中国科学院上海微系统与信息技术研究所黎华团队研究了太赫兹量子级联激光频率梳的Farey树锁定。这一研究成果于2025年3月31日发表在《光：科学与应用》杂志上。

频率梳在分子指纹、成像、通信等领域有着广泛的应用。在太赫兹频率范围内，基于半导体的量子级联激光器（QCL）是实现频率梳操作的理想平台。尽管由于四波混频锁定效应，在自由运行的太赫兹QCL中可以实现自启动频率梳操作，但谐振/非谐振微波注入、锁相和基于飞秒激光的锁定技术已被广泛用于拓宽和稳定太赫兹QCL梳。这些主动锁定方法确实对太赫兹QCL梳的频率稳定有显著影响，但它们同时也有缺点，例如引入较大的相位噪声，需要复杂的光学耦合和/或电路。

研究组演示了微波注入下太赫兹QCL频率梳的Farey树锁定。Farey分数频率和腔往返频率之间的频率竞争导致太赫兹QCL梳的频率锁定，并且可以根据Farey树层次结构的下降趋势准确预测Farey分数的频率。此外，双梳实验结果表明，采用Farey树锁定方法显著降低了双梳谱线的相位噪声。这些结果为部署紧凑、低相位噪声的太赫兹频率梳状源铺平了道路。

附：英文原文

Title: Farey tree locking of terahertz quantum cascade laser frequency combs

Author: Liu, Guibin, Ma, Xuhong, Zhou, Kang, Liu, Binbin, Zheng, Lulu, Bi, Xianglong, Wu, Shumin, Lu, Yanming, Li, Ziping, Wan, Wenjian, Zhang, Zhenzhen, Peng, Junsong, Zhang, Ya, Zeng, Heping, Li, Hua

Issue&Volume: 2025-03-31

Abstract: Frequency combs show various applications in molecular fingerprinting, imaging, communications, and so on. In the terahertz frequency range, semiconductor-based quantum cascade lasers (QCLs) are ideal platforms for realizing the frequency comb operation. Although self-started frequency comb operation can be obtained in free-running terahertz QCLs due to the four-wave mixing locking effects, resonant/off-resonant microwave injection, phase locking, and femtosecond laser based locking techniques have been widely used to broaden and stabilize terahertz QCL combs. These active locking methods indeed show significant effects on the frequency stabilization of terahertz QCL combs, but they simultaneously have drawbacks, such as introducing large phase noise and requiring complex optical coupling and/or electrical circuits. Here, we demonstrate Farey tree locking of terahertz QCL frequency combs under microwave injection. The frequency competition between the Farey fraction frequency and the cavity round-trip frequency results in the frequency locking of terahertz QCL combs, and the Farey fraction frequencies can be accurately anticipated based on the downward trend of the Farey tree hierarchy. Furthermore, dual-comb experimental results show that the phase noise of the dual-comb spectral lines is significantly reduced by employing the Farey tree locking method. These results pave the way to deploying compact and low phase noise terahertz frequency comb sources.

DOI: 10.1038/s41377-025-01819-9

Source: https://www.nature.com/articles/s41377-025-01819-9