Theoretical and Experimental Study on Optical Devices Using Highly Nonlinear Photonic Crystal Fibers

光子晶体光纤（PCF）中的强波导色散特性为非线性光学提供了独特的机会，其零色散波长远低于二氧化硅材料色散所设定的~1.3μ m的极限。通过调整空气孔直径、间距和空气孔环的数量，强波导色散原则上可以用于将零色散波长很好地扩展到可见光中，尽管在某种程度上以多模操作为代价。我们开发了一个基于全矢量有限元法的分析软件，并详细研究了零色散波长，截止波长，和泄漏损耗的参数空间中的孔径，间距，和空气孔的环数跨越的相互作用。作为一个特定的结果，我们确定了孔直径和间距的值，这有助于最短的零色散波长，而光纤仍然是单模的较长的波长。此外，将遗传算法与全矢量有限元法相结合，对色散补偿PCF（DCPCF）拉曼放大器的结构参数进行了优化。优化后的DCPCF具有负色散系数和负色散斜率，并具有增益平坦的拉曼特性，可在C波段或S波段进行宽带色散补偿。此外，测量了有和没有最小允许弯曲半径的孔辅助光纤的拉曼增益效率和色散。理论计算结果与实验结果吻合较好。

The strong waveguide dispersion in photonic crystal fibers (PCFs) provides unique opportunities for nonlinear optics with a zero-dispersion wavelength far below the limit of~1.3μ m set by the material dispersion of silica. By tuning the air hole diameter, the pitch, and the number of rings of air holes, the strong waveguide dispersion can in principle be used to extend the zero-dispersion wavelength well into the visible, albeit to some extent at the cost of multi-mode operation. We developed an analysis software based on a full-vectorial finite element method and studied in detail the interplay of the zero-dispersion wavelength, the cutoff wavelength, and the leakage loss in the parameter space spanned by the hole diameter, the pitch, and the number of rings of air holes. As a particular result, we identified the values of hole diameter and pitch which facilitate the shortest possible zero-dispersion wavelength, while the fiber is still single-mode for longer wavelengths. In addition, the genetic algorithm integrated with the full-vectorial finite element method was used to optimize the structural parameters of dispersion compensating PCF (DCPCF) Raman amplifiers. The optimized DCPCF provided negative dispersion coefficient, negative dispersion slope, and broadband dispersion compensation over C-band or S-band with gain-flattened Raman characteristics. Furthermore, the Raman gain efficiency and chromatic dispersion of a hole-assisted fiber with and without minimum allowable bending radius were measured. Numerical predictions from the theory were shown to be in good agreement with the experimental results.