Key properties and design issues for an opto-electronic oscillator

In this invited paper we review state-of-the-art opto-electronic oscillator technologies with a single optical loop, which represent emerging components for continuous-wave (CW) microwave signal generation, available for both electrical and optical carriers. Such a hybrid opto-electronic system uses an external electro-optical modulator, a filter that selects from among the possible oscillation modes, and a long, optical, single-mode fiber in a closed resonator loop. The required resonator quality factor (Q) is proportional to the product of the oscillator's frequency and the fiber's length, which introduces an optical delay with a low loss. The main focus of this paper will be on opto-electronic design issues in order to obtain a low phase noise, a high spectral purity, a high quality factor, a high long-term frequency stability, good robustness, small dimensions, a low power consumption, and a low cost. The key features of the opto-electronic oscillator prototype, where the CW microwave signal is carried to the optical domain using a laser with a 1550-nm wavelength via optical modulation, will be demonstrated.