# A Fast Computer-Generated Holographic Method for VR and AR Near-Eye 3D Display
## 3 Experiments and Result Analysis
In this case, the distance from the LCoS to the eye is less than 25 cm, which means this setup is a relatively compact display system. The experimental results of the VR setup are shown in Figure 7. Figure 7a shows the reconstructed image of the hologram calculated by the proposed algorithm. For comparison, Figure 7b shows the result of the hologram calculated using the direct point cloud algorithm [14] of the red channel data from the color 3D model. The reproductions are similar, but the computational speed of our proposed method takes only about 2 s on average whereas the 3D cloud point data  
Figure 5: The process of hologram calculation through convolution of corresponding PSF with projected images. Figure 6: Optical setup for Virtual Reality (VR) display. 76 s on average (38 times slower than our method). The comparison is based on the MATLAB 2015 with a laptop with i7-7700 HQ CPU and 16G RAM. Similarly, with the same experimental conditions, we also show another sample to demonstrate the capability of our method that can focus and defocus objects at a scene. For the tested scene, we utilize a stationary coral and a swimming fish 3D animation model (constructed using Unity3D), as shown in Figure 8. For projection of images, eight images at 0.9\({}^{\circ}\) angle interval both in the x and y directions are projected by Unity3D to generate projected images for each hologram calculation. In Figure 8a, the camera is aimed at two objects, and both are in focus yielding clear images because distance between the coral and the fish is close. As shown in Figure 8b,c, the distance between fish and coral becomes far in comparison to Figure 8a. Figure 8b,c show different focuses, where b is focused at coral and c is focused at fish. The results of Figures 7 and 8 show that the proposed holographic 3D VR display is high in image quality, free of speckle noise, and also able to realize 3D display. For the AR experiment, volume HOE is used for producing the AR 3D image due to its angle and wavelength selectivity [24; 25; 26]. The recording of the HOE is illustrated in Figure 9. The light wave emitted from the laser is filtered and collimated by lens\({}_{1}\), and then split into two parts through the beam splitter (BS). The transmitted light passes through lens\({}_{2}\) to form a convergent spherical wave, which undergoes interference with the plane wave reflected by mirror\({}_{1}\) and mirror\({}_{2}\) on the holographic material to form the HOE. The laser used for HOE recording is a single mode semiconductor laser with a wavelength of 532 nm and power of 400 mW. The lens\({}_{2}\) is a commercially available aspherical mirror with focal length of 40 mm and a diameter of 50 mm (Thorlabs, AL5040M-A, NA = 0.55). The recording material we used in the experiment is a commercial holographic film (Ultimate Holography, U04), which requires an exposure density of \(\sim\)600 ul/cm\({}^{2}\)[27]. Figure 8: Optical reconstructions of second 3D animation model. **(a)** Both in focus; **(b)** Coral in focus; **(c)** Fish in focus. Figure 4:0 Optical reconstructions. **(a)** Proposed method; **(b)** 3D cloud point data method. Using the optical recording system, the angular selectivity of the reflective volume HOE recorded without using lens\({}_{2}\) was tested, and the angular selectivity was within \(\pm 5^{\circ}\). Using the SLM described above, the diffraction angle is within \(\pm 1.89^{\circ}\), which means that most light diffracted by the SLM can be diffracted by HOE in a high efficiency. Figure 10a,b are a schematic and a photograph of AR 3D display system, respectively. The angle between the illumination light and the HOE is approximately \(30^{\circ}\). The holographic 3D real image reproduced by the optical system is imaged by the HOE and incident at human eye. Ambient light from the real object does not meet the angular selectivity of the fabricated reflective HOE, and thus can directly reach the human eye, forming a holographic AR 3D display.