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The absorbance of a free-standing ultrathin layer is limited to 50%; we overcome this limitation by numerically investigating a wavelength-selective perfect absorber based on Mie resonance and degenerate critical coupling. We extend the wavelength of close-to-unity absorbance to the entire visible region by controlling the radiative loss and intrinsic loss. Radiative loss can be controlled by embedding the Mie resonator into a thin film with the defined refractive index. Meanwhile, intrinsic loss can be controlled by addition of a dielectric cap with a higher extinction coefficient on the Mie resonator. Such all-dielectric perfect absorbers can be applied to efficient photodetectors, imaging sensor pixels, or all-optical switching devices mediated by the photothermal effect.
Xu et al. (Mon,) studied this question.