  We suggest and discuss a concept of deterministic integrated source of
non-classical light based on the coherent diffusive photonics, a coherent light
flow in a system of dissipatively coupled waveguides. We show how this
practical quantum device can be realized with a system of single-mode
waveguides laser-inscribed in nonlinear glass. We describe a hierarchy of
models, from the complete multi-mode model of the waveguide network to the
single mode coupled to a bath, analyze the conditions for validity of the
simplest single-mode model and demonstrate feasibility of the generation of
bright sub-Poissonian light states merely from a coherent input. Notably, the
generation of non-classical states occurs at the initial stages of the
dynamics, and can be accounted for in the linear model that allows us to
circumvent the prohibiting computational complexity of the exact full quantum
representation.
