Effect of thermal annealing on sensing properties of optical fiber sensors coated with indium tin oxide nano-overlays

Abstract

In this work we discuss an effect of thermal annealing on optical and electrical properties of indium tin oxide (ITO) thin films deposited on a short section of the multimode polymer-clad silica (PCS) optical fiber core. ITO films were deposited using a different configuration of high-power impulse magnetron sputtering (HiPIMS) and radio frequency magnetron sputtering (RF MS) cathodes. Due to tuned ITO film thickness it was possible to observe for these structures a lossy-mode resonance (LMR) and trace changes in the properties of films. Electrical resistance of the ITO overlays was also measured. Both optical and electrical measurements were repeated after annealing at 200°C in a tube furnace and nitrogen atmosphere. The measurements have shown that thermal annealing changes an optical response to the external refractive index (RI) of the fiber sensor and also changes the ITO layer resistivity. As an effect of thermal annealing, we observed a shift of the LMR towards longer wavelengths. In addition, as a result of annealing, the resistivity of the ITO layer was reduced.