Measurement of the cubic nonlinear susceptibility in lithium niobate

We measured the cubic nonlinear susceptibility tensor elements ( χ (3) ) for polarization along the primary crystallographic axis in titanium-indiffused lithium niobate waveguides, assessed through self-phase modulation using picosecond-duration pulses at telecommunication wavelengths. A dominant, highly temperature- and wavelength-dependent contribution from a cascaded second-order nonlinearity is observed. Through careful extraction of the cascaded effect, we quantify the intrinsic third-order susceptibility tensor elements as χ z z z z (3) ( ω ; ω , ω ,− ω )=(5.2±1.3)×10 −21 m 2 V 2 and χ x x x x (3) ( ω ; ω , ω ,− ω )= χ y y y y (3) ( ω ; ω , ω ,− ω )=(3.6±0.8)×10 −21 m 2 V 2 . These measurements underscore the substantial impact of the cascaded nonlinearity in enhancing the effective cubic nonlinearity in lithium niobate and offer precise values essential for the design of nonlinear photonic devices.