  In this paper we study the nondegenerate optical parametric oscillator with
injected signal, both analytically and numerically. We develop a perturbation
approach which allows us to find approximate analytical solutions, starting
from the full equations of motion in the positive P-representation. We
demonstrate the regimes of validity of our approximations via comparison with
the full stochastic results. We and that, with reasonably low levels of
injected signal, the system allows for demonstrations of quantum entanglement
and the Einstein-Podolsky-Rosen paradox. In contrast to the normal optical
parametric oscillator operating below threshold, these features are
demonstrated with relatively intense felds.
