低串扰大模场四芯五模微结构光纤的理论研究

Theoretical Study of Four-Core Five-Mode Microstructured Optical Fiber with Low Crosstalk and Large Mode Field Area

为满足空分复用和模分复用系统对大容量、多通道通信光纤的需求,提出了一种新型的沟槽-"十字形"空气孔辅助型多芯少模微结构光纤。利用有限元法(FEM)计算并优化光纤结构参数。结果表明:在工作波长1550 nm处,该光纤实现了LP_(01)、LP_(11)、LP_(21)、LP_(02)、LP_(31)5-LP模式的稳定传输,有效模场面积分别为113.14、159.70、174.43、104.91、192.74μm^(2),且在传输距离为10 km的情况下,芯间串扰均小于-40 dB,相对纤芯复用因子为62.722。与已报道的多芯少模光纤相比,该光纤具有低串扰和大模场面积的优点,可满足未来大容量、多通道传输系统的需求。

Objective This paper proposes a novel trench and crosses airhole-assisted multicore few-mode microstructured optical fiber(TCAH-MC-FM-MOF)to meet the demand for space-division multiplexing system and mode-division multiplexing system for large-capacity,multichannel communication fibers,the structural parameters of which are optimized using the finite element method(FEM).After optimization,the designed fiber can support the stable transmission of LP_(01),LP_(11),LP_(21),LP_(02)and LP_(31)5-LPmodes at the operating wavelength of 1550nm,and the effective mode fields are 113.14,159.70,174.43,104.91and 192.74μm^(2),respectively.The intercore crosstalk of these five modes is less than-40dB,and the relative core multiplexing factor is 62.722.Compared with its existing counterparts,this fiber has lower crosstalk and a larger mode effective field area.It is expected to meet the needs of large-capacity and multichannel transmission of the communication systems.Methods This paper proposes TCAH-MC-FM-MOF as a good candidate for large-capacity,multichannel communication fibers.The cross-section and refractive index profile are shown in Fig.1.The FEM optimizes the fiber structure to achieve the best performance based on the mode and power coupling theory.The intercore crosstalk formula of the four-core optical fiber is derived via theoretical analysis for a more accurate crosstalk calculation.The relationship between multiple structural parameters and fiber performance is exploited to achieve low intercore crosstalk and large field area.The initial fiber parameters are continuously optimized,and a set of satisfactory structural parameters is listed in Table 2.To demonstrate the advantages of TCAH-MC-FM-MOF designed in this paper,the performance of four types of multicore and few-mode fibers with different structures is compared by evaluating the intercore crosstalk LP31at the transmission distance of 100km at 1550nm.The results demonstrate that TACH-FM-MCF-MOF has the lowest crosstalk value and the best performance,as shown in Fig.7.Results and Discussions Achieving low crosstalk and a large mode field area in multicore and the few-mode microstructured optical fiber is critical for improving transmission capacity and overcoming nonlinear effects.The core size,core spacing,and doping concentration are adjusted to achieve the best performance under the premise of ensuring 5-LP mode transmission.Low refractive index grooves are added around the core to prevent beam leakage,and the width of the grooves is optimized to prevent crosstalk between the cores,as shown in Fig.3(c).As shown in Figs.4(a)and 4(d),the core size and core doping concentration are appropriately selected to achieve a large mode field area.After optimizing the structural parameters,the simulation demonstrates that the designed TCAH-MC-FM-MOF has low crosstalk,a large mode area,and good bending resistance,with a relative core reuse factor of 62.722.Conclusions TCAH-MC-FM-MOF proposed in this paper exhibits the characteristics of low crosstalk,large mode field area,and good bending resistance.When transmitting 10km at 1550nm,the designed TCAH-MC-FM-MOF has its intercore crosstalk of all modes suppressed less than 40dB,and the effective mode field area greater than100μm^(2).The effective refractive index difference of all the 5-LP modes meets the weak coupling condition,the crosstalk between modes can be ignored,and the relative core reuse factor is 62.722.Compared with other kinds of multicore few-mode fiber structures also highlights TCAH-MC-FM-MOF’s advantages in suppressing interphase crosstalk and alleviating the restrictive relationship between low crosstalk and large mode field area.Combined with SDM and MDM technology,the proposed TCAH-MC-FM-MOF is expected to meet the urgent demand for largecapacity,multichannel transmission systems.