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 Deltaphi 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 ultra-small all-optical switches that operate due to cross-phase modulation.