Vibration measurement based on an injection-locked optoelectronic oscillator

A novel, to our knowledge, vibration measurement method based on an injection-locked optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. The vibration is mapped into the phase difference between the optical carrier and the frequency-shifted light, which is realized by using a Mach-Zehnder interferometer with an embedded acousto-optic modulator. Then, based on an OEO loop, the optical phase difference is converted to the phase variation of the microwave oscillating signal. An injection-locking technology is adopted to suppress the phase noise so that the minimum detectable vibration can be enhanced. A proof-of-concept experiment is implemented. The frequency response of the system and the phase noise of the oscillating signal are measured, and the improvement of the side-mode suppression ratio is verified. The electrical spectra are measured when the vibration signal with different voltages and frequencies is imposed, which are consistent with the theoretical derivation. The vibration signal is reconstructed from the temporal waveform of the oscillating signal by a phase demodulation algorithm, and the high-frequency noise is eliminated by an undersampling method. In addition, the detectable frequency range is from 62.5 Hz to 500 kHz, and the measurement sensitivity is obtained as 1.31 rad/V at 2 kHz.