Visible-frequency asymmetric transmission devices incorporating a hyperbolic metamaterial.

Asymmetric electromagnetic transmission has been recently demonstrated using Lorentz-reciprocal devices, which exploit a variety of patterned structures of linear materials to break spatial inversion symmetry. However, nanofabrication challenges have so far precluded the fabrication of passive transmission structures with highly asymmetric responses at visible frequencies. Here we show that high-contrast asymmetric transmission of visible light can be provided by a planar device of wavelength-scale thickness incorporating a pair of nonsymmetric subwavelength gratings and a passive hyperbolic metamaterial engineered to display a transmission window centred at a lateral spatial frequency substantially exceeding the diffraction limit. Fabricated devices designed for operation at central wavelengths of 532 and 633 nm, respectively, display broadband, efficient asymmetric optical transmission with contrast ratios exceeding 14 dB. Owing to its planar configuration, small footprint and passive operation, this reciprocal transmission approach holds promise for integration within compact optical systems operating at visible frequencies.