Real-time polarization measurement with FPGA processing

Existing polarization imaging cameras typically use a set of sequential measurements and involve some physical motion of optical elements or changes in a liquid crystal element. In this paper, we present a spatially parallel polarization measurement approach that is designed to give measurements in real time. The idea is to use a group of 2×2 detectors where each detector responds to a different polarization. The signals from the detectors are sent to a digital processing unit where polarization parameters of interest are calculated in real-time. A laboratory prototype is presented that uses a quad-cell photodiode detector array with different polarizing elements placed over each detector. The signals from the detector elements are sent through amplifiers to A/D converters and then into a Field Programmable Gate Array (FPGA). This high-performance processing unit calculates various parameters such as degree of polarization and partial polarization. As the processing unit is fast, real-time operation is possible. Arrays of 2×2 groups will ultimately be required for image sensing.