Phase Cohered Optically Injection Locked Oscillators for Communication Phased Arrays

The indirect subharmonic optical injection locking is a powerful technique to synchronize oscillators up to millimeter wave frequencies, however they suffer from phase inaccuracy over the locking range, first formulated by Adler. This paper presents a method to measure this phase error and correct for it by adjusting the free-running oscillation frequency of an FET oscillator. Experiments supporting this approach are reported for two optically injection locked oscillators at 18GHz, where phase correction of ±90° are achieved by adjusting the bias current to the PET VCO.