Optical NEMS Based Force Sensor Using Silicon Nanophotonics

A line defect in a silicon two-dimensional (2-D) photonic crystal (PhC) is created as a waveguide for light propagation via the PhC. By introducing micro-cavities within the line defect so as to form the resonant band gap structure for PhC, we demonstrate a PhC waveguide (PhCWG) filter with clear resonant peak in output wavelength spectrum. We conceptualized a novel nanomechanical beam structure embedded with this PhCWG filter, i.e., a NEMS (Nanoelectromechanical system) based force sensor. Since the output resonant wavelength is sensitive to the shape of air holes and defect length of the micro-cavity. Shift of the output resonant wavelength is correlated with beam deformation or force loading for this free-standing PhCWG beam. Simply speaking, the induced strain modifies the shape of air holes and the spacing among them for micro-cavities along the silicon waveguide of PhCWG. For a silicon PhCWG beam structure with dimension of 340nm(thickness) × 5μm(width) × 20μm(length), the measurable vertical deformation of 20~25 nm at the center and detectable strain of defect length of 0.004% is derived according to simulation results.