Broadband and tunable fiber polarizer based on a graphene photonic crystal fiber

The recent flourishing development of two‐dimensional (2D) graphene has sparked considerable interest and extensive research on graphene‐based optical fiber polarizers. However, studies on graphene‐optical fiber polarizers focused on the structure with graphene films attached to side‐polished fibers, which face challenges such as low birefringence of 10¯⁶, low polarization extinction ratio (PER), and narrow polarizing window of tens of nanometers. Here, a fiber polarizer based on graphene‐photonic crystal fiber (Gr‐PCF) is proposed firstly which exhibits high birefringence of ~2.5×10¯³, high PER of ~111 dB/mm, broad polarizing window of > 400 nm, and tunable polarization states. Graphene or graphene/hBN/graphene (Gr/hBN/Gr) heterojunctions are attached to the surface of two square holes in PCF to make one of the polarizing modes attenuate significantly. The Fermi level (EF) tunability of Gr/hBN/Gr allows for switching the output light from a linear to a circular polarization state. The combination of PCF's endless single‐mode feature and graphene’s broadband optical response feature enables the fiber polarizer to exhibit a wide spectrum range with singlemode transmission characteristics.