Abstract
A theory of many-wave optics of cholesteric blue phases is developed. The solution of the phase problem (i.e. the determination of the relative phases of the Fourier harmonics of the blue-phase order parameter) by means of many-wave diffraction is discussed. In the framework of many-wave blue-phase optics, the experimentally observed intensities of the Kossel lines are described. It is shown that the (111) and (200) Bragg reflections, observed in BPII, may be caused by coherent multiple diffraction.