Second-Order Optical Nonlinearity Induced in Thermally Poled PbO–SiO2 Mixed Film on Fused Silica

Abstract

We developed a lead oxide PbO film of ∼170 nm thickness by RF sputtering on a fused silica substrate. When this film sample is annealed in an oven at 650 °C for 4 min, its physical thickness measured using a surface profiler decreases to ∼163 nm, but its optical film thickness determined using a spectrophotometer increases to 382 nm. This fact implies that PbO will diffuse into the fused silica substrate and form a PbO–SiO2 mixed film that is a graded-index planar waveguide with two transverse electric (TE) modes at 633 nm wavelength. Although the Maker fringe patterns of both fused silica and PbO–SiO2 mixed film samples thermally poled at 6 kV, 275 °C and 30 min look similar, we speculate that second-order nonlinearity exists in poled PbO–SiO2 mixed film because of the higher refractive index contrast at the air-to-film interface. A nonlinear optical coefficient of approximately 1 pm/V in poled PbO–SiO2 mixed film is calculated using a double-step nonlinear profile and grid search fitting technique. The induced second-order nonlinearity is stable for at least several months.