The "different Hilbert spaces" of a photon? What I understand of Fock states so far:
They describe the quantum state of a bunch of photons.
A single photon can be in several different energy states, and when these photons are tensored together - the basis for this is the Fock states.
A given Fock state has a certain intensity for various frequencies of light.
However light has several other properties - for example, the polarisation states which is described by a two dimensional Hilbert space for each photon, and the spatial degree of freedom, which, say for in a beam splitter set up, can also be described by a two dimensional Hilbert space. And there may be several other properties like angular momentum, etc.
How is the polarisation state of a photon related to it's energy state or related to states in the Fock basis?
Or are they separate things - Light in any Fock state (or a superposition of Fock states) can have any polarization?
If anyone can shed light on the other properties, that would be great as well. 
I come from a quantum information background, and know very little optics and electromagnetism, so if anyone could explain it from that point of view, it would be great.
 A: A photonic quantum state can consist of multiple photons, as you correctly implied. If there is a fixed number of photons in the state, then we call it a "number state" or a "Fock state." Each photon in the Fock state can carry its own set of spatiotemporal and polarization (spin) degrees of freedom. Some people say that all the photons in a Fock state must have the exact same spatiotemporal and polarization degrees of freedom, but for the sake of this discussion, we'll allow them to be different.
The polarization degrees of freedom are represented by two discreet degrees of freedom. These are also associated with the spin angular momentum. So the latter is not a separate degree of freedom.
The spatiotemporal degrees of freedom represent three continuous degrees of freedom. One can either specify them as the three components of the propagation vector $\mathbf{k}$, or as two such components and a frequency $\omega$. The fourth quantity is then related to these by the dispersion relation $\omega=c|\mathbf{k}|$. These degrees of freedom are also associated with orbital angular momentum (OAM). So OAM is not a separate degree of freedom.
As you can probably see, the total set of degree of freedom of a Fock state becomes rather complicated. To make matters worse, one can also have photonic quantum states that do not have fixed numbers of photons. So the most general state is very complicated to specify in terms of all its degrees of freedom. However, there are ways to do it ...
