Photonics-Based Radar for Sub-mm Displacement Sensing

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