Optical Properties of the Refractive Index Sensor Based on Nanoparticles Composites

Polymer microtips fabricated at the ends of multi-mode optical fibers can act as refractive index sensor transducers and as lenses. The aim of the studies was to test the possibility of improving the refractive index sensor sensitivity by adding gold nanoparticles (concentrations of 1\% and 5%) and titanium dioxide (concentrations of 5% and 16.67%) to the monomer mixture. The presence of a nanoparticle composite in the mixture creates strongly scattering centers, which results in reduced reflected signal levels and a lower value of return losses. Shifts in return loss minima for the refractive index sensors were observed. After a microtip was manufactured from UV-cured pentaerythritol triacrylate mixture on multi-mode fiber with a 105 nm core diameter, the minimum reached a refractive index value of 1.44, while when Au 1% and Au 5% composites were added, the minimum shifted to 1.48. Doping the mixture with a 1% Au composite resulted in improved transmission properties in the 600−1200 nm spectral range. An improvement in transmission in the infrared range was obtained for a microtip doped with 16.67% TiO2. Doping with titanium dioxide resulted in a significant decrease in signal in the wavelength range below 1200 nm.