Degenerate four-wave mixing for characterization of thin-film waveguides

Abstract

We demonstrate experimentally a degenerate four-wave mixing (DFWM) geometry in waveguides that permits the simultaneous determination of the optical Kerr nonlinear refractive index, the nonlinear absorption, and the nonlinear response time of thin-film materials. The geometry consists of two counterpropagating guided pump beams in a planar waveguide. The probe beam simply passes through the thin film and is not guided. By measuring the DFWM signal energy and the guided pump energy at the waveguide output, one can observe several effects simultaneously. Each effect has a different sensitivity to the nonlinearity and, used together, these effects increase the accuracy in determination of the complex n2. This technique was tested on dialkylaminonitrostilbene films. Good agreement was found between the numerical simulations and experimental data. Therefore the technique appears to be a useful characterization technique that yields, in a single setup with basic laboratory equipment, all the relevant parameters of the optical Kerr nonlinearity of thin-film planar waveguides.