Optical amplification and lasing by stimulated Raman scattering in silicon waveguides

Achieving light amplification and lasing in silicon is one of most challenging goals in silicon-based optoelectronics. As a nonlinear optical effect, stimulated Raman scattering (SRS) provides a means to generate optical gain in silicon. Recent results of a nonlinear optics approach to optical amplification and lasing in silicon at the Photonics Technology Laboratory of Intel Corporation are reviewed. This paper starts with the description of the underlying physics related to the Raman scattering in silicon and experimental results of SRS in silicon waveguides. Then, it is shown that nonlinear optical absorption associated with the two-photon absorption (TPA)-induced free carrier absorption (FCA) is a dominant loss mechanism limiting optical gain in a silicon waveguide in addition to the linear optical scattering loss due to the waveguide sidewall roughness. The design and fabrication of a low-loss silicon waveguide containing a p-i-n diode to reduce the nonlinear optical loss are described. It is demonstrated that the free carrier density inside the waveguide can be reduced significantly with a reverse bias of the p-i-n diode. As a result, net optical gain in a silicon waveguide is achieved. The design, fabrication, and characterization of a Raman silicon laser are also described. Both pulsed and continuous-wave (CW) lasing in silicon are achieved using SRS.