2015): High-sensitivity plasmonic sensor based on perfect absorber with metallic nanoring structures, Journal of Modern Optics,We propose a nanoring array structure backed by a metal mirror to achieve perfect infrared absorber with absorption as high as 99.99%. The frequency of the absorption peak strongly depends on the refractive index surrounding the structured surface, while the maximum of absorption remains constant with varying the surrounding refractive index. These features can be used as plasmonic sensor for refractive index measurement. This plasmonic sensor possesses the figure of merit 700. In addition, we investigate the effect of various materials on the performance of the sensor, including SiO 2 , TiO 2 , TiN, and Al 2 O 3 dielectric spacer and Au, Ag, Al, and Cu back plate and top structure. Due to the high sensitivity and simple sensing scheme, the sensing strategy can find potential applications in chemical and biosensor applications.
IntroductionMetallic nanoparticles have been utilized in many fascinating applications based on localized surface plasmon resonance (LSPR), such as surface-enhanced spectroscopy [1,2], detection of biomolecules [3,4], and near-field scanning optical microscopy [5]. This resonance depends strongly on the size and shape of the nanoparticles [6-9], as well as the surrounding dielectric medium [4,10]. Therefore, we can evaluate refractive sensing through the resonance shift due to the variation of the refractive index of surrounding medium. So far, various plasmonic nanostructures have been investigated for sensing a special change of refractive index [12][13][14][15]. These structures include nanospheres [16], nanorods [17], nanoshells [18], nanorice [19], nanostars [2,20], nanorings [21], and so on. Specific physical mechanisms have been also employed to explore more complex plasmonic sensors, such as electromagnetically induced transparency [22].In practical applications, intensity variation of the reflected or transmitted light is measured at a certain wavelength. Sharp peak with large modulation depth is key to obtain a high sensitivity for the LSPR sensor. To enhance the sensitivities of localized plasmon sensors, several structures have been proposed. Ameling et al. utilized the combination of localized plasmons in nanostructures and a photonic microcavity [13]. Liu et al. demonstrated a metal-dielectric-metal structure including metasurface and metallic mirror [23]. Tao et al. designed an ultrathin structure characterized by split-ring resonator-based planar