Prof.Sebastian Klembt, Topological photonics and topological lasers with coupled vertical resonators

Prof. Sebastian Klembt of Julius-Maximilians-University Würzburg (Germany) presents his work "Topological photonics and topological lasers with coupled vertical resonators"

Abstract
Topological Photonics is an emerging and novel field of research, adapting concepts from condensed matter physics to photonic systems adding new degrees of freedom. After the first demonstrations of topological photonic insulators [1], the field has moved on to study and exploit the inherent non-hermiticity of photonic systems and the interplay with their topological nature. In my talk I will discuss novel photonic lattice devices resulting from the coupling of individual vertical III-V semiconductor microresonators, forming what can be more broadly described as synthetic matter. Here, the so-called exciton-polaritons – hybrid states of light and matter – can emerge in the strong coupling regime. By choosing precise lattice geometries we are able to tailor optical band structures realizing novel photonic lattice. Here, the specific geometry as well as the hybrid light-matter nature allow for ways to break time-reversal symmetry and implement topologically non-trivial systems. Here, we were able to experimentally demonstrate the first exciton-polariton topological insulator, manifesting in chiral, topologically protected edge modes [2]. In order to study topological effects in combination with optical non-linearities, so-called topological lasers have been envisaged and realized. They exploit topological effects to efficiently couple and phase-lock extended arrays of lasers to behave like one single coherent laser. The major drawback so far is that the emission appears in the plane of the topologically protected light propagation, thus hindering light extraction. Here, we have presented the first experimental demonstration of a topological insulator vertical cavity laser array [3], using the so-called crystalline topological insulator model. Starting for the above mentioned examples, I will give an overview of the field of topological optical lattices and lasers and give an outlook on emerging novel materials beyond III-V semiconductors, such as organic materials, transition metal dichalcogenides and perovskites [4,5].

References:
[1] Rechtsman et al. Nature 496, 196–200 (2013); Hafezi et al., Nat. Photon. 7, 1001–1005 (2013)
[2] Klembt et al., Nature 562, 552–556 (2018). [3] Dikopoltsev et al., Science 373, 1514–1517 (2021)
[4] Dusel et al. Nano Lett. 21, 6398–6405 (2021). [5] Shan et al., Nat. Commun. 12, 6406 (2021)

About the speaker
Prof. Sebastian Klembt received his PhD on "II-VI microcavities for the blue-violet spectral range: Lasing in the regime of weak and strong coupling" from the University of Bremen (Germany) with Prof. Detlef Hommel (2009-2013), where he graduated with highest honors “summa cum laude”. After a couple of years as a postdoctoral fellow at Institut Néel (Grenoble, France), he became in 2015 a group leader, MSCA Fellow and later Akademischer Rat at the University of Würzburg. He is since 2020 a Junior Professor (ct.qmat cluster) in Würzburg. He focuses his research on the experimental study of strong light-matter interactions in various systems with a recent focus on optical lattices, quantum simulation and topological effects in optical systems.