Symmetry breaking induced anti-resonance in three dimensional sub-diffraction semiconducting grating

Abstract

A kind of three dimensional, sub-diffraction grating with converging-diverging channel working at terahertz regime has been developed on doped silicon wafers by wet etching. By introducing a geometric asymmetry to the vertical direction of the 3D grating, an anti-resonance is observed near the resonant wavelength of the surface plasmon polariton mode. Numerical simulations reveal that the surface waves propagating on the top and bottom surfaces are decoupled due to the symmetry breaking, which results in the destructive interference of electromagnetic field and thus the anti-resonance in the spectrum. It was also found that the bulk sensitivity of the 3D structure as a terahertz sensor can reach a value up to 8818%/RIU and a figure of merit up to 50.