Phenomenological quantum description of the ultrafast response of arrayed waveguide gratings

This work presents a detailed and quantitative quantum description of the ultrafast response of arrayed waveguide gratings (AWG) illuminated with relatively intense short pulses of light. This is achieved with no more mathematical or conceptual complexities than that required by a classical description. The presented approach is based on the phenomenological interpretation of the photon, that is, a photon is what produces a "click" in a photodetector. This phenomenological approach was combined with the application of Feynman's rules for describing interference and Bohr's correspondence principle, i.e., quantum theory should somehow converge in the limit with the classical description of the interference phenomena. This basic approach reveals that, in apparent opposition to wide-held beliefs, especially designed AWGs can be used to produce interference in conditions where the "which-path" information is available.