Frequency comb synthesized microwaves have been so far realized with tabletop systems, operated in well-controlled environments. Here, we demonstrate state-of-the-art ultrastable microwave synthesis with a compact rack-mountable apparatus. We present absolute phase noise characterization of a 12 GHz signal using an ultrastable laser at similar to 194 THz and an Er:fiber comb divider, obtaining -83 dBc/Hz at 1 Hz and < -166 dBc/Hz for offsets greater than 5 kHz. Employing semiconductor coating mirrors for the same type of transportable optical frequency reference, we show that -105 dBc/Hz at 1 Hz is supported by demonstrating a residual noise limit of division and detection process of -115 dBc/Hz at 1 Hz. This level of fidelity paves the way for the deployment of ultrastable photonic microwave oscillators and for operating transportable optical clocks. (C) 2020 Optical Society of America
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