Diamandi H Hagai, London Yosef, Bashan Gil, Bergman Arik, Zadok Avi
Faculty of Engineering and Institute for Nano-Technology and Advanced Materials, Bar-Ilan University, Ramat-Gan, 5290002, Israel.
Sci Rep. 2018 Jun 22;8(1):9514. doi: 10.1038/s41598-018-27929-6.
Opto-mechanical oscillators that generate coherent acoustic waves are drawing much interest, in both fundamental research and applications. Narrowband oscillations can be obtained through the introduction of feedback to the acoustic wave. Most previous realizations of this concept, sometimes referred to as "phonon lasers", relied on radiation pressure and moving boundary effects in micro- or nano-structured media. Demonstrations in bulk crystals required cryogenic temperatures. In this work, stimulated emission of highly-coherent acoustic waves is achieved in a commercially-available multi-core fiber, at room temperature. The fiber is connected within an opto-electronic cavity loop. Pump light in one core is driving acoustic waves via electrostriction, whereas an optical probe wave at a different physical core undergoes photo-elastic modulation by the stimulated acoustic waves. Coupling between pump and probe is based entirely on inter-core, opto-mechanical cross-phase modulation: no direct optical feedback is provided. Single-frequency mechanical oscillations at hundreds of MHz frequencies are obtained, with side-mode suppression that is better than 55 dB. A sharp threshold and rapid collapse of the linewidth above threshold are observed. The linewidths of the acoustic oscillations are on the order of 100 Hz, orders of magnitude narrower than those of the pump and probe light sources. The relative Allan's deviation of the frequency is between 0.1-1 ppm. The frequency may be switched among several values by propagating the pump or probe waves in different cores. The results may be used in sensing, metrology and microwave-photonic information processing applications.
在基础研究和应用领域，能够产生相干声波的光机械振荡器都备受关注。通过引入对声波的反馈，可以获得窄带振荡。此前该概念的大多数实现方式，有时被称为“声子激光器”，都依赖于微纳结构介质中的辐射压力和移动边界效应。在块状晶体中的演示需要低温环境。在这项工作中，在室温下的商用多芯光纤中实现了高相干声波的受激辐射。光纤连接在一个光电腔回路中。一个纤芯中的泵浦光通过电致伸缩驱动声波，而另一个不同物理纤芯中的光学探测波则受到受激声波的光弹性调制。泵浦光和探测光之间的耦合完全基于芯间光机械交叉相位调制：不提供直接光学反馈。获得了数百兆赫兹频率的单频机械振荡，边模抑制优于55dB。观察到明显的阈值以及阈值以上线宽的快速变窄。声学振荡的线宽约为100Hz，比泵浦光源和探测光源的线宽窄几个数量级。频率的相对阿伦偏差在0.1 - 1ppm之间。通过在不同纤芯中传播泵浦波或探测波，可以在几个值之间切换频率。这些结果可用于传感、计量和微波光子信息处理应用。
