We numerically demonstrate a surface plasmon resonance biosensor-based on dual-polarized spiral photonic crystal fiber (PCF). Chemically stable gold material is used as the active plasmonic material, which is placed on the outer layer of the PCF to facilitate practical fabrication. Finite-element method-based numerical investigations show that the proposed biosensor shows maximum wavelength sensitivity of 4600 and 4300 nm/RIU in ${x}$ - and ${y}$ -polarized modes at an analyte refractive index of 1.37. Moreover, for analyte refractive index ranging from 1.33 to 1.38, maximum amplitude sensitivities of 371.5 RIU⁻¹ and 420.4 RIU⁻¹ are obtained in ${x}$ - and ${y}$ -polarized modes, respectively. In addition, the effects of changing pitch, different air hole diameter of the PCF and thickness of the gold layer on the sensing performance are also investigated. Owing to high sensitivity, improved sensing resolution and appropriate linearity characteristics, the proposed dual-polarized spiral PCF can be implemented for the detection of biological analytes, organic chemicals, biomolecules, and other unknown analytes.

This letter presents a numerical investigation of a highly sensitive refractive index sensor based on surface plasmon resonance. An ultrathin niobium nanofilm is proposed as a new plasmonic material, which outperforms existing plasmonic materials. This nanofilm is employed on a photonic crystal fiber for the first time resulting sensing over a wide range of refractive indices. Finite-element method-based numerical analysis shows that maximum amplitude sensitivity of 1560 RIU $^{-1}$ and wavelength sensitivity of 8000 nm/RIU can be obtained for an analyte index of 1.40. A thin aluminum oxide (Al₂O₃) film is deposited on the outer layer of niobium film to enhance the coupling strength and in order to tune the resonance wavelength. Moreover, the effects of varying thickness of niobium nanofilm and Al₂O₃ film on sensing performance are also discussed. The proposed niobium nanofilm based sensor can be potentially implemented in biochemical and organic chemical sensing.

We propose a simple photonic crystal fiber (PCF) biosensor based on the surface plasmon resonance effect. The sensing properties are characterized using the finite element method. Chemically stable gold material is deposited on the outer surface of the PCF to realize the practical sensing approach. The performance of the modeled biosensor is investigated in terms of wavelength sensitivity, amplitude sensitivity, sensor resolution, and linearity of the resonant wavelength with the variation of structural parameters. In the sensing range of 1.33 to 1.37, maximum sensitivities of $4000nm/RIU$ and $478RIU−1$ are achieved with the high sensor resolutions of $2.5×10−5$ and $2.1×10−5RIU$ using wavelength and amplitude interrogation methods, respectively. The designed biosensor will reduce fabrication complexity due to its simple and realistic hexagonal lattice structure. It is anticipated that the proposed biosensor may find possible applications for unknown biological and biochemical analyte detections with a high degree of accuracy.

A polarization-maintaining porous-core spiral photonic crystal fiber is proposed for efficient transmission of polarization-maintaining terahertz (THz) waves. The finite element method with perfectly matched layer boundary conditions is used to characterize the guiding properties. We demonstrate that by creating artificial asymmetry in the porous core, an ultrahigh birefringence of 0.0483 can be obtained at the operating frequency of 1.0 THz. Moreover, a low effective material loss of $0.085{\mathrm{cm}}^{-1}$ and very small confinement loss of $1.91\times {10}^{-3}\mathrm{dB}/\mathrm{cm}$ are achieved for the $y$-polarization mode with optimal design parameters. This article also focuses on some crucial design parameters such as power fraction, bending loss, and dispersion for usability in the THz regime.

A novel porous-core photonic crystal fiber is presented, and its guiding properties are numerically investigated by using the finite element method. It is demonstrated that by introducing a rhombic-shaped core made of circular air holes inside the conventional hexagonal cladding, it is possible to obtain very low bending loss of $3.04\times {10}^{-11}{\mathrm{cm}}^{-1}$ at the operating frequency of 1.0 THz. In addition to this, low effective material loss of $0.089{\mathrm{cm}}^{-1}$ and very small confinement loss of $1.17\times {10}^{-3}\mathrm{dB}/\mathrm{cm}$ are achieved for optimal design parameters. Other guiding properties, including effective area, dispersion, and higher order mode characteristics are also discussed thoroughly. The design of this porous fiber is relatively simple, since it contains fewer air holes and consists of circular air holes only. Due to promising wave-guiding properties, the proposed fiber would have a great potential for terahertz imaging and flexible communication applications.