Self-Injection Locking of a Microwave Oscillator by Use of Four-Wave Mixing in an Atomic Vapor

We demonstrate self-injection locking of a low-power, compact microwave oscillator by use of feedback generated from four-wave mixing in an atomic vapor. The four-wave mixing process creates an effective microwave filter with extremely high off-resonant signal suppression. This type of locking results in a shorter locking time, increased short-term stability, improved close-in phase noise, and reduced spurious signals as compared to current techniques used in miniature atomic clocks. Other possible benefits and drawbacks are mentioned.