Opto-electronic generation of stable and low noise microwave signals

Optical technology offers a new method for generating microwave signals with extremely low noise and high stability. For that purpose a long fibre is used in the feedback loop of the oscillator. However, when using a long fibre, a lot of resonances will appear in the output spectrum, impairing the stability of oscillation. This paper introduces three new approaches for improving the frequency stability and reducing the phase noise of opto-electronic oscillators. The frequency stability is improved in two different ways: by using several fibres in the oscillator feed-back loop and/or by the insertion of an additional third-harmonic optical loop. To reduce the phase noise a special nonlinear electronic feedback technique is used. The combination of these methods can result in an optimum adjustment.