为克服传统Pound-Drever-Hall（PDH）激光稳频方法的缺点，设计了正交解调PDH激光稳频系统。该系统采用同一直接数字频率合成器(DDS)同步产生三路同频正弦信号，一路作为本振信号驱动电光调制器产生激光相位调制边带，另外两路相位差为90°的信号作为解调参考信号。采用两个模拟解调器分别获得误差信号的同相分量和正交分量，对其进行数字化采集和相敏检波运算，即可获得稳频系统的误差信号。通过正交解调PDH激光稳频关键技术研究，建立了激光频率跟踪实验系统。实验结果表明，Fabry-Perot (F-P)参考腔可以实时跟踪激光频率变化的功能，跟踪时长约1 h。

To overcome the disadvantages of traditional Pound-Drever-Hall (PDH) laser frequency stabilization method, we have design a PDH laser frequency stabilization system based on orthogonal demodulation method.The system uses the same direct digital synthesizer (DDS) to synchronously generate three sine signals with the same frequency. One signal is used as local oscillator signal to drive an electro-optic modulator so as to produce the phase sidebands, and the other two sine signals with a phase difference of 90° are used as demodulation references. The in-phase and orthogonal components of the error signal are obtained by use of two analog demodulators, and the error signal of the frequency stabilization system is obtained when both components are digitally sampled and then operated by an algorithm of digital phase-sensitive detection. The key techniques for the PDH laser frequency stabilization based on the orthogonal demodulation method have been investigated, and an experimental system of laser frequency tracking has been established. Experimental results show that the F-P cavity can track the laser frequency variation in real time, with a tracking time of approximately about 1 hour.