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 field of space optical communication, coherent communication system has the advantages of high sensitivity, compatibility with a variety of modulation formats and strong anti-interference ability compared with intensity modulation direct detection (IM-DD) system. The typical disadvantage of coherent communication system is the complexity of the receiver, which requires carrier recovery. Space optical communication is also developing from point-to-point communication to optical communication network. In this paper, a fast phase locking method based on direct phase control is proposed. After the auxiliary frequency acquisition is completed, the time to recover the carrier is equal to the loop delay. The realization of this method depends on the direct control of the local oscillator carrier phase. Different from the traditional second-order loop method, this method does not need to consider the laser linewidth. This method can greatly save the time of carrier recovery, so it can be used for fast switching of optical network channels and can improve the utilization of optical networks.
This article mainly shows that coherent accumulation of multi-aperture receiver array based on frequency modulation continuous wave (FMCW) coherent lidar has an excellent performance for the weak signal detection of target which is far distance or moving with a high velocity. This method can improve the signal and noise ratio (SNR) and detection range accuracy by multi-aperture receiver array. In addition, the analysis done by simulation shows that phase fluctuation of atmospheric turbulence has a significant influence on the performance of coherent accumulation of multi-aperture receiver array. Stimulation result shows that while μx is equal to - σ2x , the amplitude fluctuation of signal could degrade the quality of coherent accumulation based on multi-aperture receiver array and its existence leads to the worse performance before non-amplitude fluctuation. Phase fluctuation of signal deteriorates the performance of coherent accumulation while its size is big or small.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.