Study of the phase noise spectrum in RF injection-locked single-loop optoelectronic oscillators

A method for the phase noise characterization of radio frequency (RF) injection-locked single-loop optoelectronic oscillators (OEO) is presented. Based on the injection-pulling dynamics of OEO under RF injection, this method is used to compute the phase noise spectrum of a free-running single-loop OEO. An expression for the far-out phase noise spectrum of a free-running single-loop OEO is presented to capture the far-out phase noise characteristics of the OEO. Also, we derive the expression for the close-in phase noise spectrum of the free-running single-loop OEO by considering the multiplicative noise as the overall loop-gain perturbation in the OEO loop. Considering strong RF signal injection and loop-gain perturbation, the power spectral density of the overall phase noise for an injection-locked single-loop OEO is computed in terms of the noise filtering band-width, which can be controlled by changing the lock-range of the RF injection locked OEO. The close-in phase noise is optimized by properly choosing the RF injection signal power. The experimental results are also given in partial support to the conclusions of the analysis.