Phase-Matched Second-Harmonic Generation from Five-Layer Langmuir-Blodgett Film Waveguides with Large Fabrication Tolerance and Overlap Integral for Mode Conversion

Abstract

The five-layer waveguide composed of Langmuir-Blodgett films were prepared from combination of low molecular weight amphiphilic NLO dye, n-Docosyl-4-nitrophenylurea (DONPU) and SHG inactive polymer. The NLO dye was deposited as y-type LB films. The SHG efficiency of this film was dominated by the contribution from in-plane components such as d33. Other tensor components are almost negligible. The second NLO layer was deposited on PDiPF films after reversing the dipping direction to introduce the inversion of the nonlinear susceptibilities across the film. By selecting the proper combination of the SHG inert layer and SHG active layers the mode dispersion curves were compensated to have the same slopes. In fact there are four intersections of the mode dispersion curves, a very good thickness tolerance for phase-matching can be expected. Five-layer organic waveguides prepared by Langmuir-Blodgett techniques exhibit high overlap integral as well as large fabrication tolerance of thickness up to 56 nm. This large fabrication tolerance for phase-matching is 8.6 times larger than that of conventional three layer waveguide.