Research Article Plasmon-Waveguide Resonances with Enhanced Figure of Merit and Their Potential for Anisotropic Biosensing in the Near Infrared Region Said Mahajna, Michal Neumann, Ofer Eyal, and Atef Shalabney Physics and Optical Engineering Department, Ort Braude College, 21982 Karmiel, Israel Correspondence should be addressed to Atef Shalabney; shalabney@braude.ac.il Received 22 September 2016; Accepted 15 November 2016 Academic Editor: Marco Consales Copyright © 2016 Said Mahajna et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Te TM and TE guided modes in the coupled plasmon-waveguide resonance confguration are investigated in the spectral domain. Here we use the modes dispersion to study their capability for sensing in the near infrared region. It is shown that the spectral widths of the guided modes are, at least, one order of magnitude smaller than the conventional surface plasmon resonance counterpart. Te enhanced sensitivity and fgure of merit of the guided modes reveal their potential for sensing in the spectral interrogation method where the traditional confgurations are inherently limited. Moreover, the high resolution associated with the narrow resonances and the polarization dependence make these modes very promising for anisotropic biosensing in the spectral interrogation approach. Te extremely high fgure of merit, large penetration depth, and propagation distance in the near infrared region open the possibility of combining the plasmon-waveguide confguration with absorption spectroscopy techniques for molecular recognition. 1. Introduction A great deal of interest has been recently shown in optical sensors based on surface plasmon resonances (SPRs). Tese are obtained when surface plasmon waves (SPWs) are reso- nantly excited on the interface between thin flms, made of noble metals such as silver and gold, and a dielectric medium. Te SPR modes are highly sensitive to the optical properties of the adjacent dielectric medium, making them a powerful tool for biosensing and molecular detection [1–14]. Te Kretschmann–Raether (KR) confguration is widely used for SPR sensing in which a prism coupler with a high refractive index (RI) is used to achieve the momentum matching condition. Te main features that are ofen considered in SPR-based sensors are the sensitivity (  or   for angular interrogation or spectral interrogation, resp.), fgure of merit (FOM), penetration depth inside the sensed medium, and the propagation distance. Although SPR sensors exhibit the highest sensitivity among those based on the evanescent- waves phenomenon, tremendous eforts have been invested in the last two decades to improve their sensitivity, FOM, and detection limit [3]. As an extension of the SPR technique, Tollin and cowork- ers have reported on the development of a modifed design in which a dielectric layer is added on top of the thin metallic flm [15–18]. In this confguration, the so-called coupled plasmon-waveguide resonance (CPWR), the dielectric layer gives rise to the appearance of guided modes in addition to the SPR excitations. Unlike the conventional SPR structure, the additional guided modes can be excited in both TE and TM polarization state. Being excited inside the dielectric top layer, which acts as the waveguide, the guided modes have large propagation distances on the analyte interface making them highly efcient for sensing. Tis large propagation distance is realized through the extremely narrow angular bandwidths of the resonances, which in turn increase the resolution of the measurement. Moreover, the dielectric slab mechanically and chemically protects the metallic flm and increases the sensor lifetime. All these advantages made CPWR-based sensors well suited and promising for the study Hindawi Publishing Corporation Journal of Sensors Volume 2016, Article ID 1898315, 6 pages http://dx.doi.org/10.1155/2016/1898315