We developed a compact and lightweight multispectral active optical system for detection of passive diffusely-reflecting and active thermal objects. The system acts as an automatic collision avoidance system used for ultra-light UAVs. The system contains an active laser detector and a passive LWIR finder. The different types of detectors are complexed by means of neural network realized on 256 core video processor. The fast response is realized by field-programmable gate array processing of the raw signal.