I. Introduction
Integrated nanophotonics, particularly on the silicon on insulator (SOI) platform, has recently enabled the successful realization of various nonlinear optical devices on chip [1]. At the core of these advances lies the tight confinement of light within submicrometer-sized silicon nanowires that substantially increases the optical energy density, allowing nonlinear optical effects to occur at greatly reduced input powers. Planar silicon photonic crystal (PhC) waveguides represent another integrated platform, where light is confined by total internal reflection within the vertical silicon/air step index waveguide while experiencing the periodic modulation of the refractive index in the plane of the structure. While this platform provides a similar degree of optical confinement to that of silicon nanowires, it offers the additional capability to reduce significantly the speed of light propagation–-creating the so-called slow light [2], [3]. In the context of integrated nonlinear optics, slow light holds the promise for further enhancing optical nonlinear effects [4], [5].