A synthetic heterodyne interferometer for small amplitude of vibration measurement

Abstract

The homodyne interferometer has the advantages of simple optical configuration and low cost. However, it requires a caution in using an electronic filter such as high pass filter (HPF) to get rid of low frequency electronic noises and the dc offset associated with the optical intensity in the photodiode electronic circuitry. When the vibration amplitude is smaller than at least 12 of the wavelength of He-Ne laser, a problem of incorrect velocity or distorted velocity measurement can be caused since a dc value of the interference signal is eliminated by using the HPF. To solve this problem of using the HPF in the homodyne interferometer, a synthetic interferometer using a mechanical modulation method is proposed in this work by exciting a reference mirror with the displacement larger than 12 of the wavelength. In this work, the analytical work is presented to show how the synthetic interferometer solves the problem of incorrect velocity measurement by using the Fourier-Bessel function description of the interference signals. Simulation and experimental works are also presented to validate the synthetic heterodyne interferometer proposed in this work.

Wide dynamic range homodyne interferometry method and its application for piezoactuator displacement measurements

“…A large number of phase-demodulation techniques have been described in the literature to detect the induced phase shift under fading: active homodyne [12], heterodyne [13], phase quadrature [14], and synthetic heterodyne [15], among many others [10,11]. There is general agreement that heterodyne techniques, with picometer resolution, are useful when the displacement exceeds an interference fringe, while homodyne techniques are often employed when the displacement does not exceed the fringe spacing [16].…”

High-speed photoacoustic microscopy: A review dedicated on light sources

“…The phase difference in the up-shifted frequency is typically measured by an in-phase and quadrature (IQ) demodulation system, which also filters out the electromagnetic interference signals. Thus, in general, heterodyne interferometers are robust to the background noise than homodyne interferometers [ [133] , [134] , [135] , [136] ]. Compared to the interferometric method, the non-interferometric approach extracts PA signals by measuring the intensity change of the back-reflected probing light source induced by the initial pressure ( Fig.…”

A high dynamic range method for the direct readout of a dynamic phase change in homodyne interferometers

“…One of the difficulties in the application of interferometry is that the phase shift of interest is corrupted by high amplitude random drifts of the quasi-static phase (the phase difference between the two interferometer arms), due to ambient perturbations, causing signal fading. A large number of phase demodulation techniques have been described in the literature to detect the induced phase under fading: active homodyne [5], heterodyne [6], phase quadrature [7] and synthetic heterodyne [8] to name a few [9]. Each one has advantages and disadvantages, being more adequate to solve a specific class of problems, but not all.…”