  We propose and design a high-brightness, ultra-compact electrically pumped
GaSb-based laser source of entangled photons generated by mode-matched
intracavity parametric down-conversion of lasing modes. To describe the
nonlinear mixing in highly dispersive and dissipative waveguides, we develop a
nonperturbative quantum theory of parametric down-conversion of waveguide modes
which takes into account the effects of modal dispersion, group and phase
mismatch, propagation, dissipation, and coupling to noisy reservoirs. We extend
our theory to the regime of quantized pump fields with a new approach based on
the propagation equation for the state vector which solves the nonperturbative
boundary-value problem of the parametric decay of a quantized single-photon
pump mode and can be generalized to include the effects of dissipation and
noise. Our formalism is applicable to a wide variety of three-wave mixing
propagation problems. It provides convenient analytic expressions for
interpreting experimental results and predicting the performance of monolithic
quantum photonic systems.
