A fiber optic sensor based on air‐gap long period gratings for pH sensing application

In this article, a pH fiber-optic sensor based on an air-gap long period fiber grating (AG-LPG) in a multi-modes fiber is proposed. Owing to the different pH solutions to cause the index variation of surrounding AG-LPG, the grating wavelength will be shifted due to the change of the effective index both in core and cladding layers. For pH sensing applications, the experimental results show the sensitivity of 0.219 nm/pH and 0.248 nm/pH for measuring the acid and alkaline solutions respectively. This simple sensing head can be applied in a real-time and long-term monitoring pH change of drinking water or testing solutions. (c) 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:855857, 2013; View this article online at wileyonlinelibrary.com. DOI: 10.1002/mop.27466