Nonlinear absorption and dispersion in fiber-taper-coupled silicon   photonic crystal microresonators
  A technique is demonstrated which efficiently transfers light between a tapered standard single-mode optical fiber and a high-Q, ultra-small mode volume, silicon photonic crystal resonant cavity. Cavity mode quality factors of 47000 are measured, and a total fiber-to-cavity coupling efficiency of 44% is demonstrated. Using this efficient cavity input and output channel, the steady-state nonlinear absorption and dispersion of the photonic crystal cavity is studied. Optical bistability is observed for fiber input powers as low as 250 \mu W, corresponding to a dropped power of 100 \mu W and 3 fJ of stored cavity energy. A high-density effective free-carrier lifetime for these silicon photonic crystal resonators of 0.5 ns is also estimated from power dependent loss and dispersion measurements. 
Paul E. Barclay, Kartik Srinivasan, Oskar Painter