The polarization stability of single-mode fibre resonators has been recognized as a potential problem in their operation. One method to overcome the polarization drift is to use a polarization-maintaining optical fibre, in the resonator system. Even this kind of resonators, still suffer from environmentally-induced polarization instabilities. Depending on the type of resonator, these instabilities are manifest as a split resonant dip, reduced finesse, reduced fringe modulation, fringe asymmetry, and unequal spacing between successive fringes. If we assume that a non zero amount of polarization crosstalk at the coupler is inevitable, then there is only one ideal type of resonator which is free from instabilities: a resonator made from polarizing fibre (or one that incorporates a perfectly aligned polarizer in the loop). The fringe shape variation can be reduced if the resonator is made with a deliberate 90 deg. axis twist at the splice or coupler, or if it is made with a polarization-selective coupler. No practical technique has been demonstrated so far, for producing consistently stable resonators with high finesse, using birefringent fibre. This is because the tolerable amount of coupler polarization crosstalk is very small, and the above ideal form is not easily made. It is therefore important to compare the output stability of the different resonator types as well as to investigate possible techniques for passive or active stabilization of the output. In this thesis work we have developed a experimentally verifiable resonator model that can be applied to different resonator types with minor modifications. We have derived tolerances for the coupler polarization crosstalk, splice alignment, and input polarization mode purity necessary for optimum operation of each type. A fringe shape stabilization system has been constructed, for use with fibre ring resonators with power exchange between the birefringent axes. The system works by keeping the depth of successive resonant dips equal, through a feedback electronic servo system, that controls the fibre birefringence. Two schemes for controlling the fibre birefringence are investigated.
Library of Congress Subject Headings
Fiber optics; Resonators
Narayanan, S. Anantha, "Birefringent fibre ring resonators: Analysis and stabilization techniques" (1994). Thesis. Rochester Institute of Technology. Accessed from
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