Extraordinary transmission caused by symmetry breaking
  The terahertz transmission properties of symmetrical and asymmetrical annular apertures arrays (AAAs) are investigated both experimentally and numerically. It is found that only odd order resonant modes are observed for the symmetrical structures but both odd and even order resonances can be shown for the asymmetrical structures. Breaking the symmetry of AAAs by gradually displacing the H-shaped AAAs to U-shaped AAAs allows an intensity modulation depth of 99% of the second order resonance. Simulation results verify the experimental conclusions well. This result provides a tremendous opportunity for terahertz wavelength tunable filtering, sensing, and near-field imaging. 
Dan Hu, Changqing Xie, Ming Liu, and Yan Zhang
physics.optics