Low-loss, single-polarization, anti-bending, anti-resonant fiber applicable to the small flexibility field.

In this paper, a novel hollow-core anti-resonant optical fiber is proposed. We confirm that the U-shaped nested tubes can better compress the fiber core compared with the circular and semi-circular nested tubes to further reduce the loss and improve the single polarization characteristics. The proposed optical fiber has an ultra-low loss of 0.005 dB/m in the considered wavelength range. This is difficult to achieve in most of the previous studies. In the common wavelength band of 1550 nm, the designed fiber achieves a birefringence of about 3 × 10^-5 and a single polarization PER index of 2259 and is capable of polarization filtering with a broadband of 16 nm. Meanwhile, the proposed structure still has extremely excellent bending resistance. The critical bending radius of the designed structure is approximately 0.4 cm. It also confirms that our proposed structure has a certain ability to withstand harsh environments and can be widely applied in small, flexible fields. We believe that the designed structure has a wider range of applications in the field of fiber optic communication systems that are more sensitive to polarization, such as fiber optic gyroscopes, optical amplifiers, and fiber lasers.