An array of micro scanning grating interferometers (μSGIs) with tunable gratings is designed, fabricated and successfully tested for simultaneous static and dynamic displacement measurements. Each μSGI has capabilities of an optical scanning interferometer and in addition, miniaturization has made array operation feasible. All of the μSGIS in an array can actively tune the distances between the gratings and the corresponding samples, simultaneously and independent of the other gratings, to maintain a bias position in a fringe for high displacement measurement sensitivity. The μSGIs are fabricated on silicon-on-insulator (SOI) wafers and the gratings are moved by electrostatic actuation. The fabricated tunable gratings exhibit the first resonance mode at 50 kHz and a small damping ratio of ～0.05. The gratings show a sufficient (～500 nm) displacement range for tuning to a high sensitivity position, achieved with a 30 V operating voltage range. Simulation results obtained from the finite element model of the μSGI are in agreement with the experimental results. A control algorithm is implemented in real time in a field-programmable gate array (FPGA) to track the surface and to actively reduce the vibration noise. The use of the FPGA enables parallel and independent control and also operation of two μSGIs. Experimental results show that approximately 40 dB vibration noise reduction is obtained at 100 Hz with the current setup.
展开▼
