  We take a new look at plaquette-plaquette correlators in 4d compact U(1)
lattice gauge theory which are separated in time, both in the confined and the
deconfined phases. From the behaviour of these correlators we extract glueball
masses in the scalar as well as the axial-vector channels. Also in the
deconfined phase, the non-zero momentum axial-vector correlator gives us
information about the photon which appears as a massless particle in the
spectrum. Using the Luescher - Weisz multi-level algorithm, we are able to go
to large time separations which were not possible previously.
