Optothermal control of gains in erbium-doped whispering-gallery microresonators.

Erbium-doped whispering-gallery-mode (WGM) microcavities have great potential in many important applications, such as the precision detection and the micro/nano laser. However, they are sensitive to the fluctuations from the pump laser and the environment. Here we demonstrate the precise controlling of transmission spectra and optical gains using optothermal scanning methods in erbium-doped WGM microcavities. The transmission spectrum of the probe signal exhibits the transition between asymmetric Fano-like resonance and the Lorentz peak (or dip) through tuning the input frequency and the scanning speed of the pump laser. In particular, the analytical calculations can fit well with our experimental results through adiabatically eliminating the anticlockwise optical mode. This Letter shows that the optothermal control of gains is more robust to external noises, which paves a crucial step toward the application in the ultra-sensitive detection.