A bidirectional broadband multifunctional terahertz device based on vanadium dioxide

We propose a bidirectional and switchable terahertz absorber/reflector, utilizing vanadium dioxide. Detailed simulations reveal that the device is capable of achieving broadband absorption and reflection by manipulating the phase state of vanadium dioxide. Specifically, when vanadium dioxide is in its insulating phase, the device exhibits exceptional bidirectional broadband absorption characteristics, with an absorptivity exceeding 90% across a frequency range of 1.9 THz to 10 THz for both forward and backward TE/TM-polarized incident waves. Notably, this absorption behavior remains robust regardless of the polarization angle of the incident wave. When vanadium dioxide transitions to its metal phase, the device demonstrates a reflectivity of over 90% in the lower frequency range for forward and backward TE-polarized incident waves. In the higher frequency range, the device exhibits both reflection and absorption effects for TE-polarized waves. The performance of the device is insensitive to the angle of incidence of electromagnetic waves whether the vanadium dioxide is in the insulating or metallic phase. Furthermore, when the device is used as an absorber (reflector), changes in vanadium dioxide conductivity do not affect the stable performance of the device at high (low) frequencies. Given its versatility and high efficiency, the device has promising applications in a number of fields such as terahertz energy harvesting, sensing, optical switching and shielding.