Quasinormal-Mode Non-Hermitian Modeling and Design in Nonlinear Nano-Optics

Abstract

Based on quasinormal-mode theory, we propose a novel approach enabling a deep analytical insight into the multi-parameter design and optimization of nonlinear photonic structures at subwavelength scale. A key distinction of our method from previous formulations relying on multipolar Miescattering expansions is that it directly exploits the natural resonant modes of the nanostructures, which provide the field enhancement to achieve significant nonlinear efficiency. Thanks to closedform expression for the nonlinear overlap integral between the interacting modes, we illustrate the potential of our method with a two-order-of-magnitude boost of second harmonic generation in a semiconductor nanostructure, by engineering both the sign of χ (2) at subwavelength scale and the structure of the pump beam.

Tunable unidirectional nonlinear emission from transition-metal-dichalcogenide metasurfaces

“…However, all resonant modes are generally of mixed nature and to better identify their character we further performed quasi-normal mode (QNM) theory simulations 47 for metasurface C. The QNM representation allows us to quantify the coupling of the modes to free space and determine the role and weight of the individual modes into the harmonic radiation. To retrieve the characteristic wavelength and the lifetime of the QNM we consider the metasurface as an open-cavity system that supports eigenmodes and solve this complex eigenvalue (i.e., source-free) problem with finite-element numerical simulations (COMSOL).…”

Observation of Supercavity Modes in Subwavelength Dielectric Resonators

“…For the numerical simulations in Figure 2d, we apply an expansion of Maxwell's equations into the basis of resonant states (quasi-normal modes). [30,31] This value of the Q factor is limited mainly by the material loss in the ceramics (loss tangent about 10 −4 ). Explicit finite element simulations show that the pure radiative Q factor reaches a value of around 1.8 × 10 5 .…”

Nonlinear Transition-Metal-Dichalcogenide Metasurfaces

“…2a-c, respectively. However, all resonant modes are generally of mixed nature and to better identify their character we further performed quasi-normal mode (QNM) theory simulations 47 for metasurface C. The QNM representation allows us to quantify the coupling of the modes to free space and determine the role and weight of the individual modes into the harmonic radiation. To retrieve the characteristic wavelength and the lifetime of the QNM we consider the metasurface as an open-cavity system that supports eigenmodes and solve this complex eigenvalue (i.e., source-free) problem with finite-element numerical simulations (COMSOL).…”