Abstract
A frequency-encoded real-time and long-distance displacement measurement method based on two cross-referencing optoelectronic oscillators (OEOs) is proposed and experimentally demonstrated. In the system, one OEO is used for reference, and the other is used for measurement. The initial distance is evaluated by the oscillation frequency and free spectral range of the OEO for reference. The small displacement is calculated by using the frequency of the intermediate frequency (IF) signal generated by mixing the two OEOs. The two OEOs with the same characters are placed in the same environment. This protects the displacement measurement from the influence of the variation of ambient temperature. A high measurement sensitivity, which improves the precision of the displacement measurement, is also implemented due to the accumulative magnification effect at high-order resonant frequency modes. In addition, the low frequency of the IF signal, which is far smaller than the oscillation frequency of the two OEOs, allows a cost-effective and real-time measurement by a frequency counter. The proposed displacement measurement method is demonstrated experimentally. When the sampling time is 1 ms, displacement measurement errors less than ±3.71 and $\pm 11.14~\mu \text{m}$ are realized at emulated distances of around 800m and 6 km, respectively. The real-time velocity and acceleration measurements are also implemented owing to the introduction of a time signal in the measurement process.
Highlights
Real-time measurements of distance and its related parameters such as displacement, as well as velocity, are of fundamental importance in various applications, for instances, industrial manufacturing, large-scale structures assembling, and satellite geodetic surveying [1]–[3]
The electrical spectrums of the oscillation signal from the reference optoelectronic oscillators (OEOs) and the intermediate frequency (IF) signal from the electrical mixer are measured by using an electrical spectrum analyzer (Anritsu MS2725C)
In summary, we proposed and realized a frequency-encoded real-time and long-distance displacement measurement system based on two cross-referencing optoelectronic oscillators (OEOs)
Summary
Real-time measurements of distance and its related parameters such as displacement, as well as velocity, are of fundamental importance in various applications, for instances, industrial manufacturing, large-scale structures assembling, and satellite geodetic surveying [1]–[3]. PRINCIPLE Figure 1(a) shows the schematic diagram of the proposed real-time and long-distance displacement measurement method based on two cross-referencing OEOs. Two OEOs with the same architecture and the same oscillation frequency are grouped into a cross-referencing structure using DWDM.
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