Optical Heterodyne Interferometry Based on Phase Locked Loop Filtering Method to Eliminate Nonlinear Errors

Abstract

The invention discloses an optical heterodyne interference method for eliminating non-linear errors based on a phase-locked loop filtering method, and belongs to the field of optical heterodyne interference. The method comprises the steps of trying to obtain at least three paths of signals in a light path with non-linear error interference components, enabling respective periodical non-linear error interference components of the at least three paths of signals to be different from one another in phase angles of signal frequency components to be eliminated within the corresponding circumferential angle range or within the corresponding circumferential angle range excluding integral multiples of circumferential angles, and adopting phase-locked loop filters to filter the signals in an analog electric signal channel so as to adopt follow-up electronics processing to eliminate or restrain the interferential components after analog-digital conversion. According to the optical heterodyne interference method, the non-linear errors or interferential specific harmonic components can be eliminated, the adjustment process of the optical heterodyne interference method is quite easy, the 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 phase-locked loop filter method without fine adjustment to eliminate the fundamental frequency of 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 problems com...

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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 a method based on phase-locked loop filtering and FFT (fast Fourier transform) algorithm to eliminate Optical heterodyne interferometry for linear errors can eliminate nonlinear errors or specific harmonic components of interference, and eliminate the need for precision optical adjustment devices and precise adjustment processes required to eliminate nonlinear errors, making this adjustment very easy. At the same time greatly improve system performance and reduce costs

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