Measurement on Spurious Phase Stability in Optoelectronic Oscillators

Long loop delay in optoelectronic oscillator (OEO) helps to achieve high Q factor, but it also produces narrowly spaced spurious modes, which is hard to be filtered out. To suppress spurious modes, dual-loop and inject-locking structures have been studied. Besides, feedforward technique may also be used for spurious suppression. The more stable the spurious phase relative to the principal mode in OEO, the better the suppression can be obtained. To assess the phase stability of spurious mode, we built up a phase measurement system using digital IF structure. OEOs oscillated at 10GHz with different fiber lengths were set up. The results showed that the stability of the spurious phase improved with the increase of fiber length. This article provided experimental evidence of a possible method of spurious suppression for future work.