Highly sensitive demodulation of a vibration-induced phase shift based on a low-noise OEO.

A highly sensitive demodulation approach of a vibration-induced phase shift based on a low-noise optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. The vibration-induced optical phase variation is directly converted to the electrical oscillating signal of the OEO with carrier phase-shifted double-sideband (CPS-DSB) modulation, which is realized by cascading a dual-output Mach-Zehnder modulator (DOMZM) and a fiber interferometer. Theoretically, within a CPS-DSB modulated OEO, the minimum detectable optical phase shift is determined by the phase noise achievable, and the sensitivity of the optical phase shift demodulation no longer depends on its frequency. A proof-of-concept OEO oscillating at 100 MHz with ultralow phase noise is built for demonstration. The achieved minimum detectable optical phase shift is 0.58  μrad/√Hz at 1 kHz and 0.21  μrad/√Hz at 10 kHz, which are the best results ever reported, to the best of our knowledge.