Study on polarization generator based on electro-optic modulation

Abstract

Polarization state generator is an indispensable part of polarization imaging system, produces the state of polarization for the calibration or test . Based on the analysis of the existing scheme, a novel Polarization State Generator is developed , which is constituted of a linear polarizer P and two liquid crystal phase variable retarders, denoted as LCVR1 and LCVR2. The transmission axes of P and LCVR2 are oriented horizontally, while the fast axes of LCVR2 is oriented. the state of polarization of the incident light is modulated through adjusting the control voltage of LCVRS. the experimental results show that the system not only is feasible ,but also has high sensibility. A good agreement is observed between theoretical and experimental results. Introduction Polarization generator is an indispensable part of polarization imaging system, in order to measure the instrument polarization sensitivity and monitor instrument performance requirements change, has the extremely high sensitivity. Laser is a common light source in polarization calibration, therefore, the polarizer , plate or other optical devices are placed in the laser beam path , thus can obtain the required for various polarization state laser beam [1 ]. In this paper, Based on the Stokes vector and Muller matrix theory, the traditional measurement technique, rotating wave plate driven by a motor, is replaced with Liquid crystal variable retarders (LCVRS), the phase retardation is controlled by the applied voltage, the polarization state of incident light is modulated accurately, eliminating the mechanical error, the polarization of laser generated is more accurate. Theory The Stokes Vectors of the light can be used to characterize the polarization properties of the light beam. The elements with the strength of the dimension, are all real Numbers, and can be easily measured and calculated, in the practical process of polarization detection, stokes vectors has become an important method to determine the polarization of the laser beam. In the Mueller calculus, the Stokes vector is used to described the polarization state of a light beam(where T denotes transposition).where is the total light intensity, the difference between the intensity of the horizontal (X) polarized component and that of the vertical (Y) linearly polarized component, the difference between the intensity of the linearly polarized component oriented at an angle of and that of the linearly polarized component oriented at an angle of , and the difference between the intensity of the left-circularly polarized component and that of the right-circularly polarized component[2-4]. The Stokes vector of the output beam can be written as: out in S M S = × (1) where in S is the Stokes vector of the input beam and M is Mueller matrices [5] of n optical elements respectively given by 1 2 1.... M M M M M n n − = International Conference on Intelligent Systems Research and Mechatronics Engineering (ISRME 2015) © 2015. The authors Published by Atlantis Press 382 Degree of Polarization(DOP),Linear Polarization(DOLP), Circular Polarization (DOCP),azimuth (θ )and ellipticity ( e ) can be obtained as: % 100 ) ( 0 2 3 2 2 2 1 × + + = S S S S DOP (2) % 100 ) ( 0 2 2 2 1 × + = S S S DOLP (3) ] 2 , 2 [ ) ( arctan 2 1 1 2 π π θ S S = (4) ] 4 , 4 [ ) arcsin( 2 1 2 3 2 2 2 1 3 π π e − + + = S S S S (5) Institutions Optimization Design The commonly used PSG is constituted of a linear polarizer P and a quarter-wave plate . Line polarized light can be produced by adjusting P. To produce a left-handed and a right-handed circular polarized light ,the transmission axes of P is oriented horizontally ,while the fast axes of the quarter-wave plate is oriented 4 ±π . The disadvantages is big volume,slow response,great mechanical error and so on.The rotating-retarder configuration can be replaced by one liquid crystal variable retarder[3] for determination of four complete Stokes vectors. The configuration greatly improves the response speed,improves accuracy, decreases the influence of mechanical rotating at the same time, but not completely eliminated. So the scheme based on dual LCVRS is presented. The system is constituted of a linear polarizer P and two liquid crystal phase variable retarders, denoted as LCVR1 and LCVR2,the structure diagram is shown in figure 1.