Towards an Integrated Optic Phase-locked Oscillator

A recent experiment, performed at the Massachusetts Institute of Technology, has demonstrated that by locking a microwave oscillator to an optical pulse train from a modelocked laser, exceptional timing stability can be achieved. In the experiment, a 10.225-GHz microwave oscillator was locked to an optical phase detection apparatus consisting of a modelocked laser, a Sagnac interferometer, and an optical phase modulator. A relative out-of-loop timing jitter of 6.8 fs rms was measured between the locked oscillator and the optical pulse train over a 1-MHz bandwidth and a 10-hour integration period, corresponding to a stability of 1.9×10. Here, we consider the potential for an integrated version of this optical phase-locked oscillator. Detailed analysis of the components required for integration is used to estimate the timing performance of the integrated optic phase-locked oscillator. Initial estimates indicate potential for a single-sideband phase noise level of -153 dBc/Hz and corresponding jitter level of ~1 fs across a 10-MHz loop bandwidth. While this work is still in the design stages, if successful, the result will be a compact and low-power oscillator with exceptional phase noise and timing stability that can be applied across many applications including RADAR, global positioning, and communications systems.