DIFFRACTIVE ELEMENT WITH DOUBLY PERIODIC GRATINGS

摘要

The invention concerns a diffractive element, a method of producing a viewable image and an optical device. The element comprises a waveguide (30) and a diffractive out-coupling region (36) arranged on a surface (30A) or inside the waveguide (30), the out-coupling region (36) comprising a plurality of sub-regions (36A) arranged laterally with respect to each other and being adapted to couple light (32E) propagating in the waveguide (30) out of the waveguide. According to the invention, the sub-regions (36A) each comprise a doubly periodic grating pattern having a first period in a first direction and a second period in a second direction different from the first direction, and wherein there are at least two sub-regions (36A) having different grating patterns. The invention allows for combining out-coupling and exit pupil expansion on a single region of a waveguide.