A Nanoplasmonic Directional Coupler Utilizing a Backed Conductor on Dielectric Substrate With Finite Width

A new nanoplasmonic directional coupler (DC) is proposed, utilizing a conductor-backed coplanar waveguide (CPW) with a finite width. Our design approach includes first establishing a theoretical transmission-line model for the coupler, and then utilizing the characteristic parameters of related coupled CPW structures for a comprehensive analysis. The provided analysis is conducted through full-wave analysis using a conformal mapping technique (CMT), implemented in CST Microwave Studio Suite CAD simulation software. This article primarily focuses on designing and analyzing the directional coupler using a backed conductor on the dielectric substrate with finite width, applying the transmission line (TL) theory method to achieve a coupling coefficient ( $C_{C}$ ) of 3-dB. The proposed plasmonic coupler operates efficiently at optical frequencies in both the O- and L-bands. Simulations demonstrate that the coupling coefficient of the directional coupler is effectively modulated by varying the width of the backed conductor ( $w_{c}$ ). Consequently, the proposed design surpasses the performance of traditional narrow-bandwidth couplers, offering significant benefits for applications in subwavelength wireless networks and high-density nanoscale photonic integrated circuits (PICs).