Giant enhancement of second harmonic generation in multiple photonic quantum well structures made of nonlinear material

摘要

We present a general solution of second harmonic generation (SHG) in one-dimensional (1D) inhomogeneous systems. The structure consists of 1D multiple photonic quantum wells (PQWs) made of optical nonlinear material. The optimal arrangement of the polarization directions of the ferroelectric domains in multiple PQWs is determined by a simulated annealing method. We find that the conversion efficiency of SHG can be significantly enhanced when the fundamental wave frequency is aimed at one of the defect states. By tuning the polarization directions of the domains, the conversion efficiencies of "forward" and "backward" SHGs can be flexibly changed.