Optimizing Evanescent Efficiency of Chalcogenide Tapered Fiber

Evanescent wave absorption-based mid-infrared chalcogenide fiber sensors have prominent advantages in multicomponent liquid and gas detection. In this work, a new approach of tapered-fiber geometry optimization was proposed, and the evanescent efficiency was also theoretically calculated to evaluate sensing performance. The influence of fiber geometry (waist radius (R-w), taper length (L-t), waist deformation) on the mode distribution, light transmittance (T), evanescent proportion (T-O) and evanescent efficiency (tau) is discussed. Remarkably, the calculated results show that the evanescent efficiency can be over 10% via optimizing the waist radius and taper length. Generally, a better sensing performance based on tapered fiber can be achieved if the proportion of the LP11-like mode becomes higher or R-w becomes smaller. Furthermore, the radius of the waist boundary (R-L) was introduced to analyze the waist deformation. Mode proportion is almost unchanged as the R-L increases, while tau is halved. In addition, the larger the micro taper is, the easier the taper process is. Herein, a longer waist can be obtained, resulting in larger sensing area which increases sensitivity greatly.

Automated summary

This study proposes a new approach of tapered-fiber geometry optimization to improve the evanescent efficiency of mid-infrared chalcogenide fiber sensors. The influence of fiber geometry on sensing performance is discussed, and the analysis reveals that a smaller waist radius and longer taper length lead to higher evanescent efficiency. Additionally, the investigation of waist deformation shows that increasing the waist boundary radius can decrease the sensing performance.