Many applications involve the phenomenon of a material absorbing electromagnetic radiation. By exploiting wave interference, the efficiency of absorption can be significantly enhanced. Here, we propose Friedrich-Wintgen bound states in the continuum (F-W BICs) based on borophene metamaterials to realize coherent perfect absorption with a dual-band absorption peak in commercially important communication bands. The metamaterials consist of borophene gratings and a borophene sheet that can simultaneously support a Fabry-Perot plasmon resonance and a guided plasmon mode. The formation and dynamic modulation of the F-W BIC can be achieved by adjusting the width or carrier density of the borophene grating, while the strong coupling leads to the anti-crossing behavior of the absorption spectrum. Due to the weak angular dispersion originating from the intrinsic flat-band characteristic of the deep sub-wavelength periodic structure, the proposed plasmonic system exhibits almost no change in wavelength and absorption at large incident angles (within 70 degrees). In addition, we employ the temporal coupled-mode theory including near- and far-field coupling to obtain strong critical coupling, successfully achieve coherent perfect absorption, and can realize the absorption switch by changing the phase difference between the two coherent beams. Our findings can offer theoretical support for absorber design and all-optical tuning.
The study focuses on developing materials that can absorb electromagnetic radiation, such as light or radio waves, more efficiently, which is crucial for various applications, particularly in communication technologies. The researchers propose using a special state called Friedrich-Wintgen bound states in the continuum (F-W BICs) with borophene metamaterials to achieve coherent perfect absorption. This means the material can completely absorb certain frequencies of electromagnetic waves without reflecting any back. They specifically target frequencies important for communication technologies.
The metamaterials they are working with consist of borophene gratings (tiny, regular ridges made of boron) and a flat sheet of borophene. These structures can support two types of resonances: Fabry-Perot plasmon resonance and guided plasmon mode, which enhance absorption by interacting with light. By adjusting the width or the number of charge carriers in the borophene grating, they can control the absorption properties of the material. This control enables them to create a dual-band absorption peak, allowing the material to perfectly absorb two different sets of frequencies.
An intriguing aspect of their design is that it maintains stability even when the angle of incoming waves changes, making it highly practical for real-world applications where waves may not always approach head-on. They also utilize a theory called temporal coupled-mode theory to achieve strong coupling between the waves and the material, essential for achieving perfect absorption. They can even switch the absorption on and off by changing the phase difference between two light beams.
In summary, this research offers a pathway to design materials capable of perfectly absorbing specific frequencies of electromagnetic waves, which holds great potential for enhancing communication devices and other technologies reliant on efficient wave absorption.
