Metasurface waves in digital optics

Digital optics is a new discipline that aims to replace traditional curved and bulky optical elements with flat and thin ones that can be intelligently designed by a computer and be compatible with the mature semiconductor fabrication industry. Metasurface-based digital optics is characterized by enhanced or multifunctional performances, a compact footprint, and most importantly the ability to break the limitations of conventional refractive, reflective and diffractive optics. The structural inclusions on the subwavelength scale can tremendously change the light fields and give rise to novel electromagnetic modes. In particular, the coupled evanescent fields within the subwavelength structures form a special kind of wave, termed a metasurface wave (M-wave), possessing many interesting properties. This article provides a short perspective of M-waves in digital optics, with particular emphasis on the representative applications in metalenses, photolithography, and optical phased array, etc. Finally, an outlook on the generalized diffraction limit and intelligent digital optics is presented.