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.
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The data that support the findings of this study are available from the corresponding authors upon reasonable request.
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This work was supported by the DARPA SPAR program (H.K. and A.A.), the AFOSR MURI program (H.K. and A.A.), the Office of Naval Research (A.A.) and the Department of Defense (A.A.). X.N. thanks Y. Peng for the helpful discussion.
The authors declare no competing interests.
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Nagulu, A., Ni, X., Kord, A. et al. Chip-scale Floquet topological insulators for 5G wireless systems. Nat Electron 5, 300–309 (2022). https://doi.org/10.1038/s41928-022-00751-9