Guan Chunying, Tian Fengjun, Dai Qiang, Yuan Libo
Photonics Research Center, College of Science, Harbin Engineering University, Harbin 150001, China.
Opt Express. 2011 Oct 10;19(21):20069-78. doi: 10.1364/OE.19.020069.
We propose a novel embedded-core hollow optical fiber composed of a central air hole, a semi-elliptical core, and an annular cladding. The fiber characteristics are investigated based on the finite element method (FEM), including mode properties, birefringence, confinement loss, evanescent field and bending loss. The results reveal that the embedded-core hollow optical fiber has a non-zero cut-off frequency for the fundamental mode. The birefringence of the hollow optical fiber is insensitive to the size of the central air hole and ultra-sensitive to the thickness of the cladding between the core and the air hole. Both thin cladding between the core and the air hole and small core ellipticity lead to high birefringence. An ultra-low birefringence fiber can be achieved by selecting a proper ellipticity of the core. The embedded-core hollow optical fiber holds a strong evanescent field due to special structure of thin cladding and therefore it is of importance for potential applications such as gas and biochemical sensors. The bending losses are measured experimentally. The bending loss strongly depends on bending orientations of the fiber. The proposed fiber can be used as polarization interference devices if the orientation angle of the fiber core is neither 0° nor 90°.
我们提出了一种新型的嵌入式芯空心光纤，它由一个中心气孔、一个半椭圆形纤芯和一个环形包层组成。基于有限元方法（FEM）对该光纤的特性进行了研究，包括模式特性、双折射、约束损耗、倏逝场和弯曲损耗。结果表明，嵌入式芯空心光纤的基模截止频率不为零。空心光纤的双折射对中心气孔的尺寸不敏感，而对纤芯与气孔之间包层的厚度极为敏感。纤芯与气孔之间的薄包层和小的纤芯椭圆率都会导致高双折射。通过选择合适的纤芯椭圆率可以实现超低双折射光纤。由于薄包层的特殊结构，嵌入式芯空心光纤具有很强的倏逝场，因此对于气体和生化传感器等潜在应用具有重要意义。对弯曲损耗进行了实验测量。弯曲损耗强烈依赖于光纤的弯曲方向。如果光纤芯的取向角既不是0°也不是90°，则所提出的光纤可用作偏振干涉器件。
