Diffractive optical elements (DOEs) owe their optical characteristics to their ability to diffract rather than refract light. They are manufactured holographically, by microlithography, or by computer-controlled electron beam etching. They have two main advantages over conventional lenses: they can be fabricated on a thin sheet (flat or curved); and a single DOE can perform many optical operations simultaneously. The main disadvantage is serious colour dispersion; but as this is in the opposite sense to refractive dispersion, a DOE can be combined with a refractive element to form an achromatic pair. Important applications of DOEs include head-up displays for aircraft, directional diffusing focusing screens for studio cameras, and bifocal contact lenses.
— Graham Saxby
