Research On Design Of High Performance Wave Plate Measuring Instrument

The wave plate is a very important optical device,which is widely used in the fields of Applied Optics and non-destructive detection.Phase retardation and azimuth angle of fast axis are important parameters of wave plate.Accurately measuring parameters of wave plate can not only monitor the uneven stress caused by the process of processing,but also provide parameter guidance for user.With the rapid development of electronic information technology and optical application technology,especially the introduction of automatic measurement technology and digital display technology,optical precision measurement has made breakthrough progress.The traditional methods of measuring phase delay and fast axis azimuth angle of wave plate can't meet the requirements of the era of optical precision measurement.In order to accurately measure the phase retardation of wave plate and calibrate the azimuth angle of fast axis,and realize the integration and automation of measurement system,a new wave plate measurement technology based on the combination of photo-elastic modulation technology and digital phase-locked technology is proposed in this paper.A high-precision measurement method of phase retardation and azimuth angle of fast axis is proposed,and An automatic measuring wave plate system is designed and the measurement results are analyzed.Therefore,this paper mainly elaborates on the following aspectsFirstly,the optical principle of wave plate,the working principle of photo-elastic modulator and the principle of digital phase-locked were researched.A new method of measuring wave plate phase retardation and azimuth angle of fast axis based on the combination of photo-elastic modulation and digital phase-locked technology was proposed.The measuring principle was deduced by using Stokes parameter and Muller matrix.That create the conditions for designing high-precision measuring phase retardation and calibrating azimuth angle of fast axis system for wave plate.Secondly,Hardware circuit based on FPGA is designed,completed the design of powersupply circuit,analog-to-digital conversion circuit,peripheral circuit of the FPGA and serial communication circuit,and realized the design of the generating module,serial communication module,A/D acquisition clock control module,digital phase-locked module,stepper motor control module and measurement results display module based on DDS technology in the FPGA.The function simulation tests of each functional module are carried out,which lays a foundation for the integration and automation of the measurement system.Thirdly,the experimental system was built,and the quarter-wave plate was measured.The phase retardation measurement results are displayed by LCD,and the fast axis is calibrated by stepping motor.The experimental results show that the accuracy of the system for measuring the azimuth angle of the fast axis of a quarter wave plate is better than 0.31 degree,and the measurement accuracy of the phase retardation is better than 99.47%.The driving signal of the photo-elastic modulator,the driving signal of the motor and the data operation of the measurement system are all controlled by the FPGA,which realized the optical,mechanical and electronic integration and the automation of the measuring process.