The four-optical coherent mixing detection technology can improve the dynamic range of moving target detection. This method has the difficulty of distinguishing the type of mixing output signal. We propose a method to distinguish the signal type by using the different peaks of the mixed signal spectrum. Based on the statistical theory, the power spectrum function of the mixed signal is obtained, and the numerical analysis of the influence of the light source line width and the light source frequency difference on the signal power spectrum is carried out. Through numerical calculation and analysis, the results show that the increase of the light source linewidth will lead to the broadening of the signal power spectrum. When the Doppler frequency difference is greater than 1/5 times the linewidth of the light source, the power spectrum of the two homodyne coherent signals in the four-light coherent mixing can be distinguished; when the Doppler frequency difference is less than 1/5 times the light source linewidth , The power spectrum of the two homodyne coherent signals in four-optical coherent mixing can not be distinguished.
KEYWORDS: Target detection, Sensors, Doppler effect, Heterodyning, Velocity measurements, Signal detection, Laser applications, Signal to noise ratio, Linear filtering, Photodiodes
A novel single-source double-heterodyne coherent detection high-speed moving target is presented. Under a limited detector bandwidth condition, the method inherits the characteristics of dual frequency laser coherent detection and transforms the Doppler shift of a high-speed moving target to low frequency using the beat frequency difference method. Compared with the traditional heterodyne detection system, the maximum speed detectable range of the system is greatly increased. The double-heterodyne mixing process is deduced, and the relationship between the beat frequency, detector bandwidth, and maximum detectable speed of the system is obtained through analysis. Thus, the beat frequency can be dynamically adjusted for the system to adapt to different measurement environments. Different signal components and speed information extraction methods of detectors under different motion speeds are analyzed. The feasibility of the method is verified through simulation. Moreover, the data acquisition is minimal, and the system has good real-time performance.
This paper presents a method of detecting high-speed moving targets with single light source and dual frequency laser coherence.Due to the influence of cutoff response frequency of detector, the dynamic range of velocity measurement in traditional single-frequency coherent detection system is limited, and the velocity measurement of high-speed moving target cannot be realized. In this paper, six signal components are generated by four-light coherent mixing, one of which is the difference between the fixed frequency shift and the doppler frequency shift. The simulation verifies the feasibility of the method proposed in this paper, which has the characteristics of small data collection, large dynamic range, high precision and good real-time performance of the system, and improves the theoretical guidance of the method for further high-speed target detection research.
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