Precision and repeatability improvement in frequency-modulated continuous-wave velocity measurement based on the splitting of beat frequency signals

Abstract

The basic principle of frequency-modulated continuous-wave lidars is to measure the velocity of a moving object through the Doppler frequency shift phenomenon. However, the vibration generated by the moving object will cause the spectrum to broaden and the precision and repeatability of speed measurement to decrease. In this paper, we propose a speed measurement method based on H13C14N gas cell absorption peak splitting the sweep signal of a large bandwidth triangular wave modulated frequency laser. This method obtains the speed of a continuously moving target by re-splicing an accurately-split frequency sweep signal, which effectively solves the problem of simultaneous processing of excessive amounts of data when measuring the speed of a continuously moving target. At the same time, the H13C14N gas cell absorbs the spectra of specific wavelengths, which reduces the phase delay of the beat signal corresponding to the up- and down-scanning, thus reducing the signal spectrum broadening caused by frequency deviation, and improving the speed measurement resolution and range effectively. The experimental results show that for speeds of up to 30mm/s, the mean error was less than 23µm/s and the mean standard deviation was less than 61µm/s.

High-Precision Silicon-Integrated Frequency-Modulated Continuous Wave LiDAR Calibrated Using a Microresonator

“…Among them, sine wave modulation is the easiest to produce, but sine wave modulation has more complicated demodulation algorithms and lower accuracy. The most commonly used is triangular wave modulation, which can measure the distance and speed of the target at the same time, and the demodulation algorithm is relatively simple . These types of FM methods all have the problem of FM nonlinearity, and the frequency spectrum of the beat signal is broadened after fast Fourier transform (FFT), which seriously affects the demodulation of the beat signal.…”

“…However, the ranging range of this solution is limited by the length of the auxiliary MZI fiber when the measurement distance exceeds half of the length of auxiliary MZI fiber; the Nyquist sampling theorem is not satisfied during resampling, and if the fiber of auxiliary MZI is too long, it will introduce greater dispersion and increase the volume of the system . In addition, some research also cooperates with the gas cell to assist the measurement. , The gas cell has the characteristic of absorbing at a specific wavelength position, and the absorption peak position is stable. For different laser wavelength bands, different gas cells such as hydrogen cyanide and carbon monoxide gas cells can be used.…”

“…The most commonly used is triangular wave modulation, which can measure the distance and speed of the target at the same time, and the demodulation algorithm is relatively simple. 20 These types of FM methods all have the problem of FM nonlinearity, and the frequency spectrum of the beat signal is broadened after fast Fourier transform (FFT), 21 which seriously affects the demodulation of the beat signal. In this regard, many experts and scholars have also proposed various nonlinear calibration schemes, in which there are mainly 3 schemes that are used more frequently.…”

“…27 In addition, some research also cooperates with the gas cell to assist the measurement. 20,28 The gas cell has the characteristic of absorbing at a specific wavelength position, and the absorption peak position is stable. For different laser wavelength bands, different gas cells such as hydrogen cyanide and carbon monoxide gas cells can be used.…”

Frequency-swept feedback interferometry for noncooperative-target ranging with a stand-off distance of several hundred meters

“…With the above advantages, the study of FSI-based range finders has become popular since its inception in the 1980s [3]. Recently, many optimization techniques have been performed for range finding in terms of time consumption, precision, measuring range, and stability [13][14][15][16][17]. To date, a 100 kHz-level measuring rate has been realized with micrometer-scale resolution [8].…”