How bending deformation affects the performance of polarization converters based on slot waveguides

Polarization is an important characteristic of light and plays a critical role in many natural and industrial processes. In this paper, we present an optical gradient force actuated polarization converter based on a slot waveguide, which can convert linearly polarized light into circularly polarized light. The working principle of the presented polarization converter is that optical gradient forces deform the slot waveguide to adjust its birefringence, thus yielding a desired phase shift between two orthogonal components of light. An optomechanical model with all possible mechanical boundaries is developed to solve the bending deformation of polarization converters. The effective index method and dispersion relation method are used for the calculation of birefringence and optical gradient forces, respectively. The influences of the width of waveguides and the initial width of the slot on the working performance of polarization converters are discussed. It is found that these influences are independent of the mechanical boundaries. An empirical formula for describing the relation between the working power and length of polarization converters is given. This empirical formula may be helpful when designing such polarization converters.