近日，美国国家标准技术局的Scott A. Diddams及其研究小组与美国加州理工学院的Alireza Marandi等人合作并取得一项新进展。经过不懈努力，他们成功在铌酸锂纳米光子波导中产生可见到紫外的频率梳。相关研究成果已于2024年1月15日在国际知名学术期刊《自然—光子学》上发表。

据悉，非线性纳米光子器件在光学频率梳计量领域的应用，为低功耗和芯片集成的时钟、高精度频率合成以及宽带光谱学带来了新的机遇。然而，目前的大多数进展仍然局限于光谱的近红外区域，这限制了频率梳与紫外和可见光范围内的许多量子和原子系统的集成。

该研究团队通过引入多段纳米光子薄膜铌酸锂波导来克服这一缺点，该波导结合了工程色散和啁啾准相位匹配，通过结合χ⁽²⁾和χ⁽³⁾非线性来有效地产生超连续谱。在1550nm处仅使用90pJ的脉冲能量，研究人员实现了330 - 2400nm的无间隙频率梳覆盖。从近红外泵浦到350-550nm紫外可见区的转换效率为17%，研究人员对优化的支撑结构的建模预测了更高的效率。

在同一波导中，通过χ⁽²⁾非线性产生的谐波直接产生载波包络补偿频率和一种验证波长短至350nm的梳相干性的方法。这项研究结果提供了一种集成的光子学方法来生成可见和紫外频率梳，这将影响精密光谱学，量子信息处理和光学时钟在这一重要光谱窗口中的应用。

附：英文原文

Title: Visible-to-ultraviolet frequency comb generation in lithium niobate nanophotonic waveguides

Author: Wu, Tsung-Han, Ledezma, Luis, Fredrick, Connor, Sekhar, Pooja, Sekine, Ryoto, Guo, Qiushi, Briggs, Ryan M., Marandi, Alireza, Diddams, Scott A.

Issue&Volume: 2024-01-15

Abstract: The introduction of nonlinear nanophotonic devices to the field of optical frequency comb metrology has enabled new opportunities for low-power and chip-integrated clocks, high-precision frequency synthesis and broad-bandwidth spectroscopy. However, most of these advances remain constrained to the near-infrared region of the spectrum, which has restricted the integration of frequency combs with numerous quantum and atomic systems in the ultraviolet and visible ranges. Here we overcome this shortcoming with the introduction of multisegment nanophotonic thin-film lithium niobate waveguides that combine engineered dispersion and chirped quasi-phase matching for efficient supercontinuum generation via the combination of χ⁽²⁾ and χ⁽³⁾ nonlinearities. With only 90pJ of pulse energy at 1,550nm, we achieve gap-free frequency comb coverage spanning 330–2,400nm. The conversion efficiency from the near-infrared pump to the ultraviolet–visible region of 350–550nm is 17%, and our modelling of optimized poling structures predicts an even higher efficiency. Harmonic generation via the χ⁽²⁾ nonlinearity in the same waveguide directly yields the carrier-envelope offset frequency and a means to verify the comb coherence at wavelengths as short as 350nm. Our results provide an integrated photonics approach to create visible and ultraviolet frequency combs that will impact precision spectroscopy, quantum information processing and optical clock applications in this important spectral window.

DOI: 10.1038/s41566-023-01364-0

Source: https://www.nature.com/articles/s41566-023-01364-0