高性能反谐振空芯光纤导光机理与实验制作研究进展

传统实芯光纤无法克服材料本身固有的非线性、色散、瑞利散射、光照损伤等缺陷,微结构空芯光纤有望解决这些本征性问题,可以为高功率激光、非线性光学、生物光子学、量子光学、光纤传感、光通信等应用提供一个理想而方便的媒介.在技术实现的道路上存在着光子禁带空芯光纤和反谐振空芯光纤两种选项.后者具有宽带导光和高激光损伤阈值等优点,但是一直受困于较高的传输损耗.这一情况随着最近几年人们对反谐振导光机理和光纤制作技术研究的快速推进正在逐渐发生转变.本文回顾了我们团队五年来开展的系统性的理论和实验工作,介绍了一套直观的可定量计算的反谐振导光机制理论,展示了最新研制的高性能光纤.通过合理利用光纤结构中的局域性和全局性特征,突破了半解析计算反谐振空芯光纤限制损耗的难题;通过对光纤拉制条件的精密控制,制作出了紫外到中红外波段的各型光纤;并对进一步提高光纤性能和在此基础上的更丰富的光学应用研究进行了展望.

Theoretical and experimental investigation of light guidance in hollow-core anti-resonant fiber

The inherent material imperfections of solid core optical fiber, for example, Kerr nonlinearity, chromatic dispersion, Rayleigh scattering and photodarkening, set fundamental limitations for further improving the performances of fiber-based systems. Hollow-core fiber (HCF) allows the light to be guided in an air core with many unprecedented characteristics, overcoming almost all the shortcomings arising from bulk material. The exploitation of HCF could revolutionize the research fields ranging from ultra-intense pulse delivery, single-cycle pulse generation, nonlinear optics, low latency optical communication, UV light sources, mid-IR gas lasers to biochemical sensing, quantum optics and mid-IR to Terahertz waveguides. Therefore, the investigations into the guidance mechanism and the ultimate limit of HCF have become a hot research topic. In the past two decades, scientists and engineers have fabricated two types of high-performance HCFs with loss figures of 1.7 dB/km and 7.7 dB/km for hollow-core photonic bandgap fiber (HC-PBGF) and hollow-core anti-resonant fiber (HC-ARF) respectively. In comparison with the twenty-years-old HC-PBGF technology, the HC-ARF that recently appeared outperforms the former in terms of broadband transmission and high laser damage threshold together with a quickly-improved loss figure, providing an ideal platform for many more challenging applications. While the guidance mechanism and fabrication technique in HC-PBGF have been well recognized, the HC-ARF still has a lot of room for improvement. At the birth of the first generation of broadband HC-ARF, the guidance mechanism was unclear, the fiber design was far from perfect, the fabrication was immature, and the optical properties were not optimized. In the past five years, we have developed an intuitive and semi-analytical model for the confinement loss of HC-ARF and managed to fabricate high-performance nodeless HC-ARF. We further employ our theoretical model and fabrication technique to well control and design other interesting properties, such as polarization maintenance and bending loss in HC-ARF. For a long time, the anti-resonant theory of light guidance has been regarded as being qualitative, and the leaky-mode-based HC-ARF have been considered to have worse performances than the guided-mode-based HC-PBGF. Our investigations in theory and experiment negative these prejudices, thus paving the way for the booming development of HC-ARF technologies in the near future.