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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.

Recent development of perovskite solar cells (PSCs) is directed toward the search for lead-free material with superior efficiency, owing to the intoxication and stability issues associated with the lead-based PSCs. Despite the efforts, plenty of exploration is still required to attain the optimum material for perovskite, along with the electron transport layer (ETL), and hole transport layer (HTL). In this study, two less explored perovskite materials Cesium Tin Germanium Halide (CsSnGeI3) and Cesium Copper Antimony Chloride nanocrystals are compared to their Pb-based counterpart of Methylammonium Lead Iodide (MAPbI3). Thorough numerical investigations and comparative evaluation of these three material-based PSCs were done using a solar cell capacitance simulator (SCAPS-1D). Based on the suitable band alignment with the absorber layers, three selected distinct ETL (TiO2, ZnO, PCBM) and HTL (Cu2O, CZTSe, CuSCN) materials demonstrated excellent compatibility. The effect of back metal contact, temperature, series, and shunt resistance on the photovoltaic parameters was also elucidated for all three perovskite materials. Increasing the work function of back contact up to 5.9 eV improves the photovoltaic parameters, indicating selenium to be an optimum material. Numerical analysis of 27 attainable structures yields the best one to be CZTSe/CsSnGeI3/PCBM with a power conversion efficiency of 32.41% ( J S C = 28.73 mA cm−2, V O C = 1.29 V, and FF = 87.35%). The PCE obtained from these structures ranges from 25.14% to 32.41%, indicating that all the reported structures here have the potential to be highly efficient, lead-free, and stable solar cell structures.

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.

In this paper, a highly sensitive miniaturized surface plasmon resonance (SPR) based photonic crystal fiber (PCF) sensor is presented for a wide range of analyte sensing. Gold is selected as the plasmonic metal for its higher chemical stability and titanium oxide works as the adhesive layer for gold attachment on silica. The plasmonic metal and the sensing medium are placed exterior to the surface of the sensor design to make it fitting for practical applications. By a careful arrangement of the periodic arrangement of the refractive index in the design, the generation of the evanescent fields is fine-tuned to obtain the phase matching between the leaky core guided mode and the surface plasmon polariton (SPP) mode. Numerical simulations have been carried out by employing the finite element method (FEM) with the consideration of a perfectly matched layer (PML) to absorb surface radiations. The proposed sensor shows a maximum wavelength sensitivity of 34,000 nm/RIU (refractive index units) and a maximum amplitude sensitivity of 331 RIU−1, investigated by using the wavelength and the amplitude interrogation methods, respectively, for the analyte sensing range of 1.16 to 1.37 RI (refractive index). The sensor also exhibits a wavelength resolution of 2.94×10−6 RIU which indicates a high detection accuracy. On that, the proposed sensor would be an excellent candidate for a wide range of RI detection, applicable for various purposes such as chemical detections, medical diagnostics, bio-sensing, and other low RI analytes.