- Email: [email protected]
Investigated the Fano resonance in the nano ring arrangement
Optik 138 (2017) 80–86
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
Original research article
Investigated the Fano resonance in the nano ring arrangement Ferdows B. Zarrabi ∗ , Mohammad Nasser Moghadasi Faculty of Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran
a r t i c l e
i n f o
Article history: Received 16 December 2016 Accepted 17 March 2017 Keywords: FANO Nano ring Sub wavelength Controllable field enhancement Plasmonic
a b s t r a c t Field enhancement in Plasmonic and FANO mode at nano antennas are noticed recently, here, we are modeled a nano antenna for achieving Fano resonance and for this aim, we are made asymmetric formation in nano ring structure and studied the parametric effects on Fano resonance controlling. We have debated on E-field enhancements at resonances with comparison the parameters effect on Fano resonance energy. We show that the single ring has plasmonic mode and adding an inner ring made Fano resonance and shows that the energy in dark mode is increased drastically. Here, the study of the inner ring position is indicated that how the bright mode and dark mode have appeared in nano antenna. Figure of merit (FOM) is studied for different additional material effects on prototype structure and (E) variation is noticed. The structure is modeled with FDTD simulation by the CST microwave studio and for substrate; we selected SiN with a thickness of 40 nm. Here for achieving dark mode energy, novel shape of the dual ring nano antenna is suggested for concentration of the energy in small point to increase the interaction between nano particle and bio-particle. © 2017 Elsevier GmbH. All rights reserved.
1. Introduction The renewed interest in the so-called field of plasmonics has come from recent advances in the investigation of the electromagnetic properties of nano-structure materials. The ability of metallic nanostructures to confine and enhance incident radiation offers unique possibilities for manipulating light at the nanoscale by using surface plasmons. The surface plasmon polaritons (SPPs) have been noticed tremendously for enhancement of the electromagnetic energy in a subwavelength and optical regime base on Interaction of light with metal-dielectric materials and the 300–1000 nm wavelength is selected for plasmonic application [1–3]. The Metamaterial is introduced as an especial material with negative permittivity and permeability that are not available in nature and natural structures and made artificially abnormal formation in metal and recently is noticed for making nano antenna [4–6]. Enhancement of the electromagnetic field on a metal surface is taking attention for enhancing sensitivity. The quality of the spectroscopic signal of molecule absorption is important that is called surface enhanced Raman scattering (SERS) [7,8]. During the last decade, Various forms of the nano-antenna in different shape and arrangement is suggested at the optical and infrared range for bio-sensing and spectroscopy application such as monopole (nano rods) [9], Dipole [10], Bowtie
∗ Corresponding author. E-mail address: [email protected] (F.B. Zarrabi). http://dx.doi.org/10.1016/j.ijleo.2017.03.068 0030-4026/© 2017 Elsevier GmbH. All rights reserved.
F.B. Zarrabi, M.N. Moghadasi / Optik 138 (2017) 80–86
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Fig. 1. Prototype nano-antenna top view (a) nano ring antenna (b) the prototype Fano antenna.
Fig. 2. The extinction cross section for both prototype structures.
[11], disk [12] for basic model. Recently, complicated structures such as a U shape [13], SRR (split ring resonator) is developed based on the metamaterial structure [14]. The interaction between plasmon modes of individual nano-structure can generate the subradiant bonding and subradiant antibonding plasmon modes. In plasmonic nanostructures, the asymmetry line shape of the Fano resonance appears the interaction of non-radiative (dark quadrupole) modes with radiative (bright dipole) modes. In addition, the line shape of Fano resonance can be influenced by the near-field interaction between the dark and bright modes [15–17]. The Fano resonance known by the asymmetric line, shape based on hybridization of different plasmon modes and for high-Q structure [18,19]. Asymmetric structure is noticed more Fano resonances such as Ring/Disk Plasmonic Nanocavities [20], interactions between dipole and Multi-pole plasmons in T-shaped nano-rod dimer [21] or Using hotspots in a single-stone ring-like structure [22] and For symmetric formation, Heptamers disk have been studied too much for the simple arrangement [23] or necklaces arrangement [24]. In plasmonic nanostructures, the asymmetry line shape of the Fano resonance appears by interaction of non-radiative (dark quadrupole) modes with radiative (bright dipole) modes. In addition, the line shape of Fano resonance could also be influenced by the near-field interaction between the dark and bright modes [25–27]. Single Fano resonance achieves the interference between one bright mode and one dark mode, combining a bright mode with multiple dark modes can result in multiple Fano resonances [28]. Figure of merit (FOM) is a numerical value as a definition for the quality characteristic and performance of a device or a material for special parameter and in optical devices, various factors are noticed for FOM measurement such as wavelength (), current density (I) and energy change (E) [29–31]. At the first step, the ring structure is implemented and plasmonic mode is obtained. For the second step, the inner ring added to the structure, the Fano resonance is achieved, and for making asymmetric structure, the shift of the inner ring is noticed. The comparison shows how the inner ring will affect on the bright and dark mode in nano antenna. We show that
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F.B. Zarrabi, M.N. Moghadasi / Optik 138 (2017) 80–86
Fig. 3. Field enhancement for both nano-antenna. (a) Dipole mode for nano ring at 3200 nm (b) bright mode for dual ring at 2100 nm (c) (b) dark mode for dual ring at 2900 nm.
how the dark mode improve the antenna energy. The FOM factor studies show that the FOM at Fano resonance is improved in comparison to plasmonic mode. 2. Antenna design Fig. 1 shows the formations of the prototype nano ring antenna. The particle contains two rings that the outer ring is made only plasmonic resonance with outer and inner radius of 250 and 220 nm and the inner ring with outer and inner radius of 160 and 130 nm is implemented to achieve the Fano resonance. In addition, in this condition, the gaps between the rings are 5 nm and in this case the inner ring is shifted 55 nm from the center. The nano structures are placed on a SiN layer with n = 1.98 and total dimensions are 560 × 560 nm2 and thickness 50 nm. The Incident field is defined 1 V/m in X direction and a CST microwave studio full wave simulator has used for simulation with the time domain method and PML (perfect match layer) the incident wave in TE mode with plane wave is made for excitation of the nano-particle.
F.B. Zarrabi, M.N. Moghadasi / Optik 138 (2017) 80–86
83
Fig. 4. The extinction cross section for dual ring with various shifts value from center for inner ring.
3. Simulation result The Extinction cross section is studied as a factor of the probability of absorption and reflection process on the surface plasmon in nano-antenna is based on Mie theory [32] and Because of the importance of scattering quality of nano-antenna in different applications such as SERS and some biomedical applications, here Extinction cross section is obtained for the prototype structures [33]. The Extinction cross section for prototype structures is presented in Fig. 2 for conventional incident wave for both basic models. The first structure (Ring antenna) has a resonance at 2 = 3200 (nm) and at these wavelengths, the maximum of the Extinction cross section is around 2.2E + 06 and it has plasmonic mode at this wavelength. However, the second antenna (dual ring antenna) has two resonances at 2 = 2100 and 2 = 2900 (nm) and at these wavelengths, the maximum of the Extinction cross section is around 1.1E + 06 and 0.9E + 06. The second structure shows Fano resonances and the extinction cross shows the lower value at Fano resonances in comparison to plasmonic resonance. Fig. 3 (a) to (c) shows the electric field enhancement for the ring and dual ring nano-antenna at their resonance frequency. For the first structure, we have a resonance at 3200 nm with |E2 |/|Eint 2 | of 3214 (V/m)2 . For the first structure, we have two resonances at 2100 and 2900 nm with |E2 |/|Eint 2 | of 610 and 14640 (V/m)2 . For the second antenna, the first resonances occurred at bright mode and second resonance is happened at dark mode as shows in Fig. 3. The Fano resonance have improved the Energy at the dark mode more than 400%. The shift of the inner ring effect on the extinction cross section in Fig. 4 is presented. At the first situations, when the inner ring is placed at the center the bonding and antibonding modes [34,35] are appeared for dual ring nano antenna. However, by shifting the inner ring placements, appearing of the Fano modes (bright and dark) are visible at the first resonance. With 55 nm shift, the second is omitted and structures has shown only Fano resonance. Fig. 5(a)–(c) shows the electric field enhancement for the dual ring nano-antenna by various center shifts for 0, 20 and 40 nm for each resonance. Here the electric field enhancements are given for lower to higher wavelength. As shows, here for 0 nm the antenna has a bright mode for both frequencies. In addition, by applying the inner ring shift, the nano antenna shows less bright mode and it has tended to dark mode. In Fig. 5(c) the dark mode, become manifest and the antenna E-field shows more improvement in comparison by the antenna without shift of the inner ring. By Ahmadivand et al., the FOM factor is reported for four various biological material such Ether(R–O–R ) with n = 1.35, Ethylene glycol (HO–CH2CH2–OH) with n = 1.43, Chlorobenzene (C6H5Cl) with n = 1.525, and Quinoline (C6H7N) with n = 1.627 [29]. Here, the FOM factor is obtained for these materials and for DNR system, thickness of the material are assumed 60 nm [36] and this simulation we are selected same thickness for our biomaterials. The FOM results for the ring structure and dual ring model are presented at Fig. 6(a) and (b). The result shows that the FOM factor is increased in dual ring nano antenna in comparison with nano ring antenna. It confirms that the Fano resonance is useful for detection of biomaterial with more sensitivity.
4. Conclusion In this article is debated about the Fano resonance in dual ring nano antenna and shows that how the asymmetric structure improve the dark mode and this dark mode energy is improve the FOM factor in bio-sensing. The electrical field enhancement drastically at the dark mode to more than 14000.
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Fig. 5. Field enhancement for a dual ring nano antenna for various center shift for inner ring (a) without any shift (b) 20 nm shift (c) 40 nm shift.
F.B. Zarrabi, M.N. Moghadasi / Optik 138 (2017) 80–86
Fig. 5. (Continued)
Fig. 6. The figure of merit for various refractive index for all resonances (a) ring nano antenna (b) dual ring nano antenna.
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References [1] V. Giannini, A.I. Fernandez-Domínguez, S.C. Heck, S.A. Maier, Plasmonic nanoantennas: fundamentals and their use in controlling the radiative properties of nanoemitters, Chem. Rev. 111 (6) (2011) 3888–3912. [2] S. Pandesh, M. Maleki, F.B. Zarrabi, The sub-wavelength plasmonic nano-antenna based on cross structure, Optik 127 (2016) 3770–3774. [3] F.B. Zarrabi, M. Naser-Moghadasi, S. Heydari, M. Maleki, A.S. Arezomand, Cross-slot nano-antenna with graphene coat for bio-sensing application, Optics Commun. 371 (2016) 34–39. [4] A. Ahmadivand, N. Pala, Multiple coil-type Fano resonances in all-dielectric antisymmetric quadrumers, Opt. Quantum Electron. 47 (7) (2015) 2055–2064. [5] T. Hadadi, M. Naser-Moghadasi, A.S. Arezoomand, F.B. Zarrabi, Sub wavelength plasmonic nano-antenna with modified ring structure for multi resonance application and circular polarization, Opt. Quantum Electron. 48 (2) (2016) 1–9. [6] F.B. Zarrabi, H. Kuhestani, M. Rahimi, Z. Mansouri, Plasmonic cross-junction ring antenna implementation for field enhancement, Optik 126 (21) (2015) 3129–3131. [7] Y. Chu, W. Zhu, D. Wang, K.B. Crozier, Beamed Raman: directional excitation and emission enhancement in a plasmonic crystal double resonance SERS substrate, Opt. Express 19 (21) (2011) 20054–20068. [8] D. Dey, J. Kohoutek, R.M. Gelfand, A. Bonakdar, H. Mohseni, Quantum-cascade laser integrated with a metal-dielectric-metal-based plasmonic antenna, Optics Lett. 35 (16) (2010) 2783–2785. [9] L. Novotny, Effective wavelength scaling for optical antennas, Phys. Rev. Lett. 98 (26) (2007) 266802. [10] Joshua Borneman, Kuo-Ping Chen, Alex Kildishev, Vladimir Shalaev, Simplified model for periodic nanoantennae: linear model and inverse design, Opt. Express 17 (14) (2009) 11607–11617. [11] Bedir B. Yousif, Ahmed S. Samra, Optical responses of plasmonic gold nanoantennas through numerical simulation, J. Nanoparticle Res. 15 (1) (2013) 1–15. [12] D. Ahmadian, C. Ghobadi, J. Nourinia, Ultra-compact two-dimensional plasmonic nano-ring antenna array for sensing applications, Opt. Quantum Electron. 46 (9) (2014) 1097–1106. [13] A.E. Cetin, M. Turkmen, S. Aksu, H. Altug, Nanoparticle-based metamaterials as multiband plasmonic resonator antennas, Nanotechnol. IEEE Trans. 11 (1) (2012) 208–212. [14] A. Ahmadivand, R. Sinha, S. Kaya, N. Pala, Rhodium plasmonics for deep-ultraviolet bio-chemical sensing, Plasmonics (2015) 1–11. [15] B. Luk’yanchuk, N.I. Zheludev, S.A. Maier, N.J. Halas, P. Nordlander, H. Giessen, C.T. Chong, The Fano resonance in plasmonic nanostructures and metamaterials, Nat. Mater. 9 (9) (2010) 707–715. [16] C. Wu, A.B. Khanikaev, R. Adato, N. Arju, A.A. Yanik, H. Altug, G. Shvets, Fano-resonant asymmetric metamaterials for ultrasensitive spectroscopy and identification of molecular monolayers, Nat. Mater. 11 (1) (2012) 69–75. [17] P. Fan, Z. Yu, S. Fan, M.L. Brongersma, Optical Fano resonance of an individual semiconductor nanostructure, Nat. Mater. 13 (5) (2014) 471–475. [18] M. Naser-Moghadasi, F.B. Zarrabi, S. Pandesh, H. Rajabloo, M. Bazgir, Optical FANO resonance with polarization independence with novel nano-antenna, Opt. Quantum Electron. 48 (4) (2016) 1–9. [19] A. Ahmadivand, M. Karabiyik, N. Pala, Intensifying magnetic dark modes in the antisymmetric plasmonic quadrumer composed of Al/Al 2 O 3 nanodisks with the placement of silicon nanospheres, Opt. Commun. 338 (2015) 218–225. [20] A.E. Cetin, H. Altug, Fano resonant ring/disk plasmonic nanocavities on conducting substrates for advanced biosensing, ACS Nano 6 (11) (2012) 9989–9995. [21] Y. Binfeng, H. Guohua, C. Jiawei, C. Yiping, Fano resonances induced by strong interactions between dipole and multipole plasmons in T-shaped nanorod dimer, Plasmonics 9 (3) (2014) 691–698. [22] A. Ahmadivand, R. Sinha, S. Kaya, N. Pala, A molecular plasmonic Fano-router: using hotspots in a single-stone ring-like structure, Opt. Commun. 367 (2016) 123–129. [23] J. Ye, F. Wen, H. Sobhani, J.B. Lassiter, P.V. Dorpe, P. Nordlander, N.J. Halas, Plasmonic nanoclusters: near field properties of the Fano resonance interrogated with SERS, Nano Lett. 12 (3) (2012) 1660–1667. [24] A. Ahmadivand, S. Golmohammadi, M. Karabiyik, N. Pala, Fano resonances in complex plasmonic necklaces composed of gold nanodisks clusters for enhanced LSPR sensing, Sens. J. IEEE 15 (3) (2015) 1588–1594. [25] B. Luk’yanchuk, N.I. Zheludev, S.A. Maier, N.J. Halas, P. Nordlander, H. Giessen, C.T. Chong, The Fano resonance in plasmonic nanostructures and metamaterials, Nat. Mater. 9 (9) (2010) 707–715. [26] A. Lovera, B. Gallinet, P. Nordlander, O.J. Martin, Mechanisms of Fano resonances in coupled plasmonic systems, ACS Nano 7 (5) (2013) 4527–4536. [27] W. Cao, R. Singh, I.A. Al-Naib, M. He, A.J. Taylor, W. Zhang, Low-loss ultra-high-Q dark mode plasmonic Fano metamaterials, Optics Lett. 37 (16) (2012) 3. [28] M. Rahmani, B. Luk’yanchuk, M. Hong, Fano resonance in novel plasmonic nanostructures, Laser Photonics Rev. 7 (3) (2013) 329–349. [29] A. Ahmadivand, R. Sinha, N. Pala, Hybridized plasmon resonant modes in molecular metallodielectric quad-triangles nanoantenna, Opt. Commun. 355 (2015) 103–108. [30] Kenneth Diest, Vladimir Liberman, Donna M. Lennon, Paul B. Welander, Mordechai Rothschild, Aluminum plasmonics: optimization of plasmonic properties using liquid-prism-coupled ellipsometry, Optics Express 21 (23) (2013) 28638–28650. [31] Andreas Tittl, Christian Kremers, Jens Dorfmüller, Dmitry N. Chigrin, Harald Giessen, Spectral shifts in optical nanoantenna-enhanced hydrogen sensors, Opt. Mater. Express 2 (2) (2012) 111–118. [32] J.A. Scholl, A.L. Koh, J.A. Dionne, Quantum plasmon resonances of individual metallic nanoparticles, Nature 483 (7390) (2012) 421–427. [33] M. Gellner, B. Küstner, S. Schlücker, Optical properties and SERS efficiency of tunable gold/silver nanoshells, Vib. Spectrosc. 50 (1) (2009) 43–47. [34] F.B. Zarrabi, M. Mohaghegh, M. Bazgir, A.S. Arezoomand, Graphene–gold nano-ring antenna for dual-resonance optical application, Opt. Mater. 51 (2016) 98–103. [35] Chia-Yang Tsai, Shao-Ping Lu, Jyun-Wei Lin, Po-Tsung Lee, High sensitivity plasmonic index sensor using slablike gold nanoring arrays, Appl. Phys. Lett. 98 (15) (2011) 153108. [36] Y. Zhang, T.Q. Jia, H.M. Zhang, Z.Z. Xu, Fano resonances in disk–ring plasmonic nanostructure: strong interaction between bright dipolar and dark multipolar mode, Opt. Lett. 37 (23) (2012) 4919–4921.
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
Original research article
Investigated the Fano resonance in the nano ring arrangement Ferdows B. Zarrabi ∗ , Mohammad Nasser Moghadasi Faculty of Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran
a r t i c l e
i n f o
Article history: Received 16 December 2016 Accepted 17 March 2017 Keywords: FANO Nano ring Sub wavelength Controllable field enhancement Plasmonic
a b s t r a c t Field enhancement in Plasmonic and FANO mode at nano antennas are noticed recently, here, we are modeled a nano antenna for achieving Fano resonance and for this aim, we are made asymmetric formation in nano ring structure and studied the parametric effects on Fano resonance controlling. We have debated on E-field enhancements at resonances with comparison the parameters effect on Fano resonance energy. We show that the single ring has plasmonic mode and adding an inner ring made Fano resonance and shows that the energy in dark mode is increased drastically. Here, the study of the inner ring position is indicated that how the bright mode and dark mode have appeared in nano antenna. Figure of merit (FOM) is studied for different additional material effects on prototype structure and (E) variation is noticed. The structure is modeled with FDTD simulation by the CST microwave studio and for substrate; we selected SiN with a thickness of 40 nm. Here for achieving dark mode energy, novel shape of the dual ring nano antenna is suggested for concentration of the energy in small point to increase the interaction between nano particle and bio-particle. © 2017 Elsevier GmbH. All rights reserved.
1. Introduction The renewed interest in the so-called field of plasmonics has come from recent advances in the investigation of the electromagnetic properties of nano-structure materials. The ability of metallic nanostructures to confine and enhance incident radiation offers unique possibilities for manipulating light at the nanoscale by using surface plasmons. The surface plasmon polaritons (SPPs) have been noticed tremendously for enhancement of the electromagnetic energy in a subwavelength and optical regime base on Interaction of light with metal-dielectric materials and the 300–1000 nm wavelength is selected for plasmonic application [1–3]. The Metamaterial is introduced as an especial material with negative permittivity and permeability that are not available in nature and natural structures and made artificially abnormal formation in metal and recently is noticed for making nano antenna [4–6]. Enhancement of the electromagnetic field on a metal surface is taking attention for enhancing sensitivity. The quality of the spectroscopic signal of molecule absorption is important that is called surface enhanced Raman scattering (SERS) [7,8]. During the last decade, Various forms of the nano-antenna in different shape and arrangement is suggested at the optical and infrared range for bio-sensing and spectroscopy application such as monopole (nano rods) [9], Dipole [10], Bowtie
∗ Corresponding author. E-mail address: [email protected] (F.B. Zarrabi). http://dx.doi.org/10.1016/j.ijleo.2017.03.068 0030-4026/© 2017 Elsevier GmbH. All rights reserved.
F.B. Zarrabi, M.N. Moghadasi / Optik 138 (2017) 80–86
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Fig. 1. Prototype nano-antenna top view (a) nano ring antenna (b) the prototype Fano antenna.
Fig. 2. The extinction cross section for both prototype structures.
[11], disk [12] for basic model. Recently, complicated structures such as a U shape [13], SRR (split ring resonator) is developed based on the metamaterial structure [14]. The interaction between plasmon modes of individual nano-structure can generate the subradiant bonding and subradiant antibonding plasmon modes. In plasmonic nanostructures, the asymmetry line shape of the Fano resonance appears the interaction of non-radiative (dark quadrupole) modes with radiative (bright dipole) modes. In addition, the line shape of Fano resonance can be influenced by the near-field interaction between the dark and bright modes [15–17]. The Fano resonance known by the asymmetric line, shape based on hybridization of different plasmon modes and for high-Q structure [18,19]. Asymmetric structure is noticed more Fano resonances such as Ring/Disk Plasmonic Nanocavities [20], interactions between dipole and Multi-pole plasmons in T-shaped nano-rod dimer [21] or Using hotspots in a single-stone ring-like structure [22] and For symmetric formation, Heptamers disk have been studied too much for the simple arrangement [23] or necklaces arrangement [24]. In plasmonic nanostructures, the asymmetry line shape of the Fano resonance appears by interaction of non-radiative (dark quadrupole) modes with radiative (bright dipole) modes. In addition, the line shape of Fano resonance could also be influenced by the near-field interaction between the dark and bright modes [25–27]. Single Fano resonance achieves the interference between one bright mode and one dark mode, combining a bright mode with multiple dark modes can result in multiple Fano resonances [28]. Figure of merit (FOM) is a numerical value as a definition for the quality characteristic and performance of a device or a material for special parameter and in optical devices, various factors are noticed for FOM measurement such as wavelength (), current density (I) and energy change (E) [29–31]. At the first step, the ring structure is implemented and plasmonic mode is obtained. For the second step, the inner ring added to the structure, the Fano resonance is achieved, and for making asymmetric structure, the shift of the inner ring is noticed. The comparison shows how the inner ring will affect on the bright and dark mode in nano antenna. We show that
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Fig. 3. Field enhancement for both nano-antenna. (a) Dipole mode for nano ring at 3200 nm (b) bright mode for dual ring at 2100 nm (c) (b) dark mode for dual ring at 2900 nm.
how the dark mode improve the antenna energy. The FOM factor studies show that the FOM at Fano resonance is improved in comparison to plasmonic mode. 2. Antenna design Fig. 1 shows the formations of the prototype nano ring antenna. The particle contains two rings that the outer ring is made only plasmonic resonance with outer and inner radius of 250 and 220 nm and the inner ring with outer and inner radius of 160 and 130 nm is implemented to achieve the Fano resonance. In addition, in this condition, the gaps between the rings are 5 nm and in this case the inner ring is shifted 55 nm from the center. The nano structures are placed on a SiN layer with n = 1.98 and total dimensions are 560 × 560 nm2 and thickness 50 nm. The Incident field is defined 1 V/m in X direction and a CST microwave studio full wave simulator has used for simulation with the time domain method and PML (perfect match layer) the incident wave in TE mode with plane wave is made for excitation of the nano-particle.
F.B. Zarrabi, M.N. Moghadasi / Optik 138 (2017) 80–86
83
Fig. 4. The extinction cross section for dual ring with various shifts value from center for inner ring.
3. Simulation result The Extinction cross section is studied as a factor of the probability of absorption and reflection process on the surface plasmon in nano-antenna is based on Mie theory [32] and Because of the importance of scattering quality of nano-antenna in different applications such as SERS and some biomedical applications, here Extinction cross section is obtained for the prototype structures [33]. The Extinction cross section for prototype structures is presented in Fig. 2 for conventional incident wave for both basic models. The first structure (Ring antenna) has a resonance at 2 = 3200 (nm) and at these wavelengths, the maximum of the Extinction cross section is around 2.2E + 06 and it has plasmonic mode at this wavelength. However, the second antenna (dual ring antenna) has two resonances at 2 = 2100 and 2 = 2900 (nm) and at these wavelengths, the maximum of the Extinction cross section is around 1.1E + 06 and 0.9E + 06. The second structure shows Fano resonances and the extinction cross shows the lower value at Fano resonances in comparison to plasmonic resonance. Fig. 3 (a) to (c) shows the electric field enhancement for the ring and dual ring nano-antenna at their resonance frequency. For the first structure, we have a resonance at 3200 nm with |E2 |/|Eint 2 | of 3214 (V/m)2 . For the first structure, we have two resonances at 2100 and 2900 nm with |E2 |/|Eint 2 | of 610 and 14640 (V/m)2 . For the second antenna, the first resonances occurred at bright mode and second resonance is happened at dark mode as shows in Fig. 3. The Fano resonance have improved the Energy at the dark mode more than 400%. The shift of the inner ring effect on the extinction cross section in Fig. 4 is presented. At the first situations, when the inner ring is placed at the center the bonding and antibonding modes [34,35] are appeared for dual ring nano antenna. However, by shifting the inner ring placements, appearing of the Fano modes (bright and dark) are visible at the first resonance. With 55 nm shift, the second is omitted and structures has shown only Fano resonance. Fig. 5(a)–(c) shows the electric field enhancement for the dual ring nano-antenna by various center shifts for 0, 20 and 40 nm for each resonance. Here the electric field enhancements are given for lower to higher wavelength. As shows, here for 0 nm the antenna has a bright mode for both frequencies. In addition, by applying the inner ring shift, the nano antenna shows less bright mode and it has tended to dark mode. In Fig. 5(c) the dark mode, become manifest and the antenna E-field shows more improvement in comparison by the antenna without shift of the inner ring. By Ahmadivand et al., the FOM factor is reported for four various biological material such Ether(R–O–R ) with n = 1.35, Ethylene glycol (HO–CH2CH2–OH) with n = 1.43, Chlorobenzene (C6H5Cl) with n = 1.525, and Quinoline (C6H7N) with n = 1.627 [29]. Here, the FOM factor is obtained for these materials and for DNR system, thickness of the material are assumed 60 nm [36] and this simulation we are selected same thickness for our biomaterials. The FOM results for the ring structure and dual ring model are presented at Fig. 6(a) and (b). The result shows that the FOM factor is increased in dual ring nano antenna in comparison with nano ring antenna. It confirms that the Fano resonance is useful for detection of biomaterial with more sensitivity.
4. Conclusion In this article is debated about the Fano resonance in dual ring nano antenna and shows that how the asymmetric structure improve the dark mode and this dark mode energy is improve the FOM factor in bio-sensing. The electrical field enhancement drastically at the dark mode to more than 14000.
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Fig. 5. Field enhancement for a dual ring nano antenna for various center shift for inner ring (a) without any shift (b) 20 nm shift (c) 40 nm shift.
F.B. Zarrabi, M.N. Moghadasi / Optik 138 (2017) 80–86
Fig. 5. (Continued)
Fig. 6. The figure of merit for various refractive index for all resonances (a) ring nano antenna (b) dual ring nano antenna.
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F.B. Zarrabi, M.N. Moghadasi / Optik 138 (2017) 80–86
References [1] V. Giannini, A.I. Fernandez-Domínguez, S.C. Heck, S.A. Maier, Plasmonic nanoantennas: fundamentals and their use in controlling the radiative properties of nanoemitters, Chem. Rev. 111 (6) (2011) 3888–3912. [2] S. Pandesh, M. Maleki, F.B. Zarrabi, The sub-wavelength plasmonic nano-antenna based on cross structure, Optik 127 (2016) 3770–3774. [3] F.B. Zarrabi, M. Naser-Moghadasi, S. Heydari, M. Maleki, A.S. Arezomand, Cross-slot nano-antenna with graphene coat for bio-sensing application, Optics Commun. 371 (2016) 34–39. [4] A. Ahmadivand, N. Pala, Multiple coil-type Fano resonances in all-dielectric antisymmetric quadrumers, Opt. Quantum Electron. 47 (7) (2015) 2055–2064. [5] T. Hadadi, M. Naser-Moghadasi, A.S. Arezoomand, F.B. Zarrabi, Sub wavelength plasmonic nano-antenna with modified ring structure for multi resonance application and circular polarization, Opt. Quantum Electron. 48 (2) (2016) 1–9. [6] F.B. Zarrabi, H. Kuhestani, M. Rahimi, Z. 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