Optimization of detection system for low-coherence interferometric sensors based on highly birefringent fibers.

A demodulation system employing birefringent crystalline plates for decoding low-coherence interferometric sensors based on highly birefringent fibers was numerically analyzed in order to find its optimum construction. A numerical approach proposed allowed us to calculate how the parameters of the decoding system such as thickness and orientation of the crystalline plates, type of birefringent material, position of the detectors, and polarization characteristics of beam splitting plates influence the contrast of differential interference signals. Calculations were based on vectorial ray tracing algorithm applicable to isotropic as well as anisotropic media. The algorithm allowed determination of intersection coordinates with detector surface for ordinary and extraordinary rays, their phases, polarizations, and amplitudes, and finally the contrast of differential interference signals. Based on modeling results, general principles concerning system construction were formulated, which assure the highest possible contrast of interference signals and therefore maximum operation range of the sensor.