Fabrication and optical packaging of an integrated Mach-Zehnder interferometer on top of a moveable micromirror

While testing electrical properties in microsystems is a well-developed art, the testing of mechanical properties of MEMS devices is not. There is a great need for techniques that will permit the evaluation of MEMS devices, in all stages of manufacturing, with respect to material and micromechanical properties. In this contribution we propose a new approach, based on the integrated optical read-out using a Mach-Zehnder interferometer (MZI). MZI is monolithically integrated on top of a electrostatically rotatable micromirror loaded with the sensing arm of MZI. A single mode buried channel waveguide based on silica/silicon oxinitride/silica structure is used. It performs a low optical attenuation and a coupling efficiency of 55% from waveguide to a standard fiber, connecting MZI to outside world (light source and detector). The working principle of MZI read out is based on the change of effective refractive index of guided waves of MZI induced by displacement of the deformable structure, obtained via the elastooptic effect. The technology process steps with special emphasis to the fiber-to-waveguide coupling based on V-grooves is detailed here. Our goal is aiming to obtain an angular alignment of ± 0.2 deg. of V-groove walls with <110> directions and the vertical misalignment not, exceeding ± 0.6 μm.

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