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

TL;DR

This paper presents a design for twisted bilayer photonic crystals that can steer light directionally by adjusting the twist angle, achieving high efficiency and resembling blazed gratings, with potential applications in sensing and wavefront control.

Contribution

The work introduces a novel twist-controlled beam steering device using bilayer photonic crystals optimized via heuristic methods, demonstrating high efficiency and diffraction order control.

Findings

Achieves over 90% efficiency across 0-30° twist angles.

Effectively cancels undesired diffraction orders, resembling blazed gratings.

Provides a data-driven model explaining the blazing effect.

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. In order 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. The optimization is performed using high-efficiency heuristic optimization method which enabled a data-oriented approach to further understand the design operation. The optimized device demonstrates an efficiency above 90% across twist angles ranging from 0 to 30 degrees 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 degrees control range. Finally, we show 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. Our analysis is supported by a structural blazing model arising from the data-oriented statistical analysis.