An optical device comprising: a first optical waveguide having a direction of elongation, said first optical waveguide having first and second pairs of parallel faces (12a, 12b, 14a, 14b) parallel to said direction of elongation forming a rectangular cross-section for guiding light by four-fold internal reflection at said first and second pairs of parallel faces, each ray that undergoes internal reflection thereby defining a set of four conjugate propagation directions, first and second surfaces (21,22), said first surface being configured such that rays corresponding to at least part of an injected image propagating within said first optical waveguide in a first direction from a first set of conjugate propagation directions are deflected by reflection at said first surface so as to propagate in a second direction from a second set of conjugate propagation directions, said second direction being at a smaller angle to said direction of elongation than said first direction, and wherein said second surface is so as to deflect an image propagating in at least one direction from said second set of conjugate directions so as to propagate in at least one direction from said first set of conjugate directions, and to couple-out an image propagating along one direction from said first set of conjugate directions so as to exit from said first optical waveguide, characterized in that at least part of said first optical waveguide is bounded by said first and second surfaces, in that said first and second surfaces are wedge-forming surfaces, in that said second surface is parallel to said first surface, and by further comprising a light guide having two major parallel surfaces (24a, 24b), wherein said first waveguide is deployed so that an image coupled out of said first waveguide is coupled in to said light guide so as to propagate within said light guide by internal reflection at said two major parallel surfaces, said light guide further comprising a coupling-out arrangement for coupling out the image propagating within said light guide so as to direct the image towards an eye of a user. a first optical waveguide having a direction of elongation, said first optical waveguide having first and second pairs of parallel faces (12a, 12b, 14a, 14b) parallel to said direction of elongation forming a rectangular cross-section for guiding light by four-fold internal reflection at said first and second pairs of parallel faces, each ray that undergoes internal reflection thereby defining a set of four conjugate propagation directions, first and second surfaces (21,22), said first surface being configured such that rays corresponding to at least part of an injected image propagating within said first optical waveguide in a first direction from a first set of conjugate propagation directions are deflected by reflection at said first surface so as to propagate in a second direction from a second set of conjugate propagation directions, said second direction being at a smaller angle to said direction of elongation than said first direction, and wherein said second surface is so as to deflect an image propagating in at least one direction from said second set of conjugate directions so as to propagate in at least one direction from said first set of conjugate directions, and to couple-out an image propagating along one direction from said first set of conjugate directions so as to exit from said first optical waveguide, characterized in that at least part of said first optical waveguide is bounded by said first and second surfaces, in that said first and second surfaces are wedge-forming surfaces, in that said second surface is parallel to said first surface, and by further comprising a light guide having two major parallel surfaces (24a, 24b), wherein said first waveguide is deployed so that an image coupled out of said first waveguide is coupled in to said light guide so as to propagate within said light guide by internal reflection at said two major parallel surfaces, said light guide further comprising a coupling-out arrangement for coupling out the image propagating within said light guide so as to direct the image towards an eye of a user.