Optical frequency combs (OFCs), which establish a rigid phase-coherent link between the microwave and optical domains of the electromagnetic spectrum, are emerging as key high-precision tools for the development of quantum technology platforms. These include potential applications for communication, computation, information, sensing, and metrology and can extend from the near-infrared with micro-resonator combs, up to the technologically attractive terahertz (THz) frequency range, with powerful and miniaturized quantum cascade laser (QCL) FCs. The recently discovered ability of the QCLs to produce a harmonic frequency comb (HFC)—a FC with large intermodal spacings—has attracted new interest in these devices for both applications and fundamental physics, particularly for the generation of THz tones of high spectral purity for high data rate wireless communication networks, for radio frequency arbitrary waveform synthesis, and for the development of quantum key distributions. The controlled generation of harmonic states of a specific order remains, however, elusive in THz QCLs. Here, and by design, we devise a strategy to obtain broadband HFC emission of a pre-defined order in a QCL. By patterning n$n$ regularly spaced defects on the top surface of a double-metal Fabry–Perot QCL, we demonstrate harmonic comb emission with modes spaced by an (n + 1$n + 1$) free spectral range and with an optical power/mode of {\sim}{270}\;\unicode{x00B5} {\rm W}${\sim}{270}\;\unicode{x00B5} {\rm W}$.

中文翻译：

---

通过受控工程塑造太赫兹量子级联激光器中的谐波梳状状态

光学频率梳（OFC）在电磁频谱的微波域和光学域之间建立了刚性的相位相干链接，正在成为量子技术平台开发的关键高精度工具。这些包括通信、计算、信息、传感和计量方面的潜在应用，并且可以从具有微谐振器梳的近红外扩展到具有技术吸引力的太赫兹（THz）频率范围，具有强大的小型化量子级联激光器（QCL） ) FC。最近发现 QCL 能够产生谐波频率梳 (HFC)（一种具有大模间间距的 ​​FC），这引起了人们对这些设备在应用和基础物理方面的新兴趣，特别是在生成高光谱纯度的太赫兹音调方面。高数据速率无线通信网络，用于射频任意波形合成，以及用于量子密钥分配的开发。然而，在太赫兹 QCL 中，特定阶谐波状态的受控生成仍然难以实现。在这里，我们通过设计设计了一种策略，以在 QCL 中获得预定义顺序的宽带 HFC 发射。通过在双金属法布里-珀罗 QCL 的顶面上图案化n 个规则间隔的缺陷，我们演示了谐波梳状发射，其模式间隔为 ( $n$n + 1$n + 1$ ) 个自由光谱范围，光功率/模式为{\sim} {270}\;\unicode{x00B5} {\rm W}${\sim}{270}\;\unicode{x00B5} {\rm W}$ .