Tunable Absorber in the Terahertz Band Based on Black Phosphorus

This paper presents a novel tunable absorber design based on black phosphorus (BP) for regulating light absorption within a specific frequency range. The structure is made up of monolayer of BP, silicon photonic crystal, and perfect electric conductor (PEC) reflective layer. Investigate its absorption characteristics using the finite-difference time-domain (FDTD) method. The study shows that this absorber can achieve significant absorption enhancement within a specific narrow band. This enhancement mechanism is attributed to the physical principle of critical coupling. Further analysis indicates that the absorption performance largely depends on the polarization state of light, with distinctly different absorption peaks observed under TE and TM polarization. By fine-tuning the structure, incident angle, and polarization angle, the absorption characteristics can be effectively controlled. Moreover, by adjusting the electron doping concentration of the BP layer and changing the surrounding refractive index, the adaptability and tunability of the device can be enhanced. These findings are not only significant for understanding the operational mechanism of BP in optoelectronic applications but also provide an experimental basis and design insights for the development of novel tunable optoelectronic devices.