Investigations of harmonic generations in aperiodic optical superlattices

Abstract

We envisage the enhanced effect of harmonic generations from aperiodic optical superlattices (AOSs) achieved by inverting poled ferroelectric domains in samples. The search of optimal AOSs structures belongs to solving a difficult inverse source problem in nonlinear optics. We employ the simulated annealing method to successfully deal with this problem. We present the analyses of the design idea in the real-space representation and carry out several model designs. The constructed AOSs implement multiple wavelength second-harmonic generation and the coupled third-harmonic generation with an identical effective nonlinear coefficient at the preassigned wavelengths. The simulations show that the harmonic generations in the constructed AOSs can approach the prescribed goal better than those with the Fibonacci optical superlattice. The effective nonlinear coefficients versus the optical wave propagating distance from the impinging surface of incident light in the sample exhibit monotonically increasing behavior. This clearly infers that the contribution from each and every block to the optical parametric processes is in the constructive interference state. We also investigate the influence of the random fluctuation of the thickness of blocks on the performance of the constructed AOSs in detail for simulating practical fabrications and testing the performance stability of the sample.