【作者】 张心贲；

【导师】 李进延；

【作者基本信息】 华中科技大学 ， 光电信息工程， 2013， 博士

【摘要】 可见光超连续谱具有良好的空间相干性和高亮度,在生物光子学等方面有重要的应用。而光子晶体光纤由于具备灵活的色散可控性以及可实现较高的非线性系数,是目前实现超连续谱的理想介质。本论文以掺镱光纤激光器为泵浦源从扩展短波长边界、提高转换效率到特殊模式输出三个主要方面研究了高非线性光子晶体光纤中的可见光超连续谱的产生。本论文首先介绍了光纤中的超连续谱所涉及的一些非线性效应,然后详细描述光纤中非线性过程的广义非线性薛定谔方程,并比较了频域形式相对于时域的优势。结合计算光纤特性的频域有限差分法,可以准确地模拟各种光纤中的非线性过程。在扩展短波长边界方面,提出一种增强长波长倏失波的微结构纤芯光子晶体光纤。在固定零色散波长在1gm附近时,2500nm的孤子群速度匹配的波长达到403nm,这比普通光子晶体光纤扩展了60nm。同时其非线性系数也提高3倍左右,非常有利于可见光超连续谱的产生。此外,也讨论光纤特性对纤芯纳米孔的依赖性。通过模拟计算,验证了所设计光纤在可见光超连续谱产生方面的优势。在提高可见光超连续谱的转换效率方面,系统地研究了纯石英光子晶体光纤到掺锗光子晶体光纤中的切伦科夫辐射。结果表明,在双零色散点光子晶体光纤的深反常色散区泵浦可以有效地产生短波长的色散波。以掺镱光纤激光器发出的100fs脉冲为泵浦源,在平均功率达到1.27W时,实验得到了大约40%的泵浦光到信号光的转换效率,带宽达到32nm,中心波长为410nm。多芯光纤由于模式的特殊性,在非线性光学中占有一席之地。本论文研究了两种特殊的多芯光子晶体光纤：类似同轴双芯光子晶体光纤和紧密的三芯掺锗光子晶体光纤。前者通过在内层纤芯泵浦可以得到外层纤芯输出的可见光超连续谱。由于群速度匹配的确实和相隔很近的双零色散波长,输出光谱形状可以很好地控制。而在三芯掺锗光子晶体光纤通过异相位模式的远场叠加得到中空光束超连续谱。简单地通过调节入射脉冲的偏振态,可以在同相位超模和中空光束超连续谱直接随意转换。在平均功率为1.04W的100fs激光脉冲泵浦下,得到540～1540nm的中空光束超连续谱,这在原子冷却和光摄等方面很好的应用潜能。更多还原

【Abstract】 The visible supercontinuum (SC), which is characteristic of good spatial coherence and high brightness, have (has) important applications in biophotonics, etc.. By exhibiting an enhanced effective nonlinearity and promoting parametric processes, photonic crystal fibers (PCFs) thus appear to be the ideal media for SC generation. In this thesis, we study the visible SC generation in the highly nonlinear PCF for expanding the blue edge, improving the conversion efficiency and the special mode output.(1) The nonlinear process that is involved in the SC generation is introduced. And the frequency domain generalized nonlinear Schrodinger equation is described in detail. Combining the frequency-domain finite difference method, a SC generation in PCF is given.(2) A PCF with nanosize air-holes (NAHs) in the solid core for the blue extension of SC generation is investigated. The basic concept of the design is to enhance the evanescent wave in the IR part of the SC. On the premise of fixing the zero dispersion wavelength around1μm, the group-velocity of the proposed fiber can match the infrared wavelength of2.5μm with short-wavelength of403nm, which is about60nm shorter than that of conventional high-△PCF. Simultaneously, the nonlinearity is enhanced about three times. The dependence of the PCF characteristics on the NAHs is also discussed. The simulated results confirm the possibility of increasing the blue-shift of the generated SC in the designed PCFs.(3) We demonstrate the generation of highly efficient Cherenkov radiation (CR) in the fundamental mode of a GeO2-doped two zero dispersion wavelengths (ZDWs) PCF. Using a high power femtosecond Yb-doped PCF laser emitting100fs pulses as the pump source, CR with an efficiency of>40%and a bandwidth of38nm at410nm is obtained in the visible-wavelength range when the average power of the pump light is1.27W. It is that injecting the pump light in deep anomalous dispersion regime contributes to such an efficient spectral-isolated CR. The mechanism during the formation of CR is discussed and the experimental results are in good agreement with the calculation.(4) Two special multi-core photonic crystal fiber are studied:the dual-concentric-core PCF and GeO2-doped triangular-core PCF. For the former, when pumping in the inner core and the visible SC is obtain in the outer core. Since the group velocity matching is absent, the spectra in short-wavelength side can be controlled by phase-matching and in long-wavelength side the spectra is determined by the second ZDW. As a result, the output spectrum shape can be well controlled. For the latter, a GeO2doped triangular-core PCF is designed and fabricated to allow the generation of a hollow beam through a nonlinear-optical transformation by femtosecond pulses at1040nm from a high power Yb-doped PCF laser oscillator. The hollow beam SC is obtained at far field by adjusting incident light polarization to excite the high order supermode, behaving as a mode convertor. The SC ranging from540to1540nm is achieved with an average pump power of1.04W.更多还原