Analysis and design of an integrated silicon ARROW Mach-Zehnder micromechanical interferometer

An analysis and design procedure for an integrated silicon micromechanical (pressure sensitive) interferometer is presented. Optimized layer thicknesses of an SiO₂/Si₃N₄ /SiO₂/Si ARROW yield an attenuation of only 2.7×10^-3 dB/cm. Lateral confinement is accomplished with a rib in the core layer. Sensitivity to mechanical measurands is achieved by having the sensing arm of the interferometer on a thin silicon diaphragm, realized by micromachining a cavity from the back of the wafer. An applied pressure P deflects the diaphragm, causing a change in optical path length, leading to a phase shift φ with respect to the reference arm. Sensitivity is increased by thinning the diaphragm, although this increases the resonant attenuation envelope of the diaphragm. Sensitivity calculations based on a simple, first-order model of diaphragm deflection yield (∂φ)/(φ∂P)=1.29×10^-14 P for a specific diaphragm geometry. BPM simulations show that curvature losses due to the bending of the ARROW under deflection is negligible