Silicon-based Raman laser

Abstract

Silicon laser remains as the greatest challenge in the realization of silicon photonic echnology due to the inherent low internal quantum efficiency of light emission for silicon. Light amplification and lasing by stimulated Raman scattering (SRS) provides an attractive approach due to its unique wide range of operation, extensive tuning capability and simple fabrication. This research work aims to propose a novel design of silicon Raman laser and investigate its performance analytically. In this research work, we propose and analyze the introduction of bi-directional pumping scheme into the silicon laser for the first time. Fabry-Perot (FB) cavity structure with variable end-facet reflectivity is utilized in our study. In addition to adapting an existing formulation to model silicon Raman laser, we employed a much faster improved Runge-Kutta-Fehlberg (RKF) Method to solve the differential equation set. Key laser performance indicators such as output Stokes power, intra-cavity power distribution and lasing threshold are investigated in our study. Results for both one-way and bi-directional pumping schemes are illustrated under the same total input power to justify the significance of our work. Our simulation results show that the use of bi-directional pumping is an effective mechanism to reduce losses in silicon Raman laser. Intra-cavity pump power level decreases under bi-directional pumping scheme. This results in the loss reduction to subsequently enhance the pump-to-Stokes conversion efficiency. An output Stokes power enhancement of more than 20% can be achieved. We also explore the change of key laser performance indicators at bi-directional pumping when cavity end-facet reflectivity changes. Output power from silicon Raman laser is maximized by a bi-directionally pumped cavity with low end-facet reflectivity. On the other hand, bi-directional pumping is found to have negligible effect on lasing threshold due to the low TPA and FCA losses at low pumping power. Coherent anti-Stokes scattering (CARS) is another non-linear process occurring in silicon Raman laser, in addition to the dominant SRS. From our previous analytical model, we extend our investigation by incorporating CARS into our modeling. A novel two-model comparison algorithm is then built from here to analyze the effect of CARS process in the Stokes output. Our simulation shows that enhancement of CARS could effectively reduce losses and enhance Stokes output simultaneously in silicon Raman laser. A loss reduction of more than 3 dB and an output enhancement of more than 100% can be obtained from a phase-matched silicon waveguide cavity. The study on Bi-directionally pumped silicon Raman laser shows encouraging results on pump-to-Stokes conversion efficiency. With the same total pump power, bi-directional pumping is able to reduce the peak pump intensity in the cavity and therefore suppress FCA losses to enhance the Stokes power output.