Optical properties of photonic crystal slabs with asymmetrical unit cell

TL;DR

This paper analyzes the optical properties of photonic crystal slabs with asymmetrical unit cells, revealing symmetry in reflectivity and conditions for high reflectivity near resonances using scattering matrix properties.

Contribution

It introduces a symmetry analysis of photonic crystal slabs with complex unit cells based on unitarity and reciprocity of the scattering matrix.

Findings

Reflectivity remains unchanged under 180-degree rotation.

Transmissivity becomes asymmetric with diffraction or absorption.

High reflectivity occurs near quasiguided mode resonance without losses.

Abstract

Using the unitarity and reciprocity properties of the scattering matrix, we analyse the symmetry and resonant optical properties of the photonic crystal slabs (PCS) with complicated unit cell. We show that the reflectivity is not changed upon the 180deg-rotation of the sample around the normal axis, even in PCS with asymmetrical unit cell. Whereas the transmissivity becomes asymmetrical if the diffraction or absorption are present. The PCS reflectivity peaks to unity near the quasiguided mode resonance for normal light incidence in the absence of diffraction, depolarisation, and absorptive losses. For the oblique incidence the full reflectivity is reached only in symmetrical PCS.