Imaging polarimetry of a few-pixel object with a division-of-focal-plane polarization imager

We address the boundary for accurate imaging polarimetry of a few-pixel object via demosaicing of a division-of-focal-plane polarization imager and propose a new approach for improving retrieval beyond the said boundary. We examine, both by simulation and experiment, the accuracy of traditional edge-aware demosaicing in retrieving polarization properties of a small object with a radius of a few pixels. Retrieval errors are examined as a function of the spot radius, intensity, and position within the imager's pixel grid. The optimization polarimetry approach is described, in which a model image is compared to raw data, without demosaicing, and polarization properties of the source are retrieved by minimization of a cost function. The approach is demonstrated for a Gaussian beam and compared to traditional polarimetry by simulation and experiment. For a fully polarized simulated Gaussian light source of 1-pixel waist, the retrieval root-mean-square error of the degree and the angle of linear polarization are reduced from 0.27 and 14.8° to 0.08 and 5.8°, respectively. Experimental retrievals show an advantage to the proposed method in retrieving the polarization properties of few-pixel objects.