Design of two miniaturized and broadband polarization filters based on two types of square-lattice gold-filled photonic crystal fibers

•Two compact and broadband polarization filters are proposed.•The x and y polarized losses are 1831.8 and 0.18 dB/cm for Structure 1 at 1.31 μm.•The x and y polarized losses are 2265.07 and 0.5 dB/cm for Structure 1 at 1.55 μm.•The x and y polarized losses are 1942.5 and 0.43 dB/cm for Structure 2 at 1.55 μm.•Two designs with L = 300 μm have bandwidths of 1500 and 900 nm with low crosstalks. Two ultra-broadband polarization filters based on Structure 1 and Structure 2 are reported and characterized in terms of attenuation, crosstalk, bandwidth, and polarization filtering properties by the finite element method. Structure 1 is formed by introducing partial elliptical air holes in the first layer of the square-lattice gold-filled photonic crystal fiber. Based on the design solution of Structure 1, Structure 2 is arranged by using circular air holes with the changed transverse pitch to replace elliptical ones. Numerical results show that high resonance intensities of 2265.07 and 1831.83 dB/cm for y polarization, together with the corresponding x polarization losses of 0.50 and 0.18 dB/cm at respective communication wavelengths of 1.55 and 1.31 μm can be achieved by varying the gold film thickness for Structure 1.Moreover, the design of Structure 2 with all circle holes can also realize a high resonance loss of 1942.54 dB/cm for y polarization with a low loss of 0.43 dB/cm for x polarization at 1.55 μm. Structure 1 and Structure 2 with the fixed fiber length of 300 μm can obtain the crosstalk values of −590.09 and −506.07 dB at 1.55 μm, together with the bandwidths of 1500 and 900 nm, respectively. Additionally, two types of designs represent good produce tolerances. These results show a high potential of the suggested fiber for application in polarization-dependent filtering and other polarizing devices.