Subdiffraction Confinement in All-Semiconductor Hyperbolic Metamaterial Resonators

The strong optical anisotropy of hyperbolic meta-materials has enabled remarkable optical behavior such as negative refraction, enhancement of the photonic density of states, anomalous scaling of resonators, and super-resolution imaging. Resonators fashioned from these optical metamaterials support the confinement of light to dimensions much smaller than the diffraction limit. These ultrasmall resonators can be used to increase light-matter interactions for new applications in photonics. Here, we present subdiffraction mid-infrared resonators based on all-semiconductor hyperbolic metamaterials. Importantly, these resonators are fully compatible with epitaxial growth techniques and can be engineered to incorporate quantum well intersubband transitions that are degenerate with the mode of the resonators, enabling an entirely new generation of quantum optoelectronic devices. The strongest optical confinement achieved is lambda/33 for a free-space wavelength of 10 mu m, and the measured Q-factors are in the range of 14-17. The dispersion of the resonance mode is presented through both experimental data and numerical solutions, and greater than 10% tuning of the resonance frequency (106 cm(-1)) is demonstrated. Radiation patterns and radiative Q-factors are also mapped out using experimental results. Finally, the resonator structures are investigated with finite element simulations and the field profile indicates the presence of a strong vertical polarization, which is essential for coupling to intersubband transitions in quantum well structures. These extreme subdiffraction resonators could be useful for engineering novel light-matter interactions and devices in the mid-infrared.