More specifically, their algorithm seems to design linear optical systems (multiplexing,demultiplexing,phase shifting,etc are among them: actually any LT given

More specifically, their algorithm seems to design linear optical systems (multiplexing,demultiplexing,phase shifting,etc are among them: actually any LT given by a complex matrix of phasors wich is at most unitary can be realized). This matrix can be generalized to the continuous case with a self-adjoint operator but I suppose you get size restrictions to reproduce precisely a complicated operator. Switching of course is nonlinear.