Nonreciprocal infrared absorption via resonant magneto-optical coupling to InAs

Abstract

Nonreciprocal elements are a vital building block of electrical and optical systems. In the infrared regime, there is a particular interest in structures that break reciprocity because their thermal absorptive (and emissive) properties should not obey the Kirchhoff thermal radiation law. In this work, we break time-reversal symmetry and reciprocity in n-type–doped magneto-optic InAs with a static magnetic field where light coupling is mediated by a guided-mode resonator structure, whose resonant frequency coincides with the epsilon-near-zero resonance of the doped indium arsenide. Using this structure, we observe the nonreciprocal absorptive behavior as a function of magnetic field and scattering angle in the infrared. Accounting for resonant and nonresonant optical scattering, we reliably model experimental results that break reciprocal absorption relations in the infrared. The ability to design these nonreciprocal absorbers opens an avenue to explore devices with unequal absorptivity and emissivity in specific channels.

Thermal Vertical Emitter of Ultra‐High Directionality Achieved Through Nonreciprocal Magneto‐Optical Lattice Resonances

“…TM polarization modes could give the nonreciprocal responses since the electric field oscillates perpendicular to B. [39] The permittivity tensor of InAs is described as: [25,26,39,50]…”

“…The nonreciprocity becomes stronger when the ratio of |ε xy | to |ε xx | is larger. [25,39,53] Figure 1b gives the ratio of…”

“…The reflectivity of polarization conversion should be considered if the incident plane is no longer parallel to the x direction. [39,55] The directional spectral emissivity is defined by the radiation intensity of an object over that of a blackbody. Equation ( 6) could be obtained by assuming that the emission coming from the blackbody with temperature T at each port m' is reflected by the structure to port m (which is also coupled to a blackbody).…”

“…systems. [32][33][34][35][36][37][38][39][40] Magneto-optical (MO) materials like InAs enable nonreciprocal thermal radiation/absorption in the mid-and far-IR after applying external magnetic field B. To enlarge the nonreciprocity, one can use guided mode resonances (GMRs) of either photonic crystals [25,26] or the nonreciprocal materials themselves.…”

“…[41] However, the difference of the emissivity (or absorptivity) between -θ and +θ approaches zero when the scattering geometry approaches normal direction since no more GMRs occur. [39] Other nonreciprocal materials with broken time-reversal symmetry like Weyl semimetals [44][45][46] can be employed at different working wavelengths at different angles. We know of no published literature achieving strong nonreciprocal thermal radiation at nearzero angle like θ = ±1°, which may help to reduce the angular divergence of the emission at the normal direction.…”