A new concept for spatially resolved coherent detection with vertically illuminated photodetectors targeting ranging applications

Coherent Detection With Double-Side Vertically Illuminated Photodiodes for Spatially Resolved Ranging Applications

“…In this article, we compare heterodyne coherent detection with counter-propagating signal and LO to the co-propagating case with using 50-50 beam splitters. We experimentally confirm the in [7] proposed approach superseding optical beam splitters and delivering new degrees of freedom in the design of solid-state coherent lidar systems by making use of the strong intermediate frequency (IF) power dependency on the relative propagation angle between signal and LO.…”

“…The significant IF power drop under non-collinear angles of propagation of signal and LO constitutes a nuisance in freespace optical coherent detection [10], as signal and LO have to be carefully matched to guarantee efficient IF generation. In [7] we suggested the new concept of using the strong angle dependency as a key feature for deliberate suppression of signals under all angles of no interest. Sweeping the relative angle between signal and LO or using suitable lens and array combinations, one is able to create a spatially resolved coherent detection with angle resolution.…”

“…Other FPA-based coherent receivers use 50-50 optical beam splitters to combine signal and LO and therefore require accurate collinear superimposition of signal and LO and suffer from a fourfold reduction in signal strength [6], [1]. In [7], we proposed a novel approach of spatially resolved coherent detection by illuminating the photodetector chips with signal and LO from opposite sides for coherent detection. This has the potential for array configurations with coherent detection in a single photodetector.…”