A holographic system comprises a display device and a waveguide pupil expander. The display device is arranged to display a hologram and to output spatially modulated light in accordance with the hologram. The waveguide pupil expander is configured to receive spatially modulated light from the display device at the input port thereof and to expand the viewing window of the system. The waveguide pupil expander comprises first and second substantially planar reflective surfaces arranged in parallel having an optically transparent material therebetween. The first reflective surface is fully reflective and the second reflective surface is partially reflective such that light is guided from the input port to an output port at the second reflective surface by a series of internal reflections. The optically transparent material is formed by a layered glass structure arranged to maintain the integrity of the waveguide in the event of breakage of glass.