  We suggest the generation of photon pairs in a thermally induced nonlinear
periodically-poled silica fiber by spontaneous parametric down-conversion.
Photons are generated directly in eigenstates of optical angular momentum.
Photons in a pair can be entangled in these states as well as in frequencies.
We identify suitable spatial and polarization modes giving an efficient
nonlinear interaction. By changing the pump field properties both narrow- and
broad-band down-converted fields can be obtained.
