Ultralow loss hollow-core nested-tube negative curvature fiber

Hollow-core fiber (HCF) has attracted great interest from researchers because of its high damage threshold and small nonlinearity compared with solid-core fiber. However, how to reduce the loss of HCF has always been an urgent problem to be solved. Aiming to solve the problem, we propose a novel hollow-core negative curvature fiber (HC-NCF) with an elliptical nested tube and a circular nested tube. The structure of this HC-NCF is relatively simple, which greatly reduces the difficulty of fabrication. Finite element modeling has been used to simulate and calculate the confinement loss (CL) and bending loss (BL) of the fiber with different nested tube structures. Results show that the CL of the LP₀₁ mode is as low as 6.48×10^-6 dB/km at the interesting wavelength of 1.06 μm. It exhibits a minimum CL of 5.28×10^-6 dB/km at 1.01 μm with maintaining a loss of less than 0.003 dB/km over 1020 nm (0.77 μm to 1.79 μm) bandwidth. In addition, we proposed the HC-NCF has been confirmed to have better-bending resistance. Within a bending radius of 5-40 cm, the HC-NCF has a BL below 3.75×10^-4 dB/km at a 10 cm bending radius; the BL is below 1.03×10^-5 dB/km at a 40 cm bending radius.