Negative-curvature hollow-core fiber for single-mode transmission in the near-infrared spectral region

A negative-curvature hollow-core fiber (NC-HCF) is proposed for near-infrared transmission. Five large and five small negative-curvature circular tubes are placed cross-over. The effects of the thickness of the resonator t, the diameter of the large negative-curvature tubes <i>d₁</i> and the diameter of the small tubes <i>d₂</i> on the confinement loss (CL) are analyzed by using the full-vector finite element method combined with the perfect matching layer and scattering boundary conditions. The optimization results show that when the core diameter D is 100 &mu;m, the thicknesses of negative-curvature tubes t are 0.4 &mu;m and the diameters of the two kinds of circular tubes <i>d₁</i> and <i>d₂</i> are 71 &mu;m and 36 &mu;m respectively, the CL of the LP₀₁ mode is lower than 0.3 dB/km and the CL of the LP₁₁ mode is greater than 3.1×10³ dB/km in the spectral region from 1.64 &mu;m to 1.7 &mu;m. At 1.7 &mu;m, the CLs of the LP₀₁ mode d LP₁₁ mode are 0.23 dB/km and 2.7×10³ dB/km, and the high-order-mode extinction ratio (HOMER) is 1.13×10⁴. Therefore, the NC-HCF in this paper can be applied to high-power fiber transmission in near-infrared band due to its good single-mode performance and low-loss transmission characteristics in LP01 mode under the condition of large mode field.