Strongly enhanced third order nonlinear response of periodically nano-structured silicon-on-insulator (SO) measured by reflection z-scan with femtosecond pulses

We measure a strong enhancement of the third order nonlinear response of periodically nano-patterned and un-patterned silicon-on-insulator (SOI) in comparison with that of bulk silicon, using a fast reflection Z-scan setup with a high-repetition-rate fs laser (at 800 nm wavelength), and a new procedure for discrimination between electronic and thermal nonlinearities. Our procedure, with the laser working in mode-locked or in c.w. regimes, allows precise measurement of both electronic and thermal nonlinear refractive indices of nano-patterned SOI, un-patterned SOI and bulk silicon. These results could be important for nonlinear optical devices with properties controlled by nano-patterning, in silicon photonics.