基于强度调制的偏振光谱测量技术

Polarization Spectrum Measurement Technology Based on Intensity Modulation

针对现阶段强度调制偏振光谱测量技术在光程差域内不同通道间存在频谱信息串扰的不足,采用加窗插值傅里叶变换法,研究了不同切趾函数对强度调制偏振光谱测量技术的影响。首先,进行强度调制偏振光谱测量技术理论分析,完成强度调制模块的设计;其次,根据强度调制模块的设计指标,模拟入射光的光强信息及采用不同切趾函数的信息解调复原过程;最终,对强度调制偏振光谱测量系统进行仿真,根据仿真模型结合高分辨率光谱仪、平行光管等器件完成偏振光谱测量装置的搭建,进行偏振光谱测量实验。研究结果表明,偏振光谱测量系统设计指标选择合适的切趾函数可以减少光强信息截断过程中造成的频谱能量泄露,使光程差域内不同通道之间的串扰信息减少、偏振光谱复原精度提高,不同切趾函数切趾处理后线偏振光的偏振度最小误差由0.0768减小到0.0014,偏振度接近1。

As one of the common methods to measure polarization information,intensity modulated polarization spectrum measurement technology has the advantages of high real-time performance and high time resolution,and is widely used in many fields.In this method,the stokes vector of the target light is modulated to the carrier signal of different frequencies by the intensity modulation module,and the spectral information of each element is modulated to the channel of different frequencies by the Fourier transform,finally,the polarization spectrum is obtained.Although the technique of intensity modulated polarization spectroscopy is simple and effective,there are still spectral overlap to varying degrees,which makes the Stokes parameters between channels interfere with each other and affects the accuracy of spectral reduction.At the same time,to meet the requirements of wide-band detection,on the basis of a certain spectral resolution of the spectrometer,the thickness of the intensity modulation module delay is rationally designed to reduce the interval between channels in the optical path difference domain,so as to achieve the purpose of wide-band operation range.Secondly,by increasing the thickness of the delayer,the modulation information generated by the polarization module is collected with a high-resolution spectrometer to achieve a wide-band detection range.Based on using high resolution spectrometer to realize the requirement of wide band detection,aiming at the shortage of overlapping between different channels in the optical path difference domain of the current intensity modulated polarization spectrum measurement technology,the generation of aliasing error in optical path difference domain is analyzed.The influence of different toecutting functions on the measurement error of intensity-modulated polarization spectrum is studied by using windowed interpolation FFT transformation.Firstly,the theoretical analysis of intensity modulation polarization spectral measurement technology is carried out to analyze the relationship between the design of the retarder thickness in the polarization module and the spectral resolution of the spectrometer.And the design relationship between the two delayers is introduced to complete the design of the intensity modulation module.Secondly,according to the design index of the intensity modulation module,the process of demodulating and recovering the intensity information of the incoming light and the information using different toe-cutting functions is simulated.The distribution of different channels in the optical path difference domain is analyzed under different toe-cutting functions.The polarization spectrum information of different channels is restored,the four Stokes vectors are normalized,and the calculation of polarization degree and error analysis are completed.Finally,the intensity modulated polarization spectrum measurement system is simulated by ZEMAX software,and the polarization module is adjusted and installed according to the simulation model.At the same time,the polarization spectrum measurement device is built with high resolution spectrometer,parallel light tube and other devices,and the polarization spectrum measurement experiment is carried out.During the experiment,before demodulation of the metering light,it is necessary to calibrate the reference light and calculate the demodulation coefficient required in the process of demodulation.Analyze the correctness of the demodulation coefficients according to the principle of polarization spectrum measurement to eliminate the influence of installation and adjustment errors on the demodulation work.At the same time,the source spectrum of the unmodulated halogen lamp was measured and compared with the recovery result as reference light to verify the accuracy of polarization spectrum recovery under different toe-cutting functions.The results show that choosing the appropriate toe-cutting function according to the design index of the polarization spectral measurement system can reduce the spectral leakage effect caused by the truncation of light intensity information,reduce the aliasing information between different channels in the optical path difference domain,and improve the accuracy of polarization spectral recovery.The maximum error of polarization of linear polarized light with different toe-cutting functions is reduced from 0.0593 to 0.0014,and the polarization is close to 1.The above research provides an important reference for eliminating the“ring”effect caused by spectral aliasing in the process of intensity-modulated polarization spectrum measurement.