Waveguides

A projection display comprising a first waveguide element and a second waveguide element, wherein at least one of said waveguide elements is as claimed in any of the preceding claims, the projection display being arranged for displaying an image to an observer, and comprising:

• an image-providing light source device arranged to generate an image and to inject image bearing light into the first waveguide element to follow a propagation axis;
• wherein the first waveguide element has a first grating element which is arranged to direct the image bearing light internally along the propagation axis and through which the image bearing light is, outputted from the first waveguide element;
• the second waveguide element includes a coupling grating arranged to receive the image bearing light from the first waveguide element and to direct the image bearing light along the second waveguide element to follow a propagation axis;
• the second waveguide element further includes an exit grating arranged to diffract received image bearing light out of the second waveguide element towards an observer;
• wherein the first and/or the exit grating is arranged upon interaction with incident image bearing light to allow at least some incident image bearing light to exit its associated waveguide element or to direct at least some of the incident image bearing light within its associated waveguide element;
• and
• wherein the area of the first and/or the exit grating that the image bearing light is incident upon increases with distance along as saidthe propagation axis of the layer of material such that the interaction of the image bearing light associated with the grating element increases with distance along the propagation axis.