Real-time calculation method of nonlinear error in arc tangent demodulation of phase-generated carrier

Abstract

The invention discloses a real-time calculation method of a nonlinear error in arc tangent demodulation of a phase-generated carrier (PGC). Interference fringes produced by a laser interferometer aresimultaneously detected by two photoelectric detectors; and the detection centers of the two photoelectric detectors are spaced at a distance of a one-quarter-cycle interference fringe. When a measuring lens in the interferometer is moved, the to-be-measured phase of the interferometer is changed continuously; PGC demodulation is carried out on interference signals detected by the two photoelectric detectors to obtain demodulation phase values; difference processing is carried out on the demodulation phase values to obtain a phase difference; detection is carried out in real time and a peak-to-peak value of a nonlinear item of the phase difference is obtained and a non-linear error corresponding to the demodulation phase is calculated based on the peak-to-peak value. According to the invention, the non-linear error caused by the arc tangent demodulation of the PGC can be evaluated in real time. Compared with the traditional total harmonic distortion method, the real-time calculation method has the following advantages: the method is realized simply, the evaluation result is visual, and the real-time performance is good. And the method can be applied to evaluation of phase modulation non-linear errors of an interference-type optical fiber sensor or a self-mixing interferometer.

Description

technical field [0001] The invention relates to a method for evaluating nonlinear errors of phase demodulation in laser interferometers, in particular to a method for real-time calculation of nonlinear errors in phase-generated carrier (PGC) arctangent demodulation. Background technique [0002] Phase-generated carrier (PGC) modulation and demodulation technology has the advantages of high sensitivity, large dynamic range and good linearity, and is widely used in phase demodulation of interferometric fiber optic sensors, optical feedback interferometers and self-mixing interferometers. In PGC modulation and demodulation, high frequency phase carrier The phase to be measured of the laser interferometer The modulation is the sideband of the high-frequency carrier and its harmonic signals of each order, and the modulated interference signal is: where S 0 and S 1 are the amplitudes of the DC component and the AC component respectively, z is the phase modulation depth, and...

AI Technical Summary

Problems solved by technology

Although THD is an effective evaluation method for the linearity of phase demodulation, this method requires that the phase to be demodulated must be a single-frequency sinusoidal signal. Generally, it can only be evaluated by offline simulation. For the actual interference system with arbitrary changes in the phase to be measured, THD cannot be realized real-time assessment

THD is only a proportional coefficient, and the nonlinear error caused by phase demodulation cannot be directly calculated

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