摘要：

We describe the stabilization of the beatnote of an Er,Yb:glassdual-frequency laser at 1.5 μm with and without an external microwave reference. In the firstcase, a classical optical phase-locked loop (OPLL) is used, and absolute phasenoise levels as low as -117 dBrad²/Hz at 10 kHz from the carrierare reported. In the second case one or two fiber-optic delay lines are usedto lock the frequency of the beatnote. Absolute phase noise levels as lowas -107 dBrad²/Hz at 10 kHz from the carrierare measured, fairly independant of the beatnote frequency varying from 2to 6 GHz. An analysis of the phase noise level limitation is presented inthe linear servo-loop theory framework. The expected phase noise level calculatedfrom the measurement of the different noise sources fits well with the predictions.

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