**6. Conclusions**

In this paper, holographic 3D HMD suitable for observers with different pupillary distance is proposed. We built a monocular system and a binocular system using SLMs with pixel pitches of 3.74 μm and 8.1 μm for 3D HMD. Based on the experimental results, we demonstrated that the viewing angle of the reconstructed 3D image of the holographic HMD can be improved by tiled SLMs and the 4f system. In our binocular system, it reached 16.4◦, which was two-times wider than the original viewing angle formed by the monocular system. This is meaningful for holographic application in VR and AR. Holographic 3D VR and AR displays can be good candidates for true 3D near-eye display, and compared with stereoscopic display, they can give viewers a more realistic visual experience with continuous wavefront reconstruction. Thus, we demonstrate that holographic technology can be combined with VR and AR to achieve true 3D HMD, providing technical reference for 3D VR and AR applications in various fields.

**Author Contributions:** F.X. structured and wrote the paper; H.G. guided other authors to complete the paper; J.L. selected the topic; W.Z. supervised the progress of the whole work; Z.D. and S.L. supplied the materials to the paper; Y.Y. and H.Z. helped to proofread the manuscript.

**Funding:** This work was financially supported by the National Natural Science Foundation of China (Grant Nos. 11004037, 61005073, and 11474194), the Creative Research Fund of Shanghai Municipal Education Commission (14YZ009), and the Shanghai Natural Science Foundation (Grant Nos. 14ZR1415700, and 14ZR1415500), and it was also supported in part by the Open Research Fund of the Chinese Academy of Sciences (Grant No. SKLST201104).

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


c 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
