REFRACTIVE INDEX SENSING EVALUATION OF MULTI- TAPERED OPTICAL FIBERS PREPARED BY CARBON DIOXIDE LASER PROCESSING

Tapered optical fiber sensor technology has offered highly sensitive monitoring solutions to a wide range of applications, from environmental to biomedical fields. Until today, many experts have been working on tapering optical fibers to produce an optical-based viable monitoring system based on light-matter interaction. Refractive index (RI) sensing is one of the most basic sensing mechanisms in photonics. Herein, a simple, fast, and controllable tapering process was acquired by means of a carbon dioxide (CO2) laser tapering system. The use of CO2 laser allowed constant heating temperature with which clean and symmetrical multi-tapers could be produced. The interaction of CO2 laser beam and silica-based optical fiber was discussed to explain the formation of tapered fiber along with the RI sensing mechanism based on evanescence wave and analyte interaction. Sensors with 2, 3, and 4 tapers showed extremely linear responses to the refractive index change, indicated by degree of linearity values close to unity. The sensitivity increased from around 8a.u/RIU (2 and 3 tapers) to 9a.u./RIU (4 tapers). In addition, all sensors had excellent reversibility. Since MTOFs were reversible and sensitive in the wide range of refractive index, then they could be further proposed as RI-based environmental and biomedical sensors.