A waveguide 112 includes a substrate of material 134 having optical layers 148, 152 applied to two external surfaces 146, 150. This reduces the critical angle c5 of the substrate of material 134 to provide greater interaction between image bearing light following a light path 140 and a grating element 142 and/or a greater total field of view 160, when compared to the total field of view 132 of a prior art waveguide 110, that is capable of being transmitted by the waveguide 112. Such a waveguide 112 can be used in a projection display.