Chip-scale Floquet topological insulators for 5G wireless systems

Floquet topological insulators, which have an exotic topological order sustained by time-varying Hamiltonians, could be of use in a range of technologies, including wireless communications, radar and quantum information processing. However, demonstrations of photonic Floquet topological insulators have been limited to systems that emulate time with a spatial dimension, which preserves time-reversal symmetry and thus removes valuable features including non-reciprocal topological protection. Here we report photonic Floquet topological insulators based on quasi-electrostatic wave propagation in switched-capacitor networks. The approach provides non-reciprocal Floquet topological insulators for electromagnetic waves and opens a large topological bandgap that spans up to gigahertz frequencies. Our devices exploit time modulation to operate beyond the delay–bandwidth limit of conventional linear time-invariant electromagnetic structures and therefore offer large delays, despite the broad bandwidth. The Floquet topological insulator is integrated into a complementary metal–oxide–semiconductor (CMOS) chip, and we illustrate its potential for 5G wireless systems by showing that it can be used for multi-antenna full-duplex wireless operation and true-time-delay-based broadband beamforming.