Low threshold spaser based on deep-subwavelength spherical hyperbolic metamaterial cavities

We theoretically propose a design of a spaser based on spherical hyperbolic metamaterial cavities consisting of a dielectric core wrapped by several stacks of alternating layers of metal and dielectric, which can support the multipolar whispering-gallery modes (WGMs) with resonance wavelengths much larger than the cavity size. Depending on the mode order of the excited WGMs with the same angular momentum, we show that such cavities are capable of strongly confining the electric fields within different dielectric shell layers. By introducing gains into the different dielectric layers, we demonstrate that the hyperbolic cavities can act as multi-wavelength spasers with a lasing threshold as low as 811 cm(-1), operating on the WGMs with the corresponding mode order. Furthermore, we also demonstrate that the slight variation on either the number of stacks or the core radius allows for easily tuning the lasing wavelengths over a wide spectral range. Published by AIP Publishing.