기능성 폴리머 재료가 코팅된 광섬유 격자 기반 자외선 센서의 민감도 향상 연구

Abstract

In this study, a newly synthesized material is proposed to improve the ultraviolet (UV) sensitivity of a non-etched fiber bragg grating (FBG) for UV sensors, which is comparable to the high sensitivity of the previously reported UV sensor based on a diameter-downsized FBG. The photomechanical material was prepared simply by mixing an azobenzene compound and curing agent. The FBG was subsequently coated with a functional polymer using a UV curing process. We determined the best combination of the azobenzene compound, based on its UV-induced mechanical stretching, and the curing agent as a commercially available coating polymer to achieve the highest sensitivity in many combinations. The maximum wavelength shift of the non-etched FBG was 2.5 nm. The specific UV sensor coated with this mixture showed a considerable change in wavelength with respect to UV rays but no significant change in visible light. It was thus confirmed that this improved UV sensor does not react to external visible light but is sensitive to only UV light. To improve the sensitivity of the UV sensor, 0.6% tensile force was applied to the FBG, and the azobenzene compound was coated. The sensitivity was then measured. When the UV light is incident on the sensor having this tension, it was confirmed that the light sensitivity was improved by approximately twice that when the tension was not applied. In addition, the functional polymer coating needed to be physically protected because deformations can easily occur even when the optical element is bent or weakly impacted. We fabricated a simple fiber optic Fabry-Perot interferometer and analyzed the interference fringe movement in the frequency domain by UV light, and confirmed that the optical fiber actually stretched as a result of the UV-absorbed azobenzene. In addition, we proposed a simple algorithm to determine the presence and absence of UV radiation using the change in the slope of the wavelength shift over time obtained through the first derivative of the measured data. The proposed method is very easy to use, providing information at a glance, and our fast UV sensor is sufficiently powerful for applications such as corona discharge detection and lightning strike monitoring. Finally, we assessed whether the ultraviolet sensor developed can detect UV light generated at high speeds. It was confirmed that the minimum exposure time that this UV sensor can detect is 17 ms. Considering the lightning duration time of 20 ms, the UV sensor developed in this study detects momentary UV light generated from a corona discharge or from lightning. It will be applied in the future for remotely monitoring in real time defects in power lines such as corona discharge in insulators.