High-sensitivity displacement sensing based on an OEO incorporating an unbalanced MZI

An optoelectronic oscillator (OEO) for high-speed and high-sensitivity displacement sensing with extended measurement range is proposed and experimentally demonstrated. The key parts of the OEO are a broadband optical source (BOS), a Mach-Zehnder interferometer (MZI) with unbalanced arms, a spool of dispersion compensating fiber (DCF) and a photodetector (PD) which jointly act as a single-bandpass microwave photonic filter (MPF) to choose the oscillating frequency of OEO. The change of displacement between the two collimating lenses embedded in one arm of the MZI will induce the change of free spectral range (FSR) of the MZI, leading to a frequency shift of the single-bandpass MPF as well as the oscillating signal of the OEO. Thanks to the pair of collimating lenses in the MZI, a displacement sensing with a large range from 0 mm to 12 mm is carried out, and a displacement resolution of 0.07 mu m with a sensitivity of 0.285 MHz/mu m is obtained.