Structure Designof High Power Photonic Crystal Fiberand Preparation Of Er³⁺/Yb³⁺ Doped Core Materials

With the development of optical fiber communication network to the high speed, large capacity, the original fiber technology already can not adapt to the demand. In recent years, the emergence of photonic crystal fiber, especially rare earth dopeddouble clad structure has so many perfect performances, such as: ultra broadband transmission integrated optics, ultrashort pulse laser, miniature optical sensor, new type fiber amplifier that provide a good technical conditions to solve the above problems, which has been become a hot spotin the field of optical communicate technology and highperformance lasers. To total reflection photonic crystal fiber, the structure parameters and core material performanceshave an importantinfluence on mode field area, outputpower, dispersion, nonlinear and optical loss. Advanced researches has obtained progress in respect of these performances. For example, the mode field area has reached 2000³000 mm2and the output power has reached 2.5kw.In the study of photonic crystal optical fiber core materials, in addition to traditional quartz materials, rare earth doped laser materials have been applied widely. There is also insufficient about how to improve mode field area and output power of single mode fiber, broaden the core material selected range of photonic crystal fiber. For instance, how to effectively solve the contradictions of the mode field area and the output power has become a problem demanding prompt solution under the condition of guarantee of single-mode laser transmission.The influence laws of structure parameters on the performances of the total reflection double clad photonic crystal fiber are summarized;The structure of inner and outer clad layers are designed; The mode field performances of different new structures fiber are simulated and numerical analyzed via finite element method; According to the performance requirements of high output power and large mode field area of photonic crystal fiber, new cladding structures of photonic crystal fiber with a large core diameter and high power are designed and the relationships between numerical aperture and structure parameters has been studied; Two kinds of rare earth doped photonic crystal optical fiber core and cladding materials are prepared and their performances including physical and spectral are tested. The analysis results show that they are suitable for the photonic crystal fiber with high power and large mode field, which expands the selected range of fiber laser materials; The technological conditions and parameters to prepare photonic crystal fiber are discussed and perfect drawing processes are provided.1. The performance numerical analysis theories of photonic crystal fiber are compared and the main influencefactors on properties, such as: single-mode, mode field area, output power are analyzed.Thestructure characteristics and design principles have been studied for high power and large mode field fiber and 18 kinds of new structures are designed with inner cladding duty ratio of 0.2, 0.25 and 0.4, outercladof double rows of air holes, in which the fiber core are Yb³⁺ doped silicate and Er³⁺/Yb³⁺co-doped phosphate laser materials, respectively.2. The performances of different structure fibers are analyzed and simulated via Comsol software that is a secondary developed simulation way of finite element method and the beneficial experiences are gained. The structure of octagonal inner clad and inner core losing 29 air holes has better properties, of which the mode field area are 2444.21 5644.97mm2. Both output power and effectivemode field area of photonic crystal fiber performances with rare earth doped phosphate core are better than those of silicate.3. The structure of inner clad core losing 13 air holes, air hole diameter of 5 mm, hole spacing of（16）（15） mm, outer clad of double rows of air holes, air hole diameter of 7 mm and 8 mm, hole spacing of（16）（23） mm is designed. The maximum output power is 1.251×1016 W/m2, the effective diameter is 8.6mm, effective mode field area is 232.2mm2; The structure of inner clad core losing 29 air holes, outer clad of single row of air holes is designed. Theeffective diameter is 38.9mm, effective mode field area is 1187.8 mm2, the maximum output power is 4.964×1015W/m2. These results provide the beneficial experience for design and simulation of large mode field, high power, low lossphotonic crystal fiber.4. Yb³⁺ doped silicate and Er³⁺/Yb³⁺co-doped phosphate laser materials are designed and prepared. Thecomponents functions in formal are analyzed and reasonable optimize matches are made, which makesthem more suitable as photonic crystal optical fiber core materials. In terms of prepare process and conditions, new attempts are adopted and good new fiber core materialsis prepared successfully.5. The properties are tested and analyzed via J-O theoretical. The refractive index of Ytterbium doped silicate core material is 1.5762 and the fluorescence lifetime is 1.30 ms, which can be suitable for the laser pump sources of many wavelengths and has high absorption and conversion efficiency; During the prepare process of Erbium/Ytterbium co-doped phosphate laser materials, an improved method is put forward, combing shortened preheat time, controlling meltconstant temperature with increasing mix process. The refractive index of core material is 1.5621, the gain quality factor reaches ahigh level of 79.58（10-21cm2×ms）.6. Octagonal photonic crystal fibers are prepared via accumulation method.The process conditions are analyzed and determined via fluid mechanics theory and mathematical method, which has reference value in aspect ofpreparation photonic crystal fiber with excellent performances successfully.