Mach-Zehnder interferometer sensor based on the U-shaped probe for concentration sensing

A newly compact bent tapered optical fibre sensor is proposed and demonstrated for the detection of levofloxacin concentration. The structure of micro fibre Mach-Zehnder interferometer (MMZI) is fabricated using a glass processing system, demonstrating a 30 mm-long single mode fibre between two tapered fibres which has a waist diameter of 15 pm and tapering length of 6 mm. A combination of bending and tapering acts as a sensor, which results in high penetration depth of evanescent field. The sensor is sensitive to concentration variation. Upon exposure to Levofloxacin concentrations varying from 50 to 250 ppm, the U-shaped MMZI sensor sensitivity is 21 pm/ppm and a linearity of more than 98.7%, which is about 1.49 fold greater than that of a straight MMZI sensor. In addition, the U-shaped MMZI sensor is very compact in size which make this type of fibre sensor is easily measuring concentration variation in small volume. (C) 2015 Elsevier GmbH. All rights reserved.