About narrow band optical digital filters based on metamaterials

The challenge for our work is setting a band pass filter with the central frequency f0 in visible range, which presents a very narrow band, so it is very selective. The material of the filter is represented by a layered metamaterial with constituents of tens of nanometer order, disposed geometrical in a manner in which can ensure a very precise control of the plasmons propagation at layers interface. We have studied and proposed a set of structures presenting a high tuning level concerning the wave propagation. Dielectric substrate layers with metallic inclusions were considered. Absorption and transmission coefficients were determined in order to find a correlation between the geometrical parameters which ensures a very narrow band of the filter structure. Analysis was performed using a structural simulation technique with help of the HFSS program. The S parameters of the filter structures were determined using a test configuration with the sample in a channel waveguide. For a set of specific wavelengths in the domain of 420 – 580 nm, desired filters were obtained, presenting a bandwidth which represents less than 1 % of the f0 value, depending on the metamaterial properties. The external tuning of the bandwidth is in study, by modifying the propagation direction of the incident field.