Research Of The Performance Measurement And Wavefront Correction Application Of Phase-Only Liquid Crystal Spatial Light Modulator

According to the theory of advanced optical diffraction, the 3-D wave field is determined by the 2-D wavefront during propagation. Because the wavefront phase mainly indicates the character of wave field, the wavefront phase control plays an especially important role in advanced optical information process. Compared to deformable mirror, liquid crystal spatial light modulator (LC SLM) has the advantages of high spatial resolution, low cost, small size, light weight, low power. Therefore, the application of LC SLM in wavefront control and wavefront correction gets more and more attention in recent years.With the growing demand for high accuracy and high performance of wavefront control device, the testing and evaluation of LC SLM becomes an important research subject. At present, national and foreign researches test LC SLM by traditional interference mainly. But traditional methods can only fit for single-parameter testing. Other testing platforms should be set up to achieve the testing on multi-parameters, which makes the operation more complex and introduces extra errors. In order to break through the limitation of traditional measurement this thesis mainly focuses on the research of multi-parameters testing and evaluation method of phase-only LC SLM.The inherent nonlinear phase response and static error will degrade the accuracy of wavefront control. Therefore, the compensation methods on phase nonlinearity and static error should be studied to improve the linear driving capacity of LC SLM and the accuracy of wavefront control. Based on the testing and error compensation of LC SLM, the static wavefront correction experimental system is set up to explore the possibility and availability of applying LC SLM in high-accuracy and high-resolution wavefront correction.The main research works are as follows:Firstly, based on the analysis of Jones Matrix, mathematic model is established about intensity reflectivity and phase delay of parallel-aligned nematic liquid crystal cell. Through analysis of the dependent relation of two parameters with polarization angle of incident beam and output beam, necessary conditions are obtained which realize phase-only modulation and phase-amplitude modulation. This mathematic model provides theoretical evidence for the research of multi-parameters testing.Secondly, in order to solve the problem that traditional interference can not meet multi-parameter testing, a new multi-parameter test method is proposed based on Tayman-Green interference principle. This method synthesizes interference fringes move method and polarization interference method in the same experimental platform and obtains phase and intensity information by introduced double imaging system. This method realizes testing and evaluation of multi-parameters of LC SLM on the same test platform.Thirdly, the inverse interpolation method based on least-squares fitting for phase nonlinearity compensation is proposed to solve the problem of inherent phase nonlinear response characteristic of LC SLM. Phase subdivision and interpolation data dots composing are achieved by least-squares fitting on measured data. This method decreases the disturbance from measurement errors. A linear look up table is established to improve linear driving capacity of LC SLM. Based on the principles of phase conjugation and boundary defining the inherent stastic errors are compensated by phase modulation of LC SLM. The root-mean-square (RMS) of wavefront error can be reduced fromλ/8 toλ/50, and the accuracy of wavefront control of LC SLM is improved.Fourthly, statistic wavefront correction system based on LC SLM is set up. According to Zernike polynomials the primary wavefront aberrations are simulated to validate the capacity of generating and correcting various primary wavefront aberrations of LC SLM and explore a new way for improving the imaging quality of optical systems. Arbitrary wavefront with peak-valley (PV) value over a wave length approaches to standard plane wavefront with the closed loop feedback wavefront distortion correction method. The RMS of wavefront is reduced toλ/50 after correction. Therefore, these results validate the probability and availability of applying LC SLM in high accuracy and resolution wavefront correction.