Self-phase modulation in photonic-crystal-slab line-defect waveguides

The authors observed self-phase modulation in spectral domain at $1.50\mu \mathrm{m}$ in ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ -based photonic-crystal-slab line-defect waveguides. Adopting a sample with $x=0.18$ has enabled the authors to avoid two-photon absorption, causing undesirable free-carrier-induced refractive-index change. Variation of the observed spectrum with input pulse peak power is well reproduced by theoretical simulation. They find that a $1.6\mathrm{ps}$ light pulse of $2.5\mathrm{pJ}$ suffices for causing a phase shift of $\pi$ in a $1\mathrm{mm}$ long sample owing to tight light confinement and nonlinear refractive index $n_2$ due to instantaneous optical Kerr effect is $(3.8\pm 1.2)\times {10}^{-13}{\mathrm{cm}}^2∕\mathrm{W}$ . A possibility of developing ultrafast all-optical switch due to $n_2$ is discussed