With the advancement of photonic integration technology, ultra-low linewidth frequency-stabilized lasers have demonstrated significant potential in precision measurement, quantum communication, atomic clocks, etc. This review summarizes the latest developments in integrated photonics for achieving ultra-low linewidth lasers, particularly breakthroughs made by integrating Brillouin lasers. We discuss the design principles, manufacturing processes, performance characteristics, and potential value of these lasers in various applications.
