高双折射太赫兹光子晶体光纤的设计和特性分析.docx

摘要
目前,在太赫兹通信、传感中,传导性能优良的保偏波导需进一步研究。光子晶体光纤灵活的设计和优良的导光特性,使其成为光波导设计的理想结构。为实现太赫兹波导的低损耗、高双折射等特性,本文探索将光子晶体光纤结构引入太赫兹波导的研究,提出一种太赫兹高双折射光子晶体光纤。由于光纤结构器件具有低插入损耗、性能优良的特性,设计了一种基于液芯光纤结构的温控太赫兹偏振控制器。
首先,本文在太赫兹频段设计了一种新型双包层结构的高双折射光子晶体光纤。其内包层由蜂窝状晶格结构的六个椭圆空气孔组成,外包层充斥圆形空气孔。经全矢量有限元法仿真,此结构光纤的双折射系数、限制损耗及色散特性被研究分析。在 600μm 到 900μm 波段间光纤的双折射系数可达 10-3,具有较低的限制损耗。仿真表明,内包层椭圆空气孔的结构设计是实现高双折射重要因素,而限制损耗改善依赖于外包层的设置。此双包层结构对于今后设计太赫兹高双折射光子晶体光纤具有一定借鉴价值。
其次,研究了一种液晶填充太赫兹光子晶体光纤的温度敏感特性。模拟了此液芯光子晶体光纤基模的传输特性。结果表明,温度的增加使得经参数优化的液芯光纤的双折射系数连续的由 ×10-3 上升至 ×10-3,限制损耗从 降低至 。而温度的变化量对液芯光纤的色散和传输模式的影响可忽略不计。在光纤长度为 30mm 时,此液芯双折射光纤对于 400μm 的太赫兹信号可实现 360o 的偏振控制。
关键词:太赫兹;光子晶体光纤;高双折射;液晶;偏振控制
Abstract
It is crucial to fabricate a polarization maintaining waveguide with better transmission properties for the munication and sensing system in recently. With its flexible structures and perfect transmission properties, the photonic crystal fiber (PCF) has been a kind of wonderful waveguide in the optical frequencies. In this thesis, the structure of PCF is used to design the terahertz waveguide in order to fulfill the terahertz waveguide’s low transmission loss and its high birefringence. A terahertz birefringent PCF is reported in the thesis. Since munication equipments constructed on PCF have much better property, such as the low insert loss, better performance, a terahertz polarization controller based on a PCF filled with liquid crystal is present.
Firstly, a new high birefringence photonic crystal fiber (PCF) is proposed within the terahertz frequency band in the thesis. It has two types of claddings, the inner posed of six ellipse air holes arranged in a b array and the outer surrounded by circle holes. By using the full vector finite element method, the birefringence, chromatic dispersion and confinement loss of the fundamental mode are evaluated. The PCF’s
birefringence can achieve 10-3 when the wavelength increases from 600μm to 900μm, and it
has a low confinement loss. It reveals that parameter