ABSTRACT To realize wavelength‐selective perfect absorption with an ultrahigh quality factor ( Q ) in the telecom O‐band, an all‐dielectric graphene ‐loaded GaP dimer metasurface is proposed in this work. For wavelengths above 1200 nm, GaP , and SiO 2 are essentially lossless. Dissipation is dominated by monolayer graphene and can be tuned via its Fermi level. Two orthogonal, decoupled quasi‐bound states in the continuum (quasi‐BICs) are introduced by symmetry breaking, allowing independent control of their radiative decay rates. Guided by temporal coupled‐mode theory (TCMT), and first‐order electromagnetic perturbation theory, each quasi‐BIC is tuned to critical coupling (50% peak absorption) and then spectrally aligned to achieve degenerate critical coupling (DCC) and near‐unity total absorption, which can be interpreted in the input–output framework. Results show >99% absorptance at multiple target wavelengths within 1316–1342 nm ( Q > 1650, max 1877). Moreover, tuning the graphene Fermi level from 0.53 to 0.69 eV switches the absorptance from 99% to 4% (modulation depth >95%). The device also exhibits good stability of the peak wavelength position in a non‐collimated system. The demonstrated high‐Q absorption, electrical tunability, and peak‐wavelength stability in the telecom band highlight the platform's potential for quantum photonic components, such as narrowband absorptive filters, high‐extinction optical switches.
Zi et al. (2026) studied this question.