Dual-ribbon grating resonance modes: a survey based on diffraction orders.

Adjustable resonant peaks are necessary for high-precision photonic devices in biosensing, filtering, and optical communication. In this study, we focus on dual-ribbon two-dimensional gold gratings with varying periods and examine the Rayleigh conditions for different grating periods in detail to understand the excitation of resonance wavelengths. We demonstrate adjustable resonance behavior in an asymmetric dual-ribbon gold grating with periods ranging from 400 to 600 nm. The structure consists of subwavelength gold ribbons on a molybdenum disulfide (MoS) monolayer, supported by a silica substrate. At visible resonant wavelengths, analysis of the field distributions reveals surface plasmon (SP) excitation, accompanied by the transformation of propagating diffraction orders into evanescent waves. When the resonant peak occurs at the wavelength where the transmission diffraction order vanishes, SPs are excited at the MoS-gold ribbon interface and within the transmission domain. In contrast, by vanishing the reflection diffraction orders, SPs are excited at the gold ribbon-air interface and in the reflection domain. Understanding SP excitation wavelengths highlights the potential of these gratings for tunable nanoscale photonic devices. Their precise resonance control and simple fabrication make them suitable for scalable optical applications.