摘要
Optomechanics of colloidal microparticles has wide applications in biological analysis and sensing. For colloidal microspheres or microdroplets, the optomechanical force can be magnified through the cavity enhancement effect. However, it is difficult to analyze the force since the colloidal microspheres are suspended in liquid, and addressing a movable microsphere at a specific position in 3D space is also challenging. An integrated operation platform comprising waveguides and microelectromechanical systems is employed to facilitate the study of cavity-enhanced optical gradient force for colloidal microspheres, owing to the ability to precisely tune the gap between a suspended microsphere and a waveguide through dielectrophoretic force. We introduce two kinds of optomechanical coupling mechanisms at resonance, depending on the initial coupling gap before inclusion of the optical gradient force. One is self-adjusted coupling, where the coupling gap of a suspended microsphere continuously varies with the optical input power, and the other is bistable coupling, where the coupling gap hops from one state to the other as the input power exceeds over a threshold value, which is caused by the nature of nonlinear gap-dependent optical gradient force.