Non-contact Micro Vibration Measurement System Based on Optical Fiber Michelson Interferometer

Abstract

Due to its advantages of high sensitivity and wide frequency response, the optical fiber interferometric method is admirably suited for the applications of dynamic measurement. In this paper, an optical fiber Michelson interferometer is used to realize non-contact micro vibration measurement. An optical fiber collimator emits a laser beam to the measured surface and receives the reflected laser beam. The optical path change of the reflected light from the measured surface is converted to phase change through the non-balanced interferometer. Due to the external environmental effect, the initial phase random drift of fiber interferometer occurs. So the amplitude fluctuations of the interference signal seriously affect the output signal to noise ratio of the fiber interferometer. Therefore, in order to get the true phase information from interference signal, an effective method of signal demodulation is necessary to eliminate the influence of the initial phase drift in the phase measurement. In this paper, the phase signal demodulation is realized with PGC(Phase Generated Carrier) method based on ARCTAN calculation. A large amplitude phase modulation signal beyond the frequency range of the detected signal is introduced in the PGC demodulation method. The desired phase result could be obtained through ARCTAN calculation with the quotient of two orthogonal signals. The PGC method based on ARCTAN calculation eliminates the influence of the signal amplitude drift. This scheme owns a better response characteristic for the abrupt signals. In this paper, a non-contact micro vibration measurement experimental system based on the non-balanced interferometer is implemented in the laboratory. The frequency response range of 1~1KHz and the displacement resolution of 1nm in vibration situation are realized.