SPR Based Fiber Optic Sensor

SPR Based quality Optic Sensor Utilizing abridge Film of Nickel Kruti Shah and NavneetK. Sharma De objet dartment of Physics and Materials Science and Engineering,Jaypee Institute of learning Technology, A-10,Sector-62, Noida-201307,India Corresponding author emailprotectedac.in Abstract.Fiber eye detector base on summon plasmon plangency, employing thin ingest of nickel note is presented analytically. Increase in heaviness of nickel film results in the enhancement of sensitivity of the sensing element. SPR Sensor support by large burdensomeness of nickel film possesses maximum sensitivity.INTRODUCTIONSurface plasmon ring i.e. SPR principle has been an important sensing method since last thirty years. In the beginning, chemical sensing utilizing SPR is demonstrated by Liedberg et al. 1.Collective resonating oscillations of impoverished electrons survive on metal story. It produces charge density riffle locomote along the metal story. This charge density rock is tran sverse wave in nature and is identified as muster up plasmon wave. Surface plasmon wave is excited by incident p-polarized get off. For examining surface plasmon resonance, Kretschmann geometry is exercised 2, 3. Optical fiber based SPR sensors offer many advantages than prism based SPR sensors 4-6.In the past, lot of enquiry is conducted on optical fiber based SPR sensors 7-10. In recent times, nickel (Ni) is shown to exhibit sensing relevance because of its excellent magneto optical merits 11. apart from this, Ni is chemically inactive and the cost of Ni is lower than that of imposing metals. Hence, the use of Ni instead of noble metals decreases the price of SPR sensor. Current story discusses a SPR based fiber optic sensor utilizing thin film of Ni. Effect of thickness of Ni film on the sensitivity of SPR sensor is illustrated. Sensitivity is enhanced with the increase in the thickness of Ni film.THEORYSensing constitution of the sensor contains fiber core-Ni layer-sample medium. Plastic cladding about the core from the commutation part of step mogul multimode PCS fiber is eradicated and is covered with thin layer of Ni. This layer of Ni is ultimately enclosed by the sample medium. accompanying light from a white light source is allowed to enter into whiz end of the optical fiber and the transmitted light is noticed at the opposite end of the optical fiber.The core of optical fiber is organize by f utilize silica. Refractive index of fused silica alters with wavelength as, 23 22322 22221 22111b ab ab a) ( n? +? +? + = (1) Here, ? is the wavelength of incident light in m and a1, a2, a3, b1, b2 and b3 atomic number 18 Sellmeier coefficients. The values of coefficients, used in (1) are specified as, a1 = 0.6961663, a2 = 0.4079426, a3 = 0.8974794, b1 = 0.0684043 m, b2 = 0.1162414 m and b3 = 9.896161 m 12.The dielectric constant of a metal can be mentioned as, ) ( 1 ) (22? ? ? ? ?i ic pcmi mr m+ ? = + = (2) Where, ?p and ?c are plasma and collision wavelengths of the metal respectively. For, Ni p?= 2.5381 x 10-7 m andc?= 2.8409 x 10-5 m. Also, the dielectric constant of sample medium is written as,2s sn =? where, sn is refractive index of the sample medium. Resonance condition for the surface plasmon wave is written as, K Re sin nsp=12 (3) Here, 2 22s ms ms ms mspn nc K+ =+ =? is the wave vector of surface plasmon wave and c is the velocity of light in vacuum. Reflection coefficient of p-polarized light is calculated by using matrix method 13.Normalized transmitted federal agency from the sensor is computed as 14. Further, the sensitivity of sensor can be exposit as change in resonance wavelength per unit change in refractive index of sample medium 15. RESULTS AND DISCUSSION For simulation, refractive index of sample medium is presumed to be altered from 1.33 to 1.37. Values of various parameters used are mentioned as fibers numerical aperture = 0.24, core diameter of fiber = 600 m and exposed sensing region length = 1 5 mm.Transmitted origin from the sensor is measured for different thicknesses (20 nm-80 nm) of Ni layer and consequent resonance wavelengths are measured. Resonance wavelengths for different thicknesses increase linearly with increase in the refractive index of the sample medium. 20 40 60 80 0 15003000 4500 6000 7500Sensitivity (nm/RIU)Thickness of Ni layer (nm) FIGURE 1. Variation of sensitivity with thickness of Ni layer. Figure 1 represents the variation of sensitivity with Ni layer thickness.Ni layer thickness is increased from 20 nm to 80 nm. Sensitivity is enlarged with increase in Ni layer thickness. The fence for this enhancement in sensitivity is ascribed to advanced value of real part of dielectric constant of Ni. Therefore for a fixed change in refractive index of sample medium, Ni enhances the shift between resonance wavelengths. This results in enhanced sensitivity of sensor with increase in Ni layer thickness.Thus, large Ni layer thickness leads in high sensitivity of SPR based sensor.CONCLUSIONS Theoretical analysis of SPR based fiber optic sensor with thin layer of Ni is carried out. Sensitivity of SPR based sensor is enlarged with increase in Ni layer thickness. In drift to achieve highest sensitivity of the sensor, large thickness of Ni layer is advised. ACKNOWLEDGEMENTS Navneet K. Sharma wishes to thank Defence Research Development Organization (DRDO), India for the financial grant provided by means of the project number ERIP/ER/DG-ECS/990116205/M/01/1687.REFERENCESB. Liedberg, C. Nylander and I. 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