Homodyne laser interferometric displacement measuring system with nanometer accuracy

Against the environmental factors which impact of measurement accuracy of homodyne laser interferometric displacement measuring system, the integral style of layout and common-mode suppression techniques are used for the design of polarization interference optical path. In the interference optical system, the displacement of the measuring mirror are transferred into four orthogonal optical intensity signals by optical polarization interference path, which are further transferred into four orthogonal electric signals by four photodiode sensors. By differential signal processing electric circuit, the influences of zero-drift of light intensity and environmental change are reduced. By a cheap phase subdivision card using generally in optical grating displacement measuring system, the orthogonal signals in this system are sampled in 8 Megabits per second and subdivided in phase. For the measuring system, the optical source is from stabilized He-Ne laser with the wavelength of about 632.8 nm. The optical subdivision ratio is 4 and phase subdivision ratio is 256. Thus the resolution of the displacement is about 0.6 nm. Therefore, the displacement measuring system achieves sub-nano resolution and high speed for real-time dynamic measurement.