Comprehensive characterization of a general composite waveplate by spectroscopic Mueller matrix polarimetry

Composite waveplates (CWs) consisting of multiple single waveplates are basic polarization elements and widely used to manipulate the polarized light in optical systems, and their performances affect the final accuracy and precision significantly. This research proposes a method for the comprehensive characterization of an arbitrary CW based on spectroscopic Mueller matrix polarimetry. An analytical model is established to describe a general CW by extending Jones' equivalent theorem with Mueller matrix calculus. In this model, an arbitrary CW is optically equivalent to a cascaded system consisting of a linear retarder with slight diattenuation followed by an optical rotator, and its polarization properties are completely described by four polarization parameters, including the retardance, the fast axis azimuth, the rotation angle, and the diattenuation angle. Analytical relations between the polarization properties, the structure, and the Mueller matrix of the CW are then derived from the established model. By the proposed method, the polarization parameters of an arbitrary CW can be comprehensively characterized over an ultra-wide spectral range via only one measurement. Moreover, the actual structure of the CW, including the thicknesses and fast axis azimuths of the single waveplates, as well as the axis alignment errors, can be completely reconstructed from the polarization spectra. Experiments performed with a house-developed broadband Mueller matrix polarimeter on three typical CWs including a compound zero-order waveplate, an achromatic waveplate and a specially designed biplate have demonstrated the capability of the proposed method.