Second harmonic generation in thermally-poled inorganic glasses

Takebe, H., Kazansky, P.G., Russell, P.St.J. and Morinaga, K. (1996) Second harmonic generation in thermally-poled inorganic glasses. Third International Conference on Nonlinear Optics, Marco Island, United States.

Abstract

Inorganic glasses with inversion symmetry naturally have not been possessing the second order nonlinearities (SONs). However, permanent SONs with 1 pm/V (~0.2 of the value χ₂₂⁽²⁾ in LiNbO₃ have been observed in commercial fused-quartz glasses. For a typical poling condition, samples with 1 mm thick are heated to 280°C with an applied voltage of 4 kV for 15 min and then cooling till room temperature with the field applied. After this poling procedure, the SON is observed only near the anodic surface. This result leads to the interest of the possibility of parametric frequency converters and linear electrooptic modulators monolithically integrated into optical fibers or planar glass waveguides. A better understanding of the mechanism, which is not fully understood, may help improve the value of SON in poled glasses and discover novel SON inorganic glass materials. We have systematically studied the effects of poling conditions, especially poling dc voltage and time on SHG in thermally-poled fused quartz and discovered that the SH signal is proportional to the square of the applied voltage and that the speed of the poling process increases with the applied voltage. Effects of impurity concentrations such as oxygen deficient centre (ODC), Na, and OH in fused quartz glasses were also studied. A correlation of the SH signal with the ODC concentration, which was controlled by annealing temperatures (900 - 1100°C) in air, was observed. The mechanisms and materials conditions to create permanent SONs in various oxide glasses, e.g., fused quartz, sol-gel derived silica, tellurite glasses, are discussed in the light of these new results.

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