  Instabilities are predicted for a sufficiently long hollow photonic optical
fiber, or "cavity", containing a one dimensional Bose-gas in the presence of a
classical, far red-detuned, confined weak electromagnetic mode. We examine both
a single beam with Bose gas (a type of Brillouin instability) and the case of a
standing wave, or optical lattice. The instabilities of these driven systems
have pronounced spatial structure, of combined modulational instabilities in
the electromagnetic and Bose density fields. Near the critical wave vectors for
the instability the coupled modes of the BEC and light can be interpreted as
"phonons" of the optical lattice. We conjecture these spatially-structured
instabilities for the optical lattice, which we predict at weak fields, develop
into the source of spatially homogeneous heating predicted for strong fields.
