Frequency modulated continuous wave (FMCW) light detection and ranging (LiDAR) can transmit and receive high frequency signals, up to 10G~100GHz, and can achieve micron-level high precision measurement and three-dimensional imaging of objects. If the frequency sweep of FMCW LiDAR is linearized, it can be extracted by Fourier transform, but most existing lasers do not have ideal linearity. In this paper, an iterative learning method of frequency sweep compensation is used to improve the linearity of frequency sweep. The semiconductor laser is one of the core components in the control system to improve the linearity of frequency sweep. Its performance determines the signal frequency and measurement accuracy of FMCW LiDAR. In this paper, the vertical cavity surface emitting laser (VCSEL) as an example, the equivalent circuit model of VCSEL is established by rate equation. An experimental platform is built to simulate the equivalent circuit model of the parasitic network, calculate and analyze each parameter, and verify the accuracy of the parameters of the equivalent circuit model and the parameter extraction method.
KEYWORDS: Simulink, Signal processing, MATLAB, Convolution, Radar signal processing, Digital signal processing, Spectrum analysis, Modulation, Radar, LIDAR
In the process of collecting FMCW, we need to ensure the accuracy of FMCW. Therefore, there must be certain requirements for the accuracy of the collected signal. Traditional FFT has the disadvantage of spectrum leakage and is limited by the accuracy of FFT in the process of spectrum refinement, resulting in low accuracy of the collected signal. Therefore, the phase invariance of all phase FFT algorithm is used to solve this problem. In this paper, the Simulink model of all phase FFT in MATLAB is built. The model is used to realize the function of all phase FFT, and the obtained FM continuous wave signal is modulated by all phase FFT to obtain the required signal. Compared with the program in MATLAB, the system is simple and easy to understand, and can be more practical, which provides a strong reference evidence for the implementation of the subsequent hardware system.
An innovative polarization coupler based on a long-range surface plasmon-polariton waveguide, which demonstrates efficient coupling between a semiconductor laser diode and a polarization-maintaining fiber, is proposed and analyzed. The proposed coupler—with different coupling facet sizes—can simultaneously match the mode sizes of the semiconductor laser diode and the polarization-maintaining fiber and can achieve polarization light coupling between different devices according to the features of the long-range surface plasmon-polariton waveguide. The coupling efficiency and alignment tolerance of the proposed coupler are investigated using the numerical-analysis method, and the design is optimized to obtain the best properties of the coupler. The calculated optimal coupling efficiency and the insertion loss are 89.96% and 0.97 dB, respectively. Further, the device exhibits a good alignment tolerance and has widespread potential applicability in the field of optical interconnections.
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