Outdoor demonstration of range-selective digital holography for three-dimensional imaging

Frequency-modulated continuous-wave range-selective digital holography (FMCW RSDH) is a coherent imaging technique that enables selective imaging of objects, even when multiple are present in the depth of field. In this paper, the FMCW RSDH technique is demonstrated as an alternate method to record three-dimensional (3D) point clouds outdoors without mechanical scanning. The range of the RSDH system was extended by applying the frequency shift on the local oscillator (LO) beam in the RF domain (rather than the optical domain with acousto-optic frequency shifters, as was previously demonstrated), extending the potential range of operation to over a kilometer. Three-dimensional point clouds were produced with a range resolution of 8.3 cm, which was two orders of magnitude better than the optical system's non-diffraction-limited depth of field. RSDH images were recorded of a scene comprised of multiple objects distributed axially over 1.3 m at a range of 90 m. The transverse resolution and accuracy (assuming undistorted imaging) of the point clouds are governed by the sensor array and telescope, not by the mechanically scanned FMCW lidar system that was integrated with the FMCW RSDH system, and were thus observed to be an order of magnitude better than those of our scanned system. The required holographic stability of the imaged objects is reduced by orders of magnitude with FMCW RSDH compared to prior FMCW digital holographic techniques, enabling enhanced imaging of real-world scenes.