We studied the sensing properties of stereo-SRRs metamaterials composed from two twisted split-ring resonators (SRRs). Due to the strong hybridization effect in the system, the polarization state of the transmitted wave is greatly changed at resonances. Since the stereo-SRRs structure is strongly coupled to the surrounding medium, the polarization change of the transmitted waves is quite sensitive to the refractive index change of the environment medium. The polarization ratio ？ ？ / is used as sensing parameter and its figure of merit can reach 22.3 at the hybridized magnetic plasmon resonance. The results showed that the stereo-SRRs metamaterial can be applied to optical sensors an or other related field. 1. Introduction Recently, a new concept in nanophotonics named as stereometamaterial was proposed [1]. This indicated that the electromagnetic properties of plasmonic metamaterials are determined not only by the geometry structure of elements but also by the spatial arrangement of these elements. Up to now, some different stereometamaterials are reported, such as gammadions [2], spirals [3], crosses [4], and stacked wires [5]. Among them, the twisted-SRRs system, also named as stereo-SRRs, is an interesting example for investigation. According to the previous studies, the electromagnetic responses could be tuned through changing the orientation angle of the SRRs [6]; a Lagrange model was introduced to demonstrate the chiral optical properties [7] and give a good description for the polarization change of the electromagnetic wave passing through the twisted-SRRs metamaterials [8, 9]. As is well known, surface plasmon resonance and localized surface plasmon resonance based on metal structures can be used as optical sensors because the resonance modes shift with the refractive index change of the surrounding medium [10, 11]. Since the magnetic plasmon resonance had a stronger field localization and narrower response linewidth, it could also be used as sensors [12, 13]. In this work, we will show that polarization change induced by magnetic plasmon resonances in the stereo-SRRs could be strongly coupled to the environment and is sensitive to the refractive index fluctuation of the surrounding medium. Stereo-SRRs structure could possibly work as a new kind of optical sensor. 2. Design of Numerical Models Figure 1 presents one unit cell of the stereo-SRRs metamaterial with its geometry parameters. The structure is composed of two stacked SRRs, between which there is a twisted angle 90°. The period of the unit cell is ？nm. The incident electromagnetic wave
References
[1]
O. Graydon, “A clever twist,” Nature Photonics, vol. 3, no. 3, p. 176, 2009.
[2]
A. V. Rogacheva, V. A. Fedotov, A. S. Schwanecke, and N. I. Zheludev, “Giant gyrotropy due to electromagnetic-field coupling in a bilayered chiral structure,” Physical Review Letters, vol. 97, no. 17, pp. 177401–1774014, 2006.
[3]
J. K. Gansel, M. Thiel, M. S. Rill et al., “Gold helix photonic metamaterial as broadband circular polarizer,” Science, vol. 325, no. 5947, pp. 1513–1515, 2009.
[4]
M. Decker, M. Ruther, C. E. Kriegler et al., “Strong optical activity from twisted-cross photonic metamaterials,” Optics Letters, vol. 34, no. 16, pp. 2501–2503, 2009.
[5]
N. Liu, L. Langguth, T. Weiss et al., “Plasmonic analogue of electromagnetically induced transparency at the Drude damping limit,” Nature Materials, vol. 8, no. 9, pp. 758–762, 2009.
[6]
N. Liu, H. Liu, S. Zhu, and H. Giessen, “Stereometamaterials,” Nature Photonics, vol. 3, no. 3, pp. 157–162, 2009.
[7]
H. Liu, J. X. Cao, S. N. Zhu, N. Liu, R. Ameling, and H. Giessen, “Lagrange model for the chiral optical properties of stereometamaterials,” Physical Review B, vol. 81, no. 24, pp. R2414031–R2414034, 2010.
[8]
H. Liu, D. A. Genov, D. M. Wu et al., “Magnetic plasmon hybridization and optical activity at optical frequencies in metallic nanostructures,” Physical Review B, vol. 76, no. 7, pp. 0731011–0731014, 2007.
[9]
T. Q. Li, H. Liu, T. Li et al., “Magnetic resonance hybridization and optical activity of microwaves in a chiral metamaterial,” Applied Physics Letters, vol. 92, no. 13, pp. 1311111–1311113, 2008.
[10]
J. Homola, “Surface plasmon resonance sensors for detection of chemical and biological species,” Chemical Reviews, vol. 108, no. 2, pp. 462–493, 2008.
[11]
J. N. Anker, W. P. Hall, O. Lyandres, N. C. Shah, J. Zhao, and R. P. Van Duyne, “Biosensing with plasmonic nanosensors,” Nature Materials, vol. 7, no. 6, pp. 442–453, 2008.
[12]
T. Driscoll, G. O. Andreev, D. N. Basov et al., “Tuned permeability in terahertz split-ring resonators for devices and sensors,” Applied Physics Letters, vol. 91, no. 6, pp. 0625111–0625113, 2007.
[13]
J. X. Cao, H. Liu, T. Li, S. M. Wang, Z. G. Dong, and S. N. Zhu, “High sensing properties of magnetic plasmon resonance in the double-rod and tri-rod structures,” Applied Physics Letters, vol. 97, no. 7, pp. 0719051–0719053, 2010.
[14]
M. A. Ordal, L. L. Long, R. J. Bell et al., “Optical properties of the metals Al, Co, Cu, Au, Fe, Pb, Ni, Pd, Pt, Ag, Ti, and W in the infrared and far infrared,” Applied Optics, vol. 22, no. 7, pp. 1099–1119, 1983.
[15]
L. J. Sherry, S. H. Chang, G. C. Schatz, R. P. Van Duyne, B. J. Wiley, and Y. Xia, “Localized surface plasmon resonance spectroscopy of single silver nanocubes,” Nano Letters, vol. 5, no. 10, pp. 2034–2038, 2005.
[16]
N. Liu and H. Giessen, “Coupling effects in optical metamaterials,” Angewandte Chemie, vol. 49, no. 51, pp. 9838–9852, 2010.
