Inline Fiber Optic Chemical Sensor Using a Self-Aligned Epoxy Microbridge With a Metal Layer

• Published in: IEEE journal of selected topics in quantum electronics Vol. 13; no. 2; pp. 381 - 385
• Main Authors: Yun, Sung-Sik, Jo, Kyoung-Woo, Lee, Jong-Hyun
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.03.2007; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Assembly; Asymmetry; Chemical sensor; Chemical sensors; Curing; Diffusion; Diffusion layers; epoxy microbridge; Fiber optics; Gold; inline; Microorganisms; Optical fiber sensors; Optical fibers; Optical propagation; Optical refraction; Optical sensors; Optical variables control; self-aligned; Sensors
• ISSN: 1077-260X; 1558-4542
• DOI: 10.1109/JSTQE.2007.894064

We propose the use of a self-aligned epoxy microbridge with a metal layer for a low-cost, easy-to-make inline fiber optic chemical sensor that can sense the concentration of chemical solutions. The key component of the sensor is a cylindrical epoxy microbridge that can be assembled between input and output optical fibers by self-aligned UV curing. The microbridge is made from an epoxy that can rapidly diffuse liquid. The top of the microbridge was coated with Au/Ti to block diffusion of the surrounding solution and to induce optical dissipation that depends on the concentration of the chemical solution. We tested our fiber optic chemical sensor for deionized (DI) water and NaCl solution. The medium surrounding the microbridge asymmetrically diffuses into the epoxy microbridge due to the metal layer. The asymmetrical diffusion, consequently, makes a major change to the refractive index on the bottom of the microbridge, thereby altering the propagation mode of light. As a result, depending on the concentration of the NaCl solution, a fraction of the propagated light is absorbed into the metal layer. The sensitivity, which refers to the ratio of the concentration change and optical power, was experimentally confirmed to be 0.103 (wt%/photon count)