Arrangement and a method for coupling light into a plate-like light guide

An arrangement for coupling light into a plate-like light guide having two surfaces on opposite sides of the light guide, the arrangement comprising an in-coupling diffraction grating for diffracting an external light beam incident on said in-coupling diffraction grating into the light guide in a direction enabling the in-coupled light to propagate within the light guide via total internal reflections at the light guide surfaces, a deflection member arranged to deflect the light beam initially diffracted by the in-coupling diffraction grating, before it hits the in-coupling diffraction grating again, out of the path determined by the in-coupling diffraction grating in order to reduce out-coupling of the already in-coupled light through the in-coupling diffraction grating, wherein the path includes the initial direction of the in-coupled light beam and the propagation direction of the in-coupled light beam after an initial reflection at one of the light guide surfaces and wherein the deflection member is arranged to deflect the light beam initially diffracted by the in-coupling diffraction grating in a direction out of a plane defined by the directions of the incident and the initially diffracted light beams.