  In a recent paper [Phys. Rev. A {\bf 96}, 053822 (2017)], we proposed a
strategy to generate bipartite and quadripartite continuous-variable
entanglement of bright quantum states based on degenerate down-conversion in a
pair of evanescently coupled nonlinear $\chi^{(2)}$ waveguides. Here, we show
that the resources needed for obtaining these features can be optimized by
exploiting the regime of second harmonic generation: the combination of
depletion and coupling among pump beams indeed supplies all necessary
wavelengths and appropriate phase mismatch along propagation. Our device thus
entangles the two fundamental classical input fields without the participation
of any harmonic ancilla. Depending on the propagation distance, the generated
harmonics are entangled in bright or vacuum modes. We also evidence two-color
bipartite and quadripartite entanglement over the interacting modes. The
proposed device represents a boost in continuous-variable integrated quantum
optics since it enables a broad range of quantum effects in a very simple
scheme, which optimizes the resources and can be easily realized with current
technology.
