Second-order optical nonlinearity in thermally poled multilayer germanosilicate thin films

The Maker fringe method and second-harmonic light microscopy were applied to investigate the second-order optical nonlinearity induced in thermally poled silica thin films. It was found that the nonlinearity in Ge-doped film was more than three times that in pure silica film. Results from the second-harmonic microscopy revealed that, in the Ge-doped silica thin films with varying Ge-doping concentration along the thin film depth, the nonlinearity exhibited a multilayer distribution with peaks located at positions with highest contrast in Ge doping profile.