Whispering gallery mode hybridization in photonic molecules

TL;DR

This paper explores the hybridization of whispering gallery modes in photonic molecules composed of dielectric microspheres, demonstrating spectral signatures that depend on structure symmetry, topology, and atom number, with potential for controlled coupling.

Contribution

It introduces a novel analogy between quantum molecular hybridization and classical photonic structures, demonstrating WGM hybridization effects in assembled microsphere structures with experimental and simulation agreement.

Findings

Spectral splitting patterns depend on molecule symmetry and topology.

WGM hybridization can be controlled through coupling constants.

Experimental results match finite difference time domain simulations.

Abstract

This work takes inspiration from chemistry where the spectral characteristics of the molecules are determined by hybridization of electronic states evolving from the individual atomic orbitals. Based on analogy between quantum mechanics and the classical electrodynamics, we sorted dielectric microspheres with almost identical positions of their whispering gallery mode (WGM) resonances. Using these microspheres as classical photonic atoms, we assembled them in a wide range of structures including linear chains and planar photonic molecules. We studied WGM hybridization effects in such structures using side coupling by tapered microfibers as well as finite difference time domain modeling. We demonstrated that the patterns of WGM spectral splitting are representative of the symmetry, number of constituting atoms and topology of the photonic molecules which in principle can be viewed as "spectral signatures" of various molecules. We also show new ways of controlling WGM coupling constants in such molecules. Excellent agreement was found between measured transmission spectra and spectral signatures of photonic molecules predicted by simulation.