Higher-order modes suppression in negative curvature anti-resonance hollow core fibers by multiple resonant coupling

In this paper, a method to suppress the higher-order modes in the negative curvature anti-resonance hollow core fibers (NC-AR-HCFs) by utilizing multiple resonant coupling is proposed. With this method, a hollow core fiber is designed. Based on multiple resonant coupling, the loss of LP11 mode even reaches more than 105 dB/km orders of magnitude over a wide wavelength band, and the loss ratio of LP11 mode to LP01 mode of the proposed fiber remains above 105 orders of magnitude in the range of 1200 ∼ 1550 nm, which shows excellent single-mode operation. The effect of multiple resonant coupling and the effective suppression of further-higher-order modes (LP21 mode and LP02 mode) are analyzed in detail. Moreover, we demonstrate that the extra loss caused by the node effect is reduced by changing the thickness of the outer tube that decreases the fractional optical power of the outer tube wall. And the restrictive relation between the higher-order modes suppression and the reduction of bend loss is discussed. The analysis guides the design of NC-AR-HCFs with effectively suppressing higher-order modes.