SU-8 waveguiding interferometric micro-sensor for gage pressure measurement

The authors present a successful modeling, realization and characterization of a new micro-sensor based on a convenient optical principle, namely an integrated Mach–Zehnder interferometer (MZI). This MZI device is designed with a view to measuring pressure disturbances due to optical path variations. Such a system is arranged in order to work in intensity modulation scheme. Moreover, the MZI is made up of straight and bent rib optical waveguides composed of SU-8 polymer. The mainstay of the device is based on differential measurements performed by a sensing arm arranged with a micromachined membrane and actuated by a given pressure disturbance, while the second arm of the interferometer is considered as a reference one. The main parameters of each element are given by way of two modeling approaches: an optical modeling with a semi-vectorial finite difference method together with a conformal transformation, and a mechanical modeling with a finite-element method associated to the mechanical theory of membranes. So, as the pressure to be measured is applied upon the diaphragm, an optical path variation of the acting arm is induced. After the combination of both signals, the variation at the output of the system is measured. A prototype is characterized by way of a micro-optical injection bench specifically designed to allow an efficient end-fire coupling into the waveguides.