The Research And Implementation Of Polarimeter Based On Digital Image Processing And Vortex Retarder

Polarimeter is widely used in the fields of chemistry and chemical engineering,materials,physics and medicine.It is an important measuring equipment which is used the phenomenon of optical rotation effect for the determination of optical rotation angle of substances with optically active substance,and then analysis and determination of the concentration,content and purity of substances and other important parameters.Due to the polarimeter is necessary in many areas,it makes the scientific researchers are constantly in-depth study for how to measure the higher accuracy and a wider range of polarimetric method.In this thesis,we designed a polarimeter by using first-order liquid crystal polymer vortex retarder and digital image processing,conducted feasibility analysis,built and designed light path,and obtained the images containing the optical rotation information.By using MATLAB software for image processing and data fitting,the optical rotation results and concentration measurement results of sucrose solutions with different concentrations were obtained.Furthermore,we try to miniaturize the polarimeter by using FPGA hardware platform.In this thesis,the Jones matrix representation of vortex retarder is given.The optical characteristics of the first-order liquid crystal vortex retarder are simulated and analyzed.The phase distribution diagram,fast axis distribution diagram and vortex beam section diagram of first-order polymer liquid crystal vortex half wave retarder are shown.Radially polarized light and angularly polarized light generated by the first order vortex retarder are analyzed.The principle of measuring optical rotation by first order liquid crystal polymer vortex retarder is explained by Jones matrix representation.The optical path of the polarimeter proposed in this thesis does not need expensive equipment such as additional magneto-optical elements,rotating electromechanical elements,multiple photoelectric detection elements and complex optical path composition,and can reflect the optical rotation from the image and the measured value simultaneously.In the MATLAB system,multiple of image processing methods are applied for the optical rotation image to enhance the quality of the obtained image and improve the accuracy of the fitting.Through image analysis,the initial value of the system in the initial air environment is-0.7099 degrees,and the repeatability is within 0.001 degrees.Polarimeter measurement range for-90 to + 90 degrees.The standard concentrations of sucrose concentration were set at 0g/ml,0.01g/ml,0.02g/ml,0.04g/ml,0.06g/ml,0.08g/ml and 0.10g/ml respectively,and the length of the test tube was 100 mm.The final results of sucrose solution concentration showed that the repeatability stationarity of the polarimeter is about ± 0.01 degrees,the maximum relative error was about 0.243g/d L.In FPGA system,FPGA is used to directly control the CMOS image acquisition module for image information acquisition.A series of modules are designed to achieve Gaussian filtering and other digital image processing in FPGA and the process of obtaining the value of optical rotation by image information fitting.The optical rotation image used for calculation and the calculated optical rotation value information are output through the LCD panel driven by FPGA.