Optomechanically induced thermal bistability in an optical microresonator

Optomechanical systems have attracted considerable attention due to their wide applications in hybrid transduction systems, sensors, and quantum measurements. Classical optomechanical systems have various dynamical regimes that depend on the parameters, and the situation can be even more complicated when incorporated with other nonlinearities, such as the thermal nonlinearity that is common in optical resonators. Here, we experimentally and theoretically study the thermal bistability induced by optomechanical effect in a whispering-gallery mode microresonator. The mechanical oscillation modulates the intracavity photon number and modifies the thermal stability of states under a blue-detuned pump laser. Utilizing a silica microtip to suppress the mechanical motion, we identify the regions where the optical cavity temperature and detuning change due to the onset of oscillation and characterize the shifts in the detuning quantitatively. Hysteretic response in the mechanical frequency shifts (optical spring effect) to the pump wavelength is also observed to confirm the presence of bistability. The thermal dynamics discussed here is essentially different from the optomechanical heating and cooling of the effective temperature of the mechanical oscillator. This discovery shows that the thermal nonlinearity, which has been used for locking the pump frequency in the optomechanical systems, may also make some detuning states thermally unstable. Our study demonstrates an approach to characterize the detuning of the pump laser in an optomechanical resonator with thermal nonlinearity and also lays the groundwork for further understanding of dynamical effects induced by optomechanical effects.