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Author: Schmidt, Oliver G. × Author: Valligatla, Sreeramulu × Author: Wang, Jiawei × End date: 2024 × Start date: 2020 × Has files: Yes × Type: Text ×

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    Symmetry‐Induced Selective Excitation of Topological States in Su–Schrieffer–Heeger Waveguide Arrays
    (Weinheim : Wiley-VCH, 2023) Tang, Min; Wang, Jiawei; Valligatla, Sreeramulu; Saggau, Christian N.; Dong, Haiyun; Saei Ghareh Naz, Ehsan; Klembt, Sebastian; Lee, Ching Hua; Thomale, Ronny; van den Brink, Jeroen; Fulga, Ion Cosma; Schmidt, Oliver G.; Ma, Libo
    The investigation of topological state transition in carefully designed photonic lattices is of high interest for fundamental research, as well as for applied studies such as manipulating light flow in on-chip photonic systems. Herein, the topological phase transition between symmetric topological zero modes (TZM) and antisymmetric TZMs in Su–Schrieffer–Heeger mirror symmetric waveguides is reported. The transition of TZMs is realized by adjusting the coupling ratio between neighboring waveguide pairs, which is enabled by selective modulation of the refractive index in the waveguide gaps. Bidirectional topological transitions between symmetric and antisymmetric TZMs can be achieved with proposed switching strategy. Selective excitation of topological edge mode is demonstrated owing to the symmetry characteristics of the TZMs. The flexible manipulation of topological states is promising for on-chip light flow control and may spark further investigations on symmetric/antisymmetric TZM transitions in other photonic topological frameworks.
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    Selective Out‐of‐Plane Optical Coupling between Vertical and Planar Microrings in a 3D Configuration
    (Hoboken, NJ : Wiley, 2020) Valligatla, Sreeramulu; Wang, Jiawei; Madani, Abbas; Naz, Ehsan Saei Ghareh; Hao, Qi; Saggau, Christian Niclaas; Yin, Yin; Ma, Libo; Schmidt, Oliver G.
    3D photonic integrated circuits are expected to play a key role in future optoelectronics with efficient signal transfer between photonic layers. Here, the optical coupling of tubular microcavities, supporting resonances in a vertical plane, with planar microrings, accommodating in‐plane resonances, is explored. In such a 3D coupled composite system with largely mismatched cavity sizes, periodic mode splitting and resonant mode shifts are observed due to mode‐selective interactions. The axial direction of the microtube cavity provides additional design freedom for selective mode coupling, which is achieved by carefully adjusting the axial displacement between the microtube and the microring. The spectral anticrossing behavior is caused by strong coupling in this composite optical system and is excellently reproduced by numerical modeling. Interfacing tubular microcavities with planar microrings is a promising approach toward interlayer light transfer with added optical functionality in 3D photonic systems.
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    Experimental observation of Berry phases in optical Möbius-strip microcavities
    (London [u.a.] : Nature Publ. Group, 2022) Wang, Jiawei; Valligatla, Sreeramulu; Yin, Yin; Schwarz, Lukas; Medina-Sánchez, Mariana; Baunack, Stefan; Lee, Ching Hua; Thomale, Ronny; Li, Shilong; Fomin, Vladimir M.; Ma, Libo; Schmidt, Oliver G.
    The Möbius strip, a fascinating loop structure with one-sided topology, provides a rich playground for manipulating the non-trivial topological behaviour of spinning particles, such as electrons, polaritons and photons, in both real and parameter spaces. For photons resonating in a Möbius-strip cavity, the occurrence of an extra phase—known as the Berry phase—with purely topological origin is expected due to its non-trivial evolution in parameter space. However, despite numerous theoretical investigations, characterizing the optical Berry phase in a Möbius-strip cavity has remained elusive. Here we report the experimental observation of the Berry phase generated in optical Möbius-strip microcavities. In contrast to theoretical predictions in optical, electronic and magnetic Möbius-topology systems where only Berry phase π occurs, we demonstrate that a variable Berry phase smaller than π can be acquired by generating elliptical polarization of resonating light. Möbius-strip microcavities as integrable and Berry-phase-programmable optical systems are of great interest in topological physics and emerging classical or quantum photonic applications.