Optics Communications 402 (2017) 618–623 Contents lists available at ScienceDirect Optics Communications journal homepage: www.elsevier.com/locate/optcom Analytical modelization of a fiber optic-based surface plasmon resonance sensor Issam Haddouche, Lynda Cherbi *, Mohamed Lamine Ferhat Laboratory of Instrumentation, Institute of Electronics and Computer Engineering, USTHB University, Bab Ezzouar, Algeria article info Keywords: Surface plasmon resonance Fiber optic sensors Water analysis Transfer matrix method abstract In this paper, the design of an optical sensor for water analysis based on the Surface Plasmon Resonance (SPR) technique is discussed, the sensor is a metal-coated optical fiber. An analytical model is developed to study the performance of the sensor by carrying out a comparative study between the different materials that the sensor parts are made of, in order to investigate how they affect the sensitivity and resonance visibility of the SPR sensor. The credibility of results is verified using the TMM method. Calculation results of the two methods agree reasonably well with each other, and show that a smaller refractive index contrast between the optical fiber material and the outer medium can remarkably enhance sensitivity, they also reveal that working with metals having lower plasma frequency can as well improve sensor performance. Results also suggest that the visibility of the plasmonic resonance is reduced for wavelength values where light absorption by water is important. © 2017 Elsevier B.V. All rights reserved. 1. Introduction Surface plasmon resonance (SPR) is a label-free refractive index (RI) sensing technique [1], which has been extensively studied in the last years due to its various qualities. Among all existing RI sensing technologies, SPR is the most widely used, it is characterized by the lowest resolution ever achieved in the order of 10 −7 refractive index unit (RIU) [1]. Like all label-free techniques, SPR sensing gives the ability to make analyses without having to bind target-analytes to special chemi- cal markers such as fluorophores, this remarkably simplifies sensor setup and shortens sample preparation time [2]. When a surface plasmon (SP) wave propagating in a metal/dielectric interface is excited with an incident light wave, the later loses most of its energy to the SP wave if the two are phase matched at a given wavelength and angle of incidence, this is known as the resonance condition [3]. The wavelength and angle of resonance directly depend on the refractive index of the surrounding medium [4], as illustrated in Fig. 1. It is worth noting that metals are not the only materials supporting SP waves [5,6], graphene based plasmonics is also a new emerging research area that finds use in different applications such as tunable transmission applications [7] or even in fiber optic-based SPR sensing [8]. In the early years of SPR sensing, prisms were used to couple the incident light to the SP wave [9,10], subsequently optical fibers * Corresponding author. E-mail addresses: ihaddouche@usthb.dz (I. Haddouche), cherbi_lynda@hotmail.com (L. Cherbi), ferhat.mlamine@gmail.com (M.L. Ferhat). started to replace prisms in many works [11,12], providing a simpli- fied experimental setup [13]. Besides the advantages that all optical sensors provide, optical fibers have even more interesting features to be employed in the field of bio and chemical sensing such as small size, remote sensing, mechanical flexibility, large bandwidth, high voltage insulation and strong light confinement [1,14,15]. In waveguide-based SPR sensing applications, the use of gold or silver coated silica waveguides is very common. When such structures are used for aqueous media analysis, the resonance usually takes place in the visible regime near 600 nm [13,16], at such a low wavelength range the wave-analyte interaction is limited because of the tighter mode confinement [17,18]. In this work we investigate the possibil- ity of enhancing the performance of a waveguide-based SPR sensor for water analysis, by carrying out simulations for different sets of waveguide/metal layer materials. We also study the influence of light absorption by water on the behavior of the sensor in the visible and near infrared regimes. An analytical model is derived for the estimation of the SPR sensor performance, the proposed model allows a direct characterization of sensitivity with respect to different parameters in the structure, the transfer matrix method (TMM) is used for comparison. By using two different simulation methods to solve the same problem, one can make a comparison between the two so the concluded results should have more credibility [19]. The use of the TMM for the modelization of http://dx.doi.org/10.1016/j.optcom.2017.06.086 Received 16 April 2017; Received in revised form 6 June 2017; Accepted 25 June 2017 0030-4018/© 2017 Elsevier B.V. All rights reserved.