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Nanophotonics and topology have attracted considerable interest due to the unique properties they offer. One area of interest is the investigation of topological limit states (TES). These states have captured widespread attention because they are highly resistant to mistakes and imperfections.
Derived from topologically non-trivial phases, TESs provide a powerful toolkit for the architectural design of photonic integrated circuits. TES transport has led to the discovery of various intriguing optical effects and applications, including directional couplers, unidirectional waveguides, mode-locked waveguides, and pseudospin propagation in ring resonator arrays.
Scientists have recently expanded their efforts to manipulate TES by exploring techniques such as adiabatic modulation, non-linear effects and complex entanglement. Optical systems have demonstrated a number of intriguing phenomena, such as edge-to-edge topological transport and tunable localization of topological states. These phenomena have immense potential for the development of cutting-edge technologies and applications, including energy and information routing, non-linear photonics and quantum computing.
Although current methods focus on the manipulation of TESs, they have not yet paid much attention to improving the interaction between TESs. By improving the coupling between TESs, researchers can enable the exchange of light energy between different parts of a topological lattice, which can help control TES transport more flexibly.
A group of researchers from the Wuhan National Laboratory for Optoelectronics (WNLO) and the School of Optical and Electronic Information (OEI) of the Huazhong University of Science and Technology (HUST) in China recently made a major breakthrough. As reported in Advanced photonicsdeveloped an innovative approach to efficiently manipulate the TES transport for an optical channel switch on a silicon-on-insulator (SOI) chip.
Their study focused on edge-to-edge channel conversion in a four-level waveguide grating using the Landau-Zener (LZ) model. By exploiting the finite size effect in a two unit cell optical lattice, they established an alternative, efficient and dynamic method to modulate and control the transport of topological modes.
The waveguide grating they used is similar to a 2D material called Chern insulator, which is known to have TES. As the number of unit cells decreases, TESs evolve according to the LZ model. By applying the LZ single-band evolution principle, the researchers were able to dynamically control the TESs and achieve near-perfect channel conversion.
Topological LZ nanophotonic devices have the potential to be used in various other applications. They can be used as switches that operate at specific wavelengths of light. By incorporating LZ dynamics into different systems, it may be possible to create chiral channel conversions. This concept can also be extended to more complex waveguide gratings, allowing for even more advanced devices.
The researchers found that these topological LZ optical devices are quite robust, meaning they can perform well even when certain parameters are changed. This opens opportunities to develop practical devices such as optical switches for routing networks on computer chips or devices that can combine or separate multiple signals in a waveguide.
Bing-Cong Xu et al, LandauZener Topological Nanophoton Circuits, Advanced photonics (2023). DOI: 10.1117/1.AP.5.3.036005
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