Isotropic spiral plasmonic metamaterial for sensing large refractive index change.

We numerically investigate the optical properties of a spiral G-shaped metamaterial, which exhibits both a sharp resonance with a high-quality factor and a broad resonance with a long linear slope in the near-infrared region. By employing the sharp resonating mode, refractive index sensing with sensitivity up to 410 nm/RIU is demonstrated theoretically. In addition, the metamaterial shows single wavelength sensing ability, which allows fast determination of environmental refractive index changes as large as 0.5 by simply monitoring variations in the transmitted intensity of a certain wavelength, which will be beneficial to the development of refractive index sensors based on monochromatic light sources and detectors. As the resonances are independent of the polarization direction of a linearly polarized wave, the sensor manufacturing process will benefit as a result of the lack of an alignment requirement for the axis of polarizers with the metamaterials' orientation.