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Block diagram of signal processing unit implemented on FPGA board. The signal processing unit consists of four sub-modules. The function of the find-peaks module is finding the reference interferograms from channel 0 and the measurement interferograms from 1. The output-peak module is responsible for giving the necessary values to finish calculating the absolute distance. The calculatedistance module performs the final calculation of absolute distance.
Source publication
Dual-comb ranging (DCR) is an important method in absolute distance ranging because of its high precision, fast acquisition rate, and large measuring range. DCR needs to obtain precise results during distance measurements for a mobile target. However, the non-ambiguity range (NAR) is a challenge when pushing the dual-comb ranging to the industry fi...
Contexts in source publication
Context 1
... order to obtain the value of ∆t as accurately as possible, there are two parts for calculating ∆t. One part is the integer part which is obtained from find-peaks modules, the other part is the fractional part which is obtained from the calculate-distance module as depicted in Figure 5. Figure 5 shows the block diagram of the signal processing unit which was implemented on the FPGA board to obtain the value of positive integer n and measured distance D. The output results of the signal processing unit are the absolute distance L abs . ...
Context 2
... order to obtain the value of ∆t as accurately as possible, there are two parts for calculating ∆t. One part is the integer part which is obtained from find-peaks modules, the other part is the fractional part which is obtained from the calculate-distance module as depicted in Figure 5. Figure 5 shows the block diagram of the signal processing unit which was implemented on the FPGA board to obtain the value of positive integer n and measured distance D. The output results of the signal processing unit are the absolute distance L abs . ...
Context 3
... the output-peak module will calculate the positive integer n according to the algorithm described in Figure 4. The output-peak module outputs the waveform of paired peaks and the distance between paired R peaks and M peaks, and the positive integer n as denoted by n in Figure 5. The calculate-distance module will perform a fast Fourier transform (FFT) and phase fitting as illustrated in [20,22] to obtain the fractional part of delay time ∆t. ...
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Citations
... This region is named the "dead-zone" of the dual-comb range. 28,48 On the contrary, when a pulse reaches the SOA within the "slow recovery region," which corresponds to 0.1-1 ns, it can still be detected because the fast recovery of gain occurs, even if the SOA is in a state of slow recovery, which means that the dead zone does not occur in the slow recovery region. As the data process of correlation calculation effectively eliminates the negative impact of the slow recovery region, the dynamic range remains unrestricted. ...
Absolute distance measurement for multiple targets is required in industrial and scientific fields such as machine monitoring, detection of distortion in large structures, wafer alignment in semiconductor manufacturing, and the formation flying of satellites. Furthermore, the expansion of measurement channels is essential for the effective application of multi-target measurement. However, because measurement channels' expansion requires high power, it is difficult due to the low conversion efficiency of conventional systems that use a non-linear crystal for optical cross-correlation. In this study, for measurement channel expansion, time-of-flight based absolute laser ranging via high-efficiency dual-comb cross-correlation using a semiconductor optical amplifier is developed. The semiconductor optical amplifier acts as a cross-correlator, and it can produce a cross-correlation signal with a laser’s power of 50 µW because of its very high conversion efficiency. This method is suitable for expanding the measurement channels and measuring non-cooperative targets as it can detect low-power signals. The repeatability of the distance measurement is 4 µm at a single shot (37 µs) and 120 nm for 5 ms. The linearity is assessed by evaluating the R-square, which is equal to 1 within the range of significant figures. Moreover, the distance measurement of targets lying on the two axes was demonstrated to ensure the measurement channels' expansion. This measurement system has the potential to determine multiple distances, making it applicable to diverse fields such as semiconductor manufacturing, smart factories, plant engineering, and satellite formation flying.
... The non-ambiguity range (NAR) and precision are important performance parameters for distance measurement [4][5][6]. In recent years, many ADM methods have been studied, such as inter-mode synthetic wavelength interferometry [7,8], dispersive interferometry [9,10], time of flight [11,12], multi-wavelength interferometry [13,14], dual comb ranging method [15,16]. ...
In multi-heterodyne interferometry, the non-ambiguous range (NAR) and measurement accuracy are limited by the generation of synthetic wavelengths. In this paper, we propose a multi-heterodyne interferometric absolute distance measurement based on dual dynamic electro-optic frequency combs (EOCs) to realize high-accuracy distance measurement with large scale. The modulation frequencies of the EOCs are synchronously and quickly controlled to perform dynamic frequency hopping with the same frequency variation. Therefore, variable synthetic wavelengths range from tens of kilometer to millimeter can be flexibly constructed, and traced to an atomic frequency standard. Besides, a phase-parallel demodulation method of multi-heterodyne interference signal is implemented based on FPGA. Experimental setup was constructed and absolute distance measurements were performed. Comparison experiments with He-Ne interferometers demonstrate an agreement within 8.6 µm for a range up to 45 m, with a standard deviation of 0.8 µm and a resolution better than 2 µm at 45 m. The proposed method can provide sufficient precision with large scale for many science and industrial applications, such as precision equipment manufacturing, space mission, length metrology.
