Considering multi-physics requirements and loads in the early design phase as well as during the later experimental verification is especially important for the design of fusion devices due to the extreme environmental conditions and loads. Typical disciplines in design of fusion devices are thermodynamics, structural-mechanics, electro-magnetics, and optics. The interaction of these disciplines as well as an efficient approach to implement this interaction in numerical and experimental simulations is presented as applied at the new JET KL11 divertor endoscope design and verification process. The endoscope&#180s first pictures already showed the very good performance of the instrument.