| 摘要 |
Image-bearing light 12 is injected into a waveguide 10 via an input means 14 and is directed along the waveguide by total internal reflection. The light 12 is reflected from each of the four sides of the waveguide 10 along a spiral path 18 (fig.4) and passes through an output transmission grating 16. In contrast to prior art (fig.12: output beams 128 & 132), light 12 passing through the output grating 16 is diffracted only when passing through the grating along a first portion 20 of the path 18, producing a single output beam 28. This is achieved by orienting the fringes 24 of the output grating 16 at an angle so that only one of the two modes (at portions 20 & 22 of the path) is aligned at the correct angle with respect to the grating 16 for diffraction to occur. The light passing along the path 18 passes through the output grating 16 without diffraction along the second portions 22 of the path. A double image is thus avoided and manufacturing tolerances are eased. The waveguide may form part of a head-up display.
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