Contents lists available at ScienceDirect Optics & Laser Technology journal homepage: www.elsevier.com/locate/optlastec Full length article Highly sensitive fiber grating chemical sensors: An effective alternative to atomic absorption spectroscopy Lata.S. Laxmeshwar a , Mangesh S. Jadhav a , Jyoti.F. Akki b , Prasad Raikar c , Jitendra Kumar d , Om prakash d , U.S. Raikar a, ⁎ a Department of Physics, Karnatak University, Dharwad 580003, Karnataka, India b JSS college, Dharwad, Karnataka, India c Department of CAE, Centre for Post graduate studies, VTU, Muddenahalli, Chikkaballapur, Karnataka, India d Laser System Engineering Division, Raja Ramanna Centre for Advanced Technology, Indore, Madhya Pradesh, India ARTICLE INFO Keywords: Chemical sensors Short period gratings Long period gratings Zinc AAS Sensitivity ABSTRACT Accuracy in quantitative determination of trace elements like Zinc, present in drinking water in ppm level, is a big challenge and optical fiber gratings as chemical sensors may provide a promising solution to overcome the same. This paper presents design of two simple chemical sensors based on the principle of shift in characteristic wavelength of gratings with change in their effective refractive index, to measure the concentration of Zinc in drinking water using etched short period grating (FBG) and Long period grating (LPG) respectively. Three samples of drinking water from different places have been examined for presence of Zinc. Further, the results obtained by our sensors have also been verified with the results obtained by a standard method, Atomic absorption spectroscopy (AAS). The whole experiment has been performed by fixing the fibers in a horizontal position with the sensor regions at the center of the fibers, making it less prone to disturbance and breaking. The sensitivity of LPG sensor is about 205 times that of the FBG sensor. A few advantages of Fiber grating sensors, besides their regular features, over AAS have also been discussed, that make our sensors potential alternatives for existing techniques in determination of trace elements in drinking water. 1. Introduction Zinc (Zn) is an important dietary component in human beings and animals. Human beings obtain the required amount of Zn through food and water. Natural water contains very small concentration of Zn but domestic water supply may get contaminated due to Zn entering into it from deterioration of galvanized iron and dezincification of brass [1,2]. Industrial and household waste containing Zn, through leakages in sewage systems, discharge into water sources and cause severe pollu- tion in surface and underground water [3]. Due to leaching of Zn from piping and fittings, tap water has shown higher concentration of Zn [4,5] and in certain circumstances, found to have 10% contribution to the overall Zn intake in humans [6,7] . Wells also have been reported to have high concentration of Zn [5,6]. Although not considered hazar- dous, overdose of Zinc may cause nausea, vomiting, dizziness, colics, feverand diarrhea in human beings and if it exceeds a certain limit it may also prove to be toxic. Drinking water containing Zn at levels above 3 mg/litre tends to be opalescent, develops a greasy film when boiled, and has an undesirable astringent taste [5,8]. According to WHO and United States Environmental Protection Agency the max- imum permissible concentration of Zn in drinking water is 3–5 ppm [5,9]. Thus, examining concentration of Zinc in drinking water accurately is essential to make it potable. The most widely used methods of Zinc determination in drinking water are Atomic absorption spectroscopy (AAS) and inductively coupled plasma(ICP) methods. Some other methods used are Dithizone method I and the zincon method. However, all these methods are spectroscopic methods requiring costly and huge equip- ments and need proper sampling and storage [10]. They also have their limitations when concentration to be measured is in ppm level. Optical Fiber grating(OFG) sensors may provide a good option as highly sensitive chemical sensors in determining the concentration of trace elements in water. OFGs are of two types, Short period Fiber Bragg Gratings (FBG) and Long period Gratings (LPG). Both FBG and LPG sensors have already made a mark in the field of research for measurement of parameters like strain, pressure and temperature. There are a few research papers that report the use of etched FBGs and LPGs in the http://dx.doi.org/10.1016/j.optlastec.2016.11.025 Received 2 September 2016; Received in revised form 12 November 2016; Accepted 28 November 2016 ⁎ Corresponding author. E-mail address: usraykar_kud@yahoo.co.in (U.S. Raikar). Optics & Laser Technology 91 (2017) 27–31 0030-3992/ © 2016 Elsevier Ltd. All rights reserved. MARK