Third order nonlinearity characterization of optical wave-guides

We propose and demonstrate a new and simple technique for characterization of fast third order optical nonlinearity of wave-guides and bulk materials. Z-scan method, proposed and developed for bulk materials, has been preferred by experimentalists. It investigates nonlinear spatial distortions induced on a focused laser beam. In fact the technique that we present here, which we have called "D-scan", is the temporal analog of the spatial Z-scan. It is based on spectral changes of a femtosecond pulse according to the dispersion preliminary introduced on the input femtosecond pulse by a dispersive delay line. The nonlinear evolution of the output spectrum when the dispersion introduced at the input is varied from negative to positive gives a sensitive measurement of the complex third order nonlinearity. The imaginary part of nonlinear susceptibility can be deduced from the evolution of the total average transmitted power versus the input dispersion. More, the plot of the of the position of center of the output spectrum may be exploited to measure the refractive index change time response. in order to demonstrate the capability of the proposed method we have experimentally retrieve the standard value of the nonlinear coefficient nz of silica during characterization of a Short sample of a single-mode optical fiber.