DETECTION OF HIGH-FREQUENCY AND LOW-FREQUENCY VIBRATIONS USING A FEEDBACK-STABILIZED DIFFERENTIAL FIBER OPTIC INTERFEROMETER

Highly sensitive and stable detection of minute ac and pseudo-dc (i.e. , very low frequency) vibrations is performed by means of a differenti al fiber optic Michelson interferometer. Any residual instabilities ar e eliminated by means of an ac feedback control loop. The stabilizatio n technique is not affected by the variations in the reflectivity of t he sample and by launch inefficiencies into the fiber. This approach a lso provides a simple, quantitative method for calibrating sample vibr ations. Results are presented on the operation of the system in stabil izing its output as well as on the detection of the vibration of a sil icon sample.