All-fiber stable orbital angular momentum beam generatihaon and propagation

An all-fiber scheme for stable orbital angular momentum (OAM) beam generation and propagation is proposed and demonstrated. This scheme is based on a self-designed and manufactured graded-index few mode fiber (GI-FMF) and compatible mode selection coupler (MSC). The MSC, which consists of a conventional single mode fiber (SMF) and the GI-F, can effectively couple the fundamental mode in the SMF to the desired OAM mode in the GI-FMF based on phase matching condition. Meanwhile. the GI-FMF breaks the degeneracy between the desired eigenmodes and neighboring vector modes, thereby allowing the preservation and propagation of the selectively excited OAM modes. As a proof-ofprinciple, we have implemented an all-fiber device operating in stable OAM modes with vertical bar l vertical bar = 1. The experimental results show stable propagation of OAM beams with the mode purity of similar to 95% and bandwidth of 100 nm. This all fiber device could be useful for further development of wide bandwidth OAM mode division multiplexed application. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement