How to construct a Universal Linear Optical State Generator?

We consider all optical realization of a universal quantum state generator utilizing projective photon measurements to create an effective non-linearity. Specifically we are interested in finding a set of unitary optical devices required in order to generate a given quantum state for a given input and a projective measurement. We illustrate the formalism for a case of multi-photon path entangled states (N00N states). We conjecture an existence of necessary criteria connecting a size of a N00N state to a number of input modes of a generator.