Recently, perfect absorbers have been extensively studied for applications in photodetectors [1], optical sensors [2], light modulators [3,4], and other related fields. Among various types, perfect absorbers based on single-layer graphene have attracted wide attention due to the absorption properties of graphene and the resonance enhancement of the dielectric layer. Graphene is an ideal two-dimensional material for high-performance optoelectronic devices due to its full spectral response, ultra-fast light response, and ultra-high carrier mobility [[5], [6], [7], [8], [9], [10], [11]]. However, the absorption efficiency of a single-layer graphene is only 2.3% in the visible and near-infrared regions, which hinders its potential application in light absorption [12]. Therefore, enhancing the absorption efficiency of graphene is highly significant. Numerous methods have been proposed to enhance the light absorption of graphene by amplifying the local electromagnetic fields within resonant structures, such as photonic crystals [13], Fabry-Perot (F–P) cavities [14,15], dielectric grating structures [16], metamaterials [17], and metasurfaces [18].

Researchers focus on monolayer graphene absorbers that are based on tunable materials with a variable refractive index. The optical response of the light absorber can be manipulated by the tunability of certain special materials. Among these, nonlinear optical materials like lithium niobate (LN) and 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) [18,19], as well as other electro-optical (EO) materials, have garnered significant attention. The EO effect of these materials means that the refractive index of the material can be controlled by applied voltage. Compared to inorganic materials, organic nonlinear optical materials typically exhibit higher and faster nonlinearity [20], which can effectively enhance the response rate of optical devices. In addition, polymer films are easy to process, and organic crystals exhibit excellent thermal stability. Taking DAST as an example, it has a high melting point of 256 °C, indicating good thermal stability [21,22]. Therefore, organic nonlinear optical materials are extensively utilized in the fields of nonlinear optics and EO modulators.

In addition to integrating the perfect absorbers with EO material, recent studies have focused on multi-channel graphene absorbers instead of the previously reported single-channel devices [23]. For instance, Liu et al. proposed a silver nano-disk that utilizes surface plasmons and magnetic dipole resonances to achieve efficient dual-band absorption in a single-layer graphene [24]. Qing et al. introduced a system that combines guided mode resonance (GMR) and Tamm plasma polarons to achieve dual-channel absorption at 1.534 μm and 1.664 μm [25]. Hu et al. proposed an all-dielectric zero-contrast grating (ZCG) resonator to achieve perfect dual-band absorption of a single-layer graphene in the near-infrared range by exciting F–P cavity resonance and GMR [26]. Based on the concept of critical coupling, Qing and Ma et al. proposed an absorber consisting of gratings, monolayer graphene, and photonic crystals to achieve a dynamically controlled optical switch by adjusting the Fermi level of graphene [27]. The multi-channel graphene absorbers have great potential for applications in optical sensing and light detection. However, most of the previous structures focus on a fixed wavelength and lack tunability, which limits the application of such devices.

In this study, we propose a tunable dual-channel graphene absorber based on the EO effect of DAST. By integrating graphene with the F–P cavity, it is possible to achieve 99.99% absorption in the near-infrared band. On this basis, the quasi-bound states in the continuum (quasi-BICs) mode are excited, by tilting the surface grating to break the structural symmetry, achieving perfect dual-band absorption of single-layer graphene in the near-infrared range (with an absorption rate greater than 95%). By harnessing the EO effect of DAST material, it is possible to adjust the gate voltage in order to alter the refractive index of the material, as well as to fine-tune the half-width and wavelength. Finally, by utilizing the structure's polarization sensitivity, the polarization angle of the incident light is manipulated to achieve the switching of single- and dual-channel absorbers. The proposed dual-channel absorbers, implemented by F–P and quasi-BICs modes, have significant implications for the design and application of multi-channel graphene absorbers.