Mode manipulation in a ring–core fiber for OAM monitoring and conversion

Abstract The monitoring and conversion of photonic orbital angular momentum (OAM) play fundamental important roles for both classic quantum technologies, especially in low-loss transmission media such as ring-core fibers (RCFs), which make many OAM applications practical or vastly more flexible. However, a RCF, the modes associated with different states are highly overlapping due to circular refractive index distribution structure, makes it difficult distinguish monitor turn limits its inline conversion. Here, we report first experimental realization mode RCF using filters (MFs), takes advantage difference adiabatic evolution higher-order cutoff conditions tapered RCFs. Different-order can be filtered MFs geometric parameters, demonstrated by linearly polarized intensity. Combined manipulations single-mode fiber, coupling efficiency reach 90%, through spectrum realized, fabrication grating, couples one desired mode, fabricating process three long-period fiber gratings. between 0-order 1, 2- 3-order exceeds 96%. Our work provides an efficient approach convert supporting RCFs even other special further promotes improvement capacity