  We analyze the core structure of string defects in various condensed matter
systems, such as nematic liquid crystals and superfluid helium, and argue that
in certain cases the variation of the refractive index near the core is such
that it can lead to total internal reflection of light travelling along the
string core. These strings thus behave as optical fibers providing a
qualitatively new approach to optical fibers. We present a candidate for such a
fiber by looking at string segments in a thin nematic liquid crystal film on
water. We discuss various possibilities for constructing such fibers as well as
possible technological applications.
