关键词: terahertz, topological phase, dynamic control, exceptional points

Abstract: With the rapid advancement of terahertz technology, multifunctional coding metasurfaces have emerged as a significant research frontier in this domain. However, the rigid geometric structure of traditional metasurfaces poses challenges in accommodating both multifunctionality and dynamic control requirements. This study proposes an adjustable exceptional topological phase coding metasurface device based on a Dirac semimetal (DSM). By optimizing the structural parameters to excite multiple exceptional points (EPs), the resulting topological phase distribution enables multi-dimensional control of terahertz waves. The results demonstrate that, under the incidence of left-handed circularly polarized (LCP) light, the metasurface device can stably generate vortex light with a topological charge of $l = 1$. In the left- and right-handed circularly polarized channels, the wavefronts of the vortex beam and the split beam are independently controlled, enabling dual-channel digital holographic imaging of the numerals '0' and '5'. Near-field grayscale imaging of the 'little grey dog' pattern is achieved by exploiting the differentiated absorption characteristics of the EP under LCP illumination. Furthermore, by dynamically tuning the Fermi level of the DSM, reversible switching of the reflection mode state is realized under the same incident conditions. This research provides a theoretical and practical foundation for enhancing the capacity of terahertz communication systems and optimizing terahertz near-field and far-field imaging technologies. It also holds significant scientific value and application potential for advancing the development of independently adjustable multifunctional devices.

Key words: terahertz, topological phase, dynamic control, exceptional points