Research On The Technology Of Wave Plate Birefringence Test System Based On Photoelastic Modulation

In recent years,electronic technology,laser technology and other fields continue to develop,optical measurement technology has made outstanding achievements and breakthrough progress,measurement accuracy and efficiency are constantly improving,the introduction of digital display technology and automatic measurement technology also makes polarized optics have more room for development.Wave plate in the optical modulation system is a very important device,it can be applied in the optical polarization and crystal optics and other fields,its main role is to produce polarized phase changes in order to achieve the purpose of changing the polarization state of light.Therefore,the birefringence index of the wave plate will have a direct effect on the quality of the optical precision instrument,the polarization state of the laser and the communication effect.In this paper,the whole wave-plate birefringence measurement system is built.First,the parallel beams emitted by the laser are passed through the polarizer,PEM,the quarter-wave plate to be measured,the analyzer,and then into the detector.The signal processing unit designs the hardware circuit with FPGA as the core to complete the cross correlation calculation of the optical signal,and extracts the fundamental frequency,the second harmonic term,the fourth harmonic and the DC term needed for the calculation.The hardware circuit part includes the signal A/D conversion module,the USB communication module and so on.In the FPGA to achieve the A/D acquisition clock control,based on the DDS reference signal generation and digital phase-locked algorithm,and then through the USB data transfer to the LabVIEW data processing and operation.The results are stored in the host computer to complete the data processing and analysis.After test,the Circuit module can achieve the desired function,through the construction of experimental platform to get the maximum delay of the phase delay,the result is 0.02 rad.The measured fast axis angle is linearly changed with the actual value and its maximum deviation is 0.01°.It can be shown that the fast axis angle and the retardation amount of the1/4 wave plate can be measured at the same time.