Phase Noise Transfer in High-Q Quartz Phononic Frequency Combs

We report on observing significant reduction of injected phase noise (more than 20 dB over two decades with a peak reduction of 29 dB) on particular comb teeth in high-Q, phononic frequency combs in AT-cut 100-MHz shear-mode quartz resonators. A frequency comb with teeth spacing of 135 kHz was observed on the fundamental mode resonance when driven off-resonance at power levels more than 22 dBm. Teeth in this comb, which exhibited smaller deviations in frequency than the drive signal, were observed to have significantly reduced phase noise sensitivity compared to the drive. Correspondingly, increased levels of phase noise sensitivity were observed on teeth with larger frequency deviations. Similar noise transfer mechanisms between the drive and teeth in a frequency comb were observed to occur in a one-dimensional duffing oscillator. This effect opens up the possibility of utilizing phononic frequency combs to reduce the noise of conventional oscillators.