Finely Tunable Coupled Optoelectronic Oscillator Based on Injection Locking and Phase Locked Loop

A finely frequency tunable coupled optoelectronic oscillator (COEO) based on injection locking and phase locked loop is proposed and demonstrated. By investigating a dynamic relation between the frequency locking range and injection locking ratio, an optimum injection locking ratio with sufficient locking range is obtained so as finely frequency tracking and locking with high stability is achieved by tuning the frequency of the injected signal and controlling an optical tunable delay line (OTDL). Through optimizing the injection ratio, a trade-off between the suppression of the near-carrier phase noise and the excellent far-carrier phase noise is realized. In the experiment, a high quality COEO with a tuning range of 1.76 MHz and a precise tuning step of 10 Hz is demonstrated. The measured sidemode suppression ratio (SMSR) at 9.95554 GHz reaches 78.2 dB, and a frequency drift of better than 1 ppb during a 1-hour is observed. The phase noise at 10 kHz offset is measured to be −130.04 dBc/Hz, and the Allan deviation (ADEV) reaches 1.39 × 10
⁻¹³
at averaged time of 100 s.