Gas Sensing through Mixed Polarization in Birefringent Porous Silicon Thin Film

TL;DR

This paper introduces a birefringent porous silicon thin film sensor that uses mixed polarization and Fourier analysis to enhance interferometric sensing, resolving phase ambiguities and enabling multi-scale sensitivity.

Contribution

It demonstrates a novel optical sensing method utilizing mixed polarization and Fourier analysis to improve interferometric sensor performance and resolve phase and direction ambiguities.

Findings

Superposition of Fabri-Perot and birefringence oscillations observed

Three periodicity patterns identified for sensing

Phase displacements move oppositely during sensing

Abstract

The interrogation of a sensor based on a highly birefringent film irradiated by an incident beam whose polarization is oriented 45o with respect to the normal film axes is shown to display exceptional features and resolve some outstanding issues in interferometric sensing. The measured pattern as a function of wavelength is complicated displaying a superposition of Fabri-Perot and birefringence oscillations. By means of appropriate optical signal processing based on Fourier analysis, three different periodicity patterns can be elucidated when sensing a single event, improving the sensing process in several ways: it allows sensing at several sensitivity scales, and it clears out the problems of phase and direction ambiguities. A novel effect is observed in which the phase displacement of different patterns move in opposite directions as sensing takes place