Coherent detection in 3D FMCW flash LIDAR with large FOV: part II – heterodyne efficiency in the image plane

We have introduced in Part I of this two-part study a theoretical model describing speckle size evolution in the imaging plane. Part II investigates heterodyne efficiency optimization in a wide field-of-view 3D flash FMCW LIDAR system. Heterodyne efficiency quantifies the local interference contrast between the scene and local oscillator (LO) wavefronts and directly impacts signal-to-noise ratio and depth range. Based on Fink's original formulation, we derive the heterodyne efficiency expression to include polarization mismatches. Experimental system upgrades, notably improved LO beam shaping leading to a better wavefront alignment, enhance angular matching between the LO and scene beams across a ± 26° field of view. Through numerical simulations, we investigate aperture ratio and pixel size effects on heterodyne efficiency over the field of view range. Finally, experimental measurements show an enhancement of heterodyne efficiency at off-axis angles. This work provides a pathway to optimize performance in coherent LIDAR systems operating over extended fields.