分焦平面偏振图像传感器偏振主轴方向的标定

Calibration of polarization axis direction of sub focal plane polarization image sensor

分焦平面偏振图像传感器的偏振主轴方向对后续使用斯托克斯矢量进行偏振参数解算的结果准确性有重要影响。为了标定该类型传感器,提出一种基于测量分焦平面偏振图像传感器中各偏振主轴方向像素输出平均值所拟合曲线相位差的方法,并对该方法进行了仿真与实际测试。控制照射到传感器表面的线偏振光,按照设定步长旋转若干周期,传感器同时拍摄图片。选定图片的感兴趣区域,并对该区域内同偏振主轴方向的像素值求平均,获得各偏振主轴方向像素平均值随旋转角度变化的序列。使用傅里叶级数拟合法对各序列进行拟合,获得像素输出值随旋转角度变化的表达式。选定一个偏振主轴方向为基准方向,其他偏振主轴方向为该方向表达式与基准方向表达式的相位差。实际测试结果表明:标定值与名义值相差不超过0.1°。该方法的标定精度高、可操作性好,能够较好地完成分焦平面偏振图像传感器偏振主轴方向的标定任务。

The polarization axis direction of the sub focal plane polarization image sensor influences the accuracy of the polarization parameter calculation using the Stokes vector.Therefore,it is necessary to calibrate the sensor before using it.To meet this requirement,a method based on measuring the phase difference of the curve fitted by the average output value of pixels in each polarization axis direction of the sub focal plane polarization image sensor is proposed,and the simulation and actual test are conducted.First,the linearly polarized light vertically irradiating the sensor surface is rotated for several cycles according to a certain step size,and the sensor takes pictures simultaneously.Then,the region of interest of the image is selected,and the pixel values in the same polarization axis direction in the region are averaged to obtain the sequence of the average values of the pixels in each polarization axis direction changing with the rotation angle.The Fourier series fitting method is used to fit each sequence,and the expression of the pixel output value changing with the rotation angle is obtained.Finally,one polarization axis is selected as the reference direction,and the other polarization axis is the phase difference between the expression of this direction and that of the reference direction.The actual test results show that the calibration error is less than 0.1°.This method has high calibration accuracy and good operability.Furthermore,it can complete the task of calibrating the polarization axis direction of the sub focal plane polarization image sensor.