通过调整结构参数, 优化设计了一种高非线性高双折射的光子晶体光纤(PCF)。该光纤的包层结构由大小不同的圆形空气孔按六边形排列, 纤芯中心沿着x轴引入两个椭圆空气孔。采用全矢量有限元法, 并以完美匹配层作为边界条件分析了该光纤结构的模场分布、有效折射率、有效面积、非线性系数及双折射特性, 并且分析了光纤结构参数对这些特性的影响。分析表明, 调节最内层纤芯周围的大空气孔和椭圆空气孔的大小可有效地控制非线性系数和双折射特性。数值分析显示: 适当地调节结构参数后, 该光纤在波长1.55 μm处的非线性系数最大值可达53.5 W-1·km-1 ; 双折射系数为1.092 9×10-2, 比传统光纤高两个数量级。该光纤在对于非线性和双折射需求高的通信系统中具有好的应用前景。

A new type of optimized Photonic Crystal Fiber(PCF) with high birefringence and high nonlinearity was proposed by adjusting its structure parameters. The cladding of the PCF was arrayed by circular air holes of different sizes in accordance with the hexagonal lattice and two ellipse air holes were guided to its fiber core centre along the x axis. By using the full vector finite element method with anisotropic perfectly matched layers, the mode field distribution, effective index, effective mode area, nonlinearity and birefringence and the fiber structure were investigated simultaneously and the effects of different optical parameters on the optical characteristics were analyzed. The analysis shows that the birefringence and nonlinearity properties can be controlled by adjusting the sizes of large air holes and ellipse air holes. The numerical results indicate that a better result can be obtained when the parameters of the PCF are adjusted appropriately.The maximum nonlinear coefficient of 53.5 W-1·km-1 and high birefringence of 1.092 9×10-2 are obtained at 1.55 μm, in which the birefringence is two orders of magnitude higher than that of the traditional optical fiber. The modified fiber has a wide application prospect in the communication system that needs high nonlinear and high birefringence.