The influence of van der Waals forces on the waveguide deformation and power limit of nanoscale optomechanical systems

The ultra-short range force, van der Waals force (VWF), will rise rapidly when one nanoscale waveguide is close to another one, and be stronger than the external transverse gradient force (TGF). We theoretically investigate the giant influence of the VWF on the device performance in a typical optomechanical system consisting of a suspended silicon waveguide and a silica substrate including waveguide deformation stiction and failure mechanism. The device shows unique optically-activated plastic/elastic behaviors and stiction due to the VWF. When the input optical power is above the critical power, the waveguide is sticking to the substrate and the deformation is plastic and unrecoverable, even though the total force is less than the yield strength of the waveguide material. This is important and helpful for the design and applications of optomechanical devices.