Scalar and vectorial vortex filtering based on geometric phase modulation with a Q-plate

Abstract

We propose a method of scalar and vectorial vortex filtering to achieve edge enhancement by using a Q-plate. The Q-plate provides geometric phase which acts in a different way depending on the polarization state of the illuminating beam. It is shown from theoretical analysis that the scalar and vectorial vortex filtering can be changed with different illuminating polarization states. The filtering property of the system is vectorial under linear polarized illumination, while the filtering is scalar one under circularly polarized illumination. We also found that the above theory is also suitable when the center of the Q-plate is off-axis. The shadow effect caused by off-axis Q-plate can be eliminated by rotating the analyzer. In addition, we compare autofocusing Airy beam (AAB) and Gaussian beam in the theoretical and experiment sections. Higher contrast and less noise can be achieved under AAB illumination. The experimental results agree well with the theoretical expectations.