Off-axis interferometer with adjustable fringe contrast based on polarization encoding.

We propose a compact, close-to-common-path, off-axis interferometric system for low polarizing samples based on a spatial polarization encoder that is placed at the Fourier plane after the output port of a conventional transmission microscope. The polarization encoder erases the sample information from one polarization state and maintains it on the orthogonal polarization state while retaining the low spatial frequencies of the sample, and thus enabling quantitative phase acquisition. In addition, the interference fringe visibility can be controlled by polarization manipulations. We demonstrate this concept experimentally by quantitative phase imaging of a USAF 1951 phase test target and human red blood cells, with optimal fringe visibility and a single-exposure phase reconstruction.