All-optical tuning of cascaded Raman lasing in silica microsphere

Whispering-gallery mode (WGM) microcavities are known for their high-quality factor, small mode volume, and high power density. These properties have made them a subject of significant interest in both fundamental researches and practical applications, particularly in the field of stimulated Raman scattering. In this study, we combine WGM with the photothermal effect of a microsphere to achieve broadband all-optical tuning of cascade Raman laser. By employing a heating laser to preciously tuning the photothermal-induced change of both the size and refractive index of a silica microsphere, four-order cascaded Raman lasers with a wavelength from 981.0 to 1192.22 nm generated with an average wavelength tunable region of 0.449 nm. The resulting broadband tunability of emission wavelength within both the NIR-II biomedical window and Yb-doped fiber amplifier ranges for O-band optical-fiber communication, highlighting the potential applications in optical sensors, optical communication, bioimaging, and biomedical science.