Demonstration of enhanced Raman scattering in high-Q silicon nanocavities operating below the silicon band-gap wavelength

We experimentally determined the quality factor (<i>Q</i>) and the intensity of the Raman scattered light for different silicon photonic-crystal nanocavities operating at wavelengths shorter than the silicon band-gap wavelength. Despite the relatively large absorption of silicon in this wavelength region, we observed <i>Q</i> values greater than 10,000 for cavities with a resonance wavelength of 1.05 µm, and <i>Q</i> values greater than 30,000 for cavities with a resonance wavelength of 1.10 µm. Additionally, we measured the Raman scattering spectra of cavities with resonance wavelengths of 1.10 µm and 1.21 µm. On average, the generation efficiency of the Raman scattered light in a 1.10-µm nanocavity is 6.5 times higher than that in a 1.21-µm nanocavity. These findings suggest that silicon nanocavities operating below the silicon band-gap wavelength could be useful in the development of silicon-based light sources.