Directional Thermal Emission Across Both Polarizations in Planar Photonic Architectures

Abstract

Directional and spectral control of thermal emission is essential for applications in energy conversion, imaging, and sensing. Existing planar, lithography-free epsilon-near-zero (ENZ) films only support transverse-magnetic (TM) control of thermal emission via the Berreman mode and cannot address transverse-electric (TE) waves due to the absence of natural optical magnetism over optical and infrared wavelengths Here, we introduce a hyperbolic metamaterial comprising alternating layers of degenerately-doped and intrinsic InAs that exhibits an epsilon-and-mu-near-zero (EMNZ) response, enabling dual-polarized, directionally and spectrally selective thermal emission. We first theoretically demonstrate that a mu-near-zero (MNZ) film on a perfect magnetic conductor supports a magnetic Berreman mode, absorbing TE-polarized radiation in analogy to the conventional Berreman mode supported in TM polarization. Using genetic and gradient-descent optimization, we design a dual-polarized emitter with independently tunable spectral peaks and emission angles. Parameter retrieval via homogenization confirms simultaneous EMNZ points at the target wavelengths and angles. Finally, experimental measurement of a sample fabricated via molecular beam epitaxy exhibits high absorptivity peaks for both polarizations in close agreement with simulations. This work realizes lithography-free, dual-polarized, spectrally and directionally selective emitters, offering a versatile platform for advanced infrared thermal management and device integration.