Transfer of orbital angular momentum between two identical optical ring-core fibers

With the rapid advancements in optical and quantum communication, orbital angular momentum (OAM) has emerged as a promising approach for enhancing system performance, owing to its unique structural properties. However, efficiently transferring OAM modes between waveguides with low loss and stability remains a significant challenge in OAM systems. In this study, we demonstrate the transfer of arbitrary-order OAM modes from one waveguide to another with low insertion loss and stable performance, utilizing a symmetrical ring-core fiber coupler. Low-loss transfer of the third- and fourth-order OAM modes is achieved by precisely controlling the symmetrical structure of the two fibers to meet the coupling conditions, resulting in insertion losses of 0.72 and 0.51 dB at 1550 nm, respectively. Furthermore, over the wavelength range of 1500–1600 nm, the insertion loss for these modes is kept below 1.1 and 0.86 dB, respectively, exhibiting excellent spectral characteristics. In addition, the average insertion loss over the C-band for the third-order OAM mode transfer varies from 0.72 to 1.77 dB, while it is from 0.51 to 1.36 dB for the fourth-order OAM mode, both under various input polarization states, demonstrating stable performance. This function can upload and download OAM energy of arbitrary order within the waveguide, providing a new solution for the widespread application of OAM technology and contributing to the advancement of optical and quantum communication.