Fig. 1. Principle of human eye viewing images.（a）Traditional display；（b）Retinal projection displays.

Fig. 2. Image sources of RPD.（a）Image source based on LBS；（b）Image source based on SLM；（c）Image source generated by using point light source and SLM.

Fig. 3. Image source generated through SLM.（a）SLM and virtual images in different depth planes；（b）SLM and virtual images in the same depth plane.

Fig. 4. RPD AR near-eye display with off-axis optical combiner

Fig. 5. Optical combiner based on traditional geometric optical devices.（a）Principle of semi-transparent and semi-reflective mirrors；（b）Principle of prism；（c）RPDAR prototype based on geometric optics^［42］.

Fig. 6. Exposure and reconstruction optical setup of PPHOE.（a）PPHOE same side exposure；（b）PPHOE opposite side exposure；（c）Transmissive PPHOE reconstruction process；（d）Reflective PPHOE reconstruction process.

Fig. 7. Two ways to copy viewpoints.（a）Changing the position of the light source to generate multiple viewpoints；（b）PPHOE with multiple diffraction angle multiplexing.

Fig. 8. Relationship between viewpoint distance and pupil diameter.（a）Distance between viewpoints is less than the diameter of the pupil；（b）Distance between viewpoints is greater than the diameter of the pupil.

Fig. 9. Application of PPHOE in retinal projection NED.（a）Implementing viewpoint matching using SLM；（b）Using partition HOE to prevent viewpoint crosstalk.

Fig. 10. Exposure light path of full-color PPHOE

Fig. 11. Exposure and microstructure of LCHOE.（a）Coherence of two orthogonal circularly polarized beams of light；（b）Plane diagram of two orthogonal circularly polarized beams of coherent light；（c）Microstructure of transmissive LCHOE；（d）Transmissive LCHOE light reconstruction process；（e）Microstructure of CLCHOE；（f）CLCHOE light reconstruction process.

Fig. 12. Application of LCHOE in RPDAR.（a）Dual viewpoints RPD AR display system^［69］；（b）2D viewpoint replication system^［70］；（c）Active dual viewpoints switching system^［72］；（d）Improved active dual viewpoints switching system^［73］.

Fig. 13. Diffraction properties of HOE devices^［54］.（a）Diffraction efficiency spectra of photopolymer，HPDLC and CLCHOE；（b）Diffraction efficiency angle spectra under 525 nm incident light of photopolymer，HPDLC and CLCHOE.

Fig. 14. Application of metasurface in RPDAR NED.（a）Schematic diagram of metasurface structure^［77］；（b）Transmittance curves of high transparency metasurfaces^［77］；（c）Multifunctional nonlocal metasurfaces system^［78］.