Second harmonic generation from Ge doped SiO_2 (Ge_x(SiO_2)_(1-x)) thin films grown by sputtering

摘要

Second-order nonlinear optical properties of sputter-deposited Ge-doped SiO_2 thin films were investigated. It was shown that the second-order nonlinearity of SiO_2, which vanishes in the electric-dipole approximation due to the centrosymmetric structure, can be significantly enhanced by Ge doping. The observed maximum value of d_(33) was 8.2 pm/V, which is 4 times larger than d_(22) of β-BaB_2O_4 crystal. Strong correlation was observed between the d_(eff) values and the electron spin resonance signals arising from GeP_b centers, suggesting that GeP_b centers are the most probable origin of the large second-order nonlinearity.