  Laser-driven microresonators have enabled chip-integrated light sources with
unique properties, including the self-organized formation of ultrashort soliton
pulses and frequency combs (microcombs). While poised to impact major photonic
applications, such as spectroscopy, sensing and optical data processing,
microcombs still necessitate complex scientific equipment to achieve and
maintain suitable single-pulse operation. Here, to address this challenge, we
demonstrate microresonators with programmable synthetic reflection providing an
injection-feedback to the driving laser. When designed appropriately, synthetic
reflection enables deterministic access to self-injection-locked microcombs
operating exclusively in the single-soliton regime. These results provide a
route to easily-operable microcombs for portable sensors, autonomous
navigation, or extreme-bandwidth data processing. The novel concept of
synthetic reflection may also be generalized to other integrated photonic
systems.
