  Single fiber imaging technology offers unique insights for research and
inspection in difficult to reach and narrow spaces. In particular,
ultra-compact multimode fiber (MMF) imaging, has received increasing interest
over the past decade. However, MMF imaging will be seriously distorted when
subjected to dynamic perturbations due to time-varying mode coupling, and the
imaging of space objects via Gaussian beam will be relatively degraded at the
edge due to insufficient contrast. Here, a robust super-resolution imaging
method based on a ring core fiber (RCF) with orbital angular momentum (OAM) has
been proposed and experimentally demonstrated. The OAM modes propagating in the
RCF form a series of weakly-coupled mode groups, making our imaging system
robust to external perturbations. In addition, a spiral phase plate is used as
a vortex filter to produce OAM for edge enhancement, thus improving the image
resolution. Furthermore, a few-shot U-Transformer neural network is proposed to
enhance the resilience of the developed RCF-OAM imaging system against
environmental perturbations. Finally, the developed RCF-OAM imaging system
achieves biological image transmission, demonstrating the practicality of our
scheme. This pioneering RCF OAM imaging system may have broad applications,
potentially revolutionising fields such as biological imaging and industrial
non-destructive testing.
