Fast-light enhancement of an optical cavity by polarization mode coupling

We present an entirely linear all-optical method of cavity scale factor enhancement that relies on mode coupling between the orthogonal polarization modes of a single optical cavity, eliminating the necessity of using an atomic medium to produce the required anomalous dispersion, which decreases the dependence of the scale factor on temperature and increases signal-to-noise ratio by reducing absorption and nonlinear effects. The use of a single cavity results in common mode rejection of the noise and drift that would be present in a system of two coupled cavities. We show that the scale-factor-to-mode-width ratio is increased above unity for this system, and demonstrate tuning of the scale factor by (i) directly varying the polarization mode coupling via rotation of an intracavity half-wave plate, and (ii) coherent control of the cavity reflectance which is achieved simply by varying the incident polarization superposition. These tuning methods allow us to closely approach the critical anomalous dispersion condition and achieve unprecedented enhancements in scale factor and in the scale-factor-to-mode-width ratio. Based on these findings, we propose an adaptation of the traditional optical cavity gyroscope that takes advantage of polarization mode coupling to enhance the gyro scale factor, and demonstrate how the bandwidth of the scale factor enhancement for this gyroscope can be effectively broadened in comparison with fast-light gyroscopes based on atomic media.