Nanophotonics and topology have garnered significant attention due to their unique properties and the exciting possibilities they offer. One particular area of focus is the exploration of topological edge states (TESs), which have gained widespread interest due to their remarkable resistance to errors and imperfections.
TESs, arising from topologically non-trivial phases, provide a powerful toolkit for designing photonic integrated circuits. The study of TES transport has led to the discovery of intriguing optical effects and applications, such as directional couplers, one-way waveguides, mode-locked waveguides, and pseudospin propagation in ring resonator arrays.
Recently, scientists have extended their efforts to manipulate TESs by investigating techniques like adiabatic modulation, non-linear effects, and complex braiding. Optical systems have exhibited a range of fascinating phenomena, including edge-to-edge topological transport and tunable localization of topological states. These phenomena hold great potential for cutting-edge technologies and applications, such as energy and information routing, non-linear photonics, and quantum computing.
While current methods primarily focus on manipulating TESs, there has been less attention given to enhancing the interaction between TESs. By improving the coupling between TESs, researchers can facilitate the exchange of light energy between different parts of a topological lattice, enabling more flexible control over TES transport.
A significant breakthrough in this area has recently been achieved by a group of researchers from the Wuhan National Laboratory for Optoelectronics (WNLO) and the School of Optical and Electronic Information (OEI) at Huazhong University of Science and Technology (HUST) in China. As reported in Advanced Photonics, they have developed an innovative approach to efficiently manipulate TES transport for an optical channel switcher on a silicon-on-insulator (SOI) chip.
Their study focuses on edge-to-edge channel conversion in a four-level waveguide lattice using the Landau-Zener (LZ) model. By harnessing the finite-size effect in a two-unit-cell optical lattice, they have established an alternative, effective, and dynamic method to modulate and control the transport of topological modes.
The waveguide lattice employed in their study bears resemblance to a 2D material known as a Chern insulator, which harbors TESs. As the number of unit cells decreases, the TESs evolve according to the LZ model. Leveraging the LZ single-band evolution principle, the researchers successfully achieved dynamic control of the TESs, resulting in nearly perfect channel conversion.
Topological LZ nanophotonic devices hold potential for a range of other applications. They can function as switches operating at specific wavelengths of light. By incorporating LZ dynamics into different systems, it may be possible to realize chiral channel conversions. This concept can be extended to more complex waveguide lattices, enabling the development of even more advanced devices.
The researchers discovered that these topological LZ optical devices exhibit robustness, allowing them to perform reliably even when certain parameters are altered. This opens up opportunities to develop practical devices, such as optical switches for routing networks on computer chips or devices capable of combining or separating multiple signals in a waveguide.