Quantum theory analysis of loss effects in guided nonlinear-optic twin-photon generation

Integrated nonlinear-optic (NLO) devices for generation of twin-photon beams are a key device for quantum information techniques. This paper presents a quantum theory analysis on the effect of optical losses in twin-photon generation. The analysis uses a multi-mode-pair description, and is based upon unitary transformations of amplitude operators and state vectors for describing the NLO and loss phenomena in infinitesimal sections in the interaction range. Full description of the quantum states of the twin-photon beams affected by the losses is obtained. Mathematical expressions useful for prediction of the performances degradation are deduced