Optical-loss reduction and phase-matched second-harmonic generation in a four-layered polymeric waveguide

For efficient second-harmonic generation in the waveguide format, based on the modal dispersion relations for phase-matching, the overlap integral describing the overlap of the modal field distribution functions E(z) for the fundamental mode and the harmonic mode, has to be optimized. The NLO film susceptibility has to be tailored to avoid negative contributions to the overlap integral resulting from a negative part of the modal field from the harmonic mode. In a four layered waveguide, this can be accomplished by using an additional polymer layer with zero NLO film susceptibility. This additional layer also has lower optical loss, so that the total waveguide loss is also reduced