具有混合形状空气孔的OAM传输光纤设计研究

本文提出了一种新型轨道角动量模(OAM)传输的光子晶体光纤(PCF)结构,该光纤由最中心空气孔、高折射率环形层和外包层构成,其中外包层由一圈椭圆形空气孔和多圈呈周期排列的扇形空气孔共同组成,无需通过额外的掺杂,就可以使中心空气孔和外包层空气孔之间形成一个用来传输OAM光束的等效高折射率环形区。通过对该PCF的传输特性进行仿真分析,发现在1.55μm处,各模式的限制损耗维持在10^-6 dB/m-10^-10 dB/m,在C波段的色散值均维持在310 ps/(nm×km)以下,HE2,1模在1.55μm-1.6μm波段内的色散变化为3.1 ps/(nm×km)。在1.55μm处最大的Δnneff能够达到4.83×10^-3,大的有效折射率差可有效地抑制了模式间的简并,避免HE模和EH模耦合成LP模。验证了该光纤具有大带宽、小而平坦色散、大有效折射率差、低限制损耗和低非线性系数等优良性能。在1.25μm-2.0μm波段内共可以支持34个OAM模式的有效传输,每个模态都可作为独立的信道传递信息,适合用于大量数据的传输,大幅提高了光通信的系统容量和频谱效率。

Design and performance of fiber with hybrid shape air holes for OAM mode transmi ssion

This paper proposes a new photonic crystal fiber(PCF) structure for orbital angular momentum mode transmission.The fiber consists of a central air hole,a high refractive index annular zone and a cladding.The cladding layer is composed of a circleof elliptical air holes and several circles of fan-shaped air holes which are arranged in a periodic manner.Without additional doping,a high refractive index annular region can be formed between the central air hole and the cladding air hole to transmit OAM beams.The transmission characteristics of the PCF have been simulated by based on the finite element method.It is found that the limiting loss of each mode is maintained at 10^-6 dB/m^10^-10 dB/m at 1.55 μm.The dispersion values of all modes in C-band are kept below 310 ps/(nm×km),and the dispersion change of HE2,1 modes in 1.5 μm^1.6 μm band is 3.31 ps/(nm×km).The maximum Δnneff at 1.55 μm can reach 4.83×10^-3.Large effective refractive index difference can effectively restrain the degeneracy between modes and avoid coupling of HE and EH modes into LP mode.It is verified that the proposed fiber has good properties such as wide bandwidth,large effective refractive index difference,small and flat dispersion,low limiting loss and low non-linear coefficient.A total of 34 OAM modes can be effectively transmitted in the 1.25 μm^2 μm band.Each mode can be used as an independent channel to transmit information.It can transmit a large amount of data in a short distance,which may greatly improve the system capacity and spectral efficiency of the optical communication system.