Thermal behavior analysis of Raman lasing in 4H-SiC microresonators

Abstract

Raman lasing in microresonators has been observed in various material platforms, such as silicon, silica, lithium niobate, diamond, and silicon carbide. Frequency matching between cavity resonances and a Raman gain profile enables a lasing threshold as low as a milliwatt level with a continuous-wave pump. However, the distinct thermal responses of the cavity resonances and the Raman phonon frequency can induce frequency mismatch and lead to unstable Raman lasing with varying temperatures. This temperature-dependent Raman lasing has not been sufficiently investigated to date. Here, we characterize two prominent Raman phonons at 265 and 776 cm−1 in 4H-silicon carbide (SiC) microresonators and analyze their thermal evolution. We observe that the Raman signal near 776 cm−1 exhibits a thermal shift rate closely matching that of the cavity resonance, enabling stable Raman lasing for a temperature range exceeding 88 K. In contrast, Raman lasing near 265 cm−1 behaves in an unstable manner, due to the narrow Raman gain bandwidth and the large mismatch between the thermal response of the Raman gain and the cavity resonance. These findings demonstrate the stable lasing behavior of the dominant Raman signal at ∼776 cm−1 of 4H-SiC and establish crucial guidelines for achieving thermally robust Raman lasing in microresonators.