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Chip-scale Floquet topological insulators for 5G wireless systems

Abstract

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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Fig. 1: 4 × 4 dispersion-free Floquet TI using helicoidally rotating, quasi-electrostatic unit elements.
Fig. 2: Analysis of Floquet TI lattice based on resonator-free network.
Fig. 3: Measured scattering parameters and group delay of the Floquet TI IC.
Fig. 4: Measured field distributions in the decibel scale of the signal travelling through the lattice.
Fig. 5: Wireless demonstration of a four-element 730 MHz FD phased array where four transmitters (TX), receivers (RX) and antennas (ANT) are interfaced through our reconfigurable CMOS Floquet TI IC.
Fig. 6: Floquet TI leveraged as a reconfigurable antenna interface for an eight-element wideband, TTD beamformer.

Data availability

The data that support the findings of this study are available from the corresponding authors upon reasonable request.

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Acknowledgements

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.

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Contributions

A.N., A.K., A.A. and H.K. initiated the research. A.N. and A.K. simulated and taped out the device. X.N., A.N., A.K. and M.T. conducted the theoretical analysis. A.N. and S.G. conducted the experiments. H.K. and A.A. supervised the research. All the authors wrote the manuscript. A.N., X.N. and A.K. contributed equally to this manuscript.

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Correspondence to Andrea Alù or Harish Krishnaswamy.

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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

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