Polarization singularity index determination using wedge plate lateral shear interferometry

Abstract

Polarization singularity is a point in an inhomogeneous polarization distribution at which the azimuth of the polarization ellipse is indeterminate. The azimuth gradient is solenoidal around the polarization singular point. In metrology, shear interferometry enables the visualization of phase gradients in optical beams. Since the polarization azimuth gradient is related to the Stokes phase gradient, we adopt the shear interferometry technique to visualize these phase gradients for the detection of polarization singularity. We use a wedge plate lateral shear interferometer (LSI) in our experiments for the detection of the ellipse and vector field singularities. Being a self-referencing and intensity-based technique, this method is convenient for practical use. Unlike the traditional Stokes polarimetry method, where the polarization distribution at every spatial point is evaluated, this technique can distinguish degenerate states of polarization singularities simply by visual observation of intensity fringes. Index and helicity measurement of these polarization singularities without using polarization measurement methods are novel aspects of this scheme. Both theoretical and experimental results are presented to support our claim.