| Summary: | 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 (<i>R</i><sub>w</sub>), taper length (<i>L</i><sub>t</sub>), waist deformation) on the mode distribution, light transmittance (<i>T</i>), evanescent proportion (<i>T</i><sub>O</sub>) and evanescent efficiency (<i>τ</i>) 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 <i>LP</i><sub>11</sub>-like mode becomes higher or <i>R</i><sub>w</sub> becomes smaller. Furthermore, the radius of the waist boundary (<i>R</i><sub>L</sub>) was introduced to analyze the waist deformation. Mode proportion is almost unchanged as the <i>R</i><sub>L</sub> increases, while <i>τ</i> 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.
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