Optimizing Evanescent Efficiency of Chalcogenide Tapered Fiber

Abstract

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 (Rw), taper length (Lt), waist deformation) on the mode distribution, light transmittance (T), evanescent proportion (TO) and evanescent efficiency (τ) 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 Rw becomes smaller. Furthermore, the radius of the waist boundary (RL) was introduced to analyze the waist deformation. Mode proportion is almost unchanged as the RL increases, while τ 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.

Infrared Evanescent Wave Sensing Based on a Ge10As30Se40Te20 Fiber for Alcohol Detection

“…This is because the total reflection angle of light decreases with the reduction of the fiber diameter, thereby enhancing d p according to Equation (1). At the same time, the evanescent wave was influenced by high-order modes in the multimode fiber [24,31].…”

“…The light wave propagating in the optical fiber follows Maxwell’s Equations. As shown in Figure 1 , the light wave will not stop immediately at the interface between the fiber and external medium due to the continuity of the electromagnetic wave, and an electromagnetic wave called an evanescent wave would be generated on the side with low refractive index media [ 24 ]. After the action of external substances, the light will continue to transmit along the fiber with material information (molecular vibration/rotation information).…”