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  μm, 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 μm. 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. [ABSTRACT FROM AUTHOR]