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A conformal mapping approach to broadband nonlinear optics on chip

Nature Photonics (2024)Cite this article

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Abstract

Integrated nonlinear optical devices play an important role in modern optical communications; however, conventional on-chip optical devices with homogeneous or periodic translation dimensions generally have limited bandwidth when applied to nonlinear optical applications. So far there lacks a general method to design compact nonlinear optical devices capable of operating over a broadband continuous frequency range. In this work we propose a general strategy based on transformation optics to design curved accelerating waveguides with spatially gradient curvatures, which can achieve broadband nonlinear frequency conversion on chip. Through rigorous analytical calculation, we show that increasing the acceleration (that is, the gradient in the waveguide curvature) broadens the output signal spectrum in the nonlinear process. In this experiment we use sum-frequency generation for infrared signal upconversion as an example and fabricated a variety of curved accelerating waveguides using thin-film lithium niobate on insulators. Efficient sum-frequency generation is observed over a broadband continuous spectrum. Our conformal mapping approach offers a platform for various nonlinear optical processes and works in any frequency range, including visible, infrared and terahertz bands. Apart from lithium niobate on insulators, our approach is also compatible with other nonlinear materials such as silicon, silicon nitride and chalcogenide glasses and so on.

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Fig. 1: Schematic of the CAW for broadband SFG-ISU.
Fig. 2: Theoretical analysis of the SFG-ISU mechanism in CAWs.
Fig. 3: Experimental demonstration of enhanced SFG-ISU.
Fig. 4: Experimental demonstration of broadband SFG in CAWs with different accelerations.

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Data availability

The data that support the plots of this study are available. Any additional data are available from the corresponding author on reasonable request. Source Data are provided with this paper.

Code availability

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

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Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (grant nos. 92150302 and 92163216 to H. L., 62288101 to S. Z. and 12174187 to C.S.) and the National Key R&D Program of China (grant no. 2023YFB2805700 to C.S.). This work was sponsored by the National Research Foundation Singapore Competitive Research Program (grant nos. NRF-CRP22-2019-0006 and NRF-CRP23-2019-0007 to Y. L.), and A*STAR AME Programmatic Funds (grant no. A18A7b0058 to Y.L.).

Author information

Authors and Affiliations

  1. Collaborative Innovation Center of Advanced Microstructures National Laboratory of Solid State Microstructures, School of Physics Nanjing University, Nanjing, China

    Chunyu Huang, Yule Zhao, Xiaofei Ma, Zhiwei Yan, Ziyi Liu, Chong Sheng, Shining Zhu & Hui Liu

  2. School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, Singapore

    Yu Luo

  3. Key Laboratory of Radar Imaging and Microwave Photonics, Nanjing University of Aeronautics and Astronautics, Nanjing, China

    Yu Luo

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Contributions

H.L. and Y.L. conceived the idea. Y.L. performed the theoretical derivation. C.H. conceived the calculation, analysed the data and designed the sample. Z.Y and Y.Z fabricated the sample. H.L. and Y.Z. designed the experiments. C.H., Y.Z., X.M. and Z.L. performed the experiments. C.H., Y.L. and H.L. wrote the manuscript. All authors discussed the results. H.L. and Y.L. supervised the study.

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Correspondence to Yu Luo or Hui Liu.

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Supplementary Video 1

The CMOS image for 11 CAWs.

Source data

Source Data Fig. 1

Source data of Fig. 1c,d.

Source Data Fig. 2

Source data of Fig. 2d.

Source Data Fig. 3

Source data of Fig. 3c.

Source Data Fig. 4

Source data of Fig. 4a–c.

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Huang, C., Luo, Y., Zhao, Y. et al. A conformal mapping approach to broadband nonlinear optics on chip. Nat. Photon. (2024). https://doi.org/10.1038/s41566-024-01386-2

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