Novel External Gold-Coated Side-Leakage Photonic Crystal Fiber for Tunable Broadband Polarization Filter

A kind of side-leakage photonic crystal fiber (SL-PCF) with external gold-coated film is proposed by introducing a leakage channel in the x polarization direction. The effects of air-holes diameters, gold film thickness, liquid filling, and different metal coating materials on the polarization characteristics of SL-PCF are analyzed using the full vector finite element method (FV-FEM). At resonance wavelengths of 1.41 and 1.59 
$\mu$
m,the losses of x-polarized core mode are 725.74 and 1097.94 dB/cm, while that of y-polarized core mode are only 1.79 and 2.00 dB/cm. When the transmission length of SL-PCF is 1 mm, the bandwidth with extinction ratio better than 20 dB is up to 1410 nm, covering wide wavelengths from 1.09 to 2.5 
$\mu$
m. Moreover, the direction of the polarization filter and its resonance wavelength can be effectively modulated by selectively filling the liquid into the cladding air-holes and changing the coating material.Furthermore, the introduction of side-leakage channel not only increases the mode birefringence, but also enhances the fiber's sensitivity to changes in external pressure, bending, and torque. Therefore, the proposed SL-PCF not only has important applications in fiber polarization filters, but also has broad application prospects in fiber sensors.