Raman Lasing in Multimode Silicon Racetrack Resonators

Integrated Raman lasers have been well explored using silica and silicon platforms for decades. A well-known equation with negligible nonlinear losses is employed for predictions of Raman lasing threshold powers in critically coupled cavities. However, nonlinear losses are known to be highly detrimental to silicon devices. Herein, for the first time, including the effects of linear loss, nonlinear losses, and cavity design, a new general equation that predicts the onset of Raman lasing in a cavity is derived and validated experimentally. Generally, a cavity with a small effective area, a short length, and high quality factors (Qs) at both pump and Stokes wavelengths can lase at relatively low pump power. This theory is verified by the experimental results with sub-milliwatt threshold powers in 2.8 mm long multimode cavities with different Qs at different pump wavelengths. The derived Raman gain coefficients from the measurements follow the scaling rules of Raman gain. This work advances the understanding of Raman lasing in high-Q multimode cavities. It also shows that Raman lasing at O/S-band is possible in racetrack resonators without needing any reverse bias and the broad operation wavelength is promising for single-chip silicon devices operating at all communication bands.

Automated summary

For the first time, a new general equation that predicts the onset of Raman lasing in a cavity, considering linear loss, nonlinear losses, and cavity design, has been derived and experimentally validated. The study shows that cavities with small effective areas, short lengths, and high quality factors (Qs) at both pump and Stokes wavelengths can lase at relatively low pump power. The Raman lasing at O/S-band in racetrack resonators without reverse bias and the broad operation wavelength is promising for single-chip silicon devices operating at all communication bands.