(a) Schematic setup of lens-free differential holographic polarized microscopy. (b) Design of the polarization in this system. The light, which is propagating from top to bottom, passes through a left-hand circular polarizer, the birefringent sample, a λ/4 retarder film, a linear polarizer and reaches the image sensor. The orientations of the polarizing components are illustrated with red arrows, and the polarization states of the light between components are illustrated with green arrows.