We studied the injection-locking properties of a resonant-tunneling-diode terahertz oscillator in the small-signal injection regime with a frequency-stabilized continuous THz wave. The linewidth of the emission spectrum dramatically decreased to less than 120 mHz (half width at half maximum) from 4.4 MHz in the free running state as a result of the injection locking. We experimentally determined the amplitude of injection voltage at the antenna caused by the injected THz wave. The locking range was proportional to the injection amplitude and consistent with Adler’s model. While increasing the injection amplitude, we observed a decrease in the noise component of the power spectrum, which manifests the free-running state, and an alternative increase in the injection-locked component. The noise component and the injection-locked component had the same power at the threshold injection amplitude as small as 5 × 10⁻⁴ of the oscillation amplitude. This threshold behavior can be qualitatively explained by Maffezzoni’s model of noise reduction in general limit-cycle oscillators.

中文翻译：

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谐振隧道二极管太赫兹振荡器的注入锁定和降噪

我们研究了在具有稳定频率的连续THz波的小信号注入方案中，谐振隧道二极管太赫兹振荡器的注入锁定特性。由于注入锁定，发射光谱的线宽从自由运行状态下的4.4 MHz急剧降低到小于120 mHz（一半为一半的一半的一半）。我们通过实验确定了由注入的太赫兹波引起的天线注入电压的幅度。锁定范围与注入幅度成正比，并且与Adler模​​型一致。在增加注入幅度的同时，我们观察到了功率谱噪声分量的减少，这表明了自由运行状态，并且注入锁定分量也出现了增加。振荡幅度的^-4。该阈值行为可以通过Maffezzoni的通用极限周期振荡器中的降噪模型进行定性解释。