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On-chip topological beamformer for multi-link terahertz 6G to XG wireless

Nature volume 632, pages 522–527 (2024)Cite this article

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Abstract

Terahertz (THz) wireless communication holds immense potential to revolutionize future 6G to XG networks with high capacity, low latency and extensive connectivity. Efficient THz beamformers are essential for energy-efficient connections, compensating path loss, optimizing resource usage and enhancing spectral efficiency. However, current beamformers face several challenges, including notable loss, limited bandwidth, constrained spatial coverage and poor integration with on-chip THz circuits. Here we present an on-chip broadband THz topological beamformer using valley vortices for waveguiding, splitting and perfect isolation in waveguide phased arrays, featuring 184 densely packed valley-locked waveguides, 54 power splitters and 136 sharp bends. Leveraging neural-network-assisted inverse design, the beamformer achieves complete 360° azimuthal beamforming with gains of up to 20 dBi, radiating THz signals into free space with customizable user-defined beams. Photoexciting the all-silicon beamformer enables reconfigurable control of THz beams. The low-loss and broadband beamformer enables a 72-Gbps chip-to-chip wireless link over 300 mm and eight simultaneous 40-Gbps wireless links. Using four of these links, we demonstrate point-to-4-point real-time HD video streaming. Our work provides a complementary metal-oxide-semiconductor-compatible THz topological photonic integrated circuit for efficient large-scale beamforming, enabling massive single-input multiple-output and multiple-input and multiple-output systems for terabit-per-second 6G to XG wireless communications.

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Fig. 1: Multi-link THz topological beamformer silicon chip for 6G to XG wireless.
Fig. 2: Topological valley-vortices-driven robust guiding, power splitting and channel isolation.
Fig. 3: Intrinsic and NN-assisted inverse-designed topological beamformers.
Fig. 4: THz wireless communication with eight 40 Gbit s−1 links and point-to-multipoint HDTV streaming.

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Data availability

All the data in this study are openly available in the NTU research data repository DR-NTU at https://doi.org/10.21979/N9/UKLX3D.

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Acknowledgements

We acknowledge the support from the National Research Foundation (NRF) Singapore, grant no. NRF-CRP23-2019-0005 (TERACOMM). G.D. and P.S. acknowledge the characterization testbeds supported by the France 2030 programmes, PEPR (Programmes et Equipements Prioritaires pour la Recherche) and CPER Wavetech. The PEPR is operated by the Agence Nationale de la Recherche (ANR), under the grants ANR-22-PEEL-0006 (FUNTERA, PEPR ‘Electronics’) and ANR-22-PEFT-0006 (NF-SYSTERA, PEPR 5 G and beyond—Future Networks). The Contrat de Plan Etat-Region (CPER) WaveTech is supported by the Ministry of Higher Education and Research, the Hauts-de-France Regional Council, the Lille European Metropolis (MEL), the Institute of Physics of the French National Centre for Scientific Research (CNRS) and the European Regional Development Fund (ERDF).

Author information

Authors and Affiliations

  1. Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, Singapore

    Wenhao Wang, Yi Ji Tan, Thomas CaiWei Tan, Abhishek Kumar & Ranjan Singh

  2. Centre for Disruptive Photonic Technologies, The Photonics Institute, Nanyang Technological University, Singapore, Singapore

    Wenhao Wang, Yi Ji Tan, Thomas CaiWei Tan, Abhishek Kumar & Ranjan Singh

  3. Institute of Microelectronics, Agency for Science, Technology and Research, Singapore, Singapore

    Prakash Pitchappa

  4. Université de Lille, CNRS, UMR 8523 - PhLAM, Laboratoire de Physique des Lasers, Atomes et Molécules, Lille, France

    Pascal Szriftgiser

  5. Université de Lille, CNRS, UMR 8520 - IEMN, Institut d’Electronique, Microélectronique et Nanotechnologie, Lille, France

    Guillaume Ducournau

  6. Department of Electrical Engineering, University of Notre Dame, Notre Dame, IN, USA

    Ranjan Singh

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Contributions

W.W. and R.S. conceived the idea; W.W., Y.J.T., A.K. and R.S. designed the experiments; W.W. performed the simulation; Y.J.T. performed the NN-assisted inverse design of the topological beamformers; P.P. fabricated a portion of the intrinsic AB-type topological beamformer samples; T.C.T. led the overall sample fabrication; W.W. performed the on-chip transmission and two-dimensional radiation pattern measurements with the help of T.C.T.; W.W. and R.S. designed the phototunable beamforming experiment; W.W. performed the active tuning measurements with the help of T.C.T.; G.D. performed the vector network analyser transmission, antenna gain and 3D radiation pattern measurements; P.S. and G.D. performed THz wireless communication experiments; W.W., Y.J.T., A.K., G.D. and R.S. analysed all the data; W.W. and R.S. wrote the paper with inputs from all co-authors; and R.S. led the overall project.

Corresponding author

Correspondence to Ranjan Singh.

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The authors declare no competing interests.

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Nature thanks Yasaman Ghasempour, Jianwei Wang and Daniel van der Weide for their contribution to the peer review of this work. Peer reviewer reports are available.

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Extended data figures and tables

Extended Data Fig. 1 Topological power splitters.

Optical images of four-channel (4-CH) a AB-type and b BA-type topological power splitters. Type A (B) VPC unit cell is highlighted with a purple (orange) color. The AB-type and BA-type zigzag interfaces are marked with red and blue dotted lines, respectively. The 4-CH AB-type (BA-type) power splitter is composed of an AB-type (BA-type) zigzag interface on the left channel CH 1 and three BA-type (AB-type) zigzag interfaces on the right channels CHs 2-4.

Extended Data Fig. 2 Intrinsic broadband topological waveguide phased arrays.

Simulated a (c) transmission and b (d) phase of the 16 radiating channels of AB- (BA-) type four-stage topological beamformer. The 16 channels of AB- (BA-) type beamformer have similar transmission while showing intrinsic π (0) phase difference between adjacent channels over the entire broad bandwidth of 26.5 GHz (18.9 GHz). e Simulated and measured transmission of BA-type topological beamformers having different numbers of tapers by summing the transmission of all the channels. The shaded gray area of the measured transmission spectrum indicates the standard error.

Extended Data Fig. 3 Optical images of AB-type topological beamformers.

The optical images show the evolution of the AB-type topological beamformers from the zero-stage having 20 = 1 output taper to four-stage having 24 = 16 output tapers.

Extended Data Fig. 4 Evolution of the far-field radiation pattern of intrinsic AB-type topological beamformer with the stage number.

a,b,c Measured and simulated azimuthal radiation patterns of the intrinsic AB-type two-, three-, and four-stage topological beamformers at the horizontal plane (polar angle ϕ = 0°) at 0.325 THz. d,e,f Measured 3D radiation patterns at 0.325 THz for the space θ > 0°. g,h,i Measured broadband radiation patterns. As the number of taper (radiating channel) increases from 22 to 24, the gain of the main lobe increases from 12 dBi to 16 dBi.

Extended Data Fig. 5 Broadband 2π-phase control of topological beamformer’s radiating channel.

a Optical image of the taper region of the AB-type four-stage topological beamformer. Simulated b transmission and c phase of a single taper of the AB-type four-stage topological beamformer as a function of frequency and length L of the rectangular bar of the taper coupler. The transmission remains constant, while the phase undergoes a 2π variation across the entire bandwidth.

Extended Data Fig. 6 Broadband beamforming with three to eight beams.

a-f Measured and simulated radiation patterns at 0.331 THz (left panel) and measured broadband gain distributions (right panel) of the AB-type four-stage topological beamformers having three to eight radiating beams. The arrows in the left panel of a-f indicate the azimuthal angle position where the gain is measured in the right panel.

Extended Data Fig. 7 Reconfigurable photoswitching and control of the number of THz beams in 360° topological beamformer.

a Optical image of the 360° topological beamformer having six branches B1−B6. Each of the six branches transmits the THz signal into free space with a single radiated beam directed towards θB. Here θB = −120°, −60°, 0°, 60°, 120°, 180° is the orientation azimuthal angle of each branch. The ten markers centered at the domain wall denote the pump positions of a 525-nm continuous wave laser (diameter of the beam spot = 0.55 mm, pump power fluence = 902.9 W cm−2). b Measured broadband radiation patterns of the 360° topological beamformer pumped at different positions P1 −P10.

Extended Data Fig. 8 Effect of pump fluence on the gain of topological beamformer.

a Measured gain of the THz beam radiated by the B2 branch of the 360° topological beamformer at different pump fluences. The topological beamformer is pumped at position P1 marked by a yellow circle in Extended Data Fig. 7a. b Measured gain at 0.3342 THz which is indicated by a dashed line in a.

Extended Data Fig. 9 Polarization analysis of topological beamformer.

a Schematic of the experimental configuration for polarization analysis. The THz wave radiated by the topological beamformer passes through a THz polarizer in free space and then is received by another topological beamformer. The THz polarizer is a wire grid polarizer consisting of an array of metal wires on a High-Density Polyethylene (HDPE) film. Such polarizers have > 95% transmission in the 300 GHz band which is the frequency range of interest in this work. The diameter of the available surface is 40 mm, and it is POL-HDPE-CA40-OD50.8-T8 from TYDEX optics. b Normalized OTA transmittance for different polarization angle α at 0.325 THz. Maximum power is received at α = 90° and a minimum power of 0.005 is reached at α = 0°. It indicates that the THz beam radiated from the topological beamformer is highly TE-polarized with a polarization purity of 99.5%.

Extended Data Table 1 Reconfigurable photoswitching and control over the number of THz beams in the 360° topological beamformer at different pump positions P1-P10
Full size table

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Wang, W., Tan, Y.J., Tan, T.C. et al. On-chip topological beamformer for multi-link terahertz 6G to XG wireless. Nature 632, 522–527 (2024). https://doi.org/10.1038/s41586-024-07759-5

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