We highlight fundamental properties of the dual-contact diffractive optical elements (DOEs) with high-diffraction efficiency throughout the visible spectrum and its fabrication example. To obtain high-diffraction efficiency over the broad wavelength range, the refractive index difference between the two kinds of materials constituting the dual-contact DOE must satisfy the constraint condition (blazing condition) on the wavelength dependence. For this reason, it has been considered difficult to obtain a suitable material for the dual-contact DOE. In recent years, nanocomposite materials have been studied as constituting materials of dual-contact DOE. We find the combination consisting of two kinds of UV curable resins that almost satisfy the blazing condition and have excellent processability. Prototyped dual-contact DOE using those materials showed high-diffraction efficiency and low-noise level throughout the visible spectrum.