Abstract
To eliminate the serious detrimental effects caused by frequency drifts of acousto-optic frequency shifters (AOFSs) in conventional all-fiber-optic heterodyne Doppler measurement systems, a differential all-fiber-optic heterodyne configuration is proposed. By delicate arrangement of the fiber-optic path and using only one AOFS, zero drift, which commonly occurs in conventional systems, is eliminated. Based on the proposed configuration, a differential all-fiber-optic heterodyne Doppler measurement system has been built. Using a piezoelectric ceramic oscillator as the moving object, it has been verified that the proposed system is able to eliminate zero drift, and the displacement and velocity measurement accuracies reach 0.775 μm and 0.009 mm / s, respectively. It has been shown that the differential all-fiber-optic heterodyne Doppler measurement system can achieve good performance in both displacement and velocity measurements, even in a harsh environment with drastic temperature variation.
Highlights
Laser Doppler measurement is a technique based on the Doppler effect—in this technique, a laser beam is scattered by a moving object; the instantaneous velocity of the object is proportional to the Doppler frequency shift of the laser beam and can be extracted through the interference of the signal and reference beams.[1,2]
We propose a configuration of an all-fiberoptic heterodyne Doppler measurement system that includes two Mach–Zehnder interferometers using only one acousto-optic frequency shifters (AOFSs), which can synchronously obtain AOFS frequency shift and the sum of Doppler and AOFS frequency shifts; through differential treatment of the two interferometric signals obtained by the two interferometers, the measurement performance can be effectively improved
We proposed a differential all-fiber-optic heterodyne Doppler measurement system to eliminate the zero drift to improve the measurement accuracy and the minimum detectability of displacement or velocity through the well-known Doppler effect
Summary
Laser Doppler measurement is a technique based on the Doppler effect—in this technique, a laser beam is scattered by a moving object; the instantaneous velocity of the object is proportional to the Doppler frequency shift of the laser beam and can be extracted through the interference of the signal and reference beams.[1,2] Laser Doppler measurement offers the advantages of noncontact and high-sensitivity measurement, along with a large operating distance; it has been widely applied in velocimeters, displacement sensors, vibrometers, accelerometers, hydrophones, etc.[3,4,5,6,7] the conventional laser Doppler measurement system commonly uses discrete optical elements and devices, which makes the system large, complex, difficult to align, and susceptible to vibration interference, and in particular, unsuitable for deployment in confined or restricted areas. 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 severely reduce deterioration of the performance of all-fiber-optic heterodyne Doppler measurement systems. To improve the performance of all-fiber-optic heterodyne Doppler measurement systems, the zero drift caused by the drift in the frequency shift from the AOFS should be precisely eliminated. We experimentally test the system’s ability to eliminate the zero drift in heterodyne Doppler displacement and velocity measurements
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