Ultra wideband bandstop plasmonic filter in the NIR region based on stub resonators

Abstract

In this study, we propose an ultra-wideband bandstop filter (UWB-BSF) using a plasmonic MIM waveguide coupled with a stub cavity that is investigated using finite-difference time-domain (FDTD). Air and silver are used as insulators and metals, respectively; silver is characterized by the Drude model. The structure can filter the optical telecommunication wavelengths of 1550 nm and 1310 nm. The transmission peak and the resonance wavelength of the basic structure can be tuned by varying the stub resonator’s length and width. In order to improve the filtering function of the bandstop filter at broad bandwidth in the NIR region with maximum transmission peak, the number of stub resonators is increased to two, three, and four stubs with properly studied lengths and a proper horizontal distance between each two stubs. The bandwidth is enhanced from 350 nm, with two stubs, to 620 nm, with three stubs, and 770 nm, with four stubs, respectively. The corresponding filtered wavelength ranges are [1600 nm–1950 nm], [1330 nm–1950 nm] and [1180 nm–1950 nm] respectively. Moreover, with the increase in the number of stubs, the center wavelength achieves a blue shift to lower wavelengths. Further, the paper provides significant applications for plasmonic bandstop filters in highly integrated optical circuits.