DEVICE FOR EXPANDING AN EXIT PUPIL IN TWO DIMENSIONS

摘要

A diffractive beam expander (50) comprises an input grating (10), a crossed grating (20), and an output grating (30) implemented on a planar transparent substrate (7). The crossed grating (20) comprises a plurality of diffractive features (23) arranged along the lines of a first set of parallel lines (25) and along the lines of a second set of parallel lines (26) such that the lines (25) of the first set are parallel to the lines (26) of the second set. The lines of the first set have a first grating period and the lines of the second set have a second grating period. A light beam (B1) coupled into the substrate (7) by the input grating (10) impinges on the crossed grating (20) at a first location (EC1) and further locations (EC2). Interaction at the first location (EC1) provides several sub-beams (S₀₀, S₀₁, S₁₀) which propagate in different directions. Further interactions at second locations (EC2) provide further sub-beams (V₀₁, U₁₀) which propagate in the same direction as the original in-coupled light (B1). Light is subsequently coupled out of the substrate (7) by the output grating (30) to provide a light beam (B2) which is expanded in two directions (SX, SZ) with respect to the beam (B0) impinging on the input grating. A virtual display device (200) may comprise said diffractive beam expander (50).