High-power, high-speed quantum cascade lasers (QCLs) with stable emission in the mid-infrared regime are of great importance for applications in metrology, telecommunication, and fundamental tests of physics. Owing to the intersubband transition, the unique ultrafast gain recovery time of the QCL with picosecond dynamics is expected to overcome the modulation limit of classical semiconductor lasers and bring a revolution for the next generation of ultrahigh-speed optical communication. Therefore, harmonic injection locking, offering the possibility to fast modulate and greatly stabilize the laser emission beyond the rate limited by cavity length, is inherently adapted to QCLs. In this work, we demonstrate for the first time the harmonic injection locking of a mid-infrared QCL with an output power over 1 W in continuous-wave operation at 288 K. Compared with an unlocked laser, the intermode spacing fluctuation of an injection-locked QCL can be considerably reduced by a factor above $1\times {10}^3$, which permits the realization of an ultrastable mid-infrared semiconductor laser with high phase coherence and frequency purity. Despite temperature change, this fluctuation can be still stabilized to hertz level by a microwave modulation up to $\sim 18\mathrm{GHz}$. These results open up the prospect of the applications of mid-infrared QCL technology for frequency comb engineering, metrology, and the next-generation ultrahigh-speed telecommunication. It may also stimulate new schemes for exploring ultrafast mid-infrared pulse generation in QCLs.

中文翻译：

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高功率中红外量子级联激光器的谐波注入锁定

在中红外区域具有稳定发射的高功率、高速量子级联激光器 (QCL) 对于计量、电信和物理基础测试的应用具有重要意义。由于子带间过渡，具有皮秒动力学的QCL独特的超快增益恢复时间有望克服经典半导体激光器的调制限制，为下一代超高速光通信带来一场革命。因此，谐波注入锁定提供了快速调制和大大稳定激光发射超出腔长限制的速率的可能性，本质上适用于 QCL。在这项工作中，我们首次展示了在 288 K 连续波操作中输出功率超过 1 W 的中红外 QCL 的谐波注入锁定。$1\times {10}^3$，这允许实现具有高相位相干性和频率纯度的超稳定中红外半导体激光器。尽管温度发生变化，这种波动仍然可以通过微波调制稳定在赫兹水平$～18\mathrm{吉赫兹}$. 这些结果为中红外QCL技术在频率梳工程、计量学和下一代超高速通信中的应用开辟了前景。它还可能激发探索 QCL 中超快中红外脉冲生成的新方案。