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We study theoretically and numerically high density of states for hyperbolic bilayered metamaterials (HMM). It reveals that density response of HMM is reminiscent of Fermi electronic band structure of metal or semiconductors. By the method of Green function a van Hove type singularity is found in photonic density spectra of HMM with saddle point localization on photonic Fermi surface (FS) of metamaterial. Similar to the electronic systems, the photonic FS experiences instabilities induced by the changes in volume fractions of its constituents that leads to the Lifshitz type zero-temperature phase transition between FS of types I and II hyperbolic states at the topology protected critical point.

We demonstrate that the metamaterial perfect absorber behaves as a meta-cavity bounded between a resonant metasurface and a metallic thin-film reflector. The perfect absorption is achieved by the Fabry-Perot cavity resonance via multiple reflections between the "quasi-open" boundary of resonator and the "closed" boundary of reflector. The characteristic features including angle independence, ultra-thin thickness and strong field localization can be well explained by this model. With this model, metamaterial perfect absorber can be redefined as a meta-cavity exhibiting high Q-factor, strong field enhancement and extremely high photonic density of states, thereby promising novel applications for high performance sensor, infrared photodetector and cavity quantum electrodynamics devices.

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., Comment: This is the pre-peer reviewed version of the following article submitted to Laser Photonics Rev. on October 17, 2016. Revisions have been made in the published version. "Whispering gallery mode hybridization in photonic molecules", Y. Li, F. Abolmaali, K. W. Allen, N. I. Limberopoulos, A. Urbas, Y. Rakovich, A. V. Maslov, and V. N. Astratov, Laser Photonics Rev. DOI: 10.1002/lpor.201600278 (2017)