| The current dissertation proposes several photonic crystal fibers with hexagonal lattice, rectangular lattice and symmetrical dual-core rectangular lattice structures. Employing with these special structures, some novel functions such as dispersion compensation, supercontinuum generation and polarization splitter have been realized. Their optical characteristics are also simulated by various numerical methods. The main contents are listed as follows:(1) Hexagonal lattice photonic crystal fiber:a novel hexagonal honeycomb lattice photonic crystal fiber is proposed, which is composed of a central defect core, a cladding with elliptical air-hole and small round air-holes. Based on the full-vector finite element method with anisotropic perfectly matched layers, its birefringence, dispersion, nonlinearity, leakage loss and mode field are numerically investigated. The wavelength for high negative dispersion value can be adjusted by artificially choosing the parameters (Δ,η, f and d1) of proposed fiber. Numerical results indicate that the proposed fiber shows high birefringence and negative dispersion effect. The birefringence is1.02×10-2, both its dispersion and dispersion slope are negative, the dispersion slope values are between-0.132～-0.121ps·km-1·nm-2over C band, the nonlinear coefficient is45.7W-1·km-1at1.55μm, if the parameter is selected as Δ=1.15μm,77=0.5,f=0.48and d1=0.4μm. We compare hexagonal honeyco-mb lattice photonic crystal fiber and hexagonal elliptical lattice photonic crystal fiber, both of which have the same structure parameters. It is found that the hexagonal honeycomb lattice photonic crystal fiber easily obtains high birefringence, large negative dispersion and low nonlinear coefficient. It is demonstrated that the hexagonal honeycomb lattice photonic crystal fiber has huge potential in designing dispersion compensation photonic crystal fiber.(2) Rectangular lattice photonic crystal fiber:We proposed a new structure of highly nonlinear low-dispersion photonic crystal fiber with high birefringence. Its dispersion and nonlinear coefficient are investigated simultaneously by using the full-vector finite element method with anisotropic perfectly matched layers. Numerical results show that the dispersion variation is within0±0.7ps·km-1·nm-1in the C band, and the corresponding nonlinear coefficient, birefringence and leakage loss are about60.5W-1·km-1,4.92×10-3and0.27625dB/km at1.55μm, respectively. (3) Symmetrical dual-core rectangular lattice photonic crystal fibers:a kind of rectangular lattice symmetrical dual-core photonic crystal fibers has been proposed in this part. Based on the full-vector plane wave method and beam propagation method, its birefringence, dispersion and coupling length are numerically investigated. The photonic crystal fiber has high level of birefringence, as both dispersion and dispersion slope are negative. The dispersion slope values are between-0.088～-0.099ps·km-1·nm-2in the C band, if the parameter is selected as A=2.0μm and f=0.4. Correspondingly, dual-core coupling length for x-polarized and y-polarized modes are0.09225mm and0.08134mm, respectively.(4) Application:a novel hexagonal honeycomb lattice photonic crystal fiber shows negative dispersion and negative dispersion slope, so negative dispersion and negative dispersion slope is best suited for broadband dispersion compensation. Based on consideration of dispersion compensation, the novel hexagonal honeycomb lattice photonic crystal fiber can better compensate STM-28TM, as the κ value of the novel hexagonal honeycomb lattice photonic crystal fiber and STM-28TM is closer. Meanwhile, high level of birefringence in PCFs is widely applied in polarization controller, high precision optics and optical communications systems.Supercontinuum generation in a highly nonlinear dispersion-flattened photonic crystal fiber is investigated numerically. The influences of the peak power, the length of photonic crystal fiber, pulse shape and the initial pulse chirp on supercontinuum are discussed in detail by the split-step Fourier method.We propose a novel kind of polarization splitter in rectangular lattice symmetrical dual-core photonic crystal fibers. Based on mode coupling theory, the0.7322mm long splitter is proposed to achieve extinction ratio better than-10dB and a bandwidth of15.6nm. |
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