Surface-Plasmon-Mediated Extraordinary Optical Transmission and Emission Collection from a Squared Holey Lattice Hyperbolic Metamaterial

The hyperbolic metamaterials (HMMs) with extremely anisotropic permittivity are known to provide unbounded momentum (high-k) modes, leading to radiation directionality and large spontaneous emission enhancement. However, the far-field out-coupling of their high-k modes always remains a challenge, requiring complex antennas or photonic hypercrystals. Excitation of surface plasmon polaritons (SPPs) on a perforated metal surface is well-known to enhance light coupling into free space, a phenomenon commonly known as extraordinary optical transmission (EOT). Combining the EOT phenomenon into an HMM, here in this study, we designed a material that provides an emitter with dual advantages, enhanced spontaneous emission coupled to the high-k HMM modes and far-field radiation directionality enabled by the surface-plasmon-mediated EOT mechanism. Using both transfer-matrix-based analytical and computational approaches, we show that the metallic nature of a planar HMM along its surface will lead to the excitation of SPP modes in exact analogy with that of a metal film. The SPP modes in a squared holey HMM lattice successfully tune the mismatch between the HMM and free-space modes, leading to extraordinary emission collection, a significantly enhanced (up to 2 orders of magnitude) free-space out-coupling for dipole emission coupled to the HMM modes.