Ultralow loss and broadband hollow core anti-resonant fiber with nested waterdrop-shaped tube

The hollow-core anti-resonant fiber (HC-ARF) has attracted a great deal of interest due to its unique fiber properties. However, it still is a challenging work to design a HC-ARF with simple structure that can further reduce the loss while maintaining wide bandwidth and good single-mode characteristics. Based on this, we proposed two kinds of single-layer nested waterdrop-shaped anti-resonance nodeless fibers (NWANFs), and implemented a comparative study with previously proposed nested anti-resonant nodeless fiber and nested elliptical anti-resonant nodeless fiber in terms of confinement loss (CL), total loss, bending loss, and single-mode characteristics. The results show that the properties of the NWANF1# are superior to that of the other three fibers except for the higher-order mode extinction ratio. The NWANF1# demonstrates a CL of less than 5 × 10^-3 dB/km over a bandwidth range of 1.2∼2.1 µm, a total loss of less than 0.09 dB/km across the wavelength range of 1.4∼2.1 µm, a bending loss of less than 1.8 × 10^-3 dB/km for the bending radius larger than 20 cm, as well as the good single-mode characteristics across the entire bandwidth. Therefore, the proposed fiber can be applied in communication and high power transmission.