Ultrasensitive displacement sensing using photonic crystal waveguides

We present an ultrasensitive displacement sensor and sensing technique based on photonic crystal waveguides (PCWG), useful for integration with microelectromechanical system (MEMS) structures. The sensor consists of two PCWGs aligned along a common axis, one mounted on a moving part and the other fixed to a stationary substrate. A gap between the fixed and moving PCWGs creates an intersection with a third, perpendicular PCWG, which has two branches. The intensity exiting each PCWG changes when the suspended PCWG moves in plane relative to the fixed one. The difference in intensities exiting the two perpendicular PCWG branches can be correlated with the relative displacement between the fixed and moving PCWGs. Numerical simulations predict a sensitivity of similar to 1 [mu m(-1)] using a light source of 9.02 mu m. (c) 2005 American Institute of Physics.