Abstract

The intrinsic high optical nonlinearity originating from tight optical mode confinement due to inherent high index contrast between the core and cladding, along with the potential ability of dense on-chip integration with microelectronic circuits, made silicon photonics one of the rapidly growing research areas. The Kerr coefficient and Raman gain coefficient of silicon exhibits more than 200 and 1000 times larger than those of silica glass, which enable efficient nonlinear interactions of optical waves at relatively low power levels inside a short SOI waveguide. In the last several years, considerable efforts have been made to investigate the nonlinear phenomena such as self-phase modulation (SPM), cross-phase modulation (XPM), stimulated Raman scattering (SRS), four-wave mixing (FWM), nonlinear optical absorption, and so on. Almost all nonlinear properties in silicon are currently being explored to realize a variety of optical functional devices on the chip scale. Compared with the silica fibers, the silicon is a semiconductor crystal exhibiting unique features such as two photon absorption (TPA), FCD, and anisotropic and dispersive third-order nonlinearity. For example, stimulated Raman scattering (SRS) is employed to make optical amplifiers and Raman lasers. Kerr effects are successfully used for nonlinear signal processing, such as SPM and XPM. FWM as one of the Kerr effects has been used to make wavelength converters, optical parametric amplifiers and signal generators. TPA and TPA-induced free carrier generation are suitable for all-optical switching, modulation, pulse compression, and pulse characterization. In addition, nonlinear optical effects can be significantly enhanced in engineered microstructured silicon waveguides, which opens a new subfield in nonlinear optics for exploration.