多孔芯光子晶体光纤及其偏振特性

强激光与气体的长距离相互作用能产生许多新奇的物理效应，而自由空间光束的自聚焦、衍射、散射等问题限制了该科技领域的发展。本文提出了一种新型多孔芯光子晶体光纤，纤芯亚波长、低折射率空气孔可以传光，具有宽带、低损耗、单模传输特性。利用倏逝波耦合效应，研究了纤芯亚波长空气孔束缚光的原理。根据光波传输的电磁场理论，分析了低折射率空气孔中的光强增大效应。强光在空气孔中长距离传输，为光与物质的相互作用提供了新条件，可以用于气体传感、非线性光学、高集成光子技术、原子操控等。由于纤芯空气孔可以传光，改变空气孔的大小，直接影响模场分布，进而可以获得很高的结构双折射。通过光纤结构参数的合理设计，分别获得了B=4×10^-2的高双折射、纤芯直径5 μm的大模场高双折射、大模面积单偏振单模特性，在光纤偏振器、光纤滤波器、光开关及光纤传感等领域有广泛的应用前景，为新型光场调控提供了新方法。

Polarization Properties of Multi-hole Core Photonic Crystal Fiber

Gases can provide many interesting features as media for laser based application. However, the experiments in free space are intrinsically awkward because of the unavoidable diffraction and self-focusing effects at high laser power, which can lead the light to spread out and its intensity to fall as it propagates. We demonstrate a new type of porous core photonic crystal fiber for confining and guiding light in low-refractive-index and subwavelength air holes in the core. The broadband, single mode and low loss guiding properties of the fibers are studied. The propagation mechanism in low-refractive-index and subwavelength-diameter holes is analyzed by electromagnetic theory of optical waveguide transmission and evanescent wave coupling. Tightly confined light in holes, combined with long interaction lengths, provides new conditions for the interaction between light and matter, and enable a variety of applications including gas sensing, nonlinear light management, highly integrated photonics technology, atomic manipulation, etc. Because the holes of core can guide light, the mode field distribution is affected directly by changing the size of the air holes, and the high birefringence property can be obtained. By careful designing of structure parameters of the fibers, high birefringence of B=4×10^-2, high birefringence in 5 μm-diameter core, characteristics of large-mode-area, single-polarization and single-mode are obtained. These fibers have wide application prospect in fiber polarizer, filter, optical switch and fiber sensing fields. New methods are provided for the light field regulation.