A novel method for square wave pulse shaping based on field-programmable gate array (FPGA) is proposed. Aiming at the waveform distortion problem of square wave pulses caused by an erbium-doped fiber amplifiers (EDFA), a high-quality square wave pulse with a repetition frequency of 91.27 kHz and a pulse width of 650 ns is successfully obtained by using an extra-cavity pulse-shaping system. The experimental results show that the system can effectively suppress the distortion caused by gain saturation during the amplification process of the square pulse, and the consistency between the spectral envelope of the square pulse after shaping and the sinc function envelope of the ideal square wave pulse is significantly enhanced. This study applies FPGA to distortion correction after amplification of square pulses with a pulse width of hundreds of nanoseconds, and the results can provide technical support for the acquisition of high-energy and high-quality square wave pulses, and further promote their wide application in fields such as supercontinuum generation.

We compare the detection performance of coherent detectors and single photon detectors, and explain the working principle of single photon detectors under the direct detection system by utilizing binary accumulation. Based on actual lidar parameters and experimental data, the conclusion that the detection performance of coherent detectors is better than that of single photon detectors is clarified. Additionally, the influence of analog-to-digital converter sampling and polarization on coherent detection is analyzed, with relevant requirements for the design of coherent detection ladars provided. We propose a linear mode InGaAs array detector structure based on the laser local oscillator and binary accumulation, which features moderate computational complexity and better detection performance than single photon detectors. On this basis, the parameters of the lunar lidar are basically designed. This lidar can achieve high-precision three-dimensional imaging at a long range and has strong anti-background interference ability.

Multiplexed entanglement with high-capacity characteristics serves as an important resource in quantum information processing. Orbital angular momentum (OAM) multiplexing, which can support infinite optical modes in principle, is an effective way to generate multiplexed entanglement. Enhancing the channel number of OAM multiplexed entanglement is crucial for developing high-capacity quantum information protocols. In this study, we experimentally implement 29 pairs of continuous variable entangled OAM modes in the range of topological charge l from -14 to 14. By utilizing the Bessel?Gaussian modes, whose beam size increases at a slower rate with the increase of the value of l compared to the Laguerre?Gaussian modes, we experimentally realize the enhancement of channel number of OAM multiplexed entanglement. This method provides an effective solution for enhancing the data-carrying capacity of quantum information communication systems.