Feedback Enhanced Sensitivity in Optomechanics: Surpassing the   Parametric Instability Barrier
  The intracavity power, and hence sensitivity, of optomechanical sensors is commonly limited by parametric instability. Here we characterize the parametric instability induced sensitivity degradation in a micron scale cavity optomechanical system. Feedback via optomechanical transduction and electrical gradient force actuation is applied to suppress the parametric instability. As a result a 5.4 fold increase in mechanical motion transduction sensitivity is achieved to a final value of $1.9\times 10^{-18}\rm m Hz^{-1/2}$. 
Glen I. Harris, Ulrik L. Andersen, Joachim Knittel and Warwick P.   Bowen
quant-ph