Hetero-core fiber optic humidity sensor with layer-by-layer polymer film including TiO2 nanoparticles using UV light

We have developed a hetero-core structured fiber optic humidity sensor with a porous immobilized TiO₂ nano-particles. Our research group has been proposed the hetero-core optical fiber humidity sensor due to moisture absorption of the hygroscopic polymer based on optical-intensity modulation. However, the sensor had difficulty in detecting the humidity change at lower humidity range less than 50 %RH. In this paper, we present that the hetero-core fiber humidity sensor has devised to increase the sensitivity at relatively lower humidity by means of including the TiO₂ nano-particles in a porous sensitive film comparing to the conventional hetero-core fiber humidity sensor. On the other hand, a UV light has been known to make the TiO₂ nano-particles indicate super-hydrophilic reaction and photo catalytic effect. Therefore, the sensitivity of the humidity sensor can be improved using the sensitive film including the TiO₂ nanoparticles illuminated by the UV light. We tested the transmitted spectra of UV and visible band light of the proposed hetero-core fiber humidity sensor. As a result, the UV-LED light source could enhance the humidity sensitivity in the proposed hetero-core fiber optic sensor.