Type of Document Master's Thesis Author Velayudhan, Nirmalkumar Author's Email Address firstname.lastname@example.org URN etd-51697-144745 Title Analysis of Thermally Diffused Single Mode Optical Fiber Couplers Degree Master of Science Department Electrical Engineering Advisory Committee
Advisor Name Title Murphy, Kent A. Wang, Anbo Claus, Richard O. Committee Chair Keywords
- Optical Couplers
- Dopant Diffusion
- Modeling and Analysis
Date of Defense 1994-12-22 Availability unrestricted AbstractThe phenomenon of dopant diffusion as a viable means of coupler fabrication is
investigated. It is well known that the diffusion of dopants can improve the uniformity of
multimode star couplers manufactured by the fused biconical taper technique. The
theoretical basis for the same phenomenon in a single mode coupler is developed, on the
basis of the theory of diffusion and the Gaussian approximation for circular fibers.
A novel technique to manufacture and design single mode optical fiber couplers
with a minimization of the manufacturing complexity is demonstrated. Traditionally fused
biconical tapered couplers have been manufactured by twisting, fusing and elongating
optical fibers at elevated temperatures. Usually, high temperature oxy-hydrogen flames are
used for such purposes and some degree of skill is needed for a human operator. The
complexity of control procedures for automation of the process is greatly increased by the
fact that the tapering process is an integral part of the feedback loop. This can be eliminated
if a constant tension is maintained on the fibers in the heating process while heat is applied
uniformly from a source such as a platinum wire furnace. Since the refractive index
differentials responsible for the guiding phenomenon at optical frequencies are directly
dependent on concentration of dopants like fluorine and germania, radial diffusion of such
dopants causes the fiber cores that are heated in a platinum wire furnace to come closer
together. Such proximity leads to the phenomenon of evanescent field interaction or
coupling of optical power from one arm of the coupler to the other.
The time evolution of the coupling process can be predicted in theory. While initial
results are promising, the ability to automate the manufacture of couplers will be
successful only after greater control over the variables is established. It is the intention of
this work to understand the physics behind the mechanism as well as to prove the
feasibility of modeling real world phenomena under controlled conditions.
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