Dual-wavelength plasmonic perfect absorber suitable for refractive index sensing
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Dual-wavelength plasmonic perfect absorber suitable for refractive index sensing Zahra Madadi 1 & Kambiz Abedi 2
&
Ghafar Darvish 1 & Mehdi Khatir 1
Received: 25 July 2019 / Accepted: 30 September 2019 # Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract In this paper, a plasmonic perfect absorber (PPA) based on metal-insulator-metal-insulator-metal (MIMIM) structure has been designed for refractive index sensing of glucose solutions (analyte) and then a new method has been proposed for fast, low-cost, and easy measurement of sensor’s sensitivity. Simulation results show that the absorption spectrum of the proposed sensor has two resonance peaks that with an increase in analyte refractive index, both of them are red-shifted. In our proposed measurement technique, two conventional single-wavelength lasers (with wavelengths of 1050 nm and 1750 nm) are used for vertical plane wave light illumination on the structure. Then, the absorbed powers at 1750 nm (A2) and 1050 nm (A1) wavelengths are calculated and variation of the absorption ratio (A2/A1) due to change of analyte refractive index would be introduced as the sensitivity of sensor (S = Δ(A2/A1)/Δn). Obtained results show that the increase of analyte refractive index from n = 1.312 to n = 1.384 will result in an increase of sensor’s sensitivity from 9.3/RIU to 33.475/RIU. Keywords Plasmonic perfect absorber . Refractive index sensor . Absorption ratio . A new definition of sensitivity
Introduction Recently, many researchers work on modeling and construction of plasmonic perfect absorbers (PPAs) as a subset of metamaterial devices. Unit cells of the PPAs usually composed of metal-insulator-metal (MIM) structure so that an insulator layer would be sandwiched between two layers of metal. The metal layer above the insulator layer is corresponding with the pattern of a metamaterial which becomes periodic through repetition of structure’s unit cells within a certain order. The metal layer beneath the insulator layer will be designed as a continuous sheet with a thickness higher than the penetration depth of incident wavelengths; and, it acts like a perfect reflector mirror [1–3]. In such structures, surface plasmon resonances (SPRs) and surface plasmon polaritons (SPPs) will be stimulated in interfaces of metal layers and their adjacent insulator layers. These absorbers can be used as
* Kambiz Abedi [email protected] 1
Department of Electrical and Computer Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran
2
Faculty of Electrical Engineering, Shahid Beheshti University, Tehran, Iran
photonic biosensors. For example, photonic biosensors based on a periodic array of nano-patterns such as metal nano-bars, metal nano-discs, dipole nano-antennas with additional arms, circular holes, and cross-shaped apertures in the metal layer have been presented during recent years [4–10]. Sensing process in these devices takes place in a way that propagation constant of SPPs in absorber structure would be changed through chan
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