An ultrabroadband and compact square-lattice photonic crystal fiber polarization filter based on surface plasmon resonance is proposed. Four large air holes are introduced near the core to destroy the symmetry of the original fiber structure so that the resonance wavelengths of x- and y-polarized core modes can be well separated. The inner walls of two large air holes along the x polarization direction are coated with gold film to generate the surface plasmon mode. In addition, to further enhance the coupling resonance strength between the core mode and the surface plasmon polariton mode, the six air holes near the gold-coated air holes are replaced by solid glass rods. Then the dispersion characteristics and loss spectrum of the proposed polarization filter are studied by the finite-element method. The results show that when the fiber length of the proposed filter is only 700 μm, ultrawideband y-polarized light transmission with a bandwidth of up to 730 nm in the wavelength range from 0.97 to 1.70 μm can be achieved. The effective filtering range covers all optical fiber communication bands from O to U. Moreover, the filter has excellent structural tolerances. These excellent properties are expected to make it a good candidate for a broadband polarization filter.

提出了一种基于表面等离子体激元共振的超宽带紧凑型方格光子晶体光纤偏振滤波器。在纤芯附近引入了四个大的气孔，以破坏原始纤维结构的对称性，从而可以很好地分离x和y极化纤芯模的共振波长。沿x方向的两个大气孔的内壁极化方向涂有金膜以产生表面等离子体激元模。另外，为了进一步增强纤芯模式与表面等离子体激元极化模式之间的耦合共振强度，用实心玻璃棒代替了镀金气孔附近的六个气孔。然后通过有限元方法研究了所提出的偏振滤波器的色散特性和损耗谱。结果表明，当所提出的滤波器的光纤长度仅为700μm时，超宽带y可以实现在0.97至1.70μm波长范围内具有高达730 nm带宽的偏振光传输。有效的过滤范围覆盖了从O到U的所有光纤通信频段。此外，该滤波器具有出色的结构公差。这些优异的性能有望使其成为宽带偏振滤光片的理想选择。