129th CEMS Colloquium

Title

Semiconductor-based Topological Integrated Photonics

Abstract

It has been recognized that many topological phenomena initially explored in condensed matter physics can also manifest in photonic systems. A representative example is the emergence of topological edge states of light. Analogous to the topological edge states of electrons in solids, these optical edge states enable robust light transport, even in the presence of certain types of structural disorders. This distinctive property is attractive for constructing highly integrated photonic circuits.

In this context, we will discuss on-chip optical waveguides leveraging topological edge states of light, with a particular focus on valley photonic crystal (VPhC) waveguides—one of the topological waveguide platforms realized entirely using semiconductors. Following a brief introduction to VPhC waveguides, we will present the slow-light VPhC waveguides that we proposed [1] and experimentally demonstrated [2]. In contrast to conventional slow-light waveguides, where bending losses are significant, topological slow-light waveguides exhibit substantial suppression of these losses. Furthermore, we will discuss a novel class of VPhC waveguides: VPhC heterostructure waveguides [3], which support guided modes with an expansive mode width while maintaining robustness against sharp bends and defects. Quantifying the robustness of VPhC waveguides against sharp bends and random disorders, as well as elucidating the underlying physical mechanisms, is crucial not only from a scientific perspective but also for practical applications. These key issues will be briefly addressed.

In addition to the topological edge states arising from the topological properties of photonic band structures, optical states characterized by their topological properties in real space, such as optical vortices and optical skyrmions, have also garnered significant attention. Integrated photonics provides a compact and efficient platform for the generation of these optical beams. In this presentation, on-chip optical skyrmionic beam generators implemented using silicon photonics [4] will be discussed.

[1]  H. Yoshimi, et al, Opt. Lett. 45, 2648 (2020).
[2]  H. Yoshimi, et al, Opt. Express 29, 13441 (2021).
[3]  C. Zhang, et al., Opt. Mater. Express 14, 1756 (2024).
[4]  W. Lin, et al., Optica 11, 1588 (2024).

Contact

email: miho.okada@riken.jp
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