Coherent Synthetic Aperture Radar (SAR) Imaging With a 1550-nm Optical Sensor

Coherent synthetic aperture radar (SAR) is a technique for radar imaging with high range-independent lateral resolution and integration-based signal-to-noise ratio (SNR) improvement. At that, the complexity of the sensor is greatly reduced since a small antenna aperture is employed and synthetically expanded. While SAR is frequently applied to high-end microwave radar imaging, it is very difficult to implement in an optical sensor system due to the comparably high difficulty of achieving optical long-term phase stability. In this article, an optical coherent SAR imaging system with an 11° wide field of view (FoV) is presented. The sensor operates at 1550-nm wavelength and is capable of forming high-resolution SAR images over linear trajectories of 20 mm length (12.900 wavelengths) with a substantial target-to-noise ratio up to 30 dB at demonstrated ranges up to 95 mm (61.300 wavelengths). By applying a multistage phase error correction algorithm, imaging is enabled even at a very low transmit power of 32 $\mu $ W without requiring knowledge of the radar scene or applying auto-focusing techniques. Static measurements show an integration gain above 60 dB over 54 s, indicating great potential for increased ranges and aperture sizes.