  Because they coherently link radio/microwave-rate electrical signals with
optical-rate signals derived from lasers and atomic transitions, frequency
combs are having a remarkably broad impact on science and technology.
Integrating these systems on a photonic chip would revolutionize
instrumentation, time keeping, spectroscopy, navigation and potentially create
new mass-market applications. A key element of such a system-on-a-chip will be
a mode-locked comb that can be self-referenced. The recent demonstration of
soliton pulses from a microresonator has placed this goal within reach.
However, to provide the requisite link between microwave and optical rate
signals soliton generation must occur within the bandwidth of electronic
devices. So far this is possible in crytalline devices, but not chip-based
devices. Here, a monolithic comb that generates electronic-rate soliton pulses
is demonstrated.
