Ultra-Short Hollow-Core Anti-Resonant Fiber Polarization Filter Covering C+L Band Based on SPR Effect

This paper proposes an ultra-short hollow-core anti-resonant fiber (HC-ARF) polarization filter covering the C+L communication band based on the surface plasmon resonance (SPR) effect. The structure consists of six composite tubes, each formed by nesting an elliptical cladding tube with a circular cladding tube. By coating the inner wall of a pair of circular cladding tubes in the y-direction with a gold film, the SPR effect is excited to achieve selective filtering of the y-pol state. The influence of structural parameters on the filter performance is systematically analyzed using the finite element method. Simulation results show that when the device length is 2 mm, resonance wavelength of 1.538 μm, the operating bandwidth reaches 174 nm (1488–1662 nm), covering the C+L communication band, with an extinction ratio (ER) of −368 dB. For the x-polarization state, the confinement loss is only 276 dB/m, whereas the y-polarization state shows a dramatically higher loss of 21,489 dB/m. By adjusting the wall thickness of the gold-coated cladding tube or the thickness of the gold film, the resonance wavelength can be effectively tuned to achieve polarization filtering in other bands. The designed filter has potential applications in optical communication and sensing.