Frequency domain computation and stability analysis of oscillation modes of wideband optoelectronic oscillators

Optoelectronic oscillators (OEOs) use a long optical fiber delay line as a very high-Q resonator to produce very low phase noise RF/microwave oscillations. Computing all the oscillation modes and stability analysis of them in the frequency domain, in case of having wide band RF/microwave filters in their oscillation loops, is addressed in the current paper. Such a large bandwidth can be used to produce harmonic components of the oscillation or to give the possibility of sweeping the oscillation frequency in a large bandwidth by using a phase shifter and a small fiber. It is shown that in the case of OEOs with wideband RF filters, considering only the fundamental harmonic, instead of adequate number of them, may result in noticeable error in steady state computations as well as erroneous judgment about the stability of the modes. A relaxation algorithm is introduced for computing the oscillation modes. Stability analysis is performed by implementing the Nyquist stability test on a spectral domain system of equations governing the perturbations. The validity of the analysis approaches of this paper are verified by comparing their results against the time-consuming time-domain integrations.