Wavelength conversion in silicon using Raman induced four-wave mixing

Silicon integrated optics has emerged as an attractive technology for realizing passive devices because of the efficient silicon-on-insulator sSOId guiding structures and foundry compatible processing technology. However, silicon is generally perceived to be devoid of active optical properties that are needed to realize more sophisticated optical functions such as, amplification and wavelength conversion. We have recently reported the observation of stimulated Raman scattering sSRSd and coherent anti-Stokes Raman scattering sCARSd in silicon waveguides. In this letter, we demonstrate wavelength conversion of digitaland analogmodulated signals from 1542 to 1328 nm, using CARS. The conversion efficiency of this process was measured to be 1.37310−5 and is limited by the phase mismatch between the optical waves. Quasi-phase matching can be achieved by engineering the rib waveguide structure to cancel out the contribution of material dispersion using waveguide dispersion and birefringence. Silicon exhibits a gain coefficient for stimulated Raman scattering that is ,104 times higher than in glass fibers. This, along with a small mode area (due to high index contrast between silicon and SiO2/air) offers the possibility to achieve amplification and wavelength conversion in chipscale devices. In particular, parametric coupling via the Raman susceptibility, xR s3d (which is ,44 times larger than the third order nonresonant susceptibility, xNR ) offers a means to transfer information between the Stokes and anti-Stokes wavelength channels while preserving the phase of the signal. The conversion efficiency of this process is dependent upon (i) the intensity of the pump wave, (ii) the Raman susceptibility of silicon, and (iii) the phase difference between the three waves. The detailed coupled mode analysis of this process has been reported in fibers and has been analyzed in silicon waveguides. The evolution of the anti-Stokes saSd field in the presence of the pump spd and the Stokes sSd fields, assuming no initial anti-Stokes signal, is given by: