A Broadband polarization filter based on liquid crystal core and gold-coated microstructure fiber

In this paper, an ultra-broadband microstructure fiber filter is proposed and its properties are studied by full vector finite element method. Numerical results show that the effective modal index of x-polarized core mode (PCM) is much larger than those of surface plasmon polariton modes (SPPMs) in gold-coated areas. These index mismatches weaken the x-PCM's couplings with SPPMs to guarantee a very low confinement loss. As to the filtered y-PCM, it resonates with all the first three lowest order SPPMs, which is the first time to the best of our knowledge. Further studies show that better filtering performances can be achieved by complete resonances between the filtered y-PCM and 1st, 0th order SPPMs and optimized distribution of the resonant wavelengths. Through parameter optimization, an ultrabroad high loss band with loss no less than 123.49 dB/cm has been achieved within 1.1–2.0 μm. Taken extinction ratio 20 dB as criteria, a 1350 nm bandwidth can be reached within only 0.7 mm filtering length. Its operational range covers the entire O + E + S + C + L + U bands. This filter can find promising applications in the areas of optical communication and fiber sensing.