Ultrafast band-edge tuning of a two-dimensional silicon photonic crystal via free-carrier injection

Ultrafast tuning of the band edge of a two-dimensional silicon/air photonic crystal is demonstrated near a wavelength of $1.9\mu \mathrm{m}.$ Changes in the silicon refractive index are optically induced by injecting free carriers with 800 nm, 300 fs pulses. The rise time of the shift occurs on the time scale of the pulse width apart from a small component associated with carrier cooling; the recovery time is related to electron-hole recombination. The band edge is observed to shift linearly with pump beam fluence, with a shift in excess of 30 nm for a pump beam fluence of $2\mathrm{mJ}{\mathrm{cm}}^{-2}.$ A nonuniform spectral shift is attributed to finite pump beam absorption depth effects.