The invention provides a diffractive waveguide element, waveguide stack, personal display and method of forming a viewable image. The element comprises a waveguide region defined by two optical surfaces between which light can propagate by total internal reflections, the optical surfaces having surface profiles, and at least one diffractive grating capable of modifying the light filed within the waveguide region. According to the invention, the surface profile of at least one of said optical surfaces is a staircase profile.