Reconfigurable wide-angle broadband terahertz wave antireflection using a non-volatile phase-change material.

Actively wide-angle broadband terahertz (THz) antireflection (AR) coatings with a flexible reconfigurability have a great potential for the development of next-generation versatile THz components and systems with high performance. Here, we present a reconfigurable wide-angle broadband THz AR coating using a phase change material GeSbTe (GST) film, which is based on the impedance matching method. The performance of GST-based AR coating can be effectively achieved by a thermal excitation, exhibiting the complete suppression of unwanted THz-wave reflections for incidence angles from 0 to 50 in the broad frequency range of 0.1-3.0 THz. Simulation and experimental results show that the GST-based AR coating can efficiently eliminate Fabry-Perot interference caused by unwanted THz-wave reflections from the substrate, thereby significantly improving the performances of THz devices. Moreover, the active AR mechanism of the GST-based coating is investigated, which elucidates the essential role of the phase transition between the amorphous and crystalline phases in changing the conductivity of the film to achieve an impedance matching condition under thermal excitation. Additionally, the non-volatile properties of GST can enable the AR coating to retain a long-term stability for optimal wave-impedance matching without power holding requirements. Our work provides a new, to the best of our knowledge, and promising way for realizing high-performance integrated THz components and systems in the future.