Time：Jun 5, 2023
On June 2, Prof. Lin Chen from Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Prof.Cheng-Wei QiufromNational University of Singapore, Prof. Feng-Liang Dong from National Center for Nanoscience and Technology, Prof.Shang Zhang fromThe University of Hong Kong published new advances in Advanced Photonics. The paper is entitled Topological Landau-Zener Circuits.
Topology-integrated optical circuits are robust against errors from the fabrication process, so they have widely attracted the interest of study. By manipulating topological boundary states, quantized pump transport, non-Abelian braid and one-way transmission of photon states can be realized. These studies can be beneficial to the development of basic units of optical circuits, such as coupler, switcher, and multiplexer/demultiplexer, so as to effectively improve the overall performance of optical computing and optical interconnection networks.
The researchers found that the closed band gap under topological protection will open up due to finite-size effect, while the unit number of topological waveguide arrays decays. In this case, topological edge states (TESs) will suffer from two different dynamical processes, i.e., Landau-Zener tunneling and Landau-Zener single-band evolution. The ratio of TESs energy participating in these two processes is governed by the speed of evolution. Further research demonstrates that TESs propagate along one boundary when Landau-Zener tunneling occurs, while TESs transport from one boundary to another during Landau-Zener single-band evolution. Based on these dynamical characteristics of TESs, a channel converter is designed and fabricated. Whether the device will convert channel or not is controlled by the device length, wavelength and coupling coefficients between waveguides. The experiment has demonstrated a near-unity conversion efficiency at 1550 nm. In this work, the special finite-size topological waveguide arrays are introduced. Landau-Zener dynamics have been proposed to manipulate the TESs dynamically, which provides an alternative way to modulate/control the transport light. The presented topological LZ nanophotonic devices can be extended to study other optical fields in nano-photonics, such as Non-Hermitian system, Non-Abelian braiding and High-order topological phase. In the meantime, the channel converter can function as a binary optical switching function unit in optical routing networks on chip. Multiple cascaded channel converters may serve as a multiplexer or demultiplexer in an optical interconnection network.
This work was supported by the National Natural Science Foundation of China and the National Key Research and Development Program of China. This paper is jointly collaborated with Dr. Bing-Cong Xu, Dr.Ming Deng, Prof. Jian Wang, Prof.Lin Chen from Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Prof. Bi-Ye Xie from The Chinese University of Hong Kong (Shenzhen), Dr. Wei Heng, Dr. Wei-Jing Chen, Prof. Cheng-Wei Qiu fromNational University of Singapore, Prof.Li-Hua Xu, Prof. Feng-Liang Dong from National Center for Nanoscience and Technology, Prof. Shuang Zhang fromThe University of Hong Kong.
FIG.1 Landau-Zener model in finite-size topological waveguide arrays. (a) topological waveguide arrays (b) The propagation constant of a single waveguide versus its width. (c-d) The eigen-spectrum of topological waveguide arrays when unit-cell number is M = 10 (c) and M = 2 (d). (e) The Landau-Zener model in Fig. 1(d) with different coupling coefficicents.
FIG.2 Edge-to-edge channel converter with different device lengths. The field intensity distributions of E2 for edge-to-edge channel conversion of the two TESs: L = 10 um (a), L = 20 um (b), and L = 100 um (c).
FIG.3 Experimental demonstration. (a-c) The SEM imagines of the entire device and some partial details. (d-e) The stimulated optical field intensity at output port of the edge-to-edge channel converter. (f-e) Comparison between the simulated and experimental result of channel conversion efficiency, where lines labels the simulation data while the dots response to the experimental data.
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