Abstract
An optical fiber displacement sensor based on the microwave photonics interferometric (MWPI) method is proposed and experimented, which provides an ideal solution for large range displacement measurement with high resolution. The sensor used a Michelson microwave photonics interferometer to sense the displacement with one sensing arm and a length-adjusted reference arm. The displacement variation would change the period of the microwave response function of the interferometer. According to the principle that the phase difference in one free spectral range (FSR) of the microwave response function is 360°, the displacement can be retrieved by the microwave response function by means of a vector network analyzer (VNA). A programmable path-switching true time delay line was used in the reference arm to decrease the microwave bandwidth. The measurement results show that the displacement sensing range is larger than 3 m and the measurement resolution is 31 μm. Finally, the measurement stability is tested, and the factors affecting the measurement resolution of this method and the main source of errors are investigated in detail.
Highlights
Displacement measurements are fundamentally important in industrial applications, and the displacement sensors are gaining more important attention in the increasing automated industry [1].Kinds of displacement sensors have been proposed, including capacitive displacement sensors [2], eddy-current sensors [3], linear variable displacement transformer (LVDTs) [4], linear optical grating [5], laser interferometers [6], and magneto-strictive displacement sensors [7]
The white light was polarized by an optical fiber polarizer and amplitude-modulated by a RF signal from the output port of a vector network analyzer (VNA) using an electro-optic intensity modulator (EOM) that was biased at quadrature
The microwave interference fringes signal from the PD was amplified by a low noise amplifier (LNA) and the amplified RF signal was injected into the VNA
Summary
Displacement measurements are fundamentally important in industrial applications, and the displacement sensors are gaining more important attention in the increasing automated industry [1].Kinds of displacement sensors have been proposed, including capacitive displacement sensors [2], eddy-current sensors [3], linear variable displacement transformer (LVDTs) [4], linear optical grating [5], laser interferometers [6], and magneto-strictive displacement sensors [7]. Various types of optical fiber sensing techniques have been developed for displacement measurement, including Fabry-Perot interferometers [9,10], multimode interference, fiber Bragg gratings [11,12], surface plasmon resonance [13], white light interferometers (WLI) [14,15], and air-cavity methods [16]. Most of these methods rely on the optical interference with high
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