Generation of few µm high optical vortex using tunable spiral plates

Abstract
Optical vortices have been extensively explored, due to their widespread applications, spanning from optical trapping to laser processing. Previously, several methods for generating optical vortices had been reported. However, none of the previously reported methods demonstrated the design of a geometrically variable tunable spiral plate (SP) capable of tuning the optical vortex’s features. In this study, we present a three-dimensional tunable SP capable of generating desired vortex and focal characteristics. These SPs are 10 µm in width and 7–17 µm in height, generating few µm high vortices. We used the 3D finite difference time domain approach to model and simulate these SPs for incident plane waves with a wavelength of 632 nm. We show that the vortex profiles can be tweaked in two ways: by changing the SP’s geometrical features along the vertical axis, and by changing its refractive index.

---