Study Of Yb-doped, Sub-Wavelenght Air-Core And New Nonlinear Photonic Crystal Fiber

Photonic crystal fiber exhibits many characteristics which the traditional optical fiber is difficult to achieve, such as large-mode-area single-mode, highly nonlinear, dispersion tunability, photonic bandgap, high birefringence, and thus attracted widespread attention, becoming a central issue of optics and photonics research in recent years. For its application requirements in fiber laser, optical communications, and fiber sensing areas, we design and fabrication a variety of new special photonic crystal fibers, including:large-mode-area single-mode ytterbium-doped photonic crystal fibers, subwavelength air core photonic crystal fibers, highly nonlinear photonic crystal fibers, three and four zero-dispersion wavelength photonic crystal fibers.1. The mode effective indices of the Yb3+-doped photonics crystal fiber with different propagation state are analyzed for the first time. The single-mode propagation condition is presented. The mode effective indices of large-core Yb-doped photonic crystal fiber with different indices of fiber core and structure parameters are simulated by finite-element method and effective index method respectively. For single-mode fiber, the relation of the index of fiber core with the fiber structure parameters of pitch, hole-to-pitch ratio, diameter of core is obtained. The large-core single-mode Yb-doped photonic crystal fiber with a core diameter of50μm,100μm, and150μm is designed. For the design and fabrication of the rare-earth-doped photonic crystal fiber, we can adjust the index of fiber core and the fiber structure parameters to achieve large-mode-area and single-mode propagation. These provide a theory base for the design and fabrication of the fiber.2. A new method for fabrication of Yb3+-doped photonic crystal fiber is presented. Using the solution doping technique, SiO2, YiCl3, AlCl3, K2CO3are mixed in water. After evaporation and dying, well-mixed material is obtained. High concentration Yb3+-doped quartz glass is fabricated by high-temperature melting over2000℃. The control process and the temperature field distribution in the fabrication of photonic crystal fiber are studied. The fiber perform is fabricated using the Yb3+-doped quartz glass as the core of fiber. The fiber perform is draw to large core diameter Yb3+-doped photonic crystal fiber. The spectrum properties of the Yb3+-doped photonic crystal fiber are measured. Good absorption and fluorescence spectra are obtained. A new idea for fabrication of the rare-earth-doped fiber perform is proposed.3. A new hollow-core photonic crystal fiber with a subwavelength air hole in the core is proposed. The relation of mode field distributions, confinement loss and dispersion characteristics with fiber structure parameters and wavelengths is analyzed by finite-element method. The principle of guiding light in air hole is explained by diffraction and the characteristics of photonic crystal fiber. For the fiber with low loss, single-mode, tightly confined light in the air core, the ranges of structure parameters and wavelengths are obtained. An optimizational fiber structure parameters is designed, the mode of which is tightly confined in the air core, and the confinement loss α=5.9×10-5dB/km. According to the fiber structure parameters designed, PCF with a small air core is fabricated. The high intensity in an air hole, coupled with long interaction lengths, promises a new class of experiments in light-matter interaction and nonlinear fiber optics.4. Solving nonlinear Schrodinger equation by split-step Fourier method, for different pulse and PCF structural parameters, time-domain and frequency-domain variation of femtosecond laser pulses in optical fiber are obtained.The optical properties of photonic crystal fiber cladding knot are analyzed. It is contrasted the mode area, nonlinear coefficient and dispersion characteristics of the core and cladding knot. Cladding knot of photonic crystal fiber has small core and highly nonlinear characteristics. Phase-matching features are analyzed for dispersive wave generation. Variation rules of the center wavelength of the dispersive wave with the pump power and wavelength is achieved. The photonic crystal fiber designed is fabricated. The visible and infrared broadband dispersive waves above300nm are obtained in experiment. Theoretical and experimental results are completely consistent. These provide a new theoretical basis for supercontinuum broadband light source and wavelength conversion.5. The phase-mismatch characteristics of fibers with multiple zero-dispersion wavelengths are analyzed for the first time. The variation of phase-matching wavelength with the pump wavelength and the pump power is obtained. Phase matching curve is shown. The characteristics of phase-matching wavelength for different dispersion curves are analyzed. Single mode fibers with three zero-dispersion wavelengths are obtained by the design of fiber structure parameters. The dispersion characteristics of photonic crystal fibers with a small air hole in the core are analyzed. Fibers with four zero-dispersion wavelengths are designed. Closing to zero and flattened dispersion can be obtained in the fibers with multiple zero-dispersion wavelengths. The presence of multiple zero-dispersion wavelengths creates a rich phase-matching topology, which appear more four-wave mixing wavelengths, enabling enhanced control over the spectral locations of the four-wave-mixing and resonant-radiation bands emitted by solitons and short pulses.