Chemical sensor for nitrate in water using long period optical fiber grating fabricated by point by point method

Abstract

We present long period grating (LPG) fabrication and application of LPG as chemical sensor. We fabricated LPG of grating period 610µm in single mode communication grade fiber using point by point method. Here we used 12watt CO 2 laser to irradiate the fiber. The behavior of resonance wavelength of LPG was studied by immersing it in nitrate solution of concentration ranging from 10ppm to 50ppm. The results showed the linear behavior of resonance wavelength of LPG that can be used to determine the concentration of nitrate in water. Keywords-Long period grating, Chemical sensor, Carbon dioxide laser, Point by point method I INTRODUCTIONWith development in the optical fiber manufacturing fieldproduction of good quality, low loss optical fiber, conventional communication system is switching to optical fiber communication system. Further developments of optical fiber field brought out many optical devices which greatly improved the quality of the signal transmitted. In those fiber optic devices, fiber grating is one. Because of variety of spectral and dispersion characteristics, fiber gratings have various applications in fiber optic devices (including communication and sensors) such as band rejection filter [1], wavelength division multiplexing[2], gain flattening device [3], mode converters [4, 5], fiber laser [6], dispersion compensation component, gain equalizer, comb filter [7] and sensors for various parameters such as bend [8], temperature, humidity [9], pressure [10], strain [11], refractive index [12] and concentration [13].Fiber grating is region of an optical fiber (normally single mode fiber) with periodic refractive index modulation of period Λ [14]. These regular refractive index modulations facilitate interaction between the specific modes of the fiber.Fiber gratings of period of few hundred microns are known as long period gratings (LPG) which couple core mode with forward propagating cladding modes. The high attenuation of cladding modes result in the transmission spectrum of the fiber containing a series of attenuation bands centered at discrete wavelengths, each attenuation band corresponding to the coupling to different cladding mode. Phase matching between the mode propagating in the core of the fiber and a copropagating cladding mode is achieved at the wavelength λ m and is given by the relation (1)m cl co m n n λ (1) where λ m is the peak wavelength of the resonance band between the core mode and the cladding mode, co n and m cl n are effective refractive index of the core mode and of the m th order cladding mode respectively and Λ is the period of LPG. The minimum transmission of the attenuation bands is governed by the expression [15] ( ) L T m i κ 2 sin 1 − = (2) where L is the length of the LPG and m κ is the coupling coefficient for the m th cladding mode. Transmission spectrum of LPG consists of series of attenuation bands as shown in Fig.1.Figure 1. Transmission spectrum of input signal through LPG.

Development of planar electromagnetic sensor array for nitrate and sulphate detection in natural water sources

“…A low pH value caused by sulphate may increase the rate of dissolving minerals in water and then lead to excessive mineral contamination in natural water (Lenoble et al, 2013). Existing water pollution detection methods are spectrophotometry (Ball et al, 2011), ion chromatography, electrochemical sensors (Aravamudhan et al, 2007), fibre optic (Akki et al, 2012) and biosensors. However, the existing detection methods have their drawbacks, such as the need to prepare extra reagent, they are not portable, expensive, require tedious working steps, consume time and have bulky instrument size.…”

Low-Cost Sensors Array Based on Planar Electromagnetic Sensor Simulation for Environmental Monitoring

“…In this research, detection of pollutant that existed in natural water resources is the ultimate concerned. Existing water pollution detection methods are Spectrophotometry [3], Ion Chromatography, Electrochemical [4], Fibre Optic [5], and Biosensors. However, the existing detection method have it own drawbacks such as need to prepare extra reagent, not portable, expensive, required tedious working step, consume time and big instrument size.…”