Generation of coaxial vortex beams with doubled topological charges using a stacked liquid crystal structure

Optical vortices (OVs), which carry orbital angular momenta are attractive for many optical applications. A facile means of generating OVs is through the use of q-plates, which are patterned liquid crystal (LC) waveplates. However, they are limited to generating beams with topological charge +/- l. In this work, we propose a stacked LC structure consisting of patterned nematic LC with 1/4-wave retardation and planar cholesteric LC, and demonstrate its capability to generate coaxial OVs with topological charges vertical bar l vertical bar and vertical bar 2l vertical bar. As an extension of the function of conventional q-plate, this structure provides large degree of freedom in the generating OVs. (C) 2021 The Japan Society of Applied Physics