A polarization state detector (PSD) measures all parameters of the state of polarization of the detected light. The state of polarization is described by four Stokes parameters while the total phase of the light is discarded. Only four intensity measurements are needed to measure the four Stokes parameters even though the Stokes vector is defined by six intensity measurements. By using a special optical design with four photodetectors, these measurements can be conducted simultaneously. To measure the Stokes vector with high accuracy, a special beam splitter has been proposed in the literature imposing constraints on the reflectance, transmittance and retardance of the p- and s-polarized reflected and transmitted wave. Later on, several alternative designs have been proposed using two or more retarders and ordinary beam splitters. In this report another alternative design of the PSD is presented. In fact, only two instead of four waveplates are needed to get optimal results for ordinary beam splitters with suboptimal optical properties.
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