• Current Optics and Photonics
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• v.3 no.3
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• pp.204-209
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• 2019

In an optical interferometer that uses sinusoidal modulation and quadrature detection, the amplitude and offset of the interference signal vary with time, even without considering system noise. As a result, the circular Lissajous figure becomes elliptical, with wide lines. We propose and experimentally demonstrate a method for compensating quadrature detection error, based on digital signal processing to deal with scaling and fitting. In scaling, fluctuations in the amplitudes of in-phase and quadrature signals are compensated, and the scaled signals are fitted to a Lissajous unit circle. To do so, we scale the average fluctuation, remove the offset, and fit the ellipse to a unit circle. Our measurements of a target moving with uniform velocity show that we reduce quadrature detection error from 5 to 2 nanometers.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.6
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• pp.80-86
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• 2001

This paper proposes a precision displacement measuring method of detecting fringe movement of interferograms with a nanometric resolution. It is well known that the laser interferometer plays a useful and essential role in scientific and industrial application, but they have such error sources as an unequal gain of detectors, imbalanced beams, and lack of quadrature. These error sources degrade the accuracy of the interferometer. However, the fringe movement of interferograms has little relation with these error sources. In order to investigate performance of the proposed method. analysis and simulation were executed over random noise and wavefront distorion. Results of the simulation show that the proposed method is robust against these errors. Experiment was implemented to verify this method.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.9
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• pp.171-178
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• 2001

The nonlinearity of a laser interferometer usually ranges from sub-nanometer to several manometers. This nonlinearity, which has periodic characteristics, limits the accuracy of the interferometer at the sub-nanometer level. The nonlinearity error of the one-frequency homodyne interferometer with quadrature fringe detection results from a number of factors including polarization mixing by imperfect optical elements, unequal gain of photo detectors, lack of quadrature between two signals and misalignment. In this paper, we described a method for measuring and compensating the nonlinearity of homodyne interferometer using the elliptical fitting technique with least-square method. Experimental results demonstrate that $^\pm$3.5 nm nonlinearity can be reduced to $^\pm$0.2 nm level.