Parity‐time symmetry has great potential for mode selection in multimode resonators. However, in a PT‐symmetry system with saturable absorption mechanisms, the random background noise can initiate single‐mode oscillation at any of the maxima within the gain spectrum, that is, potential PT frequencies. Such randomness impedes the acquisition of high‐quality signals at desired frequencies. Here, this work proposes a method to obtain deterministic PT‐symmetry single‐mode oscillation in a filterless multimode resonator through one‐shot injection. With this technique, this work changes the system's gain spectrum and enhances the gain discrepancy. Utilizing the frequency domain saturable absorption of the resonator, oscillation at desired mode can maintain its frequency after the withdrawal of the injection signal. To validate the concept, this work establishes a polarization‐division multiplexed dual‐loop optoelectronic oscillator (OEO) with a 1‐km long cavity operated under PT‐symmetry conditions. By one‐shot injecting the PT‐OEO, this work effectively eliminates the randomness arising from the relatively flat gain spectrum, facilitating oscillation at any desired potential PT frequencies from 1.8 to 9 GHz without requiring elaborate frequency tuning structures. Moreover, the one‐shot injection technique produces ultra‐low phase noise performance, achieving a remarkable −158.6 dBc Hz−1@10 kHz. This performance level stands in close comparison with the best phase noise values recorded for OEOs.

中文翻译：

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无滤波器多模谐振器中的确定性奇偶时间对称性单模振荡


奇偶校验时间对称性在多模谐振器中的模式选择具有很大的潜力。然而，在具有可饱和吸收机制的 PT 对称系统中，随机背景噪声可以在增益频谱内的任何最大值（即潜在的 PT 频率）处引发单模振荡。这种随机性阻碍了以所需频率获取高质量信号。在这里，这项工作提出了一种通过一次性注入在无滤波器多模谐振器中获得确定性 PT 对称单模振荡的方法。通过这种技术，这项工作改变了系统的增益频谱并增强了增益差异。利用谐振器的频域可饱和吸收，在所需模式下的振荡可以在注入信号撤回后保持其频率。为了验证这一概念，这项工作建立了一个偏振分复用双环光电振荡器 （OEO），该振荡器具有在 PT 对称条件下工作的 1 公里长的腔体。通过一次性注入 PT-OEO，这项工作有效地消除了相对平坦的增益频谱产生的随机性，促进了 1.8 至 9 GHz 任何所需潜在 PT 频率的振荡，而无需复杂的频率调谐结构。此外，一次性注入技术产生了超低的相位噪声性能，实现了显著的 −158.6 dBc Hz−1@10 kHz。此性能水平与 OEO 记录的最佳相位噪声值密切相关。