## 4 Experiments and Results  
In this experiment, we took pictures of the reconstruction from the hologram at different viewpoints, which were left view, middle view, and right view, using a single SLM with pixel pitch of 8.1 \(\upmu\)m and 3.74 \(\upmu\)m, respectively. The SLMs were liquid-crystal-on-silicon (LCoS) SLMs, Holoeye Pluto (resolution: 1920 \(\times\) 1080, pixel pitch: 8.1 \(\upmu\)m), and Jasper (resolution: 4094 \(\times\) 2400, pixel pitch: 3.74 \(\upmu\)m). In Figure 9, the image is captured from the left, middle, and right viewpoints in the optical system using an SLM with a pixel pitch of 8.1 \(\upmu\)m, and the reconstructed image with the viewing angle, 3.8\({}^{\circ}\), is a cube with the letters V and R; the measured distance from the image to the camera was about 300 mm, and the lateral motion of the camera was about 20 mm. Figure 10 shows the captured image from three viewpoints from the left to the right in the optical system, which used an SLM with a 3.74-\(\upmu\)m pixel pitch. The viewing angle of this system was up to 8.2\({}^{\circ}\), and the measured distance from the image to the camera was about 300 mm, while the lateral motion of the camera was about 43 mm.  
Figure 8: Schematic diagram of the proposed binocular holographic head-mounted display system.  
Figure 7: (a) Dependence of the viewing angle on the pixel pitch of SLMs. (b) Dependence of the distance between the image and eyes on the pixel pitch of SLMs.  
By comparing Figures 9 and 10, the reconstruction quality of Figure 10 is better than that in Figure 9, because the SLM in Figure 10 has a higher resolution and smaller pixel pitch.  
We tiled two SLMs with a pixel pitch of 3.74 \(\upmu\)m and used a full-color light source, red, green, and blue lasers at wavelengths of 632.8 nm, 532.8 nm, and 473 nm, respectively. The reconstructed color image is shown in Figure 11, and the measured distance from the image to the camera was about 300 mm, while the lateral motion of the camera was about 86 mm. Compared to the system based on single SLM, its viewing angle increased significantly. It was demonstrated that large viewing angles can be obtained in this binocular holographic HMD.  
According to Equation (1), the viewing angle can reach 16.4\({}^{\circ}\), in the two tiled SLMs with a pixel pitch of 3.74 \(\upmu\)m, and it can be further increased, if the 4f system can be used in the display system to reduce the pixel pitch. The 4f system consists of two convex lenses. When the focal length of the lens close to the SLM is larger than the focal length of the lens close to the human eye, the 3D image viewing angle can be enlarged.  
Through the above work, we proved the advantages of holographic display applications in HMD, such as more realistic images, meeting human perception habits. Compared to current 3D VR and AR, holography has more feasibility for future near-eye 3D display.  
Figure 11: Pictures of the reconstructed full-color cube from different viewpoints in the binocular system. (**a**) Left viewpoint (\(-8.2^{\circ}\)); (**b**) middle viewpoint (\(0^{\circ}\)); (**c**) right viewpoint (\(8.2^{\circ}\)).  
Figure 9: Pictures of the reconstructed cube based on SLM with a pixel pitch of 8.1 \(\upmu\)m from different viewpoints. (**a**) Left viewpoint (\(-1.9^{\circ}\)); (**b**) middle viewpoint (\(0^{\circ}\)); (**c**) right viewpoint (\(1.9^{\circ}\)).