Analysis and fabrication of a volume holographic optical element-based two-dimensional exit pupil expander

This work investigates the design and fabrication of VHOE-based two-dimensional exit-pupil expanders (2D EPEs). Conventional recording of 2D EPE structures typically requires a vertical optical setup together with additional alignment procedures. In contrast, the approach presented in this paper enables the entire recording process to be carried out using a planar optical configuration. Furthermore, three representative architectures-90°-deflection, 60°-deflection, and in-line configurations-are systematically analyzed to evaluate the impact of Bragg selectivity on the field of view (FoV), providing practical design guidelines for VHOE-based 2D EPE systems. In addition, the relationship between the recording wavelength and required recording angles is investigated. When the recording wavelength differs significantly from the reconstruction wavelength, the recording condition may transition to either a transmission-type holographic configuration or a reflection-type configuration without the use of index-matching oil. These findings increase the flexibility of VHOE lightguide fabrication.