Raman gain and nonlinear optical absorption measurements in a low-loss silicon waveguide

We fabricated a low-loss (similar to0.22 dB/cm) rib waveguide (WG) in silicon-on-insulator with a small effective core area of similar to1.57 mum(2) and measured the stimulated Raman scattering gain in the WG. We obtained 2.3 dB Raman gain in a 4.8-cm-long S-shaped WG using a 1455 nm pump laser with a cw power of 0.9 W measured before the WG. In addition, we observed nonlinear dependence of Raman gain and optical propagation loss as a function of the pump power. Our study shows that this mainly is due to two-photon absorption (TPA) induced free carrier absorption in the silicon WG. We experimentally determined the TPA induced free carrier lifetime of 25 ns, which agrees well with our modeling. (C) 2004 American Institute of Physics.