study of the affecting factors on the humidity sensitivity of a polymeric film deposited on an optical fiber

Abstract

Unclad multimode fiber optic humidity sensor coated with Polyvinylpyrollidone (PVP) and polyethylene glycol (PEG) has been manufactured. The influence of the length of unclad fiber on relative change of transmission laser power was studied. We found that relative change of laser power as a function of humidity increased when unclad fiber length increases. The best length of unclad fiber was about 5cm. The effect of the number of dipping in the solution, during dip-coating process, on relative change of power has been studied. We noticed that the sensitivity decreased when the number of dipping was increased. The best number of dipping was only one. The impact of laser wavelength on relative change of laser power has been studied. It was observed that bigger wavelengths gave better results. The largest value of the fiber sensitivity was 0.199µW/RH% and with a work range of RH% (65-95). The linearity of the sensor was studied, the sensor have  R² = 0.96, and a response speed of 0.073 s/RH. Our results have shown that the manufactured sensor has a linear, fast response, small size and low cost.