Measurement of the nonlinear phase shift induced by cascaded interactions in a PPLN waveguide

We report on the measurement of the nonlinear phase shift fNL induced by a strong pump at wavelength lp on a weak signal at ls through a cascade of two second-order interactions in a periodically-poled lithium-niobate waveguide. The experiment is performed by using an interferometric scheme especially designed to be insensitive to slow mechanical and thermal drift effects. The observed behavior of fNL as a function of the pump power and of the wavelength difference lp - ls is in good agreement with the theoretical predictions. OCIS codes: 190.4390, 190.2620, 130.2790, 130.3730.