近日，美国国家标准与技术研究院&马里兰大学的Kartik Srinivasan及其研究小组取得一项新进展。经过不懈努力，他们实现光子晶体谐振器中波数选择性波长精度非线性转换。相关研究成果已于2023年11月16日在《自然—光子学》期刊上发表。

该研究团队报道了一种非线性波长转换器，其独特之处在于，它的运行并不依赖色散工程，但却能实现输出波长的高精度控制。在这项研究中，光子晶体微谐振器中的传波耦合引发了光子带隙，该带隙能在色散空间中隔离特定波数以获得非线性增益。研究人员通过模拟在三次谐波产生、克尔-微梳色散波形成和四波混频布拉格散射等应用场景，验证了该策略的广泛适用性。

在实验中，研究人员展示了克尔光参量振荡器，其中波数选择性耦合被用于指定信号模式，使得目标和实现信号波长之间的差异缩小到了0.3%。此外，利用带隙保护的波数选择性，他们实现了近300GHz的输出频率的连续调谐，而效率不受影响。这项研究结果将为非线性光学设计微谐振器带来范式转移，并在使用集成光子学构建波长精度光源的重大问题上取得重要进展。

据悉，集成的非线性波长转换器能将激光或量子发射器的光能转换成其他有用的颜色，然而，色散却限制了可实现的波长偏移范围。此外，由于几何色散的影响，制造公差降低了器件产生特定目标波长的精度。

附：英文原文

Title: Wavelength-accurate nonlinear conversion through wavenumber selectivity in photonic crystal resonators

Author: Stone, Jordan R., Lu, Xiyuan, Moille, Gregory, Westly, Daron, Rahman, Tahmid, Srinivasan, Kartik

Issue&Volume: 2023-11-16

Abstract: Integrated nonlinear wavelength converters transfer optical energy from lasers or quantum emitters to other useful colours, but chromatic dispersion limits the range of achievable wavelength shifts. Moreover, because of geometric dispersion, fabrication tolerances reduce the accuracy with which devices produce specific target wavelengths. Here we report nonlinear wavelength converters that allow output wavelengths to be controlled with high accuracy despite their operation not being contingent on dispersion engineering. In our scheme, coupling between counterpropagating waves in a photonic crystal microresonator induces a photonic bandgap that isolates (in dispersion space) specific wavenumbers for nonlinear gain. We demonstrate the wide applicability of this strategy by simulating its use in third-harmonic generation, Kerr-microcomb dispersive wave formation and four-wave mixing Bragg scattering. In experiments, we demonstrate Kerr optical parametric oscillators in which such wavenumber-selective coupling designates the signal mode. As a result, differences between the targeted and realized signal wavelengths are <0.3%. Moreover, leveraging the bandgap-protected wavenumber selectivity, we continuously tune the output frequencies by nearly 300GHz without compromising efficiency. Our results will bring about a paradigm shift in how microresonators are designed for nonlinear optics, and they make headway on the larger problem of building wavelength-accurate light sources using integrated photonics.

DOI: 10.1038/s41566-023-01326-6

Source: https://www.nature.com/articles/s41566-023-01326-6