thank you for this answer :)
Actualy l solved the problem with a workaround. At first, I manually installed arrayfire 3.8.1 and linked to the libraries/includes files (typically in /opt/arrayfire/ on Linux).
For an unknown reason, this causes a crash with openCV.
After some testing, i noticed that OpenCL backend (from ubuntu repositories) was ok, but this repo had no Cuda backend. So i installed arrayfire from the regular PPA (repo.arrayfire.com
, with Cuda 10.2), and everything is fine now.
Anyway, thanks again for your time :)