Zhao Xinyi, Liu Yunqi, Liu Zuyao, Mou Chengbo
Opt Express. 2020 Apr 13;28(8):11990-12000. doi: 10.1364/OE.389471.
We demonstrated the fabrication of bandwidth tunable ultra-broadband mode converters based on CO-laser inscribed long-period fiber gratings (LPFGs) and helical long-period gratings (HLPGs) in a two-mode fiber (TMF). The simulation and experimental results show that there is a dual-resonance coupling from LP to LP core mode at the dispersion turning point. The mode converters based on the TMF-LPFG and TMF-HLPG provide a 10-dB bandwidth of ∼300 nm and ∼297 nm, respectively, which covers O + E+S + C band. The 1 order orbital angular momentum (OAM) mode based on TMF-LPFG was generated by adjusting the polarization controllers (PCs), while the 1 order OAM mode can be generated directly by the TMF-HLPG. When the twist rate is varied from -36 rad/m ∼ 36 rad/m, the tunable range of the 10-dB bandwidth is ∼52 nm and ∼91 nm for the LPFG and HLPG mode converters, respectively. The ultra-broadband mode converter can be adopted as a bandwidth tunable mode converter, which can be applied in ultra-broadband mode-division-multiplexing transmission systems and optical fiber sensing systems based on few-mode fibers.
我们展示了基于在双模光纤（TMF）中用CO激光写入的长周期光纤光栅（LPFG）和螺旋长周期光栅（HLPG）制造带宽可调谐超宽带模式转换器。仿真和实验结果表明，在色散转折点处存在从LP到LP纤芯模式的双共振耦合。基于TMF-LPFG和TMF-HLPG的模式转换器分别提供约300 nm和约297 nm的10 dB带宽，覆盖O + E + S + C波段。通过调整偏振控制器（PC）产生基于TMF-LPFG的1阶轨道角动量（OAM）模式，而TMF-HLPG可直接产生1阶OAM模式。当扭转率在-36 rad/m至36 rad/m之间变化时，LPFG和HLPG模式转换器的10 dB带宽可调范围分别约为52 nm和约91 nm。这种超宽带模式转换器可作为带宽可调谐模式转换器，应用于基于少模光纤的超宽带模式分复用传输系统和光纤传感系统。
