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

Fiber drawing process
1. In the initial heating process, a preform with a
diameter D p is lowered into the furnace at a
velocity V p .
2. After the preform is heated, it necks down by
its own weight (or with an applied tension)
into a smaller diameter, ultimately exiting the
bottom of the furnace.
3. The lower piece of preform is cut off, and the
fiber is then put under a continuous applied
tension, exiting the bottom of the furnace at
diameter D f and velocity V f .
Once the system has reached steady state
conditions, it is possible to change two variables
to control the fiber diameter. Namely, these two
variables are the speed at which the preform is
lowered into the furnace, and the speed at which
the fiber exists.
Since the cross-sectional area of the preform
and fiber differs, the speed at which they enter
and exit also differs. The relationship between
the preform entering and fiber exiting can be
described as (when the system is in steady state):
where ρ is the density of the preform – assumed
to be constant in this process.
The preform doped at 1 wt % pyrene was
drawn after being dried in a Marshall furnace,
kept at 90ºC, for two weeks. Due to time
constraints, however, the preform was drawn
without any cladding.
Conclusion
The oscillations in diameter (Figure 6)
represent air bubbles that were formed when the
preform was heated. The bubbles are an
indication that the preform was not dried fully,
and that preforms under this process require
more time in the preheating furnace. The steady
diameter trend shows that the new
polymerization process works and creates
preforms with good material properties and
stronger control over diameter variation.
10 CMDITR Review of Undergraduate Research Vol. 1 No. 1 Summer 2004