  In this paper, we reduce the electromagnetic theory to future null infinity
and obtain a vector theory at the boundary. We compute the Poincar\'e flux
operators which could be generalized. We quantize the vector theory, and impose
normal order on the extended flux operators. It is shown that these flux
operators generate the supertranslation and superrotation. When working out the
commutators of these operators, we find that a generalized electromagnetic
duality operator should be included as the generators to form a closed symmetry
algebra.
