Wavelength tunable single-circular-polarization twisted PCF

A single-polarization fiber is an important device in many applications ranging from communications to sensors. However, most of the single-polarization fibers focus on linear polarization, and the single-polarization fiber supporting a circular polarization remains a challenge. Here, we propose a novel wavelength-tunable single-circular-polarization (SCP) twisted photonic crystal fiber (PCF). The single left-circular polarization and single right-circular polarization operate around $1.665 ~\mu \text{m}$ and $1.700 ~\mu \text{m}$ , respectively. The resonance can be tuned by adjusting the twist rate of PCF and the refractive index filling. The SCP bandwidth is up to 20 nm, and the polarization extinction ratio is as high as 1.3 dB/cm. This design not only extends the single-polarization fiber to circular polarization but also provides a twisting PCF application.