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<p>While cascaded second-order nonlinear processes have revolutionized shorter-wavelength light generation through up-conversion, their potential for longer-wavelength emission via parametric down-conversion remains fundamentally unexplored – constrained by narrow phase-matching bandwidths, insufficient parametric gain and stringent requirements on complex poling. Here, we break this paradigm through a reverse-polarization dual-layer lithium niobate nanophotonic waveguide that achieves broadband phase matching and record 15.3% conversion efficiency for mid-infrared (MIR) generation. Pumped at 1.03 μm, the cascaded optical parametric generation and difference frequency generation processes produce dynamically tunable MIR emissions spanning 2.06–3.09 μm – a relative bandwidth of 40%. By strategically engineering dispersion characteristics, we further extend the versatility of this platform: pumping at telecommunications-compatible wavelengths (1.3–1.6 μm) generates discrete MIR lines at 3.59, 3.93, 4.31, and 4.6 μm, penetrating the crucial molecular fingerprint region. This work not only establishes cascaded down-conversion as a viable strategy for efficient long-wavelength generation but also provides a blueprint for designing reconfigurable nonlinear photonic systems, with transformative implications for spectroscopy, sensing, and wavelength-division multiplexing technologies.</p>

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Cascaded nonlinear down-conversion in poling-free lithium niobate nanophotonic waveguides

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年11月13日

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  • Congliao Yan,
  • Xuan Mao,
  • Song Zhu,
  • Fakun Wang,
  • Hui Ma,
  • Shi Fang,
  • Jianbo Yu,
  • Jieyuan Cui,
  • Ming Tian,
  • Fei Huang,
  • Sha Wang,
  • Yu Luo,
  • Qi Jie Wang

摘要

While cascaded second-order nonlinear processes have revolutionized shorter-wavelength light generation through up-conversion, their potential for longer-wavelength emission via parametric down-conversion remains fundamentally unexplored – constrained by narrow phase-matching bandwidths, insufficient parametric gain and stringent requirements on complex poling. Here, we break this paradigm through a reverse-polarization dual-layer lithium niobate nanophotonic waveguide that achieves broadband phase matching and record 15.3% conversion efficiency for mid-infrared (MIR) generation. Pumped at 1.03 μm, the cascaded optical parametric generation and difference frequency generation processes produce dynamically tunable MIR emissions spanning 2.06–3.09 μm – a relative bandwidth of 40%. By strategically engineering dispersion characteristics, we further extend the versatility of this platform: pumping at telecommunications-compatible wavelengths (1.3–1.6 μm) generates discrete MIR lines at 3.59, 3.93, 4.31, and 4.6 μm, penetrating the crucial molecular fingerprint region. This work not only establishes cascaded down-conversion as a viable strategy for efficient long-wavelength generation but also provides a blueprint for designing reconfigurable nonlinear photonic systems, with transformative implications for spectroscopy, sensing, and wavelength-division multiplexing technologies.