Narrow-linewidth brillouin laser stabilized by optical self-injection locking

An apparatus comprising:

• a ring optical resonator characterized by a Brillouin shift frequency Ωa and a free spectral range νFSR;
• and
• a first pump laser source that arranged so as to (i) produce a first pump optical signal at a first pump optical frequency ν1P, and (ii) launch at least a portion of the first pump optical signal into the ring optical resonator to propagate in a forward direction around the ring optical resonator,
• the ring optical resonator and the first pump laser source being arranged so that:
• a portion of the first pump optical signal backscattered by the ring optical resonator propagates back to the first pump laser source and injection-locks the first pump laser source so that the first pump optical frequency ν1P is locked to a first resonant mode optical frequency of the ring optical resonator;
• and
• a portion of the first pump optical signal circulating in the ring optical resonator results in a first stimulated Brillouin laser (SBL) optical signal at a first SBL optical frequency ν1=ν1P−Ωa that resonantly propagates in a backward direction around the ring optical resonator and is emitted from a resonant optical mode of the ring optical resonator at a resonant mode optical frequency that is lower than the first resonant mode optical frequency.