Polarization State of Silicon Raman Lasers Dictated by Non-Degenerate Two-Photon Absorption

In this paper, we demonstrate the polarization state of the silicon Raman lasers dictated by the non-degenerate two-photon absorption (TPA) process. We measure that the lasing in silicon waveguides can be achieved when pump and signal have linear and orthogonal polarization states relative to each other or circular polarization states. Pump-signal TPA increases the loss inside the resonator significantly and does not allow lasing when they have collinear polarization states. We measure the average lasing threshold power to be 12.5 mW for orthogonal polarization states and it is increased by 12% (to 14 mW) by adjusting the pump-signal polarization states to circular polarization. Experimental results reveal that the degenerate TPA will mitigate the higher order Raman lasing in silicon waveguides for wavelengths below 2 mum because of non-degenerate TPA process