The influence of disordering of quasi-phase-matched structures on the properties of biphoton fields generated by spontaneous parametric down-conversion in periodically poled crystals is studied in the general form, taking into consideration arbitrary one-dimensional spatial distribution of the crystal second-order susceptibility It is shown that the spectral amplitudes of the biphoton wave function become complex and gain frequency- and angle-dependent phase shifts in the structures with unequal lengths of domains. Effects of the spectrum broadening and the phase shifting are expressed in terms of the crystal non-linear transfer function. Spectrum of the first-order correlation function is found to be strictly dependent on the transfer function module, but insensitive to the phase shifts Availability of the phase shifts makes the second-order temporal correlation function of the broadened as-generated biphoton field to be almost the same as in case of a single-domain crystal At the same time, possibility of strong temporal biphoton compression appears further if an additional phase-compensating element is placed after the aperiodically poled crystal.
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