Patent ID: 8514685

Claim:
A method comprising: providing a biaxial crystal; inputting light either unpolarized or circularly polarized from an unknown object through the biaxial crystal; providing a polarizing element consisting of either one of a circular polarizer, a linear polarizer, a linear polarizing beamsplitter or a linear polarizer and a controllable rotator, positioned after the biaxial crystal with respect to the propagation of the initially incident light, wherein a geometrical axis traverses through the biaxial crystal and the polarizing element, wherein the optic axis of the biaxial crystal is along the geometrical axis, and is split in two conjugate axes after the polarizing beam splitter whether using a linear polarizing beamsplitter, wherein the initial light distribution has been imaged by an optical system onto a detector, the imaging condition being determined such that the image would fall on the detector if the biaxial crystal will have been replaced by an isotropic material with an index equal to about the biaxial crystal median index, detecting the distribution of intensity of the light in one, two or more polarization states in a plane perpendicular to the geometrical axis, wherein the detected distribution of light is proportional to a derivative in one axis of the initial light distribution; imaging features of the unknown object from mathematical combinations of the detected distribution of intensity; and outputting the imaged features of the unknown object.