Enhanced Stimulated Raman Scattering in silicon nanocrystals embedded in silicon-rich nitride/silicon superlattice structures

In the last few years several strategies have been developed to engineer efficient light sources and amplifiers in Si-based materials, with the aim to demonstrate a convenient path to monolithic integration of optical and electronic devices within the mainstream Si technology In particular, light amplification by Stimulated Raman Scattering (SRS) in silicon waveguides has been recently demonstrated despite intrinsic limitations related to the nature of the bulk Si materials have been pointed out . The narrow-band (105 GHz) of stimulated Raman gain in Si limits its applicability in the context of Si photonics, and makes it unsuitable for its use in broad band division multiplexing (WDM) applications, unless expensive multi-pump schemes are implemented. Additionally, Raman amplification in Si is a small effect. Therefore, in order to build a laser based on stimulated Raman effects in Si, very high power intensity and very low absorption losses are required. Finally, Raman gain in Si is further reduced by the competing nonlinear effect of two-photon absorption. This effect generates electron-hole pairs, which remain excited in the sample for a long time (micro to milliseconds) and lead to strong absorption at both the pump and signal frequencies.