基于多像素光子计数器的弱本振激光外差信噪比分析

Analysis of Signal to Noise Ratio for Laser Heterodyne with Weak Local Oscillator Based on Multi-pixel Photon Counter

为避免传统激光外差探测中强本振信号带来的散粒噪声影响，着眼于光子级别的弱本振激光外差探测信噪比分析。将脉冲体制弱本振激光外差探测信噪比表达式应用于分段连续弱本振激光外差探测中，获得中心频率221kHz外差信号的解析，且信噪比的理论计算和实验值吻合。采用数据段细分功率谱累积技术，针对原始数据长度为4000000点的时域信号，在相同的信噪比情况下，所利用的数据量总数降低为传统功率谱累积方法的1／10，提高了’数据利用率，且在功率谱累积次数较少时，信噪改善比近似遵守m规律。最后，给出数据段细分功率谱累积技术在信噪改善比方面的限制因素，为有效利用已采样数据奠定基础。

In order to avoid the influence of the shot noise due to the powerful local oscillator （LO） in the traditional laser heterodyne detection, the signal to noise ratio （SNR） analysis of laser heterodyne detection with a weak LO under photon-level is focused. First, the expression of the SNR with a pulsed laser is applied in the condition of partial continuous wave （CW） and weak LO laser heterodyne detection, the spectrum of the heterodyne signal with the center frequency 221 kHz has been achieved, and the theoretical value of the SNR is in agreement with the experiment. Second, the techniques of data segment fractionizing and power spectral density （PSD） averaging are used in the research of SNR. The results show that the volume of the data has been decreased to 0.1 times compared with the traditional PSD averaging while the raw data length is 4000000, the data resource is fully used while in the signal processing , and the signal to noise improved ratio （SNIR） nearly obeys the rule （ m is the averaging time） under a small quantity of data segments. At last, the limited factors about the SNIR during the PSD averaging have been given so that we can make use of the data well.