隔行分层填充的太赫兹超高双折射多孔光纤

本文提出了一种对普通三角晶格多孔光纤隔行分层填充匹配材料, 实现超高模式双折射的方法. 首先, 采用全矢量有限元法对多孔度为43.08%的三角晶格多孔光纤的传输特性进行了详细研究. 随后, 为增强结构非对称性对纤芯空气孔隔行填充折射率为1.4的液体, 发现光纤的模式双折射显著提高, 在峰值处(1.1 THz)由填充前的1.05×10^-3增大到1.36×10^-2; x, y两偏振模式基模的吸收损耗系数分别由0.16 dB/cm增大到0.25 dB/cm和0.28 dB/cm; 光纤的工作带宽由1.1 THz增大到1.9 THz. 研究发现通过增大填充材料的折射率能够显著提高光纤的模式双折射; 当n=2, f=2.2 THz时, 光纤能够达到8.03×10^-2的超高模式双折射. 进一步, 采用隔行分层填充的方式, 在不同层填充不同折射率的液体, 实现折射率的梯度分布, 从而增强光纤对导模的限制能力. 结果显示, 采用该填充方法, 光纤的模式双折射在工作频段内没有峰值, 呈现单调递增的趋势. 当f=2.2 THz时, 模式双折射达到7.19×10^-2. 该设计不仅实现了超高的模式双折射, 同时还具备可调谐的特性, 对实际应用具有重要意义.

Ultrahigh birefringence terahertz porous fibers based on interlacing layered infiltration method

In this paper, an interlacing layered infiltration method is proposed, using some liquid material as the common porous fiber with triangular air-hole array in the core region, which can achieve the characteristic of ultrahigh modal birefringence in this circumstance. Förstly, the basic properties of the porous fiber with a porosity of 43.08% are thoroughly analyzed by using a full-vector finite element method, as wellas the dispersion curves of the fiber, modal birefringence, fraction of the fundamental modal power for x and y polarizations, loss characteristics, etc. Secondly, to enhance the asymmetry of the proposed structure, some liquid material with a refractive index of 1.4 is infiltrated into the air holes in the fiber core region, by using interlacing filling method. It is found that the modal birefringence of the fiber dramatically increases. At an operation frequency of 1.1 THz, the peak value of modal birefringence rises from 1.05×10^-3 to 1.36×10^-2 after the infiltration operation. The fundamental model effective material absorption loss coefficients for x and y polarization modes increase from 0.16 dB/cm to 0.25 dB/cm and 0.28 dB/cm, respectively. And the operation frequency band increases from 1.1 to 1.9 THz. Simulation results indicate that the modal birefringence of the fiber can be remarkably improved by increasing the refractive index of the infiltrated liquid material. With an operation frequency of 2.2 THz and a refractive index of 2, this fiber can realize an ultrahigh modal birefringence of 8.03×10^-2. Moreover, to achieve the gradient distribution of the refractive index, an interlacing layered infiltration method to infiltrate the liquid material with different refractive indices in different layers is employed. Results show that the confinement capability to the guided modes has been greatly enhanced. Results also show that the peak value of the modal birefringence for the fundamental modes does not exist in the operation band. It represents a monotonically increasing trend. At an operation frequency of 2.2 THz, the fiber modal birefringence can reach as high as 7.19×10^-2. This scheme presents an ultrahigh modal birefringence, and it presents the tunable characteristic as well. This study may be of significance in the practical applications in the field of THz functional devices.