Asymmetric Transmission and Diffraction Engineering in Ultrathin media via Coupled Metasurfaces

Abstract Realizing zero‐static power directional dependence of far‐field response such as asymmetric transmission (AT) in subwavelength‐thickness media at photonic wavelengths is one of the grand challenges in optoelectronics today. Structures exhibiting such behavior can unlock a range of platforms with huge societal impacts, such as directionally sensitive beam splitting, optical isolators and diodes, ultracompact cavities, and various signal multiplexing devices. Typically, asymmetric responses are achieved through breaking time‐reversal symmetry using an external magnetic field, time‐varying media, or nonlinear materials. Although these nonreciprocal systems are immune to backscattering, they suffer from the need for exotic material platforms and volatile external biases that make them susceptible to noise and drift. Here, grating‐insulator‐grating (GIG) compound metasystems hosted on a silicon nitride membrane platform providing AT in a fully passive, reciprocal noise‐free architecture are introduced. It is shown that controlling the cross‐talk between the two metasurfaces in such metasystems enables the widest AT in subwavelength‐thickness structures reported to date across telecom frequencies through engineering the density of states confined within the compound structure. The universality of the proposed design space is showcased by realizing tunable broadband response in both plasmonic and dielectric systems made from gold and silicon without the need for any external stimuli.