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Studying the physics of exceptional points using metamaterials

Final Report Summary - NHERMPHOTON (Studying the physics of exceptional points using metamaterials)

The goal of this project is to demonstrate the extraordinary physics of exceptional points of non-Hermitian optical systems using metamaterials as a generic platform. We explore new and unique ways of establishing exceptional points using metamaterials. By sweeping across an exceptional point, we can demonstrate tunability and reconfigurability of optical properties, either in scattering or emission properties with enhanced sensitivity. Apart from exploring the fundamental physics of exceptional points, the investigations point towards applications of modulators, sensing applications, 3d displays and holographic applications.

In this project, we are interested in non-Hermitian systems and therefore have been putting our focus on parity-time symmetry, a simple example of non-Hermitian systems, and the associated exceptional points. Due to the ability of metamaterials to have both magnetic and electric responses, there are more degrees of freedom to construct parity-time symmetric systems using metamaterials than using dielectrics. By cross-matching permittivity and permeability or by using bianisotropy of metamaterials with appropriate gain-loss contrast, we have developed a unique theoretical approach based on interpreting the system constitutive matrix as Hamiltonian to construct parity-time symmetric systems. On one hand, our approach gives rise to an equivalent set of special wave phenomena, such as laser-absorber, phase transition, unidirectional zero reflection, etc, proving metamaterials constitute a versatile platform for studying non-Hermiticity. On the other hand, the resonating nature of metamaterial structures enables a much smaller system thickness to have sufficient light-matter interaction, leading us to more compact parity-time symmetric systems. We have then employed microwave transmission lines coupled with metamaterial structures to experimentally demonstrate phase transition of coherent perfect absorption and unidirectional zero reflection with a subwavelength system thickness. These developments represent significant advance in concepts and represent valuable tools for constructing exceptional-point-based devices in the field of optics and classical waves in a broader context. The resonance in metamaterials can also be used to enhance sensitivity in sensing applications based on PT-symmetry.

The fellow joined the University of Birmingham as a Senior Lecturer. During the project, the fellow, leading an independent research group of students, postdocs and visiting staff, has developed collaborations with various groups in Europe, UK and US. These include Vienna University, Aalto University, Exeter University, Queen Mary University of London while maintaining his original collaborations in mainland China and industry. The project accelerates much on the development of fellow’s career, allowing him to travel around to disseminate results through 19 publications and over 20 invited talks, with a promotion to Reader in Photonics. These newly established connections to Europe will allow the fellow to increase his international visibility and competitiveness as well.