Abstract

A coupler is a device that allows interconversion of angular momentum of the optical beam among spin and orbital parts, without absorbing any angular momentum. In this paper, we demonstrate that a $q$-plate with $q = 1$ can act as a coupler for any of the polarization distribution that can be represented by a point on a Poincare sphere (PS), or on a higher-order PS, or on a hybrid-order PS. A $q$-plate with any $q$-value can act as a coupler for polarization distribution that can be represented by an equatorial point on any of these spheres. It is also possible to find a $q$-plate with an appropriate $q$-value that can act as a creation or annihilation operator that raises or lowers the polarization singularity index. The $q$-plate being a coupler and made of half-wave plate segments, the singularity index change is concomitant with the helicity inversion of C-points. Interconversion of bright and dark C-points is possible by using a $q$-plate.

© 2020 Optical Society of America

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