TAILIEUCHUNG - High precision displacement measuring interferometer based on phase modulation technique and modulation index instability elimination

A high precision displacement-measuring interferometer based on a phase modulation technique was developed. A PZT actuator was utilized to drive a mirror of a Michelson interferometer by applying a sinusoidal voltage to the PZT controller. | Journal of Science & Technology 130 (2018) 024-027 High Precision Displacement-Measuring Interferometer Based on Phase Modulation Technique and Modulation Index Instability Elimination Nguyen Vu Hai Linh, Vu Thanh Tung* Hanoi University of Science and Technology - No. 1, Dai Co Viet Str., Hai Ba Trung, Ha Noi, Viet Nam Received: August 14, 2018; Accepted: November 26, 2018 Abstract A high precision displacement-measuring interferometer based on a phase modulation technique was developed. A PZT actuator was utilized to drive a mirror of a Michelson interferometer by applying a sinusoidal voltage to the PZT controller. The path difference between two arms of the interferometer was modulated leading to modulation in the phase of the interference signal with a frequency of 3 kHz. The first and second harmonics of the interference signal were detected at the modulation index of rad, a special value when the values of the first and second orders of Bessel function are equal. The displacement was determined by the ratio of the second and third harmonic in which the effects of modulation index instability and intensity fluctuation were neglected. Moreover, the direction of the displacement that was ambiguous of the traditional interferometers was clarified in a real time. A measurement precision of 60 nm was obtained using the phase modulation interferometer. Keywords: Phase modulation, Bessel function, Modulation index, PZT actuator, Michelson interferometer. 1. Introduction* of the environment or shifting of a measured point will strongly affect the measurement uncertainty [9]. Laser interferometers are widely utilized for displacement measurements with nanometer-order uncertainty because of their inherent accuracy and their traceability to the metric standard through the frequency of the laser source. Various signal processing techniques have been developed for displacement-measuring interferometers such as homodyne [1, 2], heterodyne [3, 4] and phase .

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