SEU Made Progress in Topological Electromagnetic Metamaterials

The discovery of topological states of matter in condensed matter physics has inspired researches on analogous phenomena in classical systems, especially in photonics. Because of the unique electromagnetic features including unidirectional propagation and backscattering-immunity, topological photonic insulator offers a robust way to control electromagnetic wave. Currently, the re-configurability of topological photonic insulator is limited to specific static photonic topological functionalities, and the propagation route of guiding waves is also limited to topological interfaces on static photonic crystals, which is a waste of the inner space of topological photonic crystals. As a result, the compactness and miniaturization of topological photoelectric devices are hindered. Besides, considering device integration and manufacturing cost, the trend towards multifunctional monolithic integration is destined, attracting continuous attention to reconfigurable topological photonic insulator. Nowadays, the reconfiguration of topological photonic insulator is realized through mechanical and thermal adjustments to geometry or material parameters. However, these traditional methods are rather practically infeasible for processed topological photonic crystals, and need extra control devices, which poses difficulties on photoelectric integration and control speed improvement. Under this circumstance, the emergence of reprogrammable electromagnetic metasurfaces in recent years leads to a new digital method for ultrafast electronic control of reconfigurable topological photonic insulators.

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To integrate the flexibility of reprogrammable electromagnetic metasurfaces and the robust electromagnetic propagation ability of topological photonic crystals, the research crew designed and experimented an ultrafast reprogrammable topological electromagnetic metasurfaces where six electronically-controlled positive-intrinsic-negative diodes were placed symmetrically in honeycomb-like units to enable electrical programmability. Through the dynamic switch of diodes, the symmetry of control units will be changed, which further manipulates topological bands. 

Compared to existing reconfigurable topological photonic insulators, the reprogrammable topological electromagnetic metasurfaces proposed by this paper presents significant advantages as follows: First, as the units on reprogrammable topological electromagnetic metasurfaces can be electrically controlled and programmed independently, both its control accuracy and speed superior to that of previous insulators. What’s more, the metasurfaces can be fabricated by a widely-used printed circuit board (PCB) technology, thus it can be seamlessly integrated with PCB-based photoelectric integrated circuits. These unique innovations are crucial to the development of versatile and intelligent topological photoelectric devices, and promise considerable potentials in future practical applications. According to Prof. Alexander Khanikaev (OSA Fellow), the pioneer of topological photonics, this research marks “an important milestone in topological photonics”.

Supported by the “Revolutionary Technologies and Key Scientific Problems” special fund from National Key Research and Development Programs, the 111 Project and European Research Council (ERC), this paper was published with Academician Cui Tiejun from SEU and Prof. Nicolae C. Panoiu from UCL as the corresponding authors, Dr. You Jianwei (former post doctorate of UCL) and Dr. Ma Qian as co-first authors.