Xue Linlin, Timoteo Bras Samuel Malumba, Qiu Weiwei, Wang Zhongpeng
School of Information and Electronic Engineering, Zhejiang University of Science and Technology, Hangzhou 310023, China.
Materials (Basel). 2022 May 7;15(9):3366. doi: 10.3390/ma15093366.
We propose an all-fiber broadband circular polarizer based on leaky mode coupling and a phase-matched turning point (PMTP) in a chirped, double-helix, chiral, long-period, fiber grating (CLPG). The CLPG was coated with a material in which the refractive index was higher than that of the fiber cladding, enabling the coupling of the core mode to leaky modes to achieve a desired extinction ratio. The complex coupled-mode theory was employed to investigate the coupling mechanism and conditions under which the desired coupling efficiency could be achieved. Moreover, the PMTP in phase-matched curves, which resolved the conflict between the operating bandwidth and the grating pitch range of the CLPG and made a large bandwidth with a small grating pitch possible, was used in the design to achieve a compact structure. Finally, two broadband circular polarizers with an extinction ratio above 25 dB were simulated; one had a bandwidth of over 120 nm and a length of 3.5 cm, and the other had a bandwidth of over 300 nm and a length of 8 cm.
我们提出了一种基于泄漏模耦合和啁啾双螺旋手性长周期光纤光栅（CLPG）中的相位匹配转折点（PMTP）的全光纤宽带圆偏振器。CLPG涂覆有一种折射率高于光纤包层的材料，使得纤芯模能够与泄漏模耦合，从而实现所需的消光比。采用复耦合模理论来研究耦合机制以及实现所需耦合效率的条件。此外，设计中使用了相位匹配曲线中的PMTP，它解决了CLPG的工作带宽与光栅间距范围之间的冲突，并使得采用小光栅间距实现大带宽成为可能，从而实现紧凑结构。最后，对两个消光比高于25 dB的宽带圆偏振器进行了模拟；一个带宽超过120 nm，长度为3.5 cm，另一个带宽超过300 nm，长度为8 cm。
