  Low-noise microwave signals can be efficiently generated with
microresonator-based dissipative Kerr solitons ('microcombs'). However, the
achieved phase noise in integrated microcombs is presently several orders of
magnitude above the limit imposed by fundamental thermorefractive noise. One of
the major contributors to this additional noise is the pump laser frequency
noise transduction to the soliton pulse repetition rate via the Raman
self-frequency shift. Quiet points (QPs) allow minimizing the transduction of
laser frequency noise to soliton group velocity. While this method has allowed
partial reduction of phase noise towards the fundamental thermodynamical limit,
it relies on accidental mode crossings and only leads to very narrow regions of
laser detuning where cancellation occurs, significantly narrower than the
cavity linewidth. Here we present a method to deterministically engineer the
QP, both in terms of its spectral width, and position, showing an increased
phase noise suppression. This is achieved using coupled high-Q resonators
arranged in the Vernier configuration. Investigating a generalized
Lugiato-Lefever equation that accounts for the hybridized mode spectral
displacement, we discover a continuum of possible QPs within the soliton
existence region, characterized by ultra-low noise performance. Furthermore, we
discover that by using two controlled optical mode crossings, it is possible to
achieve regions where the QPs interact with each other enabling a substantial
increase of the noise suppression range. Our work demonstrates a promising way
to reach the fundamental limit of low-noise microwave generation in integrated
microcombs.
