Enhanced Optical Scattering in Glass Waveguides for Lab-on-Chip optimized Detection Using ITO Thin Films and Periodic Nanoarrays

The need for simple, real-time, fast, and in-situ devices for water analysis is becoming increasingly urgent. A new type of contaminant, known as emerging micro-contaminants, has been detected in water, posing a potential risk to human and environmental health. Currently, their identification relies on traditional analytical methods, which are very sensitive but also expensive and time-consuming. Optical biosensors are a promising alternative. This article proposes a concept for an optical device for biosensing applications. The focus of the study is the light coupling performance between optical channel waveguides and periodic nanoarrays in the visible spectrum. Coupling performance can be enhanced using an indium tin oxide (ITO) thin film as a buffer layer. The intensity and deflection of the guided light result from its interaction with periodic nanocylinders made of ITO or gold (Au). To optimize the configuration, the study analyzes coupling efficiency, out-of plane scattering, and the far-field projection of beam focus and diffraction angle. These factors are evaluated using the finite difference time-domain (FDTD) method. The implementation of ITO enables up to a nine fold increase in coupling efficiency, while the presence of the Au array yields a coupling efficiency of 13% at a wavelength of 580 nm. The nanoarray also induces a deflection that depends on the wavelength, a property that could be significant for directional light focusing a phenomenon with potential applications in environmental and biomedical sensing.