Non-trivial scaling of self-phase modulation and three-photon absorption in III-V photonic crystal waveguides

We investigate the nonlinear response of photonic crystal waveguides with suppressed two-photon absorption. A moderate decrease of the group velocity (similar to c/6 to c/15, a factor of 2.5) results in a dramatic (x 30) enhancement of three-photon absorption well beyond the expected scaling, proportional to 1/v(g)(3). This non-trivial scaling of the effective nonlinear coefficients results from pulse compression, which further enhances the optical field beyond that of purely slow-group velocity interactions. These observations are enabled in mm-long slow-light photonic crystal waveguides owing to the strong anomalous group-velocity dispersion and positive chirp. Our numerical physical model matches measurements remarkably. (C) 2009 Optical Society of America