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Passive bias-free non-reciprocal metasurfaces based on thermally nonlinear quasi-bound states in the continuum

Nature Photonics volume 18, pages 81–90 (2024)Cite this article

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Abstract

Non-reciprocal devices—in which light is transmitted with different efficiencies along opposite directions—are key technologies for modern photonic applications, yet their compact and miniaturized implementation remains an open challenge. Among different avenues, nonlinearity-induced non-reciprocity has attracted significant attention due to the absence of external bias and the ease of integrability within conventional material platforms. So far, nonlinearity-induced non-reciprocity has been demonstrated only in guided platforms using high-quality-factor resonators. Here we demonstrate ultrathin optical metasurfaces with a large non-reciprocal response for free-space radiation based on silicon thermo-optic nonlinearities. Our metasurfaces combine an out-of-plane asymmetry—necessary to obtain non-reciprocity—with in-plane broken symmetry, which finely tunes the radiative linewidth of quasi-bound states in the continuum. Third-order thermo-optic nonlinearities, engaged by the quasi-bound state in the continuum, are shown to enable over 10 dB of non-reciprocal transmission and less than 3 dB of insertion loss, for impinging average intensities smaller than 3 kW cm–2. Numerical calculations suggest that the build-up and relaxation times of the non-reciprocal response can approach sub-microsecond scales, only limited by thermal dissipation. The demonstrated devices merge the field of non-reciprocity with ultrathin metasurface technologies, offering an exciting functionality for signal processing and routing, communications and protection of high-power laser cavities.

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Fig. 1: Passive free-space non-reciprocity using nonlinear metasurfaces with tailored asymmetries.
Fig. 2: Fabrication and linear characterizations of metasurfaces.
Fig. 3: Experimental demonstration of nonlinearity-induced non-reciprocity.
Fig. 4: Non-reciprocal response of the same device for different excitation wavelengths.
Fig. 5: Bistability and impact of thermo-optic effects.

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Data availability

All data that support the findings of this work are available in this Article and its Supplementary Information. The raw data for all the experimental plots are available via Zenodo at https://doi.org/10.5281/zenodo.8408935.

Code availability

All numerical simulations were performed using a commercially available electromagnetic solver (COMSOL v. 6.0). All numerical results can be reproduced by following the descriptions provided in the Article and its Supplementary Information.

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Acknowledgements

We would like to thank D. Korobkin for experimental assistance in the earlier stages of this project. M.C. and A.A. acknowledge support from the Air Force Office of Scientific Research and the Simons Foundation. A.C. and A.P. acknowledge support from the research program of The Netherlands Organization for Scientific Research (NWO). Device fabrication was performed at the Nanofabrication Facility at the Advanced Science Research Center at The Graduate Center of the City University of New York.

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Authors and Affiliations

  1. Photonics Initiative, Advanced Science Research Center, City University of New York, New York, NY, USA

    Michele Cotrufo & Andrea Alù

  2. The Institute of Optics, University of Rochester, Rochester, NY, USA

    Michele Cotrufo

  3. Van der Waals-Zeeman Institute, Institute of Physics, University of Amsterdam, Amsterdam, The Netherlands

    Andrea Cordaro

  4. Center for Nanophotonics, AMOLF, Amsterdam, The Netherlands

    Andrea Cordaro & Albert Polman

  5. John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA

    Andrea Cordaro

  6. Department of Electrical and Computer Engineering, Wayne State University, Detroit, MI, USA

    Dimitrios L. Sounas

  7. Physics Program, Graduate Center of the City University of New York, New York, NY, USA

    Andrea Alù

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  1. Michele Cotrufo
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Contributions

All authors conceived the idea and the corresponding experiment. M.C., A.C. and D.L.S. designed the device and performed the numerical analysis. M.C. fabricated the devices and performed the experimental measurements with assistance from A.C. All authors analysed the data and contributed to writing the manuscript. A.A. and A.P. supervised the project.

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Correspondence to Andrea Alù.

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Nature Photonics thanks Lin Chang, Zongfu Yu and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary Sections 1–8, Figs. 1–8, Table 1 and discussion.

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Cotrufo, M., Cordaro, A., Sounas, D.L. et al. Passive bias-free non-reciprocal metasurfaces based on thermally nonlinear quasi-bound states in the continuum. Nat. Photon. 18, 81–90 (2024). https://doi.org/10.1038/s41566-023-01333-7

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