Fig. 3: Optical vortex generation in a representative twisted bilayer photonic crystal (TBPC) system.

a The mode intensity spectrum of the TBPC system. The two peaks in the spectrum are marked as “i” and “ii”, with the frequency of 193.4 THz and 211.2 THz, and the Q-factor of 3.1 × 103 and 3.4 × 103, respectively. b Electric-field profile of the BIC modes hosted in monolayer PhC. c Electric-field profiles in PhC 1 of the TBPC system at peak “i” and “ii”. d, e The electric-field distribution of the optical vortex emission 12 μm away from the TBPC surface at peak “i” (d) and “ii” (e). The upper panels depict the normalized amplitude of the LCP and RCP portions of the emission, while the lower panels are the phase distribution of the corresponding upper panels in dashed white circles.