Heterodyne Laser Doppler Vibrometer Based on Double Acousto-optic Frequency Shifters

Direction discrimination of laser Doppler velocimetry system based on acousto-optic frequency shifter

“…Acousto-optic devices [14] , are also called acousto-optic modulators or Bragg boxes, which consists of acousto-optic medium, piezoelectric transducer and sound absorption device. According to the acousto-optic effect [15] , when the driving signal drives the acousto-optic crystal to work, the driving signal is converted to an ultrasonic field by the piezoelectric transducer. This ultrasonic field causes the refractive index of the acousto-optic medium to change periodically, forming a refractive index grating, which in turn causes the incident laser to diffract.…”

Nonzero-drift differential all-fiber-optic heterodyne Doppler measurement system

“…Several studies have been conducted on accuracy or resolution improvement of all-fiberoptic heterodyne Doppler measurement systems. 19,[21][22][23] The drift in the frequency shift of an AOFS is primarily a result of the frequency drift of the driving signal and influences the accurate determination of the Doppler frequency shift caused by the moving object, which will also severely reduce deterioration of the performance of all-fiber-optic heterodyne Doppler measurement systems. For displacement measurement, the drift in the frequency shift will lead to a cumulative error during the measurement process, because displacement is obtained by integrating velocity, and errors caused by velocity deviation due to the inaccurate determination of the Doppler frequency shift will be continuously accumulated.…”

“…Another method proposed involves offsetting the frequency drift by simultaneously using two or more AOFSs to form two or more Mach-Zehnder interferometers; through differential treatment of two or more interferometric signals, the drift in the frequency shift of the AOFS can be effectively eliminated. 23 Shirai et al 21 presented a method to perform velocity measurements of a turbulent channel flow; this method removes the drift in the frequency shift by employing three AOFSs to achieve frequency shifts of 120, 80, and 60 MHz. They achieved a relative velocity accuracy of 0.16% and a minimal detectable velocity of <0.1 m∕s.…”