Stability improvement of a dual-loop optoelectronic oscillator based on self-phase locking.

In this study, we experimentally demonstrate what we believe is a novel dual-loop optoelectronic oscillator (OEO) with a self-phase locking loop (SPLL). Using this feedback loop, the phase of the oscillating signal is locked to its past by adjusting the DC bias voltage of the used Mach-Zehnder modulator. In this way, the oscillating frequency stability can be improved. Proving experiments on a 10-GHz OEO are performed. The results show that more than 20 dB improvements in the phase noise at low offset frequencies are achieved, the frequency fluctuation is reduced to less than 4 kHz in an hour, and the corresponding Allan deviation is decreased by 1 order of magnitude owing to the SPLL. This frequency stabilization scheme without use of any external reference sources has a great prospect in an integrated OEO.