Generation of space-time wave packets in modulated waveguide arrays.

Space-time wave packets (STWPs) with a linear dispersive spectrum propagate freely without diffraction. However, directly generating STWPs in integrated photonic systems remains a significant challenge. We propose to realize the generation of STWPs in modulated waveguide arrays. Benefiting from the equally spaced eigenspectra of such arrays, the linear spatiotemporal correlation between the frequency and propagation constants of eigenmodes can be constructed under the traveling-wave modulation with a single frequency. By controlling the modulation parameters, the group velocity of the STWPs can be steered to be positive, negative, and formally infinite. Furthermore, the solid and hollow STWPs can be created by coupling the odd and even eigenmodes, respectively. This work provides what we believe to be a unique platform enabling the generation of STWPs in integrated waveguide arrays, which may open an avenue for practical applications of on-chip space-time photonics.