Optical Ultra-Wideband Nano-Plasmonic Bandpass Filter Based on Gap-Coupled Square Ring Resonators

In this work, an ultra-wideband (UWB) optical bandpass filter (BPF) based on nanoplasmonic structure is designed and thoroughly analyzed. The proposed BPF structure encompasses asymmetric metal-insulator-metal (MIM) slot waveguide that incorporates a gap-coupled series and parallel square ring resonators (SRRs). The characteristic parameters of the MIM waveguide structure are analyzed with a full-wave analysis and a conformal mapping technique (CMT) using a CAD simulation software. These include the normalized propagation constant, the propagation length, and the characteristic impedance. The UWB feature of the proposed structure is mainly dictated by the coupling gaps that combine the feed line with the resonators. Increasing the sequential number of the coupled resonators enhances the optical UWB feature of the proposed design. Two structures with three and five resonators are presented to illustrate the UWB characteristics within the 1235.74-1942 nm, and 1340–2200 nm ranges, respectively. In both cases, the return loss is shown to be higher than 10dB. The proposed nanoplasmonic UWB filter in this work has the potential to replace narrow-bandwidth devices involved in multi-band transmission systems and high-density photonic integrated circuits. The outcomes of this research contribute to the advancement of UWB filter technology for next-generation communication systems and photonics.