Third-order optical nonlinearity of niobium-rich lithium niobate thin films

We have studied the third-order nonlinear optical properties of niobium-rich lithium niobite (LN) thin films prepared by magnetron sputtering at room temperature and annealed at 700 °C in high-purity oxygen. The third-order nonlinear optical properties of the LN films were investigated by the Z-scan method at a wavelength 1064 nm and a pulse duration 25 ps. The Z-scan results show that the LN films exhibit reverse saturation absorption and self-focusing behaviors. The third-order nonlinear refractive index γ and the absorption coefficient β were determined around 10−11 cm2/W and 10−7 cm/W, respectively. The γ is four orders of magnitude larger than that in the LN single crystals measured at the pulse duration 25 ps but the wavelength 532 nm, while two orders of magnitude smaller than that in the LN films measured at the wavelength of 532 nm and 800 nm, respectively. The nonlinear absorption in our LN films also significantly decreased compared with that in the reported LN films. Our results show that the optical nonlinearity of LN films can be significantly affected by the atom composition and incident wavelength, and will be of significance for LN-based integrated on-chip photonic devices.