Optoelectronic feedback on a laser diode is demonstrated to generate two distinct modes of periodic pulse-train formation depending on the injection current $J$ of the laser leading to microwave combs in two distinct regimes. For $J$ close to the threshold current $J_{th}$ , the pulse repetition rate $f_{\mathrm{ rep}}$ is the inverse of the loop delay. This behavior is attributed to feedback-induced gain-switching and leads to comb spacings in the tens of MHz range. In contrast, for $J \simeq 2J_{th}$ , the repetition rate $f_{\mathrm{ rep}}$ is observed to be related to the relaxation-oscillation frequency $f_{\mathrm{ RO}}$ . The potential to generate pulse trains and associated microwave combs may find use in metrology, optical communications, optical sampling, and spectroscopy.

中文翻译：

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增益切换与弛豫振荡的微波频率梳产生

激光二极管上的光电反馈被证明可根据注入电流生成两种不同的周期性脉冲序列形成模式 $ J $ 导致微波梳在两个不同的状态下的激光束。为了 $ J $ 接近阈值电流 $ J_ {th} $ ，脉冲重复率 $ f _ {\ mathrm {rep}} $ 是环路延迟的倒数。此行为归因于反馈引起的增益切换，并导致数十MHz范围内的梳齿间距。相反，对于 $ J \ simeq 2J_ {th} $ ，重复率 $ f _ {\ mathrm {rep}} $ 观察到与弛豫振荡频率有关 $ f _ {\ mathrm {RO}} $ 。产生脉冲序列和相关的微波梳的潜力可在计量学，光学通信，光学采样和光谱学中找到用途。