摘要
本文提出一种在同一段少模光纤上写入两个不同周期Λ1和Λ2的长周期光纤光栅构成叠栅的方法,实现了纤芯基模LP_(01)向高阶纤芯模LP_(11)模式转换的宽带宽的新型的全光纤模式转换器.利用有限元法和耦合模理论建立了模式转换器的理论分析模型.数值仿真分析了叠栅中两个子光栅周期间隔、光栅长度、耦合系数等光栅参数对模式转换器的影响.仿真分析和实验结果表明,通过改变两个子光栅的周期间隔来改变两个损耗峰的位置,形成一个损耗峰,从而可以实现宽带宽的模式转换器,其10dB带宽约是单栅的2倍.与传统的模式转换器相比,该转换器带宽宽、转换效率高,尺寸小、抗干扰能力强,可以在模分复用系统和光通信中得到广泛的应用.
Mode-division multiplexing(MDM),as one of the promising techniques for overcoming current limitation of transmission capacity in single-mode fibers(SMFs),has attracted considerable attention.A key component in the MDM system is a mode converter,which makes conversion between the fundamental mode and the higherorder mode.Many mode converters have been demonstrated,such as spatial light modulators,phase plates,silicon-based asymmetrical directional couplers,fiber-based photonic lantern,and long period fiber grating(LPFG).Compared with other methods,mode converter used LPFG is a very feasible technique,which has the advantages of small size,low loss,low backward noise,high coupling efficiency and easy fabrication.However,the limitation of the mode converter is relatively narrow bandwidth.In this paper,a novel broadband all-fiber mode converter is proposed,in which two long period fiber gratings(LPFGs)with different periods are fabricated in the same spatial domain of few-mode fiber to achieve coupling from LP01 to LP11,thus forming superimposed long period fiber gratings(SLPFGs).The influences of grating parameters,such as the interval between two periods,the length of grating and the coupling coefficient on the mode converter,are analyzed by numerical simulation.It is found that the gap between the two resonant wavelengths becomes smaller with the periodic interval decreasing,which can form one rejection band when the gap is small enough,thus a broadband mode converter can be realized.The corresponding bandwidth at a conversion efficiency of 10 dB is about twice that of traditional LPFG.Moreover,with the increase of grating length,the conversion efficiency first increases and then decreases,because coupling efficiency experiences deficient coupling,full coupling and over coupling.The effect of coupling coefficient on converter is similar to that of grating length.According to the numerical results,grating I is fabricated with,35-period.After that,the platform is rotated 180°and grating II is fabricated with,35-period by CO2 laser in tow mode fiber(TMF steped-index fiber).The bandwidths of both LPFGs at a conversion efficiency of 10 dB are about 57 nm and 67 nm respectively,while the bandwidth of SLPFG is about 153 nm.The experimental results are in pretty good agreement with the theoretical analyses.In addition,the proposed superimposed structure can also be extended to the conversion of fundamental mode into other high-order core modes.By designing the period of two sub-gratings reasonably,a wide band rejection filter with arbitrary wavelength can be realized.Compared with the traditional mode converter,the converter has the advantages of broad bandwidth,high conversion efficiency and small size,which can be widely used in the mode division multiplexing system and optical communication.
作者
薛艳茹
田朋飞
金娃
赵能
靳云
毕卫红
Xue Yan-Ru;Tian Peng-Fei;Jin Wa;Zhao Neng;Jin Yun;Bi Wei-Hong(School of Information Science and Engineering,the Key Laboratory for Special Fiber and Fiber Sensor of Hebei Province,Yanshan University,Qinhuangdao 066004,China;College of Mechanical and Electrical Engineering,Hebei Normal University of Science and Technology,Qinhuangdao 066004,China;Department of Mechanical and Electrical Engineering,Hebei Construction Material Vocational and Technical College,Qinhuangdao 066004,China)
出处
《物理学报》
SCIE
EI
CAS
CSCD
北大核心
2019年第5期141-147,共7页
Acta Physica Sinica
基金
国家自然科学基金(批准号:61475133
61575170
61605168)
河北省自然科学基金(批准号:F2016203392)
河北省应用基础研究计划重点基础研究项目(批准号:16961701D)
河北省高等学校科学技术研究基金(批准号:QN2016078)
燕山大学校内博士基金(批准号:B1011)资助的课题~~
关键词
长周期光纤叠栅
少模光纤
模式转换器
耦合系数
superimposed long period fiber gratings
few mode fiber
mode converter
coupling coefficient
