Optical waveguides – Optical fiber waveguide with cladding – Utilizing multiple core or cladding
Reexamination Certificate
1999-07-19
2001-01-09
Henry, Jon (Department: 2872)
Optical waveguides
Optical fiber waveguide with cladding
Utilizing multiple core or cladding
C385S126000
Reexamination Certificate
active
06173102
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an optical fiber coated with double photo-curable resin layers, and a method of making the same.
BACKGROUND ART
From the viewpoint of low transmission loss, silica based glass fibers have been used as optical fibers for long-distance transmission. In order to keep transmission and strength characteristics, employed is a coated optical fiber in which a primary coating made of a relatively soft resin and a secondary coating made of a relatively hard resin are applied to the surface of a glass fiber.
Conventionally used is a coated optical fiber in which, at the same time when a glass fiber is drawn from an optical fiber preform, a primary coating resin is applied thereto and cured thereon so as to form a primary coating, and then a secondary coating resin is applied to and cured on the outer periphery of the primary coating so as to form a secondary coating. On the other hand, recently has been studied from the viewpoint of improving productivity is a method in which both primary and secondary coating resins are simultaneously applied to the outer periphery of the glass fiber and are subsequently cured. In the case where such a collective coating method is employed, since the power of a light source for irradiating ultraviolet rays is limited, it has been difficult for the primary coating layer to cure sufficiently, thereby making it problematic in that the manufacturing speed is rather lowered.
In order to avoid such a problem, for example, in the collective coating method such as that mentioned above, proposed is a technique in which a photo-polymerization initiator added to the secondary coating resin is relatively lowered (Japanese Patent Application Laid-Open Gazette No. Hei. 7-168069), or a technique in which the primary coating resin and secondary coating resin are cured with their respective curing wavelength bands shifted from each other (Japanese Patent Application Laid-Open Gazette No. Hei. 1-276105).
In the former of the conventional techniques mentioned above, however, when the amount of photo-polymerization initiator added to the secondary coating resin is lowered in order to cure the primary coating resin, the curing speed of the secondary coating decreases, whereby it may become problematic in that productivity deteriorates. In the latter technique, on the other hand, it is hard to obtain resins which clearly demarcate two curing wavelength bands, thus leaving a problem to cure two resin layers efficiently.
It is an object of the present invention to provide a coated optical fiber in which not only the secondary coating resin layer but also the primary coating resin layer can be photo-cured simultaneously and efficiently to a high degree of cure, without relatively lowering the photo-polymerization initiator added to the secondary coating resin or without shifting the curing wavelength bands of primary and secondary coating resins from each other; and a method of making the same.
DISCLOSURE OF THE INVENTION
The coated optical fiber in accordance with the present invention is a coated optical fiber comprising a glass fiber constituted by a silica based glass core and cladding; and a primary coating (inner coating) and a secondary coating (outer coating) which are formed by photo-curing a primary coating resin layer (inner coating resin) and a secondary coating resin layer (outer coating resin) which are applied to an outer periphery of the glass fiber, wherein a maximum value A
s(max)
of absorbances A
s
of the secondary coating resin layer before curing with respect to light in a wavelength region of 310 to 340 nm is not more than 0.5, whereas absorbances A
p
of the primary coating resin layer before curing with respect to light in the above-mentioned wavelength region are greater than the absorbances A
s
.
The inventors have found it is necessary to satisfy the above-mentioned relationship in an optical fiber in which the primary coating and secondary coating are formed around the outer periphery of a glass fiber, in order to photo-cure not only the secondary coating resin layer but also the primary coating resin layer simultaneously and efficiently to a high degree of cure.
That is, conventionally, in the step of curing the above-mentioned two resin layers, as the manufacturing speed increases, though the secondary coating resin is cured, an uncured state has been likely to appear in the primary coating resin. The inventors have considered it attributable to the fact that, when ultraviolet rays are incident on a photo-curable resin, though an energy sufficient for curing the resin is supplied to its surface, the ultraviolet rays are attenuated as they further infiltrate into the resin, thus failing to supply a sufficient energy to the inner photo-curable resin for curing. When an uncured state occurs in the primary coating portion, the interface between the glass fiber and primary coating becomes unstable, whereby transmission characteristics may fluctuate or chemical characteristics of the resin are likely to change, thus deteriorating the reliability as a transmission medium.
The first requirement in the present invention is to use, as a secondary coating resin layer, a photo-curable resin layer of which a maximum value A
s(max)
of absorbances A
s
with respect to light in a wavelength region of 310 to 340 nm is 0.5 or less. Since the maximum value A
s(max)
of absorbances A
s
of the secondary coating resin layer is not more than 0.5 and thus is small, without the ultraviolet rays irradiated for curing being attenuated by absorption within the secondary coating resin, an energy sufficient for curing is supplied to the primary coating resin as well.
Further, in the present invention, as the second requirement, absorbances A
p
of the primary coating resin layer with respect to light in the above-mentioned wavelength region are set greater than the absorbances A
s
of the secondary coating resin layer, preferably with a difference therebetween of at least 0.3. Since the absorbances A
p
of the primary coating resin are higher than the absorbances A
s
of the secondary coating resin layer, even when the ultraviolet rays are attenuated by the secondary coating resin, those incident on the primary coating resin can be effectively utilized, thus sufficiently helping the primary coating resin to cure.
The method of making a coated optical fiber in accordance with the present invention comprises:
a first step of preparing a primary coating resin and a secondary coating resin such that a maximum value A
s(max)
of absorbances A
s
of a secondary coating resin layer before curing with respect to light in a wavelength region of 310 to 340 nm is not more than 0.5, whereas absorbances A
p
of a primary coating resin layer before curing with respect to light in the above-mentioned wavelength region are greater than the absorbances A
s
;
a second step of simultaneously applying the primary coating resin layer and the secondary coating resin layer to an outer periphery of a glass fiber constituted by a silica based glass core and cladding; and
a third step of photo-curing the primary coating resin layer and the secondary coating resin layer so as to yield the coated optical fiber.
The manufacturing method in accordance with the present invention is a method in which double photo-curable resin layers are collectively applied to the outer periphery of the glass fiber at first, and then these resin layers are cured upon one shot of light irradiation. As such a method is employed, the productivity improves, and the equipment space can be reduced, thus making it possible to reduce the manufacture cost.
Further, since a resin layer of which the maximum value A
s(max)
of absorbances A
s
with respect to light in the wavelength region of 310 to 340 nm is 0.5 or less is used as the secondary coating resin layer, the ultraviolet rays can efficiently enter into the primary coating resin, whereby a sufficient degree of cure can be secured in the primary coating resin.
Also, since the absorbances A
p
of the primary coating resin lay
Akasaka Nobuhiro
Matsuda Yasuo
Suzuki Atsushi
Henry Jon
Pillsbury Madison & Sutro LLP
Sumitomo Electric Industries Ltd.
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