The Electromagnetic Filed is a natural phenomenon which we try to model it by some sort of mathematical structures, i.e. Maxwell Field Equations. the deformation of space-time emerged after some brilliant scholars' endeavor; i.e. Poincare, Lorentz, etc..., which tied the ancient 3-D space and Time and justified their harmonious dance. But this justification was and is the direct consequence of the use of mathematics to MODEL the universe.
I think, at very first step, you need to correct the main question to mention "the mathematical model of electromagnetic field propagation" instead of "the electromagnetic field".