Low phase noise and spurious level in multi-loop opto-electronic oscillators

We report on substantial improvements of the phase noise, and especially the spurious level of the opto-electronic oscillator (OEO) by using multiple optical loops. We demonstrated a spurious level reduction of more than 30 dB in a dual loop OEO compared with that of a single loop OEO. We found the OEO's closed loop transfer function to describe very well the spurious pattern and to provide an excellent tool for the design of a low spurious multi-loop OEO. The advantages of the multi-loop OEO configuration for a widely tunable OEO will be discussed as well.