We propose a coherent light detection and ranging (LiDAR) with a low probability of intercept (LPI) based on wavelength hopping technology and phase-encoded random modulation technology to achieve long-range detection while reducing exposure risk. A theoretical analysis is constructed for the LPI LiDAR system. The multi-wavelength homodyne detection and distance estimation are achieved by the broadband 90° optical hybrid and the matched filter, respectively. Measurements are conducted under 1064 nm and 1550 nm due to the limitation of available light sources. The experimental results show that when the emission power of the two wavelengths is low, the designed LPI LiDAR can achieve sensorless detection with high distance accuracy at long distances. The used laser warning device cannot alarm the laser emitted by the designed LiDAR with continuous wave regime. The feasibility of the designed LiDAR system to realize silent detection is verified.
Time-frequency synchronization is a basic element in some fields such as deep space exploration and satellite navigation. Its accuracy and precision are closely related to the measurement results of these systems. In high signal-to-noise ratio situation, the accuracy of time-frequency synchronization is affected by the Doppler frequency shift. In this study, we propose an interpolation model that can mitigate the impact of the Doppler frequency shift, which is constructed from the prior information of the system and related to phase difference of the pseudo-random code. A coherent heterodyne ranging system is built, which is phase-modulated by pseudo-random binary code. And interpolation model is experimentally verified. The experimental results show that the ranging deviation is not more than 0.55 mm for static target. For the moving target, the ranging deviation does not exceed 0.40 mm, and the deviation of the velocity measurement is within 0.45 mm/s.
In the phase control of multiple beams, when multiple phase shifters reach the boundary at the same time, the traditional method is to reset multiple phase shifters at the same time. However, this approach leads to a significant drop in the combined beam optical power. To address this issue, we propose a new reset method. This method resets the phase shifters that reach the boundary at the same time in sequence. It helps to avoid the problems that cause large phase fluctuations and dramatic decreases in optical power. This paper presents the principle of coherent multibeam beam combining and compares the power fluctuations resulting from two different resetting methods. Theoretical derivations and numerical simulations are employed to analyze the effects. The results demonstrate that the sequential reset method yields smaller power jitter compared to the traditional reset method. Furthermore, the suppression of power jitter becomes more pronounced as the number of beams reaching the boundary simultaneously increases. To validate the feasibility of the sequential reset method, an experimental system is constructed. The experimental results reveal a remarkable 36.78% improvement in power stability when compared to the traditional reset method.
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