A new phase-gradient-based paradigm for metaphotonics: enabling large feature size designs at small wavelengths

We present a novel approach to metasurface design, shifting from traditional meta-atom-based systems to metagrating structures. In this approach, we focus on the phase gradient, recognizing that wave propagation is determined by the phase derivative rather than the absolute phase value. By employing metagratings to diffract light in the desired direction, we simplify the design process while maintaining precise control over wavefront shaping. This method significantly increases the minimum feature size to λ/(3NA) (NA: numerical aperture); e.g., an NA of 0.5 results in feature sizes as large as 2λ/3, making fabrication more straightforward and robust against errors. Using this approach, we demonstrate metalenses that reduce the fabrication requirements compared to conventional metalenses while considerably reducing the sidelobes in the focusing beam profile. Moreover, we present a fully analytical design framework, eliminating the need for time-consuming numerical simulations and complex optimization processes.