Ultra-broadband reflectionless Brewster absorber protected by reciprocity

Abstract

The Brewster’s law predicts zero reflection of p-polarization on a dielectric surface at a particular angle. However, when loss is introduced into the permittivity of the dielectric, the Brewster condition breaks down and reflection unavoidably appears. In this work, we found an exception to this long-standing dilemma by creating a class of nonmagnetic anisotropic metamaterials, where anomalous Brewster effects with independently tunable absorption and refraction emerge. This loss-independent Brewster effect is bestowed by the extra degrees of freedoms introduced by anisotropy and strictly protected by the reciprocity principle. The bandwidth can cover an extremely wide spectrum from dc to optical frequencies. Two examples of reflectionless Brewster absorbers with different Brewster angles are both demonstrated to achieve large absorbance in a wide spectrum via microwave experiments. Our work extends the scope of Brewster effect to the horizon of nonmagnetic absorptive materials, which promises an unprecedented wide bandwidth for reflectionless absorption with high efficiency.

Reflectionless anisotropic multilayers for both polarisations at grazing incidence

“…Here we extend that theory, considering anisotropic non-magnetic materials where the permittivity is a rank 2 tensor [12]. Although anisotropic materials can be extremely subtle when none of the principal axes are parallel to the surface normal (see for instance the recent discovery of 'Brewster absorbers' [13]), we leave this general case for future work. We find that for anisotropic media both the TE and transverse magnetic (TM) Helmholtz equations can be factorised into 'raising' and 'lowering' operators, and we can find materials such that the 'lowering' operators have a simultaneous eigenstate with eigenvalue zero.…”

Broadband Janus Scattering from Tilted Dipolar Metagratings

“…It should be noted that the reciprocity‐protected reflection in optics axes media has recently been observed in reflectionless Brewster absorbers. [ 47 ] Our work unravel the underlying mechanism of the phase modulation utilizing the phased‐array antenna theory. The scattering efficiency and high‐order diffractions can be precisely predicted by the analytical calculation.…”

Ultrawide‐Angle Ultralow‐Reflection Phenomenon for Transverse Electric Mode in Anisotropic Metasurface

“…[1] Based on the Fresnel formula, [2] for the case of transverse magnetic (TM)-polarized light incident at the Brewster angle, the reflection would disappear and a transparency response is obtained, which is named as the Brewster effect. During the past centuries, the Brewster effect has been widely utilized in many optical applications, such as polarizers, [3][4][5][6] dielectric properties quantifying, [7][8][9] Brewster angle microscopy, [10][11][12] extraordinary optical transmission, [13][14][15] and optical broadband angular selectivity. [16][17][18] These traditional applications are usually limited to TM, or p-polarized electromagnetic (EM) waves, the essence of which is the characteristic impedance matching between two media only being achievable at a fixed Brewster angle and under TM wave incidence.…”