Optical gradient force for tuning, actuation, and manipulation of nonlinearity in graphene nanomechanical resonator

Graphene nano-mechanical resonators integrated over waveguides provide a powerful sensing platform based on the interaction of graphene with the evanescent wave. An integrated actuation scheme that does not compromise this interaction is required for optimal usage of the ultra-sensitive platform. Conventional electrical and optical actuation techniques are not favorable towards efficient utilization of the near-field interaction. We propose tuning and actuation of these resonators using on-chip optical gradient force due to the guided wave as an alternative to these conventional techniques. We have used the fundamental quasi-TM optical mode in a silicon waveguide in a finite-element model. We obtain a force–distribution that is spatially correlated with the fundamental mechanical mode of the graphene nano-mechanical resonator. We demonstrate that for an evanescent continuous-wave (CW) optical power of 8 μW, the resonant frequency of the device can be tuned by about 24.5%. With an intensity-modulated optical power ≤0.1 μW, the mechanical mode can be driven to nonlinearity. We also demonstrate cancellation of the Duffing nonlinearity at a CW power of 5.4 μW, which can be used to improve the linear dynamic range of vibration. The distributed optical gradient force can produce linear resonant amplitudes that are 50% higher than those obtained using conventional actuation schemes. This actuation scheme is robust against fluctuations in the evanescent optical power and in the refractive index of the side-cladding of the waveguide. This ensures minimal cross-talk from the optical mode to the mechanical mode in nano-mechanical sensing applications.