Excitation of high order orbital angular momentum modes in ultra-short chiral long period fiber gratings

A class of ultra-short chiral long period fiber gratings (CLPFGs) are prepared by writing a spiral curve on the surface of a six-mode fiber. The CLPFGs are applied to excite +/- 2nd- and +/- 3rd-order orbital angular momentum (OAM) modes. The coupling efficiency of the CLPFG in these modes can be as high as 99%, when the length is only 0.5cm. The polarization characteristic of the excited higher-order OAM modes in CLPFGs was theoretically analyzed and experimentally investigated. Results show that the obtained +/- 2nd- and +/- 3rd-order OAM modes are polarization independent, as expected. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement