A differential laser Doppler system for one-dimensional in-plane motion measurement of MEMS

The differential laser Doppler technique is used to measure one-dimensional in-plane motions in micro-electro-mechanical systems in this paper. This method provides real-time measurement of the velocity and derives the displacement from the integral of velocity. The working principle and optical layout of the system are explained. The vibration of the movable comb of a silicon micromachined resonator is measured by this system and the uncertainty caused by high order modes of vibration is discussed. The repeatability of displacement measurements is 0.9 μm. Compared with computer micro-vision method, there is a discrepancy of 0.5 μm in the results of maximum amplitudes of displacements.