Optical heterodyne interference method for removing non-linear error based on square wave mean value method

Abstract

The invention belongs to the field of optical heterodyne interference, and discloses an optical heterodyne interference method for removing a non-linear error based on a square wave mean value method. The method comprises the steps that at least three paths of signals are obtained from an optical path where non-linear error interference elements exist, phase angles, on signal frequency elements to be removed, of the periodic non-linear error interference elements of the at least three paths of signals are made to be different in a corresponding circumference angle range or in a corresponding circumference angle range after integral multiples of circumference angles are removed, meanwhile, signals are filtered through a filter in an analog electrical signal channel, a phase difference between each path of measuring signals and a reference signal is computed by the adoption of the square wave mean value method, and then analog-digital conversion, displacement calculation, weighting and iterative processing are conducted so as to remove or restrain the interference elements conveniently. The optical heterodyne interference method for removing the non-linear error based on the square wave mean value method can remove specific harmonic elements of the non-linear error or the interference, the regulation process is very easy, system performance is improved, and cost is reduced.

Description

technical field [0001] The invention belongs to the field of optical heterodyne interferometry (Heterodyne Interferometry) measurement, and specifically relates to an optical heterodyne interferometry method based on a square wave average value and a phase-locked loop filtering method without fine adjustment to eliminate nonlinear errors. Background technique [0002] The laser heterodyne interferometry system can be used to measure physical quantities such as displacement and length, and is one of the best nanometer measurement methods. The system converts the measured displacement into the frequency or phase change of the heterodyne signal, and then measures this change. Since the frequency of the heterodyne signal is much lower than the optical frequency, the photoelectric signal is easy to process and can be electronically fine-tuned. Points to achieve higher measurement resolution, the resolution can reach picometer (pm) or better. [0003] However, nonlinearity proble...

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Problems solved by technology

[0005] In order to solve the technical problems existing in the existing laser heterodyne interferometry system, such as complex system, large amount of calculation, poor real-time performance, and inaccurate results, the present invention provides an optical heterodyne interferometry based on the square wave mean method to eliminate nonlinear errors, which can Eliminate the specific harmonic components of nonlinear errors or interference, and eliminate the need for precision optical adjustment devices and precision adjustment processes required to eliminate nonlinear errors, making this adjustment very easy, while greatly improving system performance and reducing costs

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