Observation of topological frequency combs.

Area of Science:

• Photonics
• Topological Physics
• Nonlinear Optics

Background:

• On-chip optical frequency combs are typically generated using single-ring resonators.
• Existing methods have limitations, restricting broader applications of frequency combs.
• Mode-locked lasers were previously required for many frequency comb applications.

Purpose of the Study:

• To experimentally demonstrate a new class of frequency combs: topological frequency combs.
• To explore nonlinear frequency comb generation in a topological system.
• To investigate combs generated in a two-dimensional lattice of ring resonators.

Main Methods:

• Fabrication of a two-dimensional lattice of hundreds of ring resonators.
• Excitation of fabrication-robust topological edge states with linear dispersion.
• Pumping these topological edge states to generate frequency combs.

Main Results:

• Demonstration of nested frequency comb generation.
• Observation of multiple edge state resonances oscillating across approximately 40 longitudinal modes.
• Spatial confinement of the generated frequency comb at the lattice edge.

Conclusions:

• Successful generation of topological frequency combs in a scalable nanophotonic platform.
• Highlighting the potential for exploring topological physics in nonlinear frequency comb generation.
• Providing a novel platform for on-chip frequency comb generation with unique properties.