A high-frequency sinusoidal phase-modulation interferometer using an electro-optic modulator: Development and evaluation

An optical interferometric instrument for the measurement of distance and position is presented. The system is based on a high-frequency sinusoidal phase-modulation interferometer. Phase modulation of the laser beam in one of the two interferometer arms is obtained by means of an electro-optic modulator operating at frequencies up to 10 MHz. The electronic unit performs synchronous demodulation of the signal coming from the photodetector. The resulting signals are fed to an up-down counting logic that is interfaced to a personal computer. The performance of the instrument has been evaluated by means of a system calibration against a reference high-precision commercial interferometer. The overall accuracy of the system resulted to be within 80 nm, at target speeds up to 1 m/s. In this article, the optical setup, the electronic equipment, and the calibration results are presented.