Abstract

We experimentally characterize and numerically model the amplification characteristics of a sub-threshold opto-electronic oscillator subject to external continuous wave radio frequency injection, as well as the transient temporal characteristics when subject to a pulsed radio frequency injection. The opto-electronic oscillator demonstrates enhanced sensitivity and amplification as threshold is approached. A radio frequency gain of 27.5 dB is demonstrated at an optical power of 0.989 times the threshold optical power. Furthermore, the transient behavior shows signatures of both the intrinsic time-delay of the opto-electronic oscillator and the finite bandwidth of the electronic radio frequency filter. Approximating higher-order group delay contributions of the experimental band-pass filter as an external time-delay allows the system to be modeled with a well-known opto-electronic oscillator rate equation model. The nonlinear, time-delayed differential equation model provides numerical agreement with experimental results. The model is approximately solved in respective analytical and transcendental regimes, giving reliable predictions compared to the experiment. It is demonstrated that small time-delay variation yields precise and predictable control over the frequency selectivity of the opto-electronic oscillator sensor.