단일벽 탄소나노튜브가 증착된 마이크로 테이퍼링 기반 장주기 광섬유 격자를 이용한 산소 측정

Abstract

Carbon nanotubes have attracted much attentions in gas sensing material due to their superior advantages such as small size (diameter= 1~100 nm), good electrical and mechanical properties. Since single-walled carbon nanotubes (SWCNTs) have unique properties such as high nonlinearity, fast response time, and saturable absorption, optical fiber devices based on SWCNTs have been widely investigated such as mode locked fiber laser, optical switch and optical fiber gas sensors. Optical fiber gas sensors based on SWCNTs is high promising devices since they have many advantages such as fast response, low cost, and immunity to electromagnetic interference. Optical fiber gas sensors are based on evanescent field interaction and the evanescent field of a guiding mode in a fiber can be directly exposed to external perpetrations by micro-tapering techniques. In this paper, we proposed the micro-tapered long-period fiber gratings (MT-LPFGs) deposited with SWCNTS for gas sensing probe. The MT-LPFGs are fabricated by tapering the fiber periodically. The fundamental core mode can be coupled to the cladding mode by periodic refractive index modulation, which produces resonant peaks in transmission spectrum. If gas molecules are adsorbed on the SWCNTs, dielectric constant of SWCNTs is changed and therefore, refractive index of SWCNTs can be changed. Since the MT-LPFGs are sensitive to the ambient index change, it is possible to detect gas molecules. We used oxygen gas for the gas sensing and the gas detection was carried out in a vacuum chamber. Before the injection of the oxygen gas, the sensor probe was heated up to 2000C for degassing the SWCNTs deposited on the MT-LPFGs. After the injection of oxygen gas, it took 80minutes to finish the reaction. The total transmission loss of 0.858dB was increased for 100% of oxygen gas. With the 10%, 50% and 100% of oxygen concentratioin, the total intensity variation were measured to be 0.085dB, 0.408dB and 0.858dB. The SWCNTs-based MT-LPFGs exhibit linear response and repeatability. Consequently, The SWCNTs-based MT-LPFGs will be useful for chemical sensing system