An optical structure for receiving light over a field of view, the light bearing first, second and third primary colour component images, the optical structure comprising a first waveguide, comprising: a first input diffraction region for receiving the light bearing each of the first, second and third primary colour component images, configured to diffract at least some of the light bearing each said primary colour component image, received over a respective first portion of the field of view, the diffracted fields of view of the primary colour component images being different, into the first waveguide to propagate along the first waveguide by total internal reflection and to transmit at least some of the light bearing each said primary colour component image that is not diffracted into the first waveguide; and a first image expansion arrangement comprising at least one diffraction region for expanding the light propagating along the first waveguide and to diffract at least a portion of the expanded propagating light out of the first waveguide, and a second waveguide comprising: a second input diffraction region for receiving the light transmitted by the first input diffraction region of the first waveguide, configured to diffract at least some of the transmitted light bearing each said primary colour component image, received over a respective second portion of the field of view, into the second waveguide to propagate along the second waveguide by total internal reflection, wherein each second portion of the field of view for each said primary colour component image is different to the respective first portion and comprises at least that portion of the field of view excluding the respective first portion of the field of view for the primary colour component image; and a second image expansion arrangement comprising at least one diffraction region for expanding the light propagating along the second waveguide and to diffract at least a portion of the expanded propagating light out of the second waveguide, such that a viewer may observe the light output by the first waveguide combined with the light output by the second waveguide. a first input diffraction region for receiving the light bearing each of the first, second and third primary colour component images, configured to diffract at least some of the light bearing each said primary colour component image, received over a respective first portion of the field of view, the diffracted fields of view of the primary colour component images being different, into the first waveguide to propagate along the first waveguide by total internal reflection and to transmit at least some of the light bearing each said primary colour component image that is not diffracted into the first waveguide; and a first image expansion arrangement comprising at least one diffraction region for expanding the light propagating along the first waveguide and to diffract at least a portion of the expanded propagating light out of the first waveguide, and a second input diffraction region for receiving the light transmitted by the first input diffraction region of the first waveguide, configured to diffract at least some of the transmitted light bearing each said primary colour component image, received over a respective second portion of the field of view, into the second waveguide to propagate along the second waveguide by total internal reflection, wherein each second portion of the field of view for each said primary colour component image is different to the respective first portion and comprises at least that portion of the field of view excluding the respective first portion of the field of view for the primary colour component image; and a second image expansion arrangement comprising at least one diffraction region for expanding the light propagating along the second waveguide and to diffract at least a portion of the expanded propagating light out of the second waveguide, such that a viewer may observe the light output by the first waveguide combined with the light output by the second waveguide.