基于弹光调制旋光测量的信号解调系统

考虑到弹光调制技术PEM（photo-elastic modulation）测量光学旋光高灵敏度、高精度的优点，设计了一种基于PEM的软硬件相互配合的旋光数据解调系统，以满足实时稳定的旋光角度测量要求。在FPGA内使用多通道直接数字频率合成技术DDS（Direct Digital Synthesis），采用同一频率控制字产生PEM的驱动信号和数字锁相的倍频参考信号，保证了信号的同频同源。弹光调制信号的交流序列和直流序列分别通过两路串口设备并行传输，LabVIEW完成串口资源配置和数据缓存，经数字锁相解调得到光学旋光角度。实验表明，在旋光角为8.52×10-5 rad时，系统的标准偏差是1.48×10-6 rad。

Signal Demodulation System Based on Measurement of Optical Rotation Using Photo-elastic Modulation

Taking the high sensitivity and high precision of measurment of optical rotation using photo-elastic modulation into account,and in order to realize the real-time and stability measurement of optical rotation angle,an PEM-based optical rotation angle data demodulation system is designed. We used the multi-channel direct digital synthesis technology of FPGA to control the driving signal of PEM and frequency-doubled reference signal of digital lock-in amplifier through the same frequency control word,so the same frequency and homology of signals can be ensured in this way.AC and DC sequences are transmitted to the PC via the two-way serial port equipment,it con?tains reference signal and test signal in the AC sequence,LabVIEW achieve port resource allocation and data cache,find a frame of data through frame detection module,then conduct digital lock-in demodulation of these data, and output the optical rotation and display the sequence waveform in the final. Experiments show that when the rota?tion angle is 8.52×10-5 rad,the standard deviation of system is 1.48×10-6 rad.