A flexible first-order OAM modes generation in ringcore fibers (RCFs) based on a mechanically-induced long-period fiber grating (MLPFG) is proposed. By directly fusion splicing a standard single-mode fiber (SMF) and RCFs, the anti-resonant reflection guidance mechanism (ARRGM) is introduced in the RCF, leading to the guided-core modes, so-called anti-resonant modes (AR modes), which have a Gaussian field distribution and are confined in low-refractive index central core of RCFs. A mechanical long-period fiber grating is used to couple the AR modes into the OAM modes propagated in the high-index ring core of the RCF. Results show that the generated OAM modes are the combination of two orthogonal linearly polarized (LP) modes with ±π/2 phase shift in the ring core. The mode conversion efficiency of OAM+1 and OAM-1 can reach 95% and 94%, respectively, indicating promising applications in sensing and communication of the RCFs.
A side-polished fiber coupler for orbital angular momentum (OAM) mode conversion was designed and fabricated with a single mode fiber (SMF) and a ring-core fiber (RCF). Based on evanescent wave coupling effect, the 974 nm pump laser in the SMF can be efficiently injected into the RCF. It can be found potential applications in OAM fiber amplifiers.
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