Modeling of multi-band circular dichroism using metal/dielectric/metal achiral metamaterials

We show that an elliptical nanohole array (ENA) penetrating through a metal/dielectric/metal (MDM) film produces multi-band circular dichroism (CD) in the near infrared (N-IR) region when the incident light is off-normal incidence. This extrinsic CD is a result of the elliptical symmetry of the nanohole, which gives rise to different polarization modes along its short and long axes. These two polarization modes introduce a net polar vector that forms a chiral triad with the off-normal incidence and the vector normal to the plane of the ENA. The proposed structure possesses four resonance peaks arising from the excitation of both internal- and external- surface plasmon polariton (SPP) modes with different diffraction orders to those wavelengths at which they couple to the incoming light. The formation of these resonance peaks is responsible for the multi-band CD.