Published July 4, 2025 | Published
Journal Article Open

Efficient and wavelength-tunable second-harmonic generation toward the green gap

  • 1. ROR icon California Institute of Technology
  • 2. ROR icon University of California, Santa Barbara

Abstract

Achieving compact and efficient visible laser sources is crucial for a wide range of applications. However, traditional semiconductor laser technology faces difficulties in producing high-brightness green light, leaving a “green gap” in wavelength coverage. Second-harmonic generation (SHG) offers a promising alternative by converting near-infrared sources to visible wavelengths with high efficiency and spectral purity. Here, we demonstrate efficient and tunable SHG within the green spectrum using a high-Q Si3N4 microresonator. On-chip green power as high as 5.3 milliwatts is generated with a conversion efficiency of 141% per watt (absolute 7.9%). A space-charge grating induced by the photogalvanic effect realizes reconfigurable grating numbers and flexible wavelength tuning over a range of 2.6 terahertz. In addition, grating formation dynamics and competition are observed. These findings underscore the potential of Si3N4 as a robust, integrative platform for on-chip, tunable green light sources.

Copyright and License

© 2025 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution License 4.0 (CC BY).

Funding

This work was supported by the Defense Advanced Research Projects Agency (HR001-20-2-0044), the Air Force Office of Scientific Research (FA9550-23-1-0587), and the Kavli Nanoscience Institute at Caltech.

Data Availability

All data needed to evaluate the conclusions in the paper are present in the paper. The data that support the plots within this paper and other findings of this study are available at Dryad (https://datadryad.org/share/2m5i38SSzasdEWbZii1B0yq86Y89d6NdMPe2zmkgbU8).

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Additional details

Created:
July 16, 2025
Modified:
July 16, 2025