Ultra-low loss, single polarization hollow-core anti-resonant fiber

In this paper we present a new hollow-core anti-resonant fiber (HC-ARF). The structural asymmetry is constructed by the introduction of elliptical quartz tubes in the core region, which can greatly improve the birefringence and enhance the polarization extinction ratio. Meanwhile, the semicircular and circular nested quartz tubes in the cladding region also contribute to the decrease of the confinement loss of the fundamental mode. A finite element algorithm is used to analyze the effects of each parameter on the performance of the designed HC-ARF. The final simulation results illustrate that the designed structure achieves the values of birefringence and polarization extinction ratio of 2.4×10−5${2.4} \times {{10}^{- 5}}$ and 257 in the common wavelength band of 1550 nm, and polarization filtering with a bandwidth of 4 nm. It is worth mentioning that the loss of the y${y}$-polarized fundamental mode in the 1550 nm wavelength band reaches an ultra-low value of 0.014 dB/m. The corresponding fundamental mode loss has remained extremely low in the wavelength range considered. Our proposed device still has good bending resistance, where the loss of the y${ y}$-polarized mode is about 0.04 dB/m and decreases gradually when the bending radius is 5 cm. We believe that the proposed HC-ARF can be used in polarization-sensitive fiber devices and can be widely applied in polarization-sensitive fiber communication systems such as fiber lasers and fiber gyroscopes.