Twist-Induced Beam Steering and Blazing Effects in Photonic Crystal Devices

Abstract

Twisted bilayer photonic crystals introduce a twist between two stacked photonic crystal slabs, enabling strong modulation of their electromagnetic properties. The change in the twist angle strongly influences the resonant frequencies and available propagating diffraction orders with applications including sensing, lasing, slow light or wavefront engineering. In this work, we design and analyze twisted bilayer crystals capable of steering light in a direction controlled by the twist angle. To achieve beam steering, the device efficiently routes input power into a single, twist-dependent, transmitted diffraction order. The outgoing light then follows the orientation of this diffraction order, externally controlled by the twist angle. Our study shows, using systematic exploration of the design space, how the device resembles blazed gratings by effectively canceling the undesired diffraction orders. The optimized devices exhibit a shared slant dependent on the selected diffraction order and that proves robust to the twist angle. Our analysis is supported by a classical blazing model and a data-oriented statistical analysis. The data-oriented approach is steered by high-efficiency heuristic optimization method, which enabled the design of optimized devices demonstrating an efficiency above 90% across twist angles ranging from 0 to 30° for both TE and TM polarizations. Extending the optimization to include left- and right-handed polarizations yields overall accuracy nearing 90% when averaged across the entire 0 to 60° control range. Finally, with the identification of the blazing effect in this initially black box structure, we show one can consider simpler design for a first prototype.