Phase-Locked Opto-Electronic Oscillator (OEO) of Ultralow Phase Noise With Record-Low Allan Deviation of 3.4 × 10⁻¹⁴ at 1 s

By phase-locking to a commercial reference microwave source with good long-term stability, but relatively poor phase noises at high offset frequencies, we successfully obtained an opto-electronic oscillator (OEO) operating at 10 GHz with unprecedented long-term stability while maintaining the OEO’s low phase noise. In particular, for the first time to the best of the authors’ knowledge, we achieved an Allan deviation of
$3.4\times {10}^{-14}$
at 1 s, a frequency drift of much less than 0.1 Hz (limited by the resolution of the measurement instrument) for over 10 h, and ultralow phase noises of −124 dBc/Hz@1 kHz and −151 dBc/Hz@10 kHz from the 10 GHz carrier, while maintaining the side-mode spur of less than 90 dB and total spur less than 70 dB. Equally as important, we applied the Laplacian domain feedback noise model to analyze the phase noise properties of the phase-locked OEO, with the analytical results successfully verified experimentally, which not only helps to understand the locking process, but also validates an effective analytical tool for optimizing the operation parameters of the phase-locked OEO. As a result, we are able to suppress the phase noise of the OEO at 10 Hz frequency from the carrier by up to 30 dB from −50 to −80 dBc/Hz, limited primarily by the open loop gain of the feedback loop and the phase noise of reference source. Our work provides a practical OEO reference design for achieving both superb long-term stability and ultralow phase noise for practical applications.