Enhanced third-order nonlinear effects in slow-light photonic-crystal slab waveguides of line-defect

We experimentally studied enhancement of the third-order nonlinear optical phenomena, i.e., self-phase modulation due to optical Kerr effect and two-photon absorption (TPA) in a small group-velocity (V-g) line-defect guided-mode of AlGaAs-based photonic-crystal slab waveguide. We found that the phase shift Delta phi or nominal Kerr constant n(2)' and TPA coefficient beta were strikingly enhanced due to small V-g as the band edge was approached, such that they were proportional to (V-g)(-2); the nonlinear refractive index n(2) is enhanced proportional to V-g(-1). We also observed that owing to this enhancement as well as an extremely small cross-section area, the energy required for inducing pi-phase shift was very small, being of an order of a few pJ for 5 ps optical pulse and for a 0.5-mm long sample. Based on those results, we discuss the possibility of developing ultra-fast and ultrasmall all-optical switches that operate due to cross-phase modulation. (C) 2009 Optical Society of America