Simulating phase coding in quantum cryptography: influence of chromatic dispersion

We demonstrate the impact of chromatic dispersion on the phase coding method in a double Mach-Zehnder implementation of an interferometric system for quantum cryptography. Formulas have been developed to explore detailed studies of the modifications on energy and position spectra which arise if chromatic dispersion is taken into account. Examples demonstrate the shifting of spectra and the appearance of oscillations depending on the wavelength and spectral broadness as well as on the phase shifters, absorbers and the dimensions of the interferometric set-up.