Study On The Technique For Measuring The Polarization State Of Light Based On Division Of Amplitude Method

Polarization is an important property of optical waves and its measurement is very significant in material science, optics, optical engineering, communications, astronomy and other fields. The division-of-amplitude photopolarimeter (DOAP) is a kind of sensor capable of fast measurement of the state of polarization of light. It divides the incident light beam into several independent small photosources by using division of amplitude method, and then instantaneously and simultaneously determines the four Stokes parameters that describe the state of polarization of light to be measured through the simultaneous detection of multi-signal channel. The DOAP has lots of advantages, such as high speed, compact structure, easiness to be installed and operated, and so on, and can be used for in situ and real time studies of the physical and chemical property of the materials. In the past twenty years, overseas researchers have done lots of work in the theory and application in this field and made a great progress. They have proposed numerous instruments of measuring the light polarization based on division of amplitude method, some of that have already been applied to the actual field. Now there is less research on the DOAP in china. Therefore, this paper performed a deep study on the technique for measuring the state of polarization of light by using the division-of-amplitude method. The main research works in this dissertation are as follows:(1) According to the working principle of the DOAP, a novel high-speed photo- polarimeter was designed. A metallic grating was designed, which can produce both reflective diffraction and transmission diffraction, and then utilized as a main beam splitter, the optical system of the polarization state detector was developed. The electronics of the instrument based on USB2.0 interface was developed, which has the functions such as photoelectric transformation, signal processing, high speed data acquisition and data transmission and so on. The software system was designed and developed. Finally, a prototype of the instrument was developed. It has no moving parts or modulator, and thus can determine rapidly the incident light polarization state.(2) A data evaluation for the grating division-of-amplitude photopolarimeter was carried out. The nonsingular instrument matrix of this instrument was obtained by Equator-Poles calibration procedure. By using the polarization state generator to produce a series of polarization states, a test was carried out to examine the working performance of the instrument after calibration. The testing results show that the mean deviations of the measured and theoretical Stokes parameters are less than 2% at 632.8nm. The main reasons of measurement deviations were analyzed in detail.(3) The measurement accuracy of the DOAP is affected by the quality of the instrument matrix. To improve the measurement precision of the DOAP, an optimization method for the instrument matrix of the DOAP based on genetic algorithm was presented. The testing results show that the better instrument matrix can be obtained by using this method.(4) To improve the working performance of the DOAP, a data processing method for the DOAP based on an artificial neural network was presented. A multilayer feedforward neural network model was set up whose inputs are the electrical signals produced by the electronics of the DOAP, and outputs are the Stokes parameters of the incident light. The mapping relationships between the electrical signals and the Stokes parameters can be determined by training the neural network. After the electrical signals are measured, the Stokes parameters of the incident light can be calculated via a trained neural network. The testing results show that the data processing method based on the neural networks is slightly better than that based on the matrix operation on the measurement precision.(5) The DOAP can be used as a polarization state detector in real-time polarimetry, ellipsometry and Mueller matrix ellipsometry. In this dissertation, the application of the DOAP in the time-resolved measurement of the sugar in solution was introduced and tested.