Enhanced Inhibited Mode-Coupling: Multi-Mode Hollow-Core Anti-Resonant Fiber Designs

Understanding the interplay between the core-guided modes and tube-modes of hollow-core anti-resonant fiber (HCARF) is essential to achieve low-loss and multi-mode guidance. In this paper, we thoroughly investigated the coupling between the core-guided modes and tube-modes of various HCARFs using extensive analytical and finite-element modeling with the aim of achieving multi-mode guidance. We found that the coupling between the core-guided modes and tube-modes can significantly be enhanced by modifying and placing the cladding tubes of nested HCARFs. We proposed a modified nested HCARF that significantly enhances the inhibited-coupling (IC) between the core-guided modes and tube-modes compared to a regular and nested HCARF design. Due to the enhanced IC between the core-guided modes and tube-modes resulting from their phase mismatch, modified nested HCARF can support as high as 50 distinct spatial modes with propagation loss $< $10 dB/km and also demonstrate low-bend loss upon tight bending at 1064 nm. Our study will provide a better understanding of the coupling between the core-guided modes and tube-modes for designing multi-mode HCARFs. It is anticipated that the extraordinary optical properties of the proposed fiber can be beneficial for several applications including high power laser beam delivery, short-haul communication, and ultrafast nonlinear optics.