Single-mode bend-resistant hollow-core fiber with multi-size anti-resonant elements

Abstract

A novel single-ring hollow-core anti-resonant fiber (HC-ARF) with multi-size tubular anti-resonant elements (AREs) that can simultaneously provide low bending losses and robust single-mode operation is proposed. Numerical results prove that the introduction of multi-size AREs can effectively improve the suppression ability to high order modes (HOMs). The HOM extinction ratio is twice as high as that of single-ring HC-ARF with uniform AREs. Meanwhile, the bending loss is reduced by at least one order of magnitude due to the suppression of bending-induced loss peaks. A single-ring 7-ARE HC-ARF with four kinds of ARE diameters is successfully fabricated. Experimental results demonstrate that under a tight bending radius of 3.5 cm, the bending loss is as low as 0.37 dB/m @1.65 μm. The measured near-field profile through a 5 m-long fiber proves a robust single-mode performance. In order to further reduce the bending loss, we proposed the modified structure by adopting the nested multi-size AREs, achieving a lower bending loss of 0.18 dB/m @1.55 μm under an extremely tight bending radius of 0.75 cm, which is the lowest bending loss among the reported HC-ARFs under such tight bending radius as far as we know. Meanwhile, single-mode performance can be also improved due to a higher HOM extinction ratio of 938. The proposed fiber has great potential for applications in high-power laser delivery and gas-filled HC-ARF lasers.