Analysis And Solving Of Modes In Bragg Fiber

Thank to the unique structure of one-dimensional photonic crystal in the cladding and the mechanism of optical guidance with wide spectra and wide angular direction, Bragg fiber becomes the hotspot in research and innovation of the next-generation microstructured bandgap fibers. Based on the light guidance with wide-spectral and wide-or omni-directional bandgap guidance, the modal cutoff inside the bandgap, and the interaction between the core-guiding mode and the defect-guiding mode, a few key problems in the physical functional devices based on Bragg fibers are investigated theoretically. Main work as follows:1. As for new-type fiber structures with high index contrast, coupled equations of transverse field, electric or magnetic field, can be acquired by taking full vector model into consideration. At discontinuities of dielectric index, rigorous boundary conditions are applied. With these results, a complex mode solver based on one-dimension full vector finite difference method can thus be developed, using PML as a numeric absorbing boundary. Then the solver is applied into solving and analyzing modes of three optical fibers with high index contrast. As for Bragg fiber, by utilizing photonic band gap diagram of its cladding, its unique light-guiding mechanism is analyzed. And then modes are also rationally categorized.2. The influences of modal cutoff inside the bandgap on the optical transmission in the fiber are analyzed theoretically, the conditions to realize single fundamental mode (HE11) transmission are founded; with analysis of relation between transmission bandwidth and fiber parameters, the design principles of Bragg fiber for broadband single fundamental mode transmission are proposed, and a wide bandwidth around 1550 nm is achieved;...