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 X 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 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 (partial derivative phi)/(phi partial derivative P) = 1.29 x 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.