Controlling the phase of optical nonlinearity with plasmonic metasurfaces

Metasurfaces are ultrathin structured surfaces that are capable of manipulating the propagation of light in an arbitrary manner. It has been endowed with various functionalities ranging from imaging to holography. In contrast to linear optical processes, the control of wave propagation and diffraction over nonlinear optical processes such as harmonic generations had been much more limited until recently, when the concept of metasurfaces was extended from linear optics to the nonlinear optical regime for manipulating the generation of harmonic signals in an unprecedented level. The key to this recent development lies in the local control over the phase and/or the amplitude of nonlinear polarizability. This new development has led to an array of interesting optical phenomena and nonlinear optical devices that went beyond what had been achieved with traditional nonlinear optical elements. In this review, we summarize the latest progress in controlling the local phase of nonlinearity with plasmonic metasurfaces, with a focus on nonlinear geometric Berry phase and wavefront engineering, and various device applications with nonlinear metasurfaces.