Cross-phase modulation due to a cascade of quadratic interactions in a PPLN waveguide

The cross-phase modulation of a weak signal has been obtained in a periodically poled lithium-niobate waveguide as a result of the quadratic interaction of the signal with the second harmonic of an intense pump field. The nonlinear phase acquired by the signal has been measured as a function of the pump field intensity and of the phase mismatch with the second harmonic field. The measurements have been performed with a properly designed experimental setup based on a Mach-Zehnder interferometric scheme, which proved to be quite insensitive to slow mechanical and thermal drifts. Numerical simulations are in good agreement with experimental results.