Polymer optical fiber grating as water activity sensor

Wei Zhang, David J. Webb

Research output: Chapter in Book/Published conference outputConference publication


Controlling the water content within a product has long been required in the chemical processing, agriculture, food storage, paper manufacturing, semiconductor, pharmaceutical and fuel industries. The limitations of water content measurement as an indicator of safety and quality are attributed to differences in the strength with which water associates with other components in the product. Water activity indicates how tightly water is "bound," structurally or chemically, in products. Water absorption introduces changes in the volume and refractive index of poly(methyl methacrylate) PMMA. Therefore for a grating made in PMMA based optical fiber, its wavelength is an indicator of water absorption and PMMA thus can be used as a water activity sensor. In this work we have investigated the performance of a PMMA based optical fiber grating as a water activity sensor in sugar solution, saline solution and Jet A-1 aviation fuel. Samples of sugar solution with sugar concentration from 0 to 8%, saline solution with concentration from 0 to 22%, and dried (10ppm), ambient (39ppm) and wet (68ppm) aviation fuels were used in experiments. The corresponding water activities are measured as 1.0 to 0.99 for sugar solution, 1.0 to 0.86 for saline solution, and 0.15, 0.57 and 1.0 for the aviation fuel samples. The water content in the measured samples ranges from 100% (pure water) to 10 ppm (dried aviation fuel). The PMMA based optical fiber grating exhibits good sensitivity and consistent response, and Bragg wavelength shifts as large as 3.4 nm when the sensor is transferred from dry fuel to wet fuel.

Original languageEnglish
Title of host publicationMicro-structured and specialty optical fibres III
EditorsKyriacos Kalli, Alexis Mendez
Place of PublicationBellingham, WA (US)
Number of pages6
ISBN (Print)978-1-62841076-1
Publication statusPublished - 19 May 2014
EventMicro-structured and specialty optical fibres III - Brussels, Belgium
Duration: 14 Apr 201415 Apr 2014

Publication series

NameSPIE proceedings
ISSN (Print)0277-786X


ConferenceMicro-structured and specialty optical fibres III

Bibliographical note

Wei Zhang and David J. Webb, "Polymer optical fiber grating as water activity sensor", Micro-structured and Specialty Optical Fibres III, Kyriacos Kalli; Alexis Mendez, Editors, Proc. SPIE 9128 (2014).

Copyright 2014 Society of Photo-Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic electronic or print reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.

DOI: http://dx.doi.org/10.1117/12.2054207


  • equilibrium relative humidity
  • fiber Bragg grating
  • PMMA
  • polymer optical fiber
  • water activity


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