Partially spatial coherent thermal emitter based on epsilon-and-mu-near-zero metamaterial

Abstract

Discovery of the accidentally degenerate Dirac cone at the band center of a photonic crystal led to all-dielectric epsilon-and-mu-near-zero metamaterial (EMNZ MM) or zero refractive index metamaterial. The liner dispersion of the Dirac cone and resulting non-zero group velocity of light at the band center allowed spatial coherency applications such as incidence angle-selective filter, directional quantum dot emitter, and directional antenna. On the other hand, thermal radiation from a heated object has been known as a textbook example of a spatially and temporally incoherent source of light. Here a partially spatially coherent thermal emitter realized by EMNZ MM-coating is suggested, analyzed with transfer matrix, demonstrated numerically and experimentally. Based on the multiple scattering theory, the condition for the accidental degeneracy can be found in an array of conventional Mie scattering rods, which allows a thermal analogy of a phase-matched array antenna. This EMNZ MM-coated thermal emitter is expected to complement the metallic loss, limited working frequency, and quadratic dispersion of previously reported partially spatially thermal emitters based on plasmonic surface wave, phonon surface wave, and photonic crystal-based directional emitters respectively. The resulting device may find its use as a compact thermal infrared source with relatively arbitrary working frequency.