Nanoplasmonic Ultrawideband Bandpass Filters Using MIM Waveguides and Stepped-Impedance Resonators for Subwavelength Wireless Networks

Abstract

This article presents the design and analysis of three new nanoplasmonic ultrawideband (UWB) bandpass filters (BPFs) using different sets of monoblock quarter-wavelength type (λg=4) stepped impedance resonators (SIRs) integrated into a simple metal-insulator-metal (MIM) waveguide-based half-wavelength (λg=2) SIR designed with three stub pillars. The proposed filter combines the low-pass and bandpass filter topology with two-wire transmission line (TL) theory by enabling impedance and phase-matching techniques instead of open-circuit stubs and SIRs on traditional TLs. Furthermore, integrating Chebyshev prototype synthesis and electromagnetic bandgap (EBG) structures significantly enhances out-of-band suppression and minimizes spurious harmonics. This hybrid analytical-physical design framework ensures broadband performance without compromising size or tunability. Three prototypes of plasmonic UWB BPF, centered at 188.515, 210.3, and 213.42 THz, and with Q-factors 4.02, 3.17, and 3.10, were rigorously analyzed using CST Microwave Studio. The designs demonstrate fractional bandwidths of 23.64%, 31.74%, and 32.28%, respectively, exceeding the performance benchmarks of conventional photonic filters. These results validate the proposed method as a novel and scalable solution for high-density, ultrabroadband plasmonic filtering in next-generation silicon photonic integrated circuits (Si-PICs).

Keywords: BPF, metal-insulator-metal (MIM), nanoplasmonics, silicon photonic integrated circuits (Si-PiCS), SIR, ultrawideband (UWB)