  Optical microcombs represent a new paradigm for generating laser frequency
combs based on compact chip-scale devices, which have underpinned many modern
technological advances for both fundamental science and industrial
applications. Along with the surge in activity related to optical micro-combs
in the past decade, their applications have also experienced rapid progress,
not only in traditional fields such as frequency synthesis, signal processing,
and optical communications, but also in new interdisciplinary fields spanning
the frontiers of light detection and ranging (LiDAR), astronomical detection,
neuromorphic computing, and quantum optics. This paper reviews the applications
of optical microcombs. First, an overview of the devices and methods for
generating optical microcombs is provided, which are categorized into material
platforms, device architectures, soliton classes, and driving mechanisms.
Second, the broad applications of optical microcombs are systematically
reviewed, which are categorized into microwave photonics, optical
communications, precision measurements, neuromorphic computing, and quantum
optics. Finally, the current challenges and future perspectives are discussed.
