Filtering Characteristics and Applications of Photonic Crystal Fibers Being Selectively Infiltrated With One Aluminum Rod

The filtering characteristics and applications of photonic crystal fibers being selectively infiltrated with one aluminum rod were investigated based on the finite-element method. The aluminum rod being selectively infiltrated into one cladding air hole acted as a defect core and generated surface plasmon polaritons on its surface. As the phase matching condition was satisfied, the light transferring in fiber core coupled to the surface of the aluminum rod and the confinement losses of core modes experienced an abrupt increase. The filtering characteristics could be modified by adjusting the fiber structure parameters, such as diameters of air holes and the aluminum rod. Two applications of the photonic crystal fibers being selectively infiltrated with one aluminum rod were studied. First, a polarization filter with ultrabroad bandwidth was designed based on the cascaded resonances between fiber core modes and surface plasmon polariton modes. The bandwidth of the polarization filter was as broad as 600 nm covering wavelengths from 1.4 to 2.0 μm. Second, an intensity-type refractive index sensor was designed based on the filtering characteristics. The output power ratio and sensitivity increased as the refractive index of analyte increases and reached to 3.91 dB and 128 dB/RIU in x-polarized direction at the analyte refractive index of 1.37, respectively.

I. Introduction

Photonic crystal fibers (PCFs), due to its virtues of design flexibility, controllable dispersion, high nonlinear, unrestrained single-mode transmission, immune to electromagnetic field, miniature size and low weight [1]–[5], have been studied sufficiently with expectation to improve the performance in photo-communication, superpower laser, amplifier, supercontinuum generation, sensors and other photonic devices [6]–[12] . The air holes being arranged periodically in the cladding of PCFs provide natural channels for the infilling of functional materials. Axial multistep injection-cure-cleave process [13], fusion splice [14], fs laser punching [15] , microscope imaging [16] and focused ion beam [17] have been utilized to achieve PCFs being selectively infiltrated with functional materials. PCFs which are infiltrated with functional materials combine micro-structure of PCFs with material's physical performance and provide a promising platform for novel photonic devices. Wang et al. [18] investigated an invertible fiber-type transformation from a photonic bandgap fiber into a nonideal waveguide and then into an index-guiding PCF via the thermo-optic effect of the fluid filled in the air holes. Olausson et al. [19] fabricated an electrically tunable Yb-doped fiber laser in the range 1040-1065 nm based on the wavelength filtering effect of a tunable liquid crystal filled photonic bandgap fiber. Thakur et al. [20] reported a magnetic field sensor with sensitivity of 24.2 pm/Oe by infiltrating magnetic fluid into cladding air holes of polarization maintaining PCF.