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A surface plasmon resonance (SPR) based photonic crystal fiber (PCF) sensor having a milled microchannel, and an open D-channel has been proposed in this paper. The sensor shows good functionality in the wide sensing range of 1.14-1.36 Refractive Index Units (RIU) of the analyte, having the capability to detect low refractive index (RI). The Finite Element Method (FEM) based numerical investigations dictate that the proposed sensor has been able to gain a maximum wavelength sensitivity of 53,800 nm/RIU according to the wavelength interrogation technique. The amplitude interrogations show that the sensor has the highest amplitude sensitivity of 328 RIU-1. The highest FOM (Figure of Merit) has been found to be 105 RIU-1. The sensor evinces a minimum wavelength resolution of $1.86\times 10 ^{-6}$ RIU, which secures high detection accuracy. A circular perfectly matched layer (PML) is implemented in the sensor's outermost layer as a boundary condition to absorb surface radiations. Gold is the plasmonic metal, while TiO2 acts as the adhesive layer for gold attachment on silica. Due to the high sensitivity with a broad range of analyte detection, the sensor is well suited for practical biochemical detection purposes.

In this paper,a polarization-maintaining single-mode rectangular-shaped hollow-core waveguide with four segmented air cladding in the terahertz (THz) regime is presented for detecting various toxic industrial chemicals. A new type of injection moldable cyclic olefin copolymer, commercially named as TOPAS is used as the base fiber material for its high optical transmission and high resistance to other chemicals. The finite element method with a perfectly matched layer as the boundary condition is employed for numerical explorations. The proposed sensor exhibits ultra-high relative sensitivity of 99.73% and ultra-low effective material loss of 0.007 cm−1 at 1.6 THz frequency for Toluene in y polarization. This sensor also evinces a high birefringence of $4.16\times 10^{-3}$ at 1.6 THz frequency. A maximum V parameter of 2.224 has been found at 2.2 THz which ensures the single-mode propagation of light. The sensor shows a very low confinement loss of $3.2\times 10^{-11}$ dB/m and a high numerical aperture of 0.3574 at 1.6 THz frequency for Hydrogen Sulfide. This paper also concentrates on other important design parameters such as bending loss, mode field radius, beam divergence and effective area for serviceability of the sensor in the THz region. This sensor can be a very good candidate for various chemical detection as well as other applications in the terahertz regime.

A highly sensitive dual-polarized 'X' oriented quadruple D-shaped open channel photonic crystal fiber (PCF) based surface plasmon resonance (SPR) sensor for various analyte detection is proposed in this paper. Gold is taken as a plasmonic material for its stability and compatibility. Silicon nitride (Si3N4) and titanium oxide (TiO2) has been used separately as an adhesive layer of gold to elevate the sustainability of the evanescent field. This paper shows a comparative study and inspects the effect of sensing performance between Si3N4 and TiO2 as an adhesive layer of gold. Numerical investigations have been followed up using the finite element method (FEM). For practical feasibility, analyte and plasmonic materials have been placed at the outer surface of the sensor. After watchful investigation, the maximum wavelength sensitivities of 21,000 nm/RIU (Refractive Index Unit) and 18,000 nm/RIU have been found for the y-polarization when using TiO2 and Si3N4, respectively. The highest amplitude sensitivities are of 914RIU−1 and 625RIU−1 for TiO2 and Si3N4, respectively. Furthermore, minimum wavelength resolutions of 4.76 × 10−6 RIU and 5.55 × 10−6 RIU have been observed in y-polarization for TiO2 and Si3N4, respectively. The sensor evinces a maximum figure of merit (FOM) of 236RIU−1 for TiO2. This sensor has the analyte sensing range of 1.31–1.38RI (Refractive Index) for TiO2 and 1.32–1.39RI for Si3N4. The sensor also delivers low confinement loss for Si3N4 and TiO2, which certifies viability in fabricating the design. Recognizing this sensor’s wavelength sensitivity, amplitude sensitivity, and sensing RI range, it could be a promising candidate for detecting different liquid analytes with excellent accuracy.

A novel PCF sensor based on surface plasmon resonance (SPR) to detect pH levels of Acetic acid aqueous solution is proposed in this paper. This proposed sensor has a sensing range for 1%-25% acetic acid aqueous solution (2.51-1.90 in pH level). Gold layer is used as plasmonic metal along with a TiO 2 layer for better plasmonic excitation and enhancing evanescent field. Analyte is passed through a rectangular channel in center and a channel surrounding the metal layer. For some analyte samples of refractive index(RI) ranging in between 1.33-1.37, we have investigated effective RI, relative sensitivity in x and y polarizations, confinement loss and effective area via Finite Element Method (FEM). As a result of proper optimization maximum wavelength sensitivity of 10,000 nm/RIU and wavelength resolution of $1\times 10^{-5}$ RIU is achieved at 1.3620 RI level which secures excessive detection reliability of minute RI changes. This sensor evinces moderated confinement loss which certifies simplicity in fabricating the design. Relation of confinement loss, relative sensitivity and effective area against wavelength show eminent indication of better sensing capability for various pH levels of acetic acid.