We propose, for the first time to our knowledge, the theoretical investigation of silicon nanocrystals-based sandwiched slot waveguides which are dispersion-engineered for exciting optical solitons inside very short structures (only 1.2？mm long). Several parametric simulations have been performed by means of finite element method in order to individuate the best waveguide cross-sections for achieving an anomalous dispersion regime around 1550？nm. 1. Introduction In the last few years, silicon has become the ideal platform for integrated optics and optoelectronics due to its broad application potential, going from optical interconnects to biosensing [1]. The quality of commercial silicon wafers driven by microelectronics industry still continues to improve while the cost continues to decrease. Moreover, the compatibility with silicon integrated circuits manufacturing and silicon micro-electromechanical systems (MEMSs) technology is very high, and it represents another important reason for this interest in silicon photonics [2, 3]. Recently, several high-speed electro-optical functionalities have been demonstrated in silicon, such as a 40？Gbit/s modulator based on free-carrier (FC) plasma dispersion effect [4]. However, in order to reach much higher speeds (100？Gbit/s and beyond), the electrical domain should be completely overcome and the information data transfer should be entirely processed in the optical domain (ultrafast all-optical processing). In this sense, a number of research study has been performed in order to exploit the ultrafast third-order nonlinear effects in silicon. As a transmission medium, silicon has much higher nonlinear effects than the commonly used silicon dioxide (i.e., optical fibers), in particular Kerr and Raman effects. Additionally, silicon-on-insulator (SOI) waveguides can confine the optical field to an area that is approximately 100 times smaller than the modal area in a standard single-mode optical fiber. Consequently, it is expected that nonlinear optical effects should occur in these waveguides at lower input powers, similar to those used in optical communications systems. For example, several recent experimental and theoretical studies have been focused for exploiting the stimulated Raman scattering (SRS) in the SOI integrated platform. In fact, the need for active devices in SOI has stimulated an increasing research effort in Raman-based light amplification [5–12] and generation [13–20]. Moreover, the ability to generate and utilize large bandwidths using parametric processes is crucial for a large range of photonic
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