Development and optimization of an integrated Faraday modulator and compensator design for optical polarimetry

摘要

In the past, Faraday based optical polarimetry approaches have shown considerable potential for the measurement of optical activity with application towards the noninvasive measurement of physiological glucose concentration. To date, most reported closed-loop systems incorporate separate Faraday components for modulation and compensation requiring two optical crystals. These systems have demonstrated significant stability and sub-millidegree rotational sensitivities; however, the main drawbacks to this approach are the optical materials (e.g., terbium gallium garnet) can be quite expensive and often custom fabricated induction coils are required. In this investigation, we propose a new design for the Faraday components capable of achieving both modulation and compensation in a single crystal device. The design is more compact and is capable of achieving similar performance with low cost commercially available inductive components. To facilitate prototype optimization, our group has developed a finite element model (FEM) that can simulate various physical parameters such as geometry, inductance, and orientation with respect to the optical rod in order to minimize power consumption and size while maintaining appropriate field strength. Performance is comparable to existing nonintegrated approaches and is capable of achieving modulation depths > 1 ° under similar operating conditions while attaining sub-millidegree linear polarization sensitivity. There is also excellent correlation between the FEM and experimental prototype with operational performance shown to be within 1.8%. The use of FEM simulations allows for the analysis of a vast range of parameters before prototypes are fabricated and can facilitate custom designs as related to development time, anticipated performance, and cost reduction.