Efficient analysis of radiation asymmetries in multilayered metagratings

Abstract Radiation asymmetry (RA) characterizes resonant modes in photonic structures that lack up-down mirror symmetry. In this paper, we introduce a novel RA pseudo-polarization vector that enables a topological analysis of RAs, providing a new method to characterize polarization singularities and their associated topological charges within parameter space. This approach is further strengthened by representing RA as a complex number mapped onto the unit disk of the complex plane, offering a comprehensive framework to evaluate a structure’s control over RA and allowing for precise optimization of target RAs. Using the proposed concept and method, we analyze RAs in trilayer metagratings. Numerical results show that a wide range of pseudo-polarization states can be achieved without breaking the structure’s inversion symmetry. The trilayer metagrating supports RAs with arbitrary directionality, and the phase difference can be continuously modulated from <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> <mml:mi>π</mml:mi> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:math> to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>2</mml:mn> <mml:mi>π</mml:mi> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:math> , allowing for precise control over both the directionality and phase difference.