Coherent Random-Modulated Continuous-Wave LiDAR Based on Phase-Coded Subcarrier Modulation

A coherent random-modulated continuous-wave (RMCW) LiDAR transmits a lightwave modulated by a pseudo-random binary sequence (PRBS). The lightwave backscattered from targets is received and used to reconstruct the PRBS. Then, the time-of-flight is extracted by correlating the reconstructed PRBS and the original PRBS. We propose a coherent RMCW LiDAR based on phase-coded subcarrier modulation, in which the impacts of internal reflection and optical Doppler frequency shift (DFS) are mitigated. A continuous lightwave is amplitude-modulated by an RF signal which is phase-coded with a PRBS. Coherent detection is used in the receiver. A beat signal that consisted of a low-frequency signal and a high-frequency signal is obtained by a single balanced photodetector (BPD). The optical DFS can be directly extracted from the low-frequency signal. It is used to compensate for the frequency offset of PRBS, which is extracted from the high-frequency signal. In addition, the background noise caused by internal reflection is suppressed by averaging over successive measurement spots. In this paper, the performance of a coherent RMCW LiDAR is firstly analyzed by numeric simulations and demonstration experiments. Then, line-scanning measurements for moving targets are implemented to demonstrate the 3D imaging capability of the proposed coherent RMCW LiDAR.

Источник квантового шума на основе детектирования дробового шума балансного фотоприемника с управляемым интегрально-оптическим светоделителем

Broadband quantum noise source based on the shot noise detection of a balanced photodetector is demonstrated. Precise electro-optical tuning of the balanced photodetector circuit was carried out by an integrated optical beam splitter in the form of the dual output Mach-Zehnder interferometer on a lithium niobate substrate. The classical component of the detected noise related to the relative intensity noise of a laser diode was suppressed by more than 15 dB. At the maximum laser power of 100 mW, power spectral density of detected shot noise was 12 dB higher than the level of technical noise of the measuring system in the frequency band above 3 GHz.

Generation of monocycle efficient terahertz pulses by optical rectification in LiNBO3 at 800 nm

Generation of efficient terahertz (THz) pulses was experimentally made by tilted pump pulse front scheme with a Mg-doped LiNbO3 crystal. In this study, a spitfire laser (Ti:sapphire laser, 800 nm, 3 mJ, 1 kHz) was used as an optical source for the generation and detection of THz pulses. The electro-optic (EO) detection optics consisting of a ZnTe crystal (1 mm in thickness) and a balanced photodetector was used. To obtain optimum THz characteristics and pump to THz power conversion efficiency, the image of the grating was made coincides with the tilted pump pulse front. The maximum THz electric field of 8.5 kV/cm and the frequency bandwidth of 2.5 THz were achieved by using pump pulse energy of 2.4 mJ and pump pulse width of 100 fs. The THz energy of 4.15 μJ was obtained and pump-to-THz conversion efficiency was estimated to be approximately 1.73 x 10-3.