Size reduction of MIM surface plasmon based optical bandpass filters by the introduction of arrays of silver nano-rods

In this paper, first a square-shaped plasmonic cavity (SSPC), which is laterally coupled to two metal-insulatormetal (MIM) waveguides, is used to create a single-mode plasmonic bandpass filter. Thereafter, we try to modify the SSPC topology so that the resonance wavelength (lambda(r)) of the filter be transferred to higher wavelengths (without increasing the SSPC size). Such a technique is equivalent to less footprint for a fixed operational wavelength. Similar ideas are already being used to decrease the size of microstrip antennas, where defects and slots are introduced to the ground plate and the radiating microstrip patch to make the antenna wideband and compact. For this purpose, we discuss the effect of different possible types of defects on the filter's performance. It is shown that among the studied topologies, the best results are obtained for circular defects with square and triangular patterns in the original SSPC. The proposed topologies can provide an approximately 50% increase in the resonance wavelength. All results are obtained using finite difference time domain method. It is worth mentioning that the metals and insulators used in this paper are silver and air and the Drude model has been used for characterization of the silver.