Single-mode large-mode-area double-ring hollow-core anti-resonant fiber for high power delivery in mid-infrared region

A novel hollow-core anti-resonant fiber with a large mode area and good single mode performance is proposed for high power delivery in mid-infrared region. The structure consists of two-layer circular tubes as the cladding. By optimizing structure parameters, a broad low-loss single-mode band, in which the fundamental mode loss is lower than 4 × 10−3 dB/m and the high order mode extinction ratio (HOMER) is higher than 1000, is achieved in the wavelength region from 2.5 to 3.3 μm in which the lowest loss of 2.87 × 10−4 dB/m occurs at 3.1 μm. The effective mode area is up to 2314 μm2 with the highest HOMER of 16,600 at the wavelength of 2.8 μm. In addition, this fiber also has good bend resistance characteristics. When the fiber is bent at the bending radius of 18 cm, the mode area reaches to 2268 μm2 with the HOMER above 100 at the wavelength of 2.8 μm. Furthermore, the effective mode area can be further increased to 4714 µm2 by increasing core radius at the cost of sacrificing single mode performance and bending resistance.