Diffractive exit-pupil expander for spherical light guide virtual displays designed for near-distance viewing

In this paper the use of diffractive exit-pupil expanders (EPEs) for implementation of compact and ergonomically friendly head-worn virtual displays is studied. We show that exit-pupil expansion of a virtual display designed for near-distance viewing is possible with a diffractive EPE having spherical shape. An analytical model for ray propagation through the proposed EPE is derived. The resulting expressions are used to characterize the geometrical distortions and the lateral color introduced in the pupil expansion process. Moreover, the resolution properties of the EPE are calculated using numerical simulations and compared with the acuity of the human eye. The results show that pupil expansion ratios enabling natural eye movements in typical near-to-eye display applications can be achieved while maintaining the information content of a virtual display.