Ultrafast tuning of two-dimensional planar photonic-crystal waveguides via free-carrier injection and the optical Kerr effect

Femtosecond pump-probe reflectivity and second-harmonic spectroscopy experiments are used to investigate the optical tuning of leaky modes in a two-dimensional GaAs photonic-crystal waveguide. For above bandgap excitation with 270 fs, 800 nm pulses with a pump fluence of 100 mu J cm(-2), a blueshift of 16 +/- 2 nm is measured for a 1900 nm leaky mode, as observed from the shift of the resonantly enhanced second-harmonic pulse. Theoretical calculations of carrier-induced changes in the refractive index from band filling, bandgap shrinkage, and Drude contributions are in good agreement with the results. Recovery occurs within 2 ps and is attributed to recombination via deep-centered defects. For below bandgap excitation with 166 fs, 1900 nm pulses with a fluence of 800 mu J cm(-2), redshifts >= 1.5 nm of the 1360 nm leaky mode are induced via the optical Kerr effect during the early part of the pump pulse, but thereafter the mode is blueshifted, owing likely to free carriers injected into or from deep-centered defects. (c) 2005 Optical Society of America.