In nanophotonics, light is manipulated by interactions with designed subwavelength structures, fully harnessing wave interference and creating large responses that are unimaginable in ray optics. This talk will discuss new theoretical frameworks for analyzing scattering via resonances and for identifying fundamental limits to designed scattering response.
First, we develop a new resonance-based construction of scattering matrices in open electromagnetic systems. We use quasinormal modes to develop an exact, ab initio generalized coupled-mode theory from Maxwell’s equations. This quasinormal coupled-mode theory, which we denote “QCMT,” enables a direct, mode-based construction of scattering matrices without resorting to external solvers or data. We consider canonical scattering bodies, for which we show that a conventional coupled-mode theory model will necessarily be highly inaccurate, whereas QCMT exhibits near-perfect accuracy.
Second, for arbitrary scattering matrices, we obtain power-concentration bounds for wave scattering by generalizing classical brightness theorem to wave scattering. We show that power per scattering channel generalizes brightness, and the rank of an appropriate density matrix generalizes etendue to states with arbitrary coherence. The bounds apply to nonreciprocal systems that are of increasing interest, and we demonstrate their applicability to maximal control in nanophotonics for metasurfaces and waveguide junctions. Through inverse design, we discover metasurface elements operating near the theoretical limits.
Friday, April 8, 2022 - 10:00am