A Method To Determine The Azimuth Of Polarization Axes Of PMF Based On The Characteristics Of Backward Diffractive Patterns

In the applications of polarization maintaining fiber (PMF), the precision alignmet of the polarization axis of PMF is one of the key technologies. A new method to determine the azimuth of polarization axes of PMF was researched in order to polish PMF on certain azimuth of PMF and to make it possible to observe the side polishing state as PMF was polished on the side-polished fiber machine. Furthermore, it would provide a new method to determine the azimuth of polarization axes of PMF when the forward side viewing method is invalidated.When a PANDA fiber was illuminated by a laser beam transversely to the longitudinal axis of optical fiber, a diffractive pattern around the PANDA fiber in 360°space was generated. According to an investigation of the backward diffractive pattern based on image processing and correlation, we found that both the lengths and the center positions of bright fringes on the backward diffractive pattern were related to the azimuth of polarization axes of PANDA fibers as the PANDA fiber was rotated on its longitudinal axis. So the curve of the length or curve of the center position of bright fringes can be used for the determination of the azimuth of polarization axes of PANDA fibers. It is more sensitive to determine the azimuth as the curve of length of bright fringes was chosen as the characteristic parameter other than the curve of center position. A new method based on the two characteristic parameters of backward diffractive patterns was put forward to determine the azimuth of polarization axes of PANDA fibers and a resolution of 1°was achieved. The correlations among diffractive patterns were done to validate the new method. The experiment results of the method of characteristics and those of the correlation fitted well. The correlations of gray patterns or of binary patterns were done respectively. The correlation values showed that binary patterns was more sensitive to determine the azimuth than gray one.Furthermore, when rotating the optical fiber for varying the diffractive light pattern, the bright and dark regions converging and diverging in a pattern from a bright central region. It means that the change of converging and diverging pattern indicated that the position of birefringent axes of the fiber was at 0°or 90°. The conversion occured in every 90°. During the conversion, the change of central bright region was the most sensitive one. A resolution of 0.2°was achieved near 0°and 90°. It is good for making PMF device.This technology can be used for determining any azimuth of polarization axes of PMF, especially for the situation that the forward patterns can not be observed.The application of the method was done for Fiber Side-polished Machine.The innovations of this thesis are as follows:1. The characteristics were gotten to determine the azimuth of PANDA fibers according to the curve of the length and the curve of the center position of bright fringes. Experiments showed that the both of the curves were well for increasing the precision of determining azimuth of PANDA fibers.2. A new experimental method was put forward based on the characteristics of backward diffractive patterns. Based on the two characteristics and the sensitivity characteristic of converging and diverging in a pattern of bright central region, a resolution of 0.2°was achieved in these conversion positions.