Investigtion of extraordinary optical transmission properties for double-layered nano-hole perforated gold films

Sub-wavelength periodic nano-holes produce extraordinary optical transmission (EOT) and have been used in biochemical sensing. However, to date the widely used single-layered nano-hole film turns to have reached its limit in accuracy and sensitivity. To provide new insights, this paper proposes to combine the classic Fabry-Pérot interferometer with nano-hole array structure so that both the high-reflectance mirrors of the interferometer are one single-layered nano-hole film. We explored the optical transmission properties for such double-layered nano-hole gold films by simulation studies, and found that i) the transmission spectrum for different in-plane hole-hole misalignments tends to be identical when the layer-layer gap is big enough (e.g., 600 nm), ii) the transmittance doubles in comparison to the single-layered nano-holes when the gap satisfies the resonant condition of the Fabry-Pérot interferometer, and iii) the sensitivity for sensing the refractive index of medium doubles as well and the full width at half maximum for the peak resonant wavelength gets sharper. These favorable properties enable the double-layered nano-holes to outperform the single-layered in accuracy and sensitivity.