Doctoral Dissertations

C. Wayne Long

Date of Award

8-1989

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Engineering Science

Major Professor

Walter Frost

Committee Members

Robert E. Turner

Abstract

Fiber optic technology is undergoing rapid development with many applications requiring direct fusion of short filaments to form one long continuous fiber. Automatic devices have been developed to heat the fiber ends in an electric discharge and bring them into contact for fusion to occur. Current practice is to establish splicing parameters for each unique splicing condition through experimental testing. This study develops an analytical model for the arc fusion splicing process. The model enables parametric studies, sensitivity analysis, quick determination of optimum splicing procedures for unique conditions, and can be used to provide analytical guidance in experimental research.

A physical model of the fiber optic splicing process is developed which incorporates heat transfer along with thermal and viscoelastic strain. An empirical model of electric discharge heating is used to supply an energy source model to one-dimensional heat transfer calculations of radiation, conduction, and convection. A numerical model is employed where temperatures are calculated for each grid element of the fiber at each time step. Physical properties of the high silica fiber optic material are modeled as functions of temperature. A two-dimensional physical model of viscoelastic glass flow is developed from force balance considerations and considers deformation due to thermal, viscous and elastic strain. Maxwell stress-strain relationships are assumed.

Finite difference numerical algorithms are derived for an Lagrangian viewpoint. Simultaneous equations for heat transfer are solved implicitly in a tri-diagonal matrix routine. Simultaneous equations for viscoelastic flow are solved by back substitution techniques that account for boundary condition transitions upon gap closure.

Experiments were conducted using a commercial arc fusion splicer to provide experimental verification of the analytical model. Evolution of the fiber distortion was photographically recorded for repeated heating cycles of a continuous element and a free end respectively. The geometric distortion of the element with time was compared to predictions obtained with the analytical model.

The analytical model was found to display all of the physical phenomenon of the fiber deformation observed in the experiment including an unsymmetrical necking down and eventual separation of the filament. Magnitudes of the deformations were, in general, found to be overpredicted after several heating cycles.

Preliminary results indicate the relative importance of the convection heat transfer coefficient in determining the fiber's temperature profile. Viscoelastic response of the glass filament's free surface is shown to be dominated by surface tension forces. Surface profiles show a tendency to evolve unsymmetrically into a necked down region which must be countered by a press stroke during an actual splicing process.

It is concluded that the analytic model correctly simulates all major phenomenon associated with the arc fusion splicing process. Therefore, it constitutes an attractive alternative to large-scale experimentation for obtaining large data bases to be used in parametric and sensitivity analysis.

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