Investigations of harmonic generations in aperiodic optical superlattices

We envisage the enhanced effect of harmonic generations from aperiodic opti cal superlattices (AOSs) achieved by inverting poled ferroelectric domains in samples. The search of optimal AOSs structures belongs to solving a diff icult inverse source problem in nonlinear optics. We employ the simulated a nnealing method to successfully deal with this problem. We present the anal yses of the design idea in the real-space representation and carry out seve ral model designs. The constructed AOSs implement multiple wavelength secon d-harmonic generation and the coupled third-harmonic generation with an ide ntical 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 s uperlattice. The effective nonlinear coefficients versus the optical wave p ropagating distance from the impinging surface of incident light in the sam ple 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 influen ce 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. (C) 2000 American Institu te of Physics. [S0021-8979(00)00511-9].