**3.2 SRS in nanostructured silicon-based materials**

In our previous papers [2, 33–35] experimental results of spontaneous Raman scattering measurements in silicon nanostructures at the wavelength of interest for telecommunications (1.54 μm), were showed. Due to the phonon confinement model, two significant enhancements of the Raman spectra in silicon quantum dots respect to silicon were obtained: the broadening of spontaneous Raman emission and the tuning of the Stokes shift. In detail, in silicon quantum dots with a crystal size of 2 nm an important broadening of about 65 cm<sup>−</sup><sup>1</sup> and a peak shift of about 19 cm<sup>−</sup><sup>1</sup> were demonstrated. Taking into account that the width of C-band telecommunication is 146 cm<sup>−</sup><sup>1</sup> , we have that more than the half of C-band could be covered using silicon quantum dots, without implementing the multi-pump scheme.

In this paragraph, comparison among experimental investigations of SRS in amorphous silicon nanoparticles and in silicon micro- and nano-crystals, at the wavelengths of interest for telecommunications, are reported. We considered three different samples:


Results obtained can be summarized as follows:


The obtained results are summarized in **Figure 4** where the Raman gain is plotted as a function of the Raman bandwidth for the considered nanostructured silicon-based materials. By combining our earlier results on the broadening of the Raman gain spectra [33–35] with the observation of higher Raman gain [2, 36–42], bring us to state that the traditional trade-off between gain and bandwidth is overcome in low dimensional materials [30].
