Fano resonances and strong field enhancements in arrays of asymmetric plasmonic gap-antennas

In this paper, we numerically study the optical responses of arrays of asymmetric plasmonic gap antennas and show that they support Fano resonances due to symmetry-breaking. The resonance properties can be controlled by the asymmetry. Quality factors more than 30 are achieved, and an enhancement of the electric field exceeding 40 times is predicted to be obtained in antennas with 10-nm wide gaps at the resonance in the near-infrared range. Furthermore, similar designs can be applied in the THz range, and even higher quality factors and stronger field enhancements can be realized. The combination of Fano resonances with gap effects of metallic nanostructures provides an effective way for improvement in light trapping and field enhancement and may find applications in nonlinear optics, sensing, photothermal heat generation, and other areas. (paper)