Extraordinary optical absorption based on guided-mode resonance.

We propose a novel structure that can achieve extraordinary optical absorption over the visible spectrum, based on the guided-mode resonance effect. An optical metal grating with moderate thickness and high filling factor can lead to coupling between the quasi-guided-mode and cavity mode. The resonant interaction between the two modes can influence the field distribution, such as the magnetic field near the grating, which results in extraordinary absorption. Absorption efficiency can be optimized up to 99.16%. We also show that the absorption peak can be readily tuned just by varying the subwavelength grating period.