Simultaneous observation of phase-stepped images for birefringence measurement

Abstract

An instantaneous phase-stepping and subsequent phase analysis method, using a CCD camera with a form-birefringent micro-retarder array, is proposed for two-dimensional birefringence distribution measurement. A birefringent sample placed behind a polarizer and a quarter-wave plate is analyzed by the proposed method. Light emerging from the sample is recorded using a CCD camera that has micro-retarder array on the CCD plane. This micro-retarder array has four different principal directions. That is, an image obtained by the CCD camera contains four data corresponding to four different optical axes of the retarder. The four images separated from the image recorded by the CCD camera are reconstructed using gray level interpolation. Then, the distributions of the Stokes parameters that represent the state of polarization are calculated from the four images. The birefringence parameters, that is, the principal direction and the phase retardation are then obtained from these Stokes parameters. This method is applicable to real-time inspection of optical elements as well as the study of mechanics of time-dependent phenomena because multiple exposures are unnecessary for sufficient data acquisition in the completion of data analysis.