Steve D.
Are you asking? ...."an oscillation (of what?) in space and time"? or "an oscillation of spacetime?"
If we accept GR field equations in its terms of a stress energy tensor, then the field is raw energy that can be conceived of as continuously coming into being as a consequence of what mathematically we would describe as the difference between a straight line and a curved line, hence the tighter the curvature the higher the stress energy.
Semi-Classically (3D) the energy field could be deemed primordial and an oscillation of which would satisfy the question "of what" in Steve Agnew's nicely written brief. His distinction of a linearly polarized photon is provocative, and I agree with you that this discussion is opening some contextually good avenues of approach to modeling the characteristics of EM observations to a physical shaping of a theoretical photon. The possible axial rotation of a soloton and the directional vector of electric field on its surface might produce a rationale for that physical rotation, rotating from the orthogonal to linear (as we speak of a conical section rotating) polarization dependent on the emission source. jrc