Thin-Film Resonance Supporting Coatings Deposited onto Optical Waveguides Towards the Fabrication of Sensing Devices

Different resonances can be supported by thin-film coated optical waveguides depending on the electrical properties of the coating material. One case occurs when the real part of the thin-film permittivity is negative and higher in magnitude than both its own imaginary part and the permittivity of the material surrounding the thin-film. This case is known as surface plasmon resonance (SPR). Other case occurs when the real part of the thin-film permittivity is positive and higher in magnitude than both its own imaginary part and the permittivity of the material surrounding the thin-film. This case is known as lossy mode resonance (LMR). These phenomena have originated many patents, which have been exploited within the last decades originating many applications. Among them, the fabrication of highly versatile sensing platforms, capable of detecting the substance in contact with the coating by monitoring the refractive index variations of the external medium has been one of the leading topics. The intrinsic properties of the materials used to fabricate the thin-films are essential to determine the final properties of these devices. This permits to tune the sensitivity by adjusting the properties of the materials in order to obtain highly sensitive devices with many different applications in the detection of biological and chemical species. In this article, we review different patents, which address these phenomena by using different optical waveguide configurations and coating materials in order to obtain more sensitive, accurate, portable and easy to use devices.