Zhejiang Sci-tech University

Shihua Zhang

Liping Yan

Benyong Chen

The present invention discloses a real-time normalization apparatus and method of the PGC demodulation in a sinusoidal phase modulation interferometer. An optical setup containing a measuring interferometer and a monitoring interferometer is constructed. An electro-optic phase modulator is placed in the common reference arm of the two interferometers. High-frequency sinusoidal wave modulation and low-frequency triangular wave modulation are applied to the electro-optic phase modulator at the same time. Sinusoidal modulation is used for generating phase carrier, and PGC demodulation is performed to obtain quadrature signals containing the phase information to be measured. Triangular wave modulation makes the quadrature signals change periodically. Ellipse fitting is performed on the Lissajous figure corresponding to the quadrature signals, and real-time normalization of the PGC demodulated quadrature signals is achieved. By calculating the variation of the phase difference between the two interference signals, the measured displacement is obtained, and nanometer scale displacement measurement is achieved.

Real-time normalization apparatus and method of phase generated carrier demodulation in sinusoidal phase modulation interferometer

A method of air refractive index correction for an absolute long distance measurement adopting a two-color method based on a single wavelength and a synthetic wavelength is provided. Two lasers emit two laser beams with a constant single wavelength and a variable wavelength, respectively, to form a synthetic wavelength chain from large to small through a laser interferometric system. Each order of the synthetic wavelength chain is used to obtain a series of the estimate values of optical distance with gradually increasing accuracy. After optical distances corresponding to a minimum synthetic wavelength and a single wavelength are obtained simultaneously, the corrected absolute distance is achieved according to the principle of the two-color method for air refractive index correction. The method can realize full-path correction of air refractive index along the actual path of the distance measurement, and has low requirements on the measurement precision of environmental parameters such as temperature and pressure.

Method of air refractive index correction for absolute long distance measurement

An absolute distance measurement apparatus and method using laser interferometric wavelength leverage includes a light source system, a wavelength-leverage laser interferometric system and an interference signal processing and controlling system. The light source system outputs a orthogonally linearly polarized beam with the wavelength &#x3bb;and the wavelength &#x3bb;. The orthogonally linearly polarized beam projects onto the wavelength-leverage laser interferometric system to form the interference beam. The interference beam projects onto the interference signal processing and controlling system. In the wavelength-leverage laser interferometric system, the synthetic wavelength and the single wavelength as well as the measured absolute distance and the moving displacement of the cube-corner prism in the reference arm form a wavelength-leverage absolute distance measurement relationship.

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Zhejiang, China

Shihua Zhang