Coherent perfect absorption via bound states in the continuum in periodic silver grating–borophene structures

Efficient and dynamically controllable electromagnetic absorption is essential for integrated optoelectronic systems. Here, we propose a periodic silver grating–borophene structure that supports coherent perfect absorption mediated by a bound state in the continuum (BIC). By tuning the silver grating width, a parameter-dependent BIC is formed through the complete suppression of radiative leakage. The corresponding evolution of the absorption spectra, quality factor, and electric field distributions reveals that the BIC originates from the cancelation of radiation channels rather than from the disappearance of the mode itself. Based on this mechanism, the structure is further optimized to achieve critical coupling in the telecommunication band, where the single-port absorption reaches the theoretical limit of 0.5. By introducing two counter-propagating coherent beams, perfect absorption is obtained, and reversible switching between coherent perfect absorption and coherent perfect transmission is realized through phase modulation. In addition, the absorber exhibits a clear transverse magnetic-selective response and moderate polarization tolerance under oblique incidence. These results provide a compact borophene-based platform for tunable telecommunication-band absorbers, optical switches, and phase-controlled photonic modulation.