Signal processing method of a laser synthetic wavelength interferometer

A laser synthetic wavelength interferometer that uses a large synthetic wavelength to subdivide fringes formed by a small single wavelength is described. This study emphasizes the interference signal processing for the interferometer to realize precision measurement. A novel fringe counting method of correcting the integer number of the interference fringe according to the displacement which corresponds to the fraction number is proposed. Through this method, the integer fringe counting error can be eliminated. The realization of the method is designed in detail. The experimental setup was constructed and the displacement experiment was performed in the range of 15 µm with 1 µm increment. The experimental results show that the average error is −2.64 nm and the standard deviation is 0.47 nm. This demonstrates the feasibility of the signal processing method for the laser synthetic wavelength interferometer