Nonlinear femtosecond pulse tuning of 2-D photonic crystals

We demonstrate how ultrashort optical pulses can be used to tune the optical properties of a photonic crystal using the real (Kerr) and imaginary (two photon absorption) parts of a third order optical nonlinearity. We demonstrate this effect by tuning the long (1.6 μm) and short wavelength (1.3 μm) band-edges of a stop-gap in a 2-D silicon photonic crystal. From pump-probe reflectivity experiments using 150-200 fs pulses, we observe that a 2 μm pulse induces optical tuning of the 1.3 μm edge via the Kerr effect whereas a 1.76 μm pulse induces tuning of the 1.6 μm band edge via both Kerr and Drude effects with the latter related to 2-photon induced generation of free carriers with a lifetime of ~ 700ps. In separate experiments we show how the properties of the pump eigenmode can influence the magnitude and temporal dynamics of the tuning behavior. When carriers are injected via a pump eigenmode for which the initial carrier distribution is inhomogeneous, diffusion is responsible for an initially fast (10 ps time scale) component of the recovery of the probe reflectivity with surface recombination accounting for a slower response (700 ps time scale) after the carriers are nearly uniformly distributed within the silicon backbone. When carriers are initially generated homogeneously, surface recombination alone controls the time evolution of the probed mode.