All-Dielectric Fiber Meta-Tip for Alignment-Tolerant Bidirectional Interconnect Between Single-Mode and Multi-Mode Fibers

The growing demand for enhanced data transmission and network scalability requires connecting multi-mode fibers (MMFs) to single-mode fibers (SMFs). However, conventional fiber-optic connector systems face challenges such as one-way transmission, alignment issues, and bulkiness. In this study, an all-dielectric metasurface (MS)-based fiber-coupling system engineered to facilitate alignment-tolerant bidirectional optical interconnect at a communication wavelength of 1550 nm is proposed and demonstrated. The system features meticulously aligned fiber meta-tips incorporating an MS integrated onto SMF and MMF facets. The MS collimates the divergent beam emitted from the fiber facet and focuses the collimated beam propagating through free space, enabling bidirectional transmission of optical signals between the SMF and MMF. The achieved performance includes a coupling efficiency of −5.6 dB, optimal radial and axial tolerances of 40 and 600 µm, respectively, an extinction ratio of 13.8 dB, and a signal-to-noise ratio of 24.3 dB at 10.3 Gb s⁻¹. The proposed fiber meta-tips highlight the potential of lab-on-fiber technology for optical communication, trapping, and biological sensing.