  The stability of phase domains and spatial solitons in DOPO under the
presence of an injected signal is investigated. The injected signal prevents
the nondegenerate regime and, for a particular value of the phase, preserves
the equivalence between the two homogeneous states, allowing the domain
formation and, in particular, the stability of solitons. The main conclusion is
that injection facilitates the experimental observation of solitons in
degenerate OPOs.
