Theoretical Design And Second-Order Nonlinear Effect Investigation Of Novel Photonic Crystal Fibers

As the most significant achievement of optical fiber technology in the past decade, photonic crystal fibers (PCFs) have been extensively studied due to their many unique properties. Nowadays, with the appearance of new methods for fabricating PCF, PCFs have been used generally in optical fiber communication, sensing, bio-medical and many other fields. Therefore, to design novel high-performonce PCFs is a continual challenge. For the purpose of solving some problem in the PCF design process, several new types of high-performance PCFs are proposed in this dissertation, and the transmission properties of these PCFs are numerically investigated in detail. The main contents are as follows:(1) The guided modes in the rectangular-lattice PCFs are investigated theoretically, and we label these guided modes in the same way as in rectangle dielectric waveguide. In addition, according to the minimum waveguide sectors and their appropriate boundary conditions, the guided modes in the proposed PCFs can be classified into four non-degenerate modal classes.(2) A new type of ultrahigh birefringent rectangular-lattic PCF with low confinement is proposed. The influences of fiber parameters on the modal birefringence and the confinement loss are studied in detail. The numerical results show that the modal birefringence in this proposed PCF can be up to5.62X10"2at the wavelength of1.55μm. Moreover, when the birefringence is as high as4X10-2, the confinement loss of χ-polarized mode is as small as0.005dB/km. Finally, the changes of the modal birefringence and the confinement loss of the PCF for the fluctuations of fiber parameters from the ideal conditions are investigated, and the results show that the proposed PCF is robust to fabrication imperfections.(3) Two new types of dispersion-flattened PCFs (DF-PCFs) with highly nonlinear and ultralow confinement loss are proposed. These new PCF structures adopt hybrid cladding. By optimizing these fiber structures, the ultra-flattened dispersion of0.931ps/(nm-km)(DF-PCF1) and1.553ps/(nm-km)(DF-PCF2) can be achieved in the wavelength range from1.3to1.6μm with confinement losses lower than0.001dB/km in the same wavelength range. Meanwhile, the nonlinear coefficients of our proposed PCFs are as high as23.833W-1km-1(DF-PCF1) and29.654W-1(DF-PCF2). Furthermore, the changes of the chromatic dispersion and the nonlinerity of the proposed DF-PCFs for the fluctuations of fiber parameters from the ideal conditions are investigated, and the results show that the proposed DF-PCFs is robust to fabrication imperfections.(4) A new type of highly nonlinear slotted square-lattice PCF is proposed. The nonlinearity and the dispersion features of the proposed PCF are numerically investigated. The numerical results show that, ultrahigh nonlinear coefficient of the order of104W-1km-1can be achieved at the wavelength of1.55μm in the proposed PCF. Moreover, zero dispersion at1.55μm can be achieved simply by modifying the fiber parameters.(5) A new type of highly nonlinear dispersion-flattened slotted spiral PCF is proposed. The nonlinear coefficients of quasi-TE mode and quasi-TM mode at1.55μm in our proposed PCF are both greater than220W-km-1by optimizing the fiber structure. Furthermore, ultra-flattened dispersion can be obtained over a150nm wavelength range. Finally, the influences of fiber parameters on the chromatic dispersion and the nonlinearity of the proposed PCF are investigated in detail.(6) An appropriately designed PCF that allows to satisty the phase-matched condition for second-harmonic generation is proposed. The phase matching condition for second-harmonic generation can be realized over a large wavelength range simply by modifying the air holes size and the lattic pitch. The numerical results show that the efficiency of second-harmonic generation in the poled PCF decreases with the wavelength increasing, and the effective phase-matched fiber length can be greatly lengtheded. In addition, the phase matching condition for sum-frequency generation can also be realized in our proposed PCF. The efficiency of sum-frequency generation at different wavelengths is discussed.