Janus vortex beams realized via liquid crystal Pancharatnam–Berry phase elements

Abstract

Emerging as a family of waves, Janus waves are known to have "real" and "virtual" components under inversion of the propagation direction. Although tremendous interest has been evoked in vortex beams featuring spiral wavefronts, little research has been devoted to the vortex beam embedded Janus waves, i.e., Janus vortex beams. We propose a liquid crystal (LC) Pancharatnam-Berry (PB) phase element to demonstrate the realization of the Janus vortex beams and the modulation of the associated orbit angular momentum (OAM) and spin angular momentum (SAM). The generated Janus vortex beams show opposite OAM and SAM states at two distinct foci, revealing a spin-orbit interaction during propagation enabled by the LC PB phase element, which may play special roles in applications such as optical encryption and decryption. Other merits like reconfigurability and flexible switching between Janus vortex beams and autofocusing or autodefocusing vortex beams additionally increase the degree of freedom of manipulating vortex beams. This work provides a platform for tailoring complex structured light and may enrich the applications of vortex beams in classical and quantum optics.

Two-Dimensional Polarization Gratings Realized via Photopatterning Liquid Crystals

“…By loading the 2D PG phase patterns into the DMD (1920 × 1080 pixels with each pixel size 10.8 μm × 10.8 μm) exposure system, and after an 18-step five-time partly overlapping dynamic exposure process (see Supporting Information Figure S2 for a schematic illustration of the LC 2D PGs’ exposure and fabrication process), the 2D PG phase structures in Figure a2 and b2 can be precisely duplicated to LC cells, which are composed of two SD1-coated indium–tin–oxide glass substrates separated by 4 μm spacers. After the capillary filling of nematic LC E7, director variant LC 2D PGs can be well formed. − Based on the pixel size of the DMD chip, by using a 10× objective lens, the lateral resolution of the written patterns can reach ∼1 μm. Thanks to the fluidity of LCs, the final LC director distribution is continuous at the molecular level.…”