Analysis of noise mechanisms limiting the frequency stability of microwave signals generated with a femtosecond laser
Analysis of noise mechanisms limiting the frequency stability of microwave signals generated with a femtosecond laser
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DOI：
10.1109/jstqe.2003.819093
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发表时间：
2003-07-01
影响因子：
4.9
通讯作者：
Hollberg, L
中科院分区：
文献类型：
--
作者：
Ivanov, EN;Diddams, SA;Hollberg, L
从飞秒激光器的超短光脉冲序列照射的光电探测器中提取的微波信号的频谱中观察到过量的相位噪声。这种噪声影响了飞秒激光器从光域到微波域的频率转移的稳定性。对多余相位噪声的一些贡献与飞秒激光器的固有光束指向波动和检测光的光功率波动有关。由于光电探测器中的功率-相位转换、空间相关的时间延迟以及使脉冲形状失真的光电二极管非线性，这些因素导致脉冲重复率的谐波处的过量相位噪声。通过对激光束的空间滤波和功率的主动控制，将与光电探测过程的过量噪声相关的脉冲重复频率的额外分数频率波动从6（.）10（-14）至约3（.）10（-15）超过1 s的平均值。还检查了其他噪声机制的影响，例如激光散粒噪声和微波放大器引入的相位噪声，但发现其水平不太显着。
Excess phase noise is observed in the spectrum of the microwave signal extracted from a photodetector illuminated by a train of ultrashort light pulses from the femtosecond laser. This noise affects the stability of frequency transfer from optical to microwave domains with the femtosecond laser. Some contributions to the excess phase noise are related to intrinsic beam-pointing fluctuations of the femtosecond laser and optical power fluctuations of the detected light. These factors contribute to excess phase noise at the harmonics of the pulse repetition rate due to power-to-phase conversion in the photodetector, spatially dependent time delays, and photodiode nonlinearities that distort the pulse shape. With spatial filtering of the laser beam and active control of its power, the additional fractional frequency fluctuations of pulse repetition rate associated with the excess noise of the photodetection process were reduced from 6(.)10(-14) to approximately 3(.)10(-15) over 1s of averaging. The effects of other noise mechanisms, such as laser shot noise and phase noise introduced by a microwave amplifier, were also examined but were found to be at a less significant level.