Integrated high sensitivity displacement sensor based on micro ring resonator

A novel integrated high sensitivity displacement sensor based on micro ring resonator is described. It includes the high sensitivity of optical sensors and the compactness and potential for mass production of the MEMS sensors. In this design, GaAs-Al_0.6Ga_0.4As platform was chose for its high-index contrast. A bus waveguide couples to a micro ring resonator and they are integrated on the supporting point of a cantilever. We can obtain the value of displacement sensor by means of monitoring the changes in the transmission spectrum of the ring resonator due to the photo-elastic effect and the change of circumference as the deformation of cantilever. This method has high sensitivity and can be used in harsh environments such as ultra-high vacuum (UHV) systems and electromagnetically active environments. Finite Element Method (FEM) simulations were carried out to obtain the optimum sensor design and Beam Propagation Method (BPM) simulation was used to obtain the transfer characteristics of the bus waveguide and the micro ring resonator. In this paper, operation principles and sensitivity analysis are discussed in detail. Different types of ring resonators are studied in order to achieve high sensitivity and the radius of 20 mum of ring resonator is chose eventually. Further more, because of the fabrication limit, the FIB (Focused Ion Beam) is used to etch the gap between waveguide and ring resonator accurately after RIE etching, which can control the gap to less than 100 nm, and the whole manufacturing process is also presented.