Raman scattering from acoustic modes in Si/Ge superlattice waveguides

This paper discusses the design of acoustic vibrational modes in Si/Ge planar optical waveguides and its application in creating silicon-based Raman devices with a flexible spectrum. It addresses the deficiencies of the recently demonstrated Raman-based silicon lasers and amplifiers as they relate to spectral and low efficiency limitations of bulk silicon. The treatment is for in-plane scattering in a forward scattering configuration. In addition to calculating the spectrum and the efficiency for Raman active modes, it is shown that the negligible wave-vector of the phonons involved in this type of scattering allows for the use of the bandgap “pinching” effect to arrive at specific layer thicknesses for Si and Ge that optimize the scattering efficiency.