Double-Clad Anti-Resonant Hollow-Core Fiber With Inner Cladding Tube Offset for Mode Tailoring

We demonstrate a double-clad anti-resonant hollow-core fiber (DC-ARF) with an offset inner cladding structure for effective mode tailoring. The DC-ARF consists of six thin-walled, azimuthally offset inner tubes enclosed within a thicker outer cladding tube, which is further connected to silica jacket through a single node. Asymmetric offset arrangement of inner cladding tubes generates two enlarged gaps based on mode field distribution of LP<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub>-like mode, ensuring high-order mode (HOM) suppression. Numerical simulations show that light guidance is achieved through leakage from the larger gaps followed by anti-resonant reflection back into the core. And wavelength disparity between fundamental mode and HOMs provides inherent mechanism for preferential HOM suppression. Through structural optimization, significantly improved mode purity is achieved. The fabricated DC-ARF features two large azimuthal gaps of 70° and operates at a wavelength of 1.06 μm. Experimental results confirm that only the fundamental mode remains when the fiber length exceeds 0.5 m. Furthermore, a 1-m-long DC-ARF improves the input beam quality by approximately 40%, demonstrating its mode tailoring capability. Our work offers valuable guidance for mode tailoring, and the proposed DC-ARF has great potential in single-mode laser transmission, biomedical systems, and optical communications.