Spectral control by engineering of a synthetic dimension in a fast gain laser

Photonic platforms serve as tools to overcome the limitations of real electronic systems and emulate solid-state phenomena such as Anderson localization, topological matter states, non-Hermitian dynamics, and artificial electromagnetic fields for photons. These simulators can also leverage light properties like wavelength and polarization, increasing the dimensionality of the system’s parameter space for better control. Recent studies have identified Quantum Walk Combs in circular Quantum Cascade Lasers with fast saturable gain, where phase modulation gives rise to coherent side-mode generation and broad bandwidth spectra. This behavior mimics a 1D tight binding lattice with nearest-neighbor coupling and full band population. In this work, we explore the impact of an artificial magnetic field flux on this lattice by introducing controllable next-nearest neighbor coupling. We reveal that the band structure breaks time-reversal symmetry and show that this effect maps onto the laser’s optical spectra. Experimental measurements of the spectra show remarkable agreement with the simulated ones, indicating potential advancements in frequency comb generation and shaping.