Common-path spectral-domain optical low coherence interferometric system for the measurement of small changes in refractive index of Liquid Crystal cell

Abstract

We report the measurement of small changes in the refractive index of liquid crystal (LC) with applied voltage using a common-path spectral-domain optical low coherence interferometric system. Changes in the spectral modulations were observed as a function of voltage applied to the LC cell in steps. Hilbert transform fringe analysis was used for the extraction of the phase of the spectral interference fringe signal. The change in the refractive index of the LC material as a function of voltage was then determined from the phase information. The present system is common-path, yields a higher stability in measurement and compensates the optical length perturbation and hence can be used in real time.