Nonlinear photonic crystals: from 2D to 3D

Nonlinear photonic crystals are microstructures with quadratic nonlinearity (χ(2)) that have been extensively used for the generation and control of coherent light at new frequencies. Thanks to the recent invention of 3D χ(2)-nonlinearity engineering techniques using femtosecond laser pulses, studies of intense light interaction with 3D nonlinear photonic crystals are now experimentally feasible. Here we review the latest research advances in nonlinear photonic crystals, focusing especially on the fabrication, characterization, and application of 3D structures. We also discuss the future development of 3D nonlinear photonic crystals with properties and functionalities that are either difficult or virtually impossible to achieve with lower dimensional structures.