Abstract

By adopting self-injection locking (SIL) technology in an external injection locking (EIL) optoelectronic oscillator (OEO), a highly improved side mode suppression ratio (SMSR) and low phase noise microwave signal generator is designed. The EIL ranging is closely related to the frequency spacing ranging of the free-running OEO, which is the reverse of the oscillation loop length, and limits the phase noise performance. Here SIL technology is introduced to significantly increase the Q-factor of the OEO without degrading the SMSR by setting the longer loop without oscillation. Both the simulation and experimental results are carried out to confirm the conclusion. Additionally, an SMSR up to 86 dB and phase noises as low as ${-}{88.80}\;{\rm{dBc/Hz}}@{{100}}\;{\rm{Hz}}$ and ${-}{122.83}\;{\rm{dBc/Hz}}@{{10}}\;{\rm{kHz}}$, respectively, are demonstrated. Furthermore, the frequency overlapping Allan deviation of the proposed OEO scheme is also enhanced by ${{1}}{{{0}}^3}$ times, which benefits from the external injection technology compared with the free-running OEO. In addition, the SMSR and phase noise modification dependence on the fiber length, the RF source quality and external injection power, as well as the frequency tunability, are detailed and discussed to reveal the compatibility combination mechanism of the EIL and the SIL.

© 2022 Optica Publishing Group

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