物理科学与技术学院知识库

微纳光纤结型谐振器以其独特的波长选择特性以及优异的谐振增强特性使其在光通信和光信息处理领域引起了广泛的关注。其结构稳定、制作简单以及易于集成等优点，使得微纳光纤结型谐振器所制作的光学滤波器、光学传感器、光学分束器等器件得到了广泛的应用。随着人们对高速、大带宽的信号传输需求，利用全光通信的方式实现对光信号调制和探测已成为现今科研领域的热点问题。而器件的可调谐特性是实现全光调制的基础，因此，围绕微纳光纤结型谐振器的可调谐特性的研究受到大家的热捧。全光调谐的本质是一束光信号对于另外一束光信号的控制。利用光学非线性效应去实现对器件的全光调谐已成为热点研究问题。但是，传统的标准光纤非线性系数很低，这一致命的缺点极大地阻碍了微纳光纤结型谐振器实现有效全光调谐的可能性。为了提高光纤的非线性系数，人们想到利用微纳光纤周围的倏逝场，将具有高非线性系数的二维材料石墨烯包覆在微纳光纤表面，通过增强光与石墨烯之间的相互作用来提高光纤的非线性系数，实现有效的全光调谐。
石墨烯作为一种单原子层厚度的新型二维材料，由于其突出的稳定性，独特的能带结构，简单的制备方法以及优异的光学特性使其在科研领域炙手可热。作为研究光与物质相互作用的基础，利用火焰拉锥技术可以制作出损耗极低、倏逝场强的微纳光纤器件，通过与石墨烯巧妙的结合，可以显著的增强光与石墨烯的相互作用，为以微纳光纤为基础的全光可调谐器件的研究提供了崭新的思路。基于此，我们提出了一种全新结构的石墨烯辅助的全光可调谐微纳光纤结型谐振器，为研究以微纳光纤腔型谐振器件实现高速全光调制提供了新的方向。通过外部泵浦光的直接照射，实现了光与石墨烯的直接相互作用。利用石墨烯的热光效应以及光学非线性效应，完成了对微纳光纤结型谐振器传输损耗、消光比以及谐振波长等参数的有效调谐，其传输损耗的调谐效率增加了69倍，消光比的调谐效率增加了125倍，谐振波长的调谐范围可覆盖光纤的整个波长透明窗口。

Microfiber knot resonator has attracted wide attention in the field of optical communication and optical information processing due to its unique wavelength selection characteristics and excellent resonant enhanced characteristics. Because of its low cost, stable structure, simple fabrication process and easy integration of optical devices, microfiber knot resonators have been widely applied as optical filters, optical modulators, optical sensors and other devices. With the demand for high-speed and large bandwidth, the use of all optical communication to achieve modulation and detection of optical signals has become a hot topic in the field of scientific research. The tunable characteristics of devices are the basis of all optical modulation. Therefore, the research on tunable characteristics of microfiber knot resonators is highly appreciated.The essence of all-optical tuning is light-control-light. The use of optical nonlinear effects to realize light-control-light has become a hot topic. However, the traditional standard optical fiber nonlinearity coefficient is very low. This fatal disadvantage greatly hinders the possibility of effective all-optical tuning of microfiber knot resonator. In order to improve the nonlinear coefficient of optical fiber, the method of adding high nonlinear materials in the traditional optical fiber has been proposed, but its nonlinear coefficient is still very low. The other way to increase fiber nonlinear coefficient is proposed, which is used two-dimensional graphene materials to coating on the surface of microfiber to improve the nonlinear coefficient of the fiber by enhancing the interaction between light and graphene.
    Graphene is a new type of two-dimensional material with thickness of single atomic layer. Because of its outstanding stability, unique energy band structure, simple preparation method and excellent optical properties, graphene is hot in research field. As the basis for the study of the interaction between light and matter, a microfiber with low loss and strong evanescent field can be produced by using the flame drawing taper technology. Through the ingenious combination of graphene and microfibers, the interaction between light and graphene can be enhanced significantly. It provides a new idea for the research of all optical tunable devices based on microfiber.Based on the above, we propose a new structure of graphene assisted all optical tunable microfiber knot resonator, which lays a solid foundation for the research of high-speed all-optical modulation with micro cavity fiber resonator. Direct interaction between light and graphene is achieved by irradiation of the external pump light. By using the thermal optic effect and optical nonlinear effect of graphene, the effective tuning of the transmission loss, extinction ratio and resonant wavelength of the microfiber knot resonator is realized. The tuning efficiency of the transmission loss is increased by 69 times, and the tuning efficiency of the extinction ratio is increased by 125 times. The tuning range of the resonant wavelength can cover the transparent window of the entire wavelength of the fiber used.