Second-order nonlinearity of thermally poled lead -silicate glass waveguides.

摘要

Electro-optic switches and modulators are very important devices in optical communication systems. Fabrication of such devices requires materials with a second order optical nonlinearity; however, silica-based glass is largely limited in this area due to its spatial inversion symmetry. The invention of thermal poling technique in 1991 changed this picture, and a large research effort was stimulated by this discovery with the aim of creating a large permanent chi(2) in glassy materials. In this dissertation, the high second-order optical nonlinearity of the thermally poled lead-silicate glass waveguides was reported.;A laser ablation setup was designed and built for the growth of lead-silicate glass thin films. Depositions under various laser fluence, substrate temperatures, background gas pressures, and post-deposition annealing temperatures were performed. Optimum growth parameters were determined for waveguide applications. Thin films with very low particle density, small particle size and relatively high uniformity were fabricated successfully.;The large nonlinearity localized within the PbO-glass layer was found by scanning the probe laser beam across an angle-polished sample, and a peak second-order nonlinear susceptibility chi(2) as high as 15 pm/V was achieved in the PbO-glass layer. A simple theoretical model based on charge transport in the different materials during poling was proposed and the complex chi(2) profile was explained. The large third-order nonlinearity of lead glass played a key role in the generation of the large second harmonic signal. The average electrooptic nonlinearity gammae-o for a waveguide mode was about a factor of three larger than for silica-based waveguides. Studies of UV stability of the induced nonlinearity, and the relations between SH signal and the thickness and type of films were also carried out.;Theoretical simulations of the channel waveguides of lead-silicate glass were performed to improve the structure design, as well as to predict the device characteristics. The electro-optic nonlinearity for an optical signal guided in the poled device was estimated to be 21.5 pm/V. For the integrated push-pull MZI waveguides with 10 mm interaction length, a half-wave voltage Vpi as low as +/-10 V will be achievable.