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Adapted poling to break the nonlinear efficiency limit in nanophotonic lithium niobate waveguides

Nature Nanotechnology volume 19, pages 44–50 (2024)Cite this article

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Abstract

Nonlinear frequency mixing is a method to extend the wavelength range of optical sources with applications in quantum information and photonic signal processing. Lithium niobate with periodic poling is the most widely used material for frequency mixing due to its strong second-order nonlinear coefficient. The recent development using nanophotonic lithium niobate waveguides promises to improve nonlinear efficiencies by orders of magnitude thanks to subwavelength optical confinement. However, the intrinsic nanoscale inhomogeneity of nanophotonic lithium niobate waveguides limits the coherent interaction length, leading to low nonlinear efficiencies. Here we show improved second-order nonlinear efficiency in nanophotonic lithium niobate waveguides that breaks the limit imposed by nanoscale inhomogeneity. This is realized by developing the adapted poling approach to eliminate the impact of nanoscale inhomogeneity. We realize an overall second-harmonic efficiency of 104% W−1 (without cavity enhancement), approaching the theoretical performance for nanophotonic lithium niobate waveguides. The ideal square dependence of the nonlinear efficiency on the waveguide length is recovered. Phase-matching bandwidths and temperature tuneability are improved through dispersion engineering. We finally demonstrate a conversion ratio from pump to second-harmonic power greater than 80% in a single-pass configuration with pump power as low as 20 mW. Our work therefore breaks the trade-off between the conversion ratio and pump power, offering a potential solution for highly efficient and scalable nonlinear-optical sources, amplifiers and converters.

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Fig. 1: Adapted poling for nanophotonic lithium niobate waveguides with nanoscale inhomogeneity.
Fig. 2: Performance comparison between periodic and adapted poling approaches.
Fig. 3: Ultra-efficient nanophotonic lithium niobate waveguides.
Fig. 4: Towards ultimate second-order nonlinearity performance.

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Data availability

The data generated and/or analysed in this work are available from the corresponding author upon reasonable request.

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Acknowledgements

This work is supported in part by the US Department of Energy, Office of Advanced Scientific Computing Research (Field Work Proposal grant no. ERKJ355); Office of Naval Research (grant no. N00014-19-1-2190); NSF-ERC Center for Quantum Networks (grant no. EEC-1941583). The reactive ion ether used in this study was acquired through an NSF MRI grant (no. ECCS-1725571). Device fabrication was performed in the OSC cleanroom at the University of Arizona.

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Authors and Affiliations

  1. Wyant College of Optical Sciences, University of Arizona, Tucson, AZ, USA

    Pao-Kang Chen, Ian Briggs, Chaohan Cui, Liang Zhang, Manav Shah & Linran Fan

  2. Department of Physics, University of Arizona, Tucson, AZ, USA

    Pao-Kang Chen

  3. Chandra Department of Electrical and Computer Engineering, the University of Texas at Austin, Austin, TX, USA

    Linran Fan

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Contributions

P.-K.C. and L.F. conceived the experiment. P.-K.C. fabricated the device, performed the measurement, analysed the data and developed the simulation in useful discussion with C.C. and L.Z. P.-K.C. and I.B. optimized the poling condition. I.B. and M.S. optimized the fabrication procedure. P.-K.C. and L.F. wrote the manuscript. L.F. supervised the work.

Corresponding author

Correspondence to Linran Fan.

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Competing interests

All information in this work is covered by a pending patent application (application number 63302331) filed by P.-K.C. and L.F. The other authors declare no competing interests.

Peer review

Peer review information

Nature Nanotechnology thanks Andy Boes, Wolfram Pernice and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 Device cross-section.

SEM image of the nanophotonic lithium niobate waveguide cross-section.

Extended Data Fig. 2 Simulated effective refractive index and poling period.

Simulated effective refractive index at wavelength 1550nm (a), 775nm (b), and poling periods (c) with different lithium niobate device thicknesses.

Extended Data Fig. 3 Temperature tunability.

Peak wavelengths of second-harmonic spectrum obtained in the 21-mm waveguide with adapted poling under different temperatures.

Extended Data Fig. 4 Dispersion engineering.

(a) Simulated group velocity mismatch, (b) temperature tuning dispersion value.

Extended Data Table 1 Comparison of different lithium niobate device designs
Full size table

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Chen, PK., Briggs, I., Cui, C. et al. Adapted poling to break the nonlinear efficiency limit in nanophotonic lithium niobate waveguides. Nat. Nanotechnol. 19, 44–50 (2024). https://doi.org/10.1038/s41565-023-01525-w

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