Anil Kumar

This study theoretically investigates an optical fiber structure coated with a bilayer film of zinc oxide (ZnO) and lithium fluoride (LiF) for ethanol detection. The ZnO thin film exhibits lossy mode resonance (LMR) in the visible and near-infrared spectrum (400 – 1500nm), which serves as the basis for designing a refractive index (RI) sensor by appropriately selecting the ZnO thickness. To further enhance the resonance characteristics, a dielectric layer of LiF is introduced between the unclad fiber core and the ZnO coating. It Improves phase matching and generates sharper LMR dips with a narrower full width at half maximum. The proposed structure is also analyzed using two different core materials: pure silica and 4% Ge-doped silica. A comparative study of their sensing performance is also presented. Its sensing performance is examined by varying the thicknesses of the ZnO and LiF layers to identify the optimal structural parameters. The designed fiber-optic sensor is then evaluated for detecting ethanol concentrations in ethanol–water mixtures (RI =1.33 for 0% ethanol and RI =1.36 for pure ethanol) using both s- and p -polarized incident light. Calibration curves demonstrating the relationship between resonant wavelength shifts and the RI of the sample are presented. This sensor achieves excellent sensitivities of 1163 nm RIU ⁻¹ for s -polarization and 1475 nm RIU ⁻¹ for p -polarization, making it promising for the development of High-Figure of Merit biochemical sensors for potential applications.

Attenuation characteristics of germanium (Ge) film clad planar optical waveguide are theoretically studied at the spectral wavelength of 0.6328 μm. Thin films of Ge are found to possess greater attenuation values than the other recognized materials. The existence of these greater attenuations is caused by lossy modes that are sustained by these films. It has been shown that the attenuation of the TM mode can be greatly increased by adding a high-index buffer layer between the Ge layer and the dielectric guide. It occurred because of the resonant coupling between the lossy modes supported by the Ge layer and the waveguide modes. Moreover, it is claimed that by adding a dielectric superstrate layer above the Ge thin film, the strength of the TM mode in the proposed structure can be further attenuated to an ultra-high value. In this study, a TE pass polarizer is proposed having a high extinction ratio of 30582.15 dB. Attenuation results are presented, after optimization of several parameters like thicknesses of Ge, buffer, and superstrate layers along with environmental stability of the suggested structure. The generated field distribution profiles are also in good agreement with the obtained attenuation results.

ZnO thin film is theoretically investigated to explore its sensing characteristics using Fresnel reflection coefficients. Although SPR (Surface plasmon resonance) spectrum of the ZnO film has been investigated by the scientific community at a large scale but its LMR (Lossy Mode Resonance) spectrum is yet to be investigated in depth. Spectral interrogations of ZnO thin film placed on the glass prism are carried out for the generation of LMRs. The results are presented for TE as well as TM polarizations. The effect of a matching layer, inserted between substrate (prism) and ZnO thin film is also discussed in detail. A substantial improvement in the sensitivity is observed after introducing the optimized matching layer. FWHM (Full width at half maximum) of the various sensor configurations is calculated and it is inferred that a high index matching layer gives higher sensitivity. On the other hand, a low index matching layer results in higher resolution. It is shown that a high sensitivity value of 5220 nm/RIU can be achieved for TM polarization. The proposed sensor configurations with clad index range (1.44–1.48) may find applications to sense various petroleum products.