Temperature stable and versatile polarization modulators for bioimaging applications

Abstract

Polarization imaging has found many applications ranging from material sciences to biomedical applications to astronomy. A widely used class of polarimeters is based on Liquid Crystal Variable Retarders (LCVR). Indeed, LCVRs are ideal for imaging application: they are versatile polarization modulators with fast response times and a large aperture. However, the main drawback of such systems is their strong dependence on temperature. As a consequence, they require frequent and time-consuming calibration procedures. In this work, we propose a new design for a temperature-stable Variable Retarders cell compatible with LCVR-based polarimeter designs. We formalize a phenomenological model for the temperature dependency of LCVRs and derive theoretical expressions for the working points of the temperature stable cells. We used a heated enclosure to validate the proposed design experimentally. Stable operation of a single cell built from commercially available LCVRs is demonstrated on a wide range of temperatures (25-50°C). Two cells were then combined to obtain a Polarization State Analyzer (PSA), acting either as a standalone Stokes polarimeter or as part of a Muller polarimeter in combination with a Polarization State Generator (PSG). In both cases, excellent stability is demonstrated compared to similar LCVR based polarimeters.