Optimization of second-order nonlinearity in UV-poled silica glass

Abstract Second-order optical nonlinearity was induced by ultraviolet (UV)-poling in Ge-doped SiO2 thin films prepared by radio-frequency sputtering. Effects of sputtering, poling conditions and other treatment on the intensity and decay of second harmonic generation (SHG) were investigated. The d coefficient which is a measure of SHG intensity was found to depend on oxygen flow content during sputtering and on Ge-content with an optimum at around 1 cm3/min and 50 mol%, respectively. The UV-poling conditions largely enhance d coefficient which saturates at poling fields equal or larger than E p =1×10 5 V/cm and at total excitation energy of 1 kJ. Preannealing in vacuum enhanced d coefficient with the maximum of 12.5±0.6 pm/V was achieved by annealing at 500°C for 24 h. The addition of hydrogen prior to UV-poling largely improved the decay of d coefficient from several months to around 7 years.