Closed Loop Micromanipulators for Optical Metrology

The use of light beam micromanipulators in space subsystems has received particular attention in recent years. To compensate for changes in system parameters during the flight, these devices require closed loop control. This paper reports on an integrated feedback mechanism devised for flexural tortional devices. It consists in using monolithically embedded photodetectors to measure the portion of incident light crossing an aperture created in the manipulator. The manipulator position is determined from the detector section shadowed by the displaced aperture. A model is presented for the electrostatically actuated manipulator, predicting effects of structural parameters on angular displacement and resolution. As proof of concept, photodiode assisted closed loop manipulators were microfabricated in varying configurations on Si wafer. Their characteristics of deflection versus actuation voltage were better than those predicted by the model. The feedback mechanism was validated in light of the good agreement between differential photocurrents measured from contiguous photodiodes and theoretical prediction. Details on device modeling, microfabrication, and characterization are reported.