Soliton metacrystals: topology and chirality

The work studies a new kind of metamaterial built from a repeating pattern (“metacrystal”) of dissipative optical solitons inside a single ring microresonator. By changing the spacing within each unit cell (a bound pair of solitons), the authors control the resulting electromagnetic metamaterial behavior in the radio to terahertz range. They report the metacrystal’s band structure and topological properties. The topological nature is supported by the presence of π steps in the Zak phase experienced by the crystal phonons. They also show that introducing defects—by removing several solitons—creates phononic edge states. Finally, optical frequency combs from the soliton metacrystals display a “spectral butterfly” pattern, interpreted as a signature of spatio-temporal chirality.