Theoretical Study On Transmission Characteristics Of Pulse In Chiral Fiber

Currently,the network plays very important roles in our daily life.Actually,the most part of network can be viewed as optical one because it is supported by the optical fiber communication which is fast developed with increasing demand on the information of the people.Although the capacity have already reached a surprising degree of 100 Tb/s for the single-core fiber,there is still needs to make breakthrough in the limitation for the information transmission capacity and to overcome the bottleneck of devices for rapidly distributing and controlling information.In fact,the revolution gradually occurs due to employing the novel materials,novel structures and novel mechanism.Our work just follows this development tendency.We try to make our contribution in exploring new kinds of fibers and derivative devices based on some unique materials,because of different response of chiral materials to opposite circularly polarized light,namely leftand right-handed circularly polarized(LCP and RCP)light,the fiber composed of such media should posses novel properties in linear and nonlinear aspects.We take the chiral fiber and its derivative devices as the research topic and hope it will be meaningful to explore the unique roles of chirality in tailoring the transmission characteristics of pulses.The main contents of this dissertation are organized as follows:In the first chapter,the development tendency of fibers communication and optical network is reviewed and summarized.The chirality-relevant concepts are introduced.The classification for different type of chirality,namely the dielectric one and the structural one is given.The corresponding materials are also differentiated.The general description of electromagnetic property of chiral materials is given by the constitutive relations.The significances of research on the chiral fiber and its derivative devices,especially nonlinear counterpart are emphasized.In the second chapter,the pulse propagation with self-phase modulation in a single nonlinear chiral fiber and its applications is investigated.From Maxwell's equations and Post's constitutive relations,a generalized chiral nonlinear Schr?dinger equations(CNLSEs)for single circularly polarized component is derived.The CNLSEs govern light transmission through a dispersive nonlinear chiral fiber,in which chirality plays unique roles in the evolution of pulse like optical soliton in the aspect of attenuation and nonlinearity.Simulations are based on split-step beam propagation method reveal the role of chirality in the pulse evolution.The application of nonlinear optical rotation is also discussed.Third chapter deals with the case when a single pulse with two opposite circularly polarized components say,the left-and right-handed circularly polarized(LCP and RCP)components,propagate in a single chiral fiber.Through the similar procedures to that in chapter two,we derive the generalized coupled chiral nonlinear Schr?dinger equations(CCNLSEs),which govern the evolution of the pulse with LCP and RCP components existing simultaneously.Simulations reveal the unique role of chirality in the formation of stable solitons with cooperation of GVD and nonlinearity.We have also investigated modulation instability(MI)in nonlinear chiral fiber.The differences in gain spectrum of the modulation instability for LCP and RCP components are analyzed.Finally,in Chapter four,the behaviors of the nonlinear chiral fiber couplers are investigated.Firstly,we established the generalized coupled chiral nonlinear Schr?dinger equations(CCNLSEs)for the couplers,which govern the interactions of different components from the two waveguides of the coupler.This set of equations include several coupling mechanisms contributed from self phase modulation(SPM),cross phase modulation(XPM)and chirality.Using the Runge-Kutta method,the linear behavior for low-power continuous wave(CW)and the characteristics of nonlinear switching for high-power CW in the couplers are explored.The interesting role of chirality in regulating the behavior of the different components in the coupler is demonstrated.We found that the chirality can provide an additional degree of freedom,which may find applications in design of such a kind of device used in optical communication and remote sensing.