  Optical microcavities are essential in numerous technologies and scientific
disciplines. However, their application in many areas relies exclusively upon
discrete microcavities in order to satisfy challenging combinations of
ultra-low-loss performance (high cavity-Q-factor) and cavity design
requirements. Indeed, finding a microfabrication bridge connecting ultra-high-Q
device functions with micro and nanophotonic circuits has been a long-term
priority of the microcavity field. Here, an integrated ridge resonator having a
record Q factor over 200 million is presented. Its ultra-low-loss and flexible
cavity design brings performance that has been the exclusive domain of discrete
silica and crytalline microcavity devices to integrated systems. Two distinctly
different devices are demonstrated: soliton sources with electronic repetition
rates and high-coherence Brillouin lasers. This multi-device capability and
performance from a single integrated cavity platform represents a critical
advance for future nanophotonic circuits and systems.
