Chen Pao-Kang, Briggs Ian, Cui Chaohan, Zhang Liang, Shah Manav, Fan Linran
Wyant College of Optical Sciences, University of Arizona, Tucson, AZ, USA.
Department of Physics, University of Arizona, Tucson, AZ, USA.
Nat Nanotechnol. 2024 Jan;19(1):44-50. doi: 10.1038/s41565-023-01525-w. Epub 2023 Oct 26.
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 10% W (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.
非线性频率混合是一种扩展光源波长范围的方法，在量子信息和光子信号处理中有着应用。具有周期性极化的铌酸锂由于其强大的二阶非线性系数，是频率混合中使用最广泛的材料。最近利用纳米光子铌酸锂波导的发展有望由于亚波长光学限制而将非线性效率提高几个数量级。然而，纳米光子铌酸锂波导固有的纳米级不均匀性限制了相干相互作用长度，导致非线性效率较低。在此，我们展示了纳米光子铌酸锂波导中二阶非线性效率的提高，打破了纳米级不均匀性所带来的限制。这是通过开发适应性极化方法来消除纳米级不均匀性的影响而实现的。我们实现了10% W的整体二次谐波效率（无腔增强），接近纳米光子铌酸锂波导的理论性能。恢复了非线性效率对波导长度的理想平方依赖性。通过色散工程改善了相位匹配带宽和温度可调性。我们最终在泵浦功率低至20 mW的单程配置中展示了从泵浦到二次谐波功率的转换比大于80%。因此，我们的工作打破了转换比和泵浦功率之间的权衡，为高效且可扩展的非线性光源、放大器和转换器提供了潜在的解决方案。
