ECOC 1975 - ECOC 2013

54
PLASTIC COATING OF OPTICAL GLASS FIBER
A. Isomura, Y. Yamamoto, T. Yamanishi*
1. IntroductiQn
In order to obtain practical cables of optical glass fibers, the improvement
of the mechanical properties of glass fiber is one of the most important
problems; the glass fiber is so brittle and its diameter is so small that
handling performances of the fiber must be made easy through improving the
mechanical properties.l) 2) For this purpose some studies were made on
plastic coating, considering important two factors associated with the
mechanical properties of glass fiber: the adhesive property and Young's
modulus of coating plastic, and coating method. We found that glass fiber
coated with a kind of thermosetting plastic in tandem with fiber drawing
had good mechanical properties, and thermosetting plastic prevented the
surface cracks on the fiber from propagating. This paper describes the
approach of our studies, the properties of the improved optical glass waveguide
and some aging stabilities.
2. The approach of our studies
Although there are some methods for improving mechanical properties, we
selected plastic coating method taking into consideration easy set-up in
manufacturing processes, and variety in appricable plastics. On the
studies of plastic coating, we considered chemical and mechanical properties
of coating plastic, and coating methods. For chemical and mechanical
properties we considered the adhesive properties to glass fiber, and the
Young's mudulus of coating plastic. To relax stress concentration at the
cracks on the surface of glass fiber, we should select at first such a
plastic that can adhere to the fiber. When the plastic can adhere to the
fiber, there are some interfacial interaction between plastic and fiber, so
that uniform stress may be loaded to the fiber. Next we had better select
such a plastic that has high Young's modulus. Because the coating layer
must have enough strength to protect against crack propagation. So in case
of plastic having high modulus, the coating thickness may be thin, and then
we can make the optical waveguide diameter small, of course in addition to
these properties, the plastic must not cause fiber-break by heat expansion,
for instance, and have good aging stabilities such as heat aging, water
sensitivity etc.
Furthermore the second plastic coating should be needed for the improvement
of handling performances, because the primary coating is so thin that the
resultant diameter is too small to handle. We coated some plastic on the
primary coating fibers by extrusion. In the second coating we must consider
its large thermal coefficient compared with that of glass. When the
coating thickness is very large, the tensile stress by heat expansion of
plastic may cause fiber-break.
*Sumitomo Electric Ind., Ltd.