Opt Lett. 2019 Jan 1;44(1):61-64. doi: 10.1364/OL.44.000061.
A polarization-independent orbital angular momentum (OAM) generator, based on a chiral fiber grating (CFG), is proposed and demonstrated for the first time, to the best of our knowledge. Helical phases were successfully excited in this device for the arbitrary polarization states of the input light, and the resulting OAM modes could be produced with a desired polarization state. The employed CFG was fabricated by twisting a fused few-mode fiber during hydrogen-oxygen flame heating. The polarization characteristics, helical phase, and purity of the coupled modes in the CFG were experimentally investigated for varying input light polarization states. The results showed that the coupled higher-order modes had the same polarization as the input fundamental mode. The chirality of the excited OAM was polarization-independent and determined solely by the helicity of the CFG. The purity of the OAM mode was higher than 93% with a slight fluctuation of 2% which occurred during measurement processing.
我们首次提出并展示了一种基于手性光纤光栅（CFG）的偏振无关轨道角动量（OAM）发生器。在该器件中，成功激发了任意偏振态输入光的螺旋相位，并且可以产生具有所需偏振态的 OAM 模式。所使用的 CFG 是通过在氢氧火焰加热过程中扭转熔接多模光纤制成的。实验研究了 CFG 中耦合模式的偏振特性、螺旋相位和纯度随输入光偏振态的变化。结果表明，耦合的高阶模式与输入基本模式具有相同的偏振。激发的 OAM 的手性与偏振无关，仅由 CFG 的螺旋决定。OAM 模式的纯度高于 93%，在测量过程中略有波动，为 2%。
