基于手征光纤光栅的全光纤型圆偏振起偏器的研究-电磁场与微波技术专业论文.docx

ABSTRACT Circular polariz创ion technology in fiber optics is of great importance in the applications of optical measurements ，optical sensing and optical communications. However，it is to be improved. Herein ，to realize an all-fiber circular polarizer is one of the most urgent demands. To accelerate the applications of circular polarization technology，we present all-fiber circular polarizers based on the chiral fiber grating which is fonned by twist a stress-induced high-birefringence (Hi-Bi) fiber with a high twist rate at its melting state. In this thesis，we focus on chiral fiber gratings based on stressinduced high-birefringence fibers and their applications on circular polarizers. Firstly，by using coupled-mode the。可and with the view of local modes，theoretical analysis model for chiral fiber gratings is developed. 丁he mode coupling mechanism in chiral fiber gratings is well explained，and the necessary condition to realize circular polarizers is revealed for the first time. By using the theoretical model based on coupled-mode analysis，characteristics of long-period chiral fiber gratings are investigated. The dependences of fiber parameters on characteristics of chiral fiber gratings are analyzed，and guidelines to practical design are given. 丁he inf1uences of the random variations of the twist rate and twist length on the performances of circular polarizers are also s阳died，and 由e precision requirements in fabrications are suggested for the required performance specifications. Since the bandwidth of the circular polarizer based on long-period chiral fiber gratings with uniform twist rates is only several nanometers ，it may be too narrow for most applications. We propose a new scheme of a broadband circular polarizer fonned by twisting a Hi-Bi fiber with a slowly varying twist rate. The characteristics of long-period chiral fiber gratings with the linearly varying twist rates are investigated by using adiabatic coupling principle. The conditions of adiabatic co