Revolutionizing optical control with topological edge conditions

Nanophotonics and topology have gained significant interest because of the unique properties they offer. One area of ​​focus is topological edge state (TES) investigation. This state has attracted widespread attention because it is highly resistant to error and imperfection. Arising from topological nontrivial phases, TES provides a powerful tool for the architectural design of photonic integrated circuits. TES transport has led to the discovery of a variety of interesting optical effects and applications, including directional coupling, one-way waveguide, mode-locked waveguide and pseudospin propagation in ring resonator arrays.

Scientists have recently expanded their efforts to manipulate TES by exploring techniques such as adiabatic modulation, nonlinear effects, and complex braiding. Optical systems have exhibited a variety of interesting phenomena, such as end-to-end topological transport and adaptable topological state localization. This phenomenon has great potential for the development of cutting-edge technologies and applications, including energy and information routing, nonlinear photonics and quantum computing.

While current methods focus on the manipulation of TES, they have not paid much attention to enhancing interactions between TES. By increasing the coupling between TES, researchers can enable the exchange of light energy between different parts of the topological lattice, which can help control the transport of TES in a more flexible way.

A group of researchers from the Wuhan National Optoelectronics Laboratory (WNLO) and School of Optical and Electronic Information (OEI) at Huazhong University of Science and Technology (HUST) in China recently made a significant breakthrough. As reported in Advanced Photonics, they developed an innovative approach to efficiently manipulate TES transport for optical channel switching on silicon-on-insulator (SOI) chips. Their study focuses on edge-to-edge channel conversion in a four-level waveguide lattice using the Landau-Zener (LZ) model. By exploiting finite size effects in a two-unit cell optical lattice, they established an alternative, effective, and dynamic method to modulate and control the transport of topological modes.

The waveguide lattice they used is similar to a 2D material called a Chern insulator, which is known to have TES. When the number of unit cells decreased, TES evolved according to the LZ model. By applying the LZ single-band evolution principle, the researchers can dynamically control TES and achieve near-perfect channel conversion.

Topological LZ nanophotonic devices have the potential to be used in a variety of other applications. They can be used as switches that act on certain wavelengths of light. By incorporating LZ dynamics into different systems, it is possible to make chiral channel conversions. This concept can also be extended to more complex waveguide grids, enabling more sophisticated devices.

The researchers found that the LZ optical devices of this topology are quite robust, meaning they can perform well even when certain parameters are changed. This opens up 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.

Read the article Open Access Gold by B.-C. Xu, B.-Y Xie, L.-H. Xu, et al., “Landau-Zener Topological Nanophotonic Circuits,” Photo continued. 5(3), 036005 (2023), two 10.1117/1.AP.5.3.036005.