is coated with a coating to give a loose tube in an extruder 2. In the process, a pressurizing apparatus 3 or a form adjusting device 4, etc. is used if necessary. The coated element wire 1 of the optical fiber is once cooled in a cooling bath 5 and then drawn between the first capstans 6 and the second capstans 8 while heated at the melting temperature in a heating furnace 7 to reduce the diameter thereof. Thus, the coating is closely adhered to the elment wire 1 of the optical fiber. The resultant optical fiber is then passed through dancer rolls 9 for the optical fiber and wound onto a bobbin 10 under low tension. Althrough the glass fiber part is not subjected to a compression strain, the coating material stores a great extension strain and shrinks by the heat treatment. Thus, the shrinkage strain is conversely applied to the glass fiber part by the shrinkage force.

Description

[Detailed Description of the Invention] Technical Field of the Invention: The present invention provides a method for producing a cored optical fiber in which shrinkage strain in the longitudinal direction is applied to a glass fiber in advance to prevent breakage due to static fatigue deterioration of the glass fiber. It is related to.

Technical background: Optical fibers in current optical cables are inevitably stretched due to residual elongation strain during cable formation, elongation strain during cable installation, and linear expansion strain due to cable temperature.

Prior art and problems: Conventional optical fibers are classified into two types based on their cross-sectional structure. One type is a tight-coated core wire in which the coating material adheres to the optical fiber, and the other is a loose tube core wire in which there is a gap between the coating material and the original fiber, forming a tube shape. be.

By the way, as mentioned above, due to its nature, static fatigue progresses when elongation stress is applied to glass fibers, so there is a problem in optical fibers with the conventional structure that they will break after a certain period of time. Ta.

Purpose of the invention: The purpose of the present invention is to apply shrinkage strain to the glass fiber in advance, and to prevent static fatigue such that the glass fiber still does not reach the elongated state even after the elongation strain expected in the use condition is applied. A manufacturing method for optical fiber cores that can guarantee safety against static fatigue, especially for tight-coated core wires, in which shrinkage strain is applied to the canth fiber portion in advance to ensure safety against static fatigue. The purpose is to provide a manufacturing method. Embodiments of the present invention will now be described with reference to the drawings.

Embodiments of the invention: The figures schematically show the manufacturing process of a cored optical fiber according to the invention. The optical fiber strand 1 is coated by an extruder 2. At this time, the coating is applied so that it does not adhere to the optical fiber 1 and forms a loose tube shape. To enable loose tube type extrusion, a pressurizing device 6 is installed as necessary.
Alternatively, use a shaping table 4 or the like. The optical fiber coated in the form of a loose tube is once cooled in the cooling bath 5 and guided to the first capstan B. After that, the heating furnace 7 heats the first capstan 6 and the second capstan again to the melting temperature.
It is stretched and reduced in diameter by tension between it and the capstan 8.

At this time, care must be taken to ensure that the stretched optical fiber is sufficiently supplied from the supply section 11. for that purpose,
It is desirable that the passage of the optical fiber is arranged in a straight line up to the extension part. At this point, the coating tightly adheres to the optical fiber 1 due to diameter reduction. Thereafter, it is wound onto a bobbin 10 with low tension via an optical fiber dancer loaf 9. In the optical fiber core wire manufactured by the above process, the glass fiber portion has not yet received compressive strain, but the coating material has accumulated a large amount of elongation strain. However, by heating the optical fiber, the coating material shrinks. At this time, shrinkage strain is applied to the glass fiber portion due to the shrinkage force of the O coating material.

Specific examples of the present invention are shown below. Optical fiber wire with an outer diameter of 0.4 mmφ and nylon with an outer diameter of 0.98 ffl? 71
After coating and extruding it into a tube shape with an inner diameter of 3.5 mm, the second capstan was set to take off at a speed 1.12 times faster than the first capstan, and the first capstan was heated to a temperature of 160°C. By drawing the optical fiber 1 between the second capstan, a dense four-branch type optical fiber core having an outer diameter of 0.9 mm was obtained.

When the core optical fiber was heat-treated at a temperature of 100C for 6 hours, it was confirmed that about 0.5% shrinkage strain was added to the glass fiber.

Effects of the Invention: As described above, when coating an optical fiber, the present invention first extrudes the coating into a tube shape and then stretches and reduces the diameter while heating it again, thereby applying elongation strain to the coating. This method is characterized by applying shrinkage strain to the optical fiber by shrinking the coating by heating it again after it is tightly attached to the fiber, which is effective in ensuring safety against static fatigue of the optical fiber core wire. Very dog-like.

[Brief explanation of drawings]

The figure is a diagram showing an outline of the manufacturing process of the bovine fiber core wire according to the present invention. 1... Optical fiber wire, 2... Extrusion tower:, 6...
Pressure device inside the target, 4...forming table for tube extrusion, 5
... Cooling tank, 6... First capstan, 7... Heating furnace, 8... Second capstan, 9... Optical fiber dancer roller, 10... Winding bobbin, 11...
・Patent applicant: Nippon Telegraph and Telephone Public Corporation (1 other person) Representative patent attorney: Hisashi Tamamushi Gobu

Claims (1)

[Claims] A method for manufacturing an optical fiber core wire in which an optical fiber wire is densely coated with a resin, including a step of extruding and coating the optical fiber wire into a tube shape without closely contacting the resin, and a step of extruding the resin coating into the tube shape. forming a cored optical fiber by drawing it to a desired length and reducing its diameter to bring the tubular coating into close contact with the optical fiber; 1. A method for producing a coated optical fiber, comprising the steps of: reheating the coated optical fiber, and shrinking the coated optical fiber in the length direction by thermal contraction generated in the resin coating.