Research On Theoretical Model, Structural Designing And Fabricating Technique For Photonic Crystal Fibers

Since the first convincing photonic crystal fiber (PCF) was emerged from the fiber drawing tower in 1996, this new kind of fiber had been attracted a wide spread attention from academic circle of the world. Due to possessing many unique properties compared with traditional fibers, PCF has greatly application potential in the field of optical communication, optical sensing and optical information processing. Recent years, some great breakthroughs have been obtained in the theoretical research of PCF, and many new kinds of novel structure and potential application have been proposed and proved. Moreover, the fabricating technique of PCF has been great improved in some advanced laboratories. However, we have to recognize that so many technical challenges still remain in the practical application of this new kind of fiber. And most important one in our opinion is how to realize a steady, universal and low cost fabrication method, in addition, developing some splicing and testing equipments that are feasible for PCF's field application are absolutely necessary work.This dissertation is supported by the National High Technology Research and Development Programs of China "Novel special fibers" and by National Nature Science Fund "Dispersion compensation photonic crystal fiber". It mainly focuses on three aspects: the theoretical model for analyzing PCF, structural designing of polarization maintaining PCF and dispersion compensation PCF, and fabricating and splicing technique for PCF. The main achievements of the dissertation are listed as follows:1. Based on multi-layer waveguide theory, a simple model for approximate bandgap structure calculation for a special structure of all-solid photonic bandgap fiber is proposed. Its accuracy is proved by comparing its results with the results from the accurate full-vector plane-wave method. The most advantages of the proposed model are high efficiency and less memory consuming.2. Based on the photo of the fiber's cross section, we reconstruct the fabricated PCF's structure and introduce into the FEM software using our image recognition algorithms. And then, analyze the characteristics of the fiber structure using the FEM tools. This method improves the accuracy of forecasting the transmission properties of the fabricated PCF, and offers some necessary basis for feedback of controlling parameters when drawing the PCFs.3. For the PCFs with non-uniformly holes, the normal method for judging mode cutoff based on fundamental space-filling mode is no longer applicable. Aiming at this issue, we deeply study a method for judging mode cutoff by analysis on the break phenomena of the mode field radius during the increasing of wavelength, and prove the accuracy of this method by comparative analysis.4 Two new structure of polarization maintaining index-guiding PCF are proposed, and they are based asymmetry of cladding region's structure and core region's structure, respectively. Then, a new structure of polarization maintaining PBG-guiding PCF is proposed. It not only has as high birefringence as the order of 10^-3, but also has two single-polarization single-mode ranges at varying normalized wavelength.5. The effect of the structural parameters on the dispersion in a kind of dispersion compensation PCF structure which consists of a Germanium doped inner core and pure silica outer core is analyzed in detail. Based on this results, two dispersion compensation PCF structure are designed, which are aim at the applications of WDM system and single-wavelength optical transmission system, respectively. Moreover, we fabricate these two kinds of PCF structure, and achieve success in fiber's structural integrity. In addition, we also propose another feasible design of dispersion compensation PCF with large mode field area. This structure employs a ring of Fluorin-doped rods as outer ring core and pure silica as inner core. Due to pure silica inner core, this kind of PCF can avoid bringing additional loss or increasing the nonlinear effect, and the ability of antinuclear radiation is improved.6. The fabricating process of PCF is investigated and the key technique is achieved. The method of gas-filling in fiber drawing process is realized. And based on this method, many kinds of normal hexagonal PCFs, polarization maintaining PCFs and dispersion compensation PCFs are fabricated successfully. We also find out a series of optimal splicing parameters for splicing between PCF and SMF or two PCFs using a conventional fusion splicer. Under these splicing parameters, PCFs can be spliced with relative low loss and without holes collapse.