The Study of Thermal Effect Suppression and Wavelength Dependence of Azobenzene-coated FBG for UV Sensing Application

Abstract

In the paper, we have demonstrated an azobenzene-coated fiber Bragg grating (FBG) for monitoring ultraviolet light (UV) intensity in remote measurement. The elasticity of the coated azobenzene polymer is changed by the UV light, which induces a center wavelength change corresponding to the change of the FBG's grating period. The wavelength shift resulting from both UV light and other light with the wavelength out of the UV range was about 0.18 nm. In order to improve the accuracy of the measurement, the center wavelength shift caused by radiant heat of the light source was sufficiently removed by using a thermal filter. The amount of the center wavelength shift was consequently reduced to 0.06 nm, compared to the result without the thermal filter. Also, the FBGs coated by using azobenzene polymer were produced by two different methods; thermal casting and UV curing. Considering temperature dependence, UV curing is more suitable than thermal casting in UV sensor application of the azobenzene-coated FBG. In addition, we have confirmed the wavelength dependence of the optical sensor by means of four different band pass filters. Thus, we found out that the center wavelength shift per unit intensity is 0.029 [arb. unit] as a maximum value at 370 nm wavelength region and that the absorption spectrum of the azobenzene polymer was very consistent with the wavelength dependence of the azobenzene-coated FBG.

Sensitivity improvement of UV FBG sensor by downsizing grating diameter

“…A broadband light source (super luminescent light emitting diode, (SLED) @ 1550 nm) was used. And UV lamp (Acticure, EFOS Inc. lamp spectrum [10]) with a spectral band ranging from 270 to 600 nm is used. With the combination of an optical spectrum analyzer (OSA) and LabVIEW, the spectral data are obtained ( Fig .5(a)).…”

Improving the Sensitivity of an Ultraviolet Optical Sensor Based on a Fiber Bragg Grating by Coating With a Photoresponsive Material

“…이 광센서의 원리는 자외선광 노출 유무에 따라 광섬유격자에 코팅된 아조벤젠 폴리머가 수축 또는 이완을 하게 되어 광섬유격자에 장력을 유도한다. 따라서 자외선광에 노출에 의한 광섬유격자 간격을 변화시 켜 최종적으로 스펙트럼상에서 광섬유격자의 중심파장이 이 동하게 되고, 이 이동량을 분석하여 자외선광의 세기를 측정 하는 원리이다 [6,8,9] . 본 논문은 기존에 개발된 자외선 센서에 민감도 향상 방법 으로 광섬유격자에 영향을 주지 못하고 지나간 잔광을 다시 반사시켜 아조벤젠 폴리머에 재흡수 시키는 연구를 수행하 였다.…”