Coated optical fiber and fabrication process therefor

Details Coated optical fiber and fabrication process therefor Coated optical fiber and fabrication process therefor

1996-08-06

1997-12-30

Ullah, Akm E.

Optical waveguides

Optical fiber waveguide with cladding

Utilizing multiple core or cladding

65435, G02B 602, G02B 622

Patent

active

057039887

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a coated optical fiber, and a process and an apparatus for fabricating a coated optical fiber. More specifically, the present invention relates to a coated optical fiber which is suitably usable as strands for constituting a multi-strand (or multi-count) optical fiber cable, and a process and an apparatus which are capable of efficiently fabricating a coated optical fiber having a good resistance to an external flaw.


BACKGROUND ART

In recent years, for the purpose of meeting the diversification in the demand for communication and of meeting an increase in the communication traffic, the conversion of subscriber lines into optical fiber transmission lines is now in progress, especially in urban areas. At present, the optical communication systems for subscribers are mainly constituted by private systems for handling large-capacity communication such as image data communication, and multiplexed systems for handling telephone communication and low-speed digital communication, and therefore the number of the optical fibers required for these systems is rather limited.
However, in the near future, when the communication handling the large-capacity information such as image data is generalized so that it is popularized even in ordinary homes, it is predicted that it will become necessary to replace all of the current subscriber lines comprising copper wires, with optical fibers so as to meet the demand of the users.
In order to carry out a design (i.e., Fiber-To-The-Home (FTTH) design) such that all of the wires constituting the above-mentioned subscriber line networks should be replaced with optical fibers, it is necessary to use a cable (multi-strand optical fiber cable) containing therein a large number of assembled optical fibers. At present, as an optical fiber cable which is expected to replace a copper wire cable currently used, it has been investigated to introduce an ultra-high-strand (or ultra-high-count) optical fiber cable which has an outside diameter accommodable in a current pipe line (inside diameter: 75 mm) for laying copper wire cables, and also has a number of strands or counts (e.g., 4000 strands) which is comparable to the number of conductor pairs in a current copper wire cable (3600 pairs) (Tomita et al.; Proceedings of Spring National Conference of the Institute of Electronics, Information and Communication Engineers, B-871, in 1991).
In order to realize such an ultra-high-strand optical fiber cable, it is absolutely necessary to reduce the outside diameter (outside diameter reduction) of a coated optical fiber, whereas at present, the optical fiber cable contains about 1000 strands, and the outside diameter of each strand is 250 .mu.m.
A coated optical fiber comprises a light-transmitting fiber, and a resin coating layer disposed on the outer periphery (or circumference) of the light-transmitting fiber. The coating layer has a function of absorbing pressure externally applied thereto so as to prevent the bending of the light-transmitting fiber and to maintain the light transmission characteristics of the fiber, and also has an important function of preventing an external flaw of the fiber. It is difficult to change the outside diameter of the standardized light-transmitting fiber per se. Therefore, in order to reduce the outside diameter of the coated optical fiber, it is necessary to reduce the thickness of the above-mentioned coating layer.
However, such reduction in the outside diameter of the coated optical fiber or reduction in the coating layer thickness can cause a problem in the quality of the optical fiber, especially, a problem of deterioration in the fiber strength (mechanical characteristic). Such deterioration in the fiber strength not only decreases the productivity of the fiber markedly, but also invites a serious problem in the quality assurance of the optical fiber cable.
Accordingly, in order to reduce the thickness of the coating layer while preventing the external flaw of the light-transmitting fiber (i.e., while mai

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