In this work, we study some periodically nanostructured silicon-on-insulator samples that could be considered as a composite material and described by effective medium theory. We present our theoretical and experimental studies on effective linear refractive index and third-order optical nonlinear response of silicon-on-insulator with 1D periodic nanostructures. Using reflection intensity-scan method in continuous wave regime (at 808 nm wavelength) and in femtosecond pulsed laser regime (at 775 nm wavelength and 140 fs pulse duration), we show that the thermal effects and electronic third-order optical nonlinearities are larger than those obtained on bulk silicon and unstructured SOI. Our results may be important for ultrafast silicon photonics.
In this paper, we study the dependence of effective optical linear and nonlinear refractive indices of nano-porous silicon
layers on crystalline silicon substrates on fill fraction, at different light wavelengths in visible and near-infrared. Simple
approximative formulae, in the frame of Bruggeman's formalism, that describe the dependences of effective optical
linear and nonlinear refractive indices of nano-porous silicon on fill fractions and on wavelength, in the range of 620 -
1000 nm, are derived. Experimental results with reflection intensity scan show a good agreement with the data provided
by our formulae and the exact results of Boyd-Bruggeman's formalism for the third order nonlinearity, in the case nanoporous
silicon with different porosity and at light wavelengths in the mentioned spectral range.
The results obtained using Z-Scan methods (transmission -- TZ-Scan and multiple-pass -- MZ-Scan) for the characterization of the partial transparent nonlinear optical materials (NOM) are presented. For a typical NOM, a monocrystalline Si wafer with thickness 0.4 mm, at λ = 1060 nm, the nonlinear bulk effects are dominant in comparison with the nonlinear effects produced by the entrance interface (due to the sufficient large transmission of Si). In this case, the MZ-Scan at low laser intensity (several MW/cm<sup>2</sup>) can be analyzed similarly to the TZ-Scan, considering the multiple passes inside the sample and linear Fresnel reflections on both sample faces. Due to these multiple passes inside the sample, the sensitivity of the method is increased. The nonlinear optical susceptibility experimentally determined by multiple-pass Z-Scan is in agreement with a theoretical estimation of this parameter, with the results of other treatments of MZ-Scan and TZ-Scan and with its values obtained by two and four-wave mixing.