Tapered optical fibers using CO₂laser and their sensing performances

In this paper, we proposed a simple tapering process of optical fibers using controlled CO2 laser. This is a response to the call for the rapid development of affordable, efficient, and reliable optical sensors. A laser with power of 36 W was focused on a small section of three optical fibers having core/cladding diameters in micrometer of 10/125 (sensor A), 62.5/125 (sensor B), and 200/225 (sensor C). The sensors were tested on solutions having refractive indices of 1.3325 to 1.4266. Our investigation revealed that sensor C offered highest sensitivity. Therefore, further characterizations on its sensing characteristics were conducted. Over 6 times repetitive measurement, sensor C showed excellent repeatability with average sensitivity and detection limit of 4.5941(78) a.u./RIU and 3.97 × 10-4 RIU, respectively. The tapered large core fiber also had good reversibility. Furthermore, the stability test by applying sensor C to solutions with low, medium, and high refractive indices also showed that the sensor was relatively stable. Within 60 minutes measurement, we noticed increasing trends of normalized intensities. However, the intensity increment percentages were relatively small, i.e., 0.27%, 1.17%, and 1.75% respectively for refractive indices of 1.3325, 1.3921, and 1.4266. Thus, excellent tapered optical fiber sensor could be produced using CO2 laser.