Whispering gallery mode hybridization in photonic molecules

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.
The authors gratefully acknowledge support from U.S. Army Research Office through Dr. J. T. Prater under Contract No. W911NF‐09‐1‐0450 and DURIP W911NF‐11‐1‐0406 and W911NF‐12‐1‐0538. This work was also supported by Center for Metamaterials, an NSF I/U CRC, Award No. 1068050. Also, this work was sponsored by the Air Force Research Laboratory (AFRL/RYD, AFRL/RXC) through the AMMTIAC contract with Alion Science and Technology and the MCF II contract with UES, Inc.