Study On The Dispersion Tailoring And Grating Resonances For All-Solid Photonic Bandgap Fibers

All-solid photonic bandgap fiber (PBGF) is one kind of micro-structured fibers and the light is guided through the fiber by use of the bandgap effect. Compared with air-core PBGF, all-solid PBGF has numerous benefits. For example, it could be fabricated more easily and thus it could be fabricated with a lot of novel and complicated fiber structure. Besides, Bragg gratings could be fabricated on it due to the existence of Ge-doped cladding rods. All these benefits would greatly broaden the application of PBGF. Consequently, it quickly becomes a hot research issue after its birth in University of Bath in 2004. In this dissertation, we propose a novel design to improve the dispersion characteristics of all-solid PBGF and discuss a method to design the dispersion of such fiber. Besides, the Bragg gratings are successfully fabricated on such fiber. The spectral characteristics and mode couplings are illustrated as well. The contents of the dissertation include the followings in detail:1. By use of full-vector finite element method (FEM) and plane wave expansion method (PWEM), we study the dispersion characteristics of all-solid PBGF. Besides, we propose an all-solid PBGF with novel cladding structure. We theoretically simulate the guiding characteristics, especially the waveguide dispersion and the confinement loss of the proposed fiber. The results demonstrate that the proposed fiber could simultaneously obtain large dispersion and low confinement loss, which improves the dispersion characteristics of all-solid PBGF.2. We design the dispersion of the all-solid PBGF by changing the cladding structure: we theoretically study how the two factors -number and place of the introduced defect rods- affect the waveguide group velocity dispersion (GVD) and the third order dispersion (TOD) of the fiber. The result demonstrates that we could adjust the two factors to change the waveguide GVD and the TOD. Consequently, we could design a fiber to obtain the large waveguide GVD with certain TOD by adjusting the two factors;3. FBGs inscribed in the cladding high-index rods of all-solid photonic bandgap fibers are first reported. Not only the guided mode resonance, but also supermode resonances are observed. We demonstrate that only those supermodes with certain phase relationships and symmetric mode field profiles are responsible for the supermode resonances. The dynamics of the FBG growth in this kind of fiber, including bandgap shift and the variations of the resonance peaks are described theoretically and experimentally. The bend response of the FBG is investigated, which is direction-dependant because of the asymmetric index modulation over the cladding rods.