Circular polarization beam splitter based on helically twisted dual hollow-core anti-resonant fiber

Manipulating the spin and orbital angular momentum of light in hollow-core anti-resonant fibers has gained growing interest in the optical community. Sparked by the space-division multiplexing technologies, we have proposed a circular polarization beam splitter (CPBS) based on helically twisted dual hollow-core anti-resonant fiber (TDHC-ARF). The designed CPBS has a length of 17.47 cm, an operating bandwidth of 68 nm, a polarization extinction ratio greater than 20 dB and a higher-order mode extinction ratio exceeding 100 with the operating wavelength ranging from 1.412 to 1.48 μm. The coupling characteristics of circularly polarized eigenmodes supported in the TDHC-ARF are investigated by employing the finite-element method combined with transformation optics technique. To verify the capability of the splitter, we have developed a code to simulate the light propagation in three-dimensional TDHC-ARF based on the full-vector finite-element beam propagation method for helicoidal waveguides. It was demonstrated that when the linearly polarized Gaussian beam composed of circularly polarized lights with opposite handedness is incident from one core, the CPBS can spatially separate the incident light into orthogonal circularly polarized components in two different cores. Our work paves the way for designing the all-fiber optical devices based on hollow-core anti-resonant fiber, opening up applications in optical information processing and communication.