Improving the Side-mode Suppression Ratio and Reducing the Frequency Drift in an Opto-Electronic Oscillator With a Feedback Control Loop and Additional Phase Modulation

We present two stabilization methods for an opto-electronic oscillator. By using a frequency discriminator with a feedback control loop the long-term stabilization was improved, and a frequency drift of 0.05 ppm/K was achieved without any fiber thermal stabilization. In addition, the phase-noise degradation as a result of the discriminator control loop was investigated. To the best of our knowledge, this has not been done before for this type of method. Our study revealed that a properly designed control loop does not increase the phase noise. The second stabilization method was used to increase the side-mode suppression ratio. This was achieved with an additional control loop in the form of an oscillator-loop phase modulation. In this way, a 5-dB increase in the side-mode suppression ratio was recorded. The phase-noise degradation was less than 1 dB in the close-in region. The two methods were designed to operate simultaneously. This design provides both simplicity and cost effectiveness for the stabilized opto-electronic oscillator.