中文摘要：

设计了一种新型的石墨烯-空心光纤可调谐结构,将石墨烯涂覆在空心光纤的空气孔内表面上,利用有限元法研究了该结构的电光调制特性.研究表明,改变石墨烯的化学势既可以调控光纤的相位和开关特性,还可以调谐光纤损耗峰与次峰的位置、强度和宽度.然而,改变空气孔半径和石墨烯层数不会改变开关点和损耗峰与次峰的位置,只会改变损耗差和损耗峰的强度和宽度,而且由N层石墨烯引起的损耗差是单层的N倍.这是因为石墨烯的介电常数决定了光纤的有效折射率和损耗,改变石墨烯的化学势可以改变石墨烯的介电常数,而改变空气孔半径和石墨烯层数不会改变石墨烯的介电常数,却改变了石墨烯和光的作用强度.经过参数优化之后,我们提出一种基于五层石墨烯涂覆空心光纤的电吸收型调制器,工作在1180—1760 nm波段,具有小尺寸（5 mm×125μm）、宽光带宽（580 nm）、高消光比（16 dB）、高调制带宽（64 MHz）和低插入损耗（1.23 dB）特性.研究结果对基于石墨烯的可调谐光纤光子器件的设计和应用提供了理论参考.

英文摘要：

Active manipulation of light in optical fibers has been extensively studied with great interest because of the structure simplicity, small footprint, low insertion loss and the compatibility with diverse fiber-optic systems. While graphene can be seen to exhibit a strong electro-optic effect originating from its gapless Dirac-fermionic band structure, there is no report on the electro-absorption properties of all-fiber graphene devices. Here a novel tunable graphene-based hollow optical fiber structure is designed with graphene coated on the inner wall of the fiber central core. Evanescent field of the guided mode propagating in the hollow optical fiber interacts with a monolayer or stacked multilayer graphene, which could modulate the intensity of the propagating mode via altering the chemical potential of the graphene by an external electric field. A full vector finite element method is adopted to analyse the influences of the chemical potential, the air- hole＇s radius and layers of graphene on the electro-optic modulation properties of the structure. Numerical simulation results show that by adjusting the chemical potential of graphene, the phase and on-off features of the fiber can be tuned correspondingly, as well as the position, magnitude and width of the loss peak and the sub-peak. However, the air-hole＇s radius and layers of graphene will only affect the loss variation, the magnitude and width of the loss peak and the sub-peak, but have no influence on the on-off point and the position of the loss peak and the sub-peak. In addition, the loss variation caused by N-layer graphene is N times that of the monolayer graphene. Since it is the dielectric constant of graphene that determines the effective refractive index and the loss of the fiber, the dielectric constant is only related to its chemical potential while independent of the air-hole＇s radius and the layers of graphene. Finally, an optimal electro-absorptive modulator based on the penta-layer graphene-coated hollow optical fiber is proposed for