Comparison of Optical Frequency Comb and Sapphire Loaded Cavity Microwave Oscillators

The single-sideband phase noise power spectral density and Allan deviation of a portable microwave oscillator system based on an optical frequency comb stabilized to an ultra-low expansion Fabry-Perot reference cavity is characterized at carrier frequencies of 4.0, 8.0, and 16.0 GHz. Compared to industry standard sapphire loaded cavity oscillators, the photonic microwave oscillator shows superior phase noise at offset frequencies < 100 Hz, and similar performance for offset frequencies from 100 Hz to 100 kHz. At 1-kHz offset, the phase noise power spectral density is better than −140 dBc/Hz at each carrier frequency. Relative frequency stability of
$3.0 \times 10^{-14}$
obtains at an averaging time of 400 ms.