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

Abstract

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 (MoS₂) 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 MoS₂-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.

Fig. 1

Schematic of light diffraction from the unit cell of a grating with period P and incident angle of . The thickness of the arrows illustrates the light intensity. The incident light has the thickest arrow.

Fig. 2

Schematic of the studied grating with Au ribbons on silica substrate that the MoS₂ monolayer is inserted between them. In the unit cell of the grating, there are two ribbons with different widths ( and ) that are separated by different spacings ( and ). The height of both ribbons is equal and is denoted by h.

Fig. 3

(a) Reflection spectrum () of the structure with  nm,  nm, and different values of and . As a reference, the reflection spectrum of a fully symmetric structure with  nm is inserted with the black solid line as a reference. The red oval shape that is marked as 1 is illustrative for the reflection peak at  nm. (b) , , and and , , and for the structure with  nm. (c)/ (d) , , and / , , and spectrum of the structure with  nm and  nm.

Fig. 4

(a) Reflection spectrum () of the structure with  nm,  nm, and different values of and . As a reference, the reflection spectrum of a fully symmetric structure with  nm is inserted with a black solid line. The two red oval shapes marked as 1 and 2 are illustrative for the reflection peaks at  nm and  nm, respectively. (b) , , and and , , and for the structure with  nm. (c)/ (d) , , and / , , and spectrum of the structure with  nm and  nm.

Fig. 5

field distribution of the structure with  nm,  nm, and  nm/  nm, and  nm at (a)/ (c)  nm (b)/ (d)  nm.

Fig. 6

(a) Reflection spectrum () of the structure with  nm,  nm, and different values of and . As a reference, the reflection spectrum of a fully symmetric structure with  nm is inserted with a black solid line. (b) , , and and , , and for the symmetric structure with  nm. (c)/ (d) , , and / , , and spectrum of the structure with  nm and  nm.

Fig. 7

field distribution of the symmetric structure with  nm,  nm, and  nm at (a)  nm and (b)  nm. In asymmetric structure with  nm,  nm, and  nm and  nm, the field distribution is shown at (c)  nm and (d)  nm.