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 SiO/sub 2//Si/sub 3/N/sub 4//SiO/sub 2//Si ARROW yield an attenuation of only 2.7/spl times/10/sup /spl minus/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 /spl phi/ 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 (/spl part//spl phi/)/(/spl phi//spl part/P)=1.29/spl times/10/sup /spl minus/14/ P for a specific diaphragm geometry. BPM simulations show that curvature losses due to the bending of the ARROW under deflection is negligible.<
>