Modern broadband telecommunications require microelectromechanical filters which mechanically vibrate at ultra-high frequencies up to several gigahertz. Heterodyne interferometers, so-called laser-Doppler vibrometers (LDVs), provide a sensitive and contactless measurement technique for vibrations in such filters, but are limited in GHz heterodyning by the efficiency drop of acousto-optic frequency shifters. Heterodyning by frequency-offset locking of two lasers in an optoelectronic phase-locked loop (OPLL) overcomes this limitation. This is demonstrated with our LDV setup with heterodyning up to via offset locking of two semiconductor lasers at visible wavelength. The experiments show a vibration-amplitude resolution of less than per for frequencies higher than up to . The bandwidth is only limited by our photodetectors. This amplitude resolution already qualifies our LDV for vibration measurement of microelectromechanical filters at ultra-high frequencies. We present a comprehensive model for the vibration-amplitude resolution of a LDV with this technique including the laser linewidths, the OPLL transfer function, and interferometer delays. The experiments with our LDV validate the model predictions from numerical simulations. Finally, we discuss the collapse of the heterodyne carrier at vanishing mutual coherence due to interferometer delays, the transition to shot-noise-limited detection, and provide design recommendations.

中文翻译：

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使用频率偏移锁定半导体激光器在超高频下进行外差干涉测量

现代宽带电信需要微机电滤波器，它可以在高达几千兆赫的超高频率下进行机械振动。外差干涉仪，即所谓的激光多普勒振动计 (LDV)，为此类滤波器中的振动提供了一种灵敏且非接触式的测量技术，但由于声光移频器的效率下降而在 GHz 外差方面受到限制。通过光电锁相环 (OPLL) 中两个激光器的频率偏移锁定进行外差克服了这一限制。这在我们的 LDV 设置中得到了证明，该设置具有外差直至可见波长的两个半导体激光器的偏置锁定。实验表明，对于高于 0.0 的频率，振动幅度分辨率小于 . 带宽仅受我们的光电探测器的限制。这种幅度分辨率已经使我们的 LDV 有资格在超高频下对微机电滤波器进行振动测量。我们使用这种技术提出了 LDV 振动幅度分辨率的综合模型，包括激光线宽、OPLL 传递函数和干涉仪延迟。我们的 LDV 实验验证了数值模拟的模型预测。最后，我们讨论了由于干涉仪延迟导致相互相干消失时外差载波的崩溃、向散粒噪声限制检测的过渡，并提供设计建议。我们使用这种技术提出了 LDV 振动幅度分辨率的综合模型，包括激光线宽、OPLL 传递函数和干涉仪延迟。我们的 LDV 实验验证了数值模拟的模型预测。最后，我们讨论了由于干涉仪延迟导致相互相干消失时外差载波的崩溃、向散粒噪声限制检测的过渡，并提供设计建议。我们使用这种技术提出了 LDV 振动幅度分辨率的综合模型，包括激光线宽、OPLL 传递函数和干涉仪延迟。我们的 LDV 实验验证了数值模拟的模型预测。最后，我们讨论了由于干涉仪延迟导致相互相干消失时外差载波的崩溃、向散粒噪声限制检测的过渡，并提供设计建议。