Multi-channel higher-order OAM generation and switching based on a mode selective interferometer
Guowei Wu, Xiaowen Wu, Shecheng Gao, Jiajing Tu, Ji Zhou, Qi Sui, Weiping Liu, Zhaohui Li
Abstract
A multi-channel orbital angular momentum (OAM) mode generation and switching scheme is proposed and demonstrated based on an in-fiber mode selective interferometer (MSI), which is formed in a four-mode fiber. The MSI consists of two strong modulated long-period fiber gratings (LPFGs), which realizes the mode selected coupling between a target mode pair. With the optimized structural parameters, the MSI can couple a launched LP 01 (or OAM 0 ) into a desired higher-order azimuthal mode (HAM, LP l 1 or OAM ± l , l ≥1) at multiple wavelength channels and generate the HAM with high-purity. To verify this concept, we fabricate two LPFGs in a four-mode fiber with designed distance and hence realize a MSI which can generate the second-order HAM (OAM 2 or LP 21 ) at 17 wavelength channels. The mode conversion efficiency is more than 90% at 17 wavelengths and the corresponding mode purity is no less than 97%, respectively. In addition, we also demonstrate that the selected mode pair (OAM 0 and OAM 2 ) can be switched at multiple channels by changing the state of the MSI. This MSI can also be used as a wavelength band-rejection filter on different spatial modes and find potential applications in optical communications and sensing.