Photonics-based Radar for Sub-mm Displacement Sensing

Photonics-based multiband radars have been demonstrated where photonics is exploited for multiple RF signal generation and detection by means of a single optical local oscillator that replaces the conventional cascades of electrical local oscillators. The ultra-wide band and high stability of photonics and the use of a single local oscillator assure very low system phase noise and phase coherence among the RF signals. This phase coherence among multi-band signals is exploited to perform differential phase estimation in enhanced sub-millimeter displacement measures. The system employs stepped frequency continuous waves simultaneously in the S- and X-band, measuring the differential phase over a frequency span up to 7.4GHz. The high coherence among the two frequency bands, provided by the photonic architecture, enables very precise displacements measures, allowing to obtain sub-millimeter precision without using correction algorithms. The presented experimental results demonstrate a precision < 200m in a range up to 3km. Moreover, the sharing of the same hardware to handle a multi-band operation allows a great reduction of size, weight, power and footprint of the overall system