Polished fiber optic couplers are widely used as building blocks for interferometric sensors. The development of fiber optic sensors was facilitated by the availability of adjustable couplers in the early 1980s, which were widely used in prototypes and experiments. This document outlines the theoretical and practical aspects of polished coupler and resonator technology.
First, a matrix technique is presented which permits calculation of the characteristics of non ideal birefringent coupler devices, including asymmetry effects. A method for modeling complex fiber optic resonant topologies is also introduced, which allows for backscattering effects. Together, these permit computer simulation of most of the linear errors in resonant cavities, and permit comparison of different topologies.
Fiber optic coupler polishing is described, for the first time in such detail. A survey of substrate preparation techniques is made, and an advanced groove-generation machine is presented, which produces very consistent substrate grooves. Specific materials and polishing compounds are listed, providing the reader a "recipe" for processing of PM fiber couplers. Design and operation of a state-of-the-art principal axis alignment system is discussed, with approximately ±2-deg accuracy. Assembly techniques for adjustable couplers, and for the first time, optical contact bonded couplers. An attempt is made to remove some of the mystery from this ancient "black art."
Resonators were constructed from the couplers, and data is presented for four devices made. Polarization-maintaining fiber couplers were spliced onto fiber coils, both polarization-maintaining and single-polarization types. A spliceless all-polarization-maintaining ring was also assembled, having a finesse in excess of 300. All of the resonators had very low polarization cross-coupling and lineshape asymmetry.
Thesis Supervisor: Dr. Shaoul Ezekiel, Professor of Aeronautics and Astronautics
Draper Supervisor: Dr. Raymond Carroll, Principal Member of the Technical Staff
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Revised 1 December, 2001
Copyright © 2001 by Silicon Valley Photonics, Ltd. All rights reserved.