CMDITR Review of Undergraduate Research - Pluto - University of ...

Fiber cladding preparation
In order for light to pass through an optical
fiber, there must be total internal reflection. Total
internal reflection is a phenomenon that occurs
between two materials of differing indices of
refraction, where a light signal is reflected away
from the material with the lower index of
refraction. Through this successive bouncing
back and forth, a light signal is able to travel
through a fiber.
Polymer optical fiber is usually composed of
three materials: the core material, cladding, and
final layer coating. The core is the material
through which the light moves.
Surrounding the core is a material with a
lower index of refraction than the core, called the
cladding. Light that hits the core-cladding
interface at an angle greater than the critical
angle is reflected away from the cladding, and
light is able to “bounce” through the fiber core.
Two methods are used to prepare cladding.
The first method is a cascaded draw in which the
cast preform is inserted into cascaded acrylic
tubes. The second method is one previously
carried out by Peng et al 4 where a Teflon line
was fixed in the center of a mold, with MMA
polymerizing around it. The Teflon line was
removed, and then dye-doped monomer was
poured into the hole and subsequently
polymerized.
A line of Teflon was inserted into a 1”
diameter test tube with a Teflon plug weight into
the bottom of the tube. An initial amount of
MMA was placed in the tube, and polymerized
in a heated bath at 75°C. This attached the
Teflon plug to the bottom of the tube. MMA
monomer was poured in the tube, and the Teflon
line was pulled through the center of a makeshift
cap at the top of the tube. The tube and monomer
underwent the same 15-minute preheat, and was
slowly lowered into the heated bath (maintained
at 75°C) at speeds of approximately 12 microns
per second. Once MMA was fully polymerized,
the Teflon line was easily pulled out. However,
the process has still yet to be perfected.
In future research of fabrication of cladding
for fibers, it is recommended augmenting the
speeds at which the Teflon-lined preform
polymerize, so there is less bubble formation in
the cladding. Much more attention should be
paid to the diameter variation of the Teflon line,
and efforts should be made to place Teflon line
closer to the exact center of the tube.
CMDITR Review of Undergraduate Research Vol. 1 No. 1 Summer 2004 9