偏孔光纤偏振器及其特性研究

By combining the special structured optical fiber technology and the ultra-wide bandwidth polarization effect of the graphene, we develop a broadband fiber graphene polarizer based on a side-hollow fiber. By introducing a relative big air hole in the cladding near the core, we can get a strong evanescent wave at the interface between the fiber core and the air, which can solve the problems in traditional fiber polarizers that part of cladding have to be removed by side-polished method to get strong evanescent wave. If a graphene layer is fabricated on the surface of the air hole, a graphene polarizer with broad working band can be obtained owing to the different transmission loss between the two polarization modes that transmitting along the graphene. Comparing to the traditional fiber polarizers based on metal film or dielectric film which only support a unique polarization mode and has a strict demand on the thickness of the film, the output polarization modes of the graphene fiber polarizer can be tuned by applying electric or magnetic field or doping some materials in the graphene. In addition, there is not a strict demand on the thickness of the graphene film for the graphene polarizer. The most important characteristic is that the bandwidth of the graphene polarizer can cover from visible to the near infrared light. The proposed broadband graphene fiber polarizer in the project has an important scientific significance and application value for the development of optical polarizer with ultra-wide bandwidth and the miniaturization of optical devices.

本项目将特种结构光纤技术与石墨烯对电磁波的超宽带宽的极化效应相结合，发展一种基于偏孔光纤的超宽带宽石墨烯光纤偏振器。通过在光纤包层靠近纤芯的位置引入一个较大的空气孔，使纤芯与空气孔的界面处具有强的倏逝场，解决了传统光纤偏振器需要对光纤进行侧面抛磨才能获得较强倏逝场的问题。将石墨烯薄层制作于空气孔内壁，利用不同偏振模式在石墨烯中的传输损耗不同这一特性，构建宽带宽石墨烯偏振器。相对于传统基于金属膜或介质膜的光纤偏振器只能有一个偏振态输出、对金属膜或介质膜厚度要求严格、工作带宽窄的特性，石墨烯光纤偏振器可以通过外加电场、磁场或掺杂改变石墨烯的化学势，进而可以选择石墨烯偏振器的输出为TE模或TM模，而且对于石墨烯膜的厚度要求不严格，更重要的是可以实现从可见光到近红外波段的超宽谱偏振调制。本项目的研究工作对于发展超宽带宽的光纤偏振器件和光学器件的微小型化具有重要的科学意义和实用价值。

光学偏振器在光纤通信和光纤传感系统中具有重要作用，尤其是相干光通信、量子光通信和光纤陀螺的重要组成部分，它可以有效地避免光学系统的信号衰落和误差。传统的偏振器件体积都比较大，而且工作带宽有限，稳定性差，无法满足光纤通信和传感技术领域对于光学偏振器小型化、集成化的要求和日益增加的工作带宽的需求。而近年来发展的基于倏逝场的全光纤偏振器，虽然具有结构紧凑、损耗低、稳定性好等优点，但是由于这种金属包层型光纤偏振器的工作带宽严格受到相位匹配条件的限制，这类偏振器只能工作在某个特定的波长范围，从而限制了其应用范围。.本项目面对目前光学偏振器存在的诸多问题，发展了一种基于石墨烯的宽带宽、高消光比的光纤偏振器。研究内容包括：石墨烯的制作；偏孔光纤和大空气孔内表面芯光纤的设计、制作和测试；石墨烯与光纤的相互作用机理研究；基于偏孔单模光纤石墨烯偏振器的制作和特性测试；基于大空气孔内表面芯石墨烯偏振器的制作和特性研究；基于微纳光纤石墨烯偏振器的设计制作及偏振特性研究。对制作的光纤石墨烯偏振器的偏振特性在980nm，1310nm和1550nm三个波长上分别进行了实验测试，验证了该光纤石墨烯偏振器的工作带宽至少从可以覆盖980nm到1550nm范围。该偏振器的偏振消光比在1550nm最高可达47dB。本项目的研究工作对于发展超宽带宽的光纤偏振器件和光学器件的微小型化具有重要的科学意义和实用价值。