针对锁模激光器微弱回波信号探测的需求, 提出了一种基于高速相关采样和在线实时并行累加处理算法相结合的方法, 对传统的模拟取样积分方法进行了改进, 可实现无参考信号条件下的实时数字累加检测。设计并实现了一套基于该方法的锁模激光器微弱回波信号检测原型系统, 使用12 bit@900 MSPS模拟-数字转换芯片(ADC)ADS5409对经光电转换之后的锁模激光回波信号进行波形采样, 并利用现场可编程逻辑门阵列(FPGA)芯片Kintex-7实现对ADC的控制及在线数据处理。系统测试结果表明,对于重复频率为8 MHz、平均功率为0.04 nW的锁模激光回波信号, 通过在FPGA内进行16 000次脉冲波形精确累加,可实现信号的有效检出, 且从波形采集完毕到输出检测结果的延时小于100 ns, 达到了高度的实时性。经900次重复实验, 检测效率达到100%, 且无“虚警”情况发生。

According to the demands of mode-locked laser weak echo signal detection, a method which combined high-speed correlation sampling and parallel accumulation based on Field-Programmable Gate Array (FPGA) was proposed. This method overcame the shortcomings of the traditional sampling integral algorithm and can work real-timely without reference signal. Besides, a mode-locked laser weak echo signal detection system based on this method was designed and implemented. This system mainly consisted of a 12 bit@900 MSPS Analog-to-Digital Converter(ADC) chip, ADS5409, which sampled the echo signal and a FPGA chip, Kintex-7, which was in charge of controlling and on-line calculation. To the signal with the repetition frequency of 8 MHz and the average power of 0.04 nW, by accumulation of 16 000 pulses, this system can realize efficient detection and the calculation latency is shorter than 100 ns. In 900 experiments, the correct rate of the detection system reaches as high as 100% without false alarm.