Study On The Transmission Characteristics Of Dielectrically Chiral Fiber Grating

Fiber Bragg grating (FBG) had been invented since the late 1970s. Because of their fine filtering characteristics as well as temperature and strain sensitivity, FBG is applied widely in optical fiber communication, sensoring and measurement. At the same time, chiral optical fiber, which has novel transmission characteristics, receives much attention from researchers. Researches show that, in some case, the modes may be divided into left circularly polarized(LCP) and right circularly polarized(RCP) mode with different propagation constants respectively, which cause the difference in response between LCP and RCP mode in optical devices.We design a dielectrically chiral fiber Bragg grating, which is working as a new kind of optical communication device with characteristics of circular polarization. It has unique features in the filtering and optical splitter.Firstly, from Maxwell's equations and the constitutive relation, the chiral Helmholtz equation is derived. Then, based on the perturbation, the coupled mode equation is derived for chiral fiber grating. Using the method that we have obtained, The filtering characteristics for LCP and RCP light are calculated in the regular chiral FBG. And the time delay and dispersion properties are also studied.In order to calculate the complex nonperiodic fiber structure, the transfer matrix method is developed which is suitable for calculating the nonperiodic chiral fiber gratings. As a example, apodized chiral fiber grating and chirped chiral fiber grating are investigated respectively. Correspondingly, the filtering time delay and dispersion properties are obtained for LCP and RCP light.