| In this thesis, The characteristics and applications of fiber-optic parametric process are summarized firstly by analyzing the development and the trend of the fiber amplifiers. The challenges which fiber-optic parametric process faces are also pointed out. With the development of high-power pump and new-style fibers, fiber-optic parametric process has attained renewed interest and a new platform is provided for investigating different aspects related to linear, nonlinear and ultrafast fiber optics. So the effects of ultrafast FWM in a fiber are studied, and the technique schemes are promoted for widely tunable fiber-optic parametric amplifiers (FOPAs) and fiber-optic parametric oscillators (FOPAs). Some issues of beam combining are also studied in the last part of the thesis.Our work in the thesis includes the following parts:1. The nonlinear coupled-amplitude equations are applied and the split step Fourier method is used to build a perfect mathematics model. The effects of ultrafast four-wave mixing (FWM) in a fiber are analyzed. For the transmission of ultrashort pulses, the contributions of self-phase modulation, cross-phase modulation, FWM, temporal walk-off, group-velocity dispersion and third-order dispersion make it complicated in the process of pulse transmission. In this research, according to the size of the effects, the nonlinear process is discussed in two steps to discuss the effects of the temporal walk-off, GVD and TOD on FWM respectively. A platform is built for the following reserschs of fiber optical parametric amplifiers (FOPAs) and fiber-optical parametric oscillators (FOPAs).2. Phase-matching features in the FWM process and gain spectra of both the single-pump and double-pump FOPAs are analyzed in detail. The effects of high-order dispersions on the phase-match are researched by the use of newly developed photonic crystal fibers (PCFs), which exhibit flexibility in enhanced nonlinearity and engineerable dispersion. Different performances of FO15As are found in two distinct working regimes (the normal and anomalous dispersion regimes). So an approach is made to build a widely tunable FOPA with flat gain spectrum. Impacts of higher-order dispersions and temporal walk-off on the gain spectra are also discussed.3. The modulation instability (MI) is studied in a fiber. Phase-matching condition of four-wave mixing is analyzed by use of higher-order dispersion in PCFs. It is found that MI occurs not only in the anomalous-dispersion regime but also in the normal-dispersion regime of a fiber. A balance among the different orders of fiber dispersion can support a widely tuning modulation instability gain for pumping wavelength in the normal dispersion regime. An approach is made to build a widely tunable FOPO by use of PCFs as the gain medium, Results of numerical simulations are alse gived.4. Some issues of beam combining are researched, which are independent of the above parts.The development of high-power fiber lasers is studied. Two approaches including coherent and incoherent beam combining of fiber array are compared in detail. A theoretical model is built to analyze the effects of parameters of a fiber array on the far-field distribution. The effects of phase errors and space errors on the beam quality (M2 factor) are also studied. Results indicate that the element numbers should be increased to achieve high power and the space between adjacent elements should be reduced to maintain a good beam quality, which is basically the same for both coherent and incoherent beam combining.The research work has produced 9 papers and were published in Optics Communications, J. Opt. A: Pure Appl. Opt., Optics & Laser Technology etc. respectively.
|
PDF Full Text Request