Phase control of optically injection locked oscillators for phased arrays

The most suitable architecture for millimeter-wave frequencies is based on the transmit/receiver (T/R)-level data mixing architecture, where a frequency reference is provided to local oscillators in the subarrays to have them frequency and phase synchronized. The indirect subharmonic optical injection locking has the benefit of a high degree of frequency synchronization up to millimeter-wave frequencies; however, the local oscillators suffer from phase inaccuracy over the locking range, first formulated by R. Adler (1946). A scheme is proposed to measure this phase error and correct for it by adjusting the free-running oscillation frequency of a voltage controlled oscillator (VCO). Experiments supporting this approach are reported for two optically injection locked oscillators at 18 GHz, where controlled phase shifts over -90 degrees to 78 degrees are achieved by adjusting the bias current to a yttrium-iron-garnet (YIG) tuned VCO.<>