Effects of polarisation and spatial coherence in the pupil expansion with crossed gratings in an AR display

Pupil replication with crossed gratings in an AR display is modelled and characterised. It is found that, compared to linear gratings, crossed gratings in a hexagonal lattice offer an additional degree of freedom to control the angular spread of pupils and can potentially improve the uniformity of the pupil map. In terms of characterisation, the model explains well the trend observed in experiments. Good quantitative agreement of the relative pupil intensity is obtained for a number of the measured waveguides.