Nonlinear Moiré Superlattice for Super‐Resolution Nondestructive Detection of Nonlinear Photonic Crystals

Abstract The moiré effect is a universal phenomenon originating from the interference of waves, and it is widely applied in metrology as well as superconductor phenomena in graphene. The present study demonstrates a nonlinear moiré effect originating from the moiré superlattices of two nonlinear photonic crystals (NPCs). It is experimentally shown that these nonlinear moiré superlattices facilitate the nondestructive detection of nonlinear photonic crystals. Two identical periodically poled lithium niobates (PPLNs) are used to observe the nonlinear moiré effect originating from the nonlinear moiré superlattices. This is followed by a demonstration of the detection capability of the nonlinear optical method for dissimilar PPLNs and calculation of the period detection range. The theoretically and experimentally obtained periods of the target PPLN are consistent, and the resolution of the nonlinear moiré effect surpasses to that of presently used optical systems. Furthermore, the detection range of the nonlinear moiré effect enables the sub‐micrometer‐ and nanometer‐scale detection of the nonlinear photonic crystal structure using only an optical microscope. The present study conceptually extends the conventional moiré lattice to nonlinear optics, and it can also be extended to other fields where nonlinear effects cannot be avoided, such as polaritons and Bose–Einstein condensates.