The gist of it: this is an interesting approach but it is also a useful example of the challenges that AR/VR optics face, mostly the result of the physiology of the human eye. It’s one adaption of hardware that seems to work for people who fall within a certain range with their pupil diameter. Want a successful relationship with the human eye? Well, it’s complicated.
| Items | Specification |
|---|---|
| Display | FHD (1920 × 1080) OLED |
| Lens 1_1 and 1_2 | Achromatic, focal length 20 mm |
| 2nd lens (trans-reflective concave mirror) | Focal length 24.8 mm |
| Used image resolution | 1458 × 820 pixels |
| HFOV | 35.3 degree |
| Eye relief (ER) | 19.1 mm |
| Best focus position | 1.5 Diopter (0.67 m) |
| PD/DOF range | 0.89 mm, 1.08 mm, 1.53 mm, 3.0 mm/3.0 Diopter, 2.0 Diopter, 1.0 Diopter, 0.26 Diopter |
| Corresponding diffraction limit optical system | |
| Do | 64.84 mm |
| De | 40.16 mm |
| Do:De | 1.61:1 |
| 1st lens | EFFL 17.46 mm |
| Main optics lens | EFFL 24.8 mm |
| Simplified eye lens model | Single paraxial lens (EFFL 16 mm) and variable image plane position for focus adjustment |
Traditional 3D displays present a three-dimensional image by using binocular parallax, where each eye sees a slightly different image, thereby creating the illusion of depth. However, these displays focus accurately only at a specific screen depth, not the full range of perceived depth. Because our eyes have a narrow depth of field (DOF) – the distance between the nearest and farthest objects that appear in acceptably sharp focus – these 3D displays have limitations on the DOF where clear 3D images can be seen.
To overcome this problem, researchers at the Korean Institute of Science and Technology propose finding the right optical conditions to extend this DOF and analyzing phenomena related to this. The Rayleigh criterion and the Strehl ratio are used to create a standard for this extended DOF. The Rayleigh criterion is a formula used to predict the limit of resolution for an optical system, while the Strehl ratio is a measure of the quality of optical imaging systems. The research then proposes a practical optical structure, based on a flat panel display, that can effectively extend the DOF. This would be especially useful for near-eye displays used in Augmented Reality (AR), Virtual Reality (VR), and Mixed Reality (MR) technologies. By determining the optical conditions and standards for an extended DOF, the research anticipates being able to create 3D displays capable of providing clearer 3D images over a wider range of perceived depth. This could be valuable for developing more realistic and immersive 3D displays in various fields. This is about improving 3D displays to make the 3D images clearer over a wider range of depth, which could help make VR, AR, and MR experiences more immersive and realistic.
The testing involved using a fixed focal length camera to replace the human eye’s perception of the virtual image. Multiple patterns were used as test images, arranged along the optical axis of the system. The contrast values were measured from the images captured by adjusting the camera’s focus across different spatial frequencies of the virtual image. These contrast values were used to verify whether the calculated DOF range for each aperture condition was accurate.
The results from the experiment were compared with simulation results. The comparison showed that the experimental results reasonably matched the simulation results, particularly when the pupil diameter (PD) was less than 2 mm. It was observed that as the PD decreased, the contrast at the best focus was maintained over a wide focus range, as predicted by the simulation. However, the improvement in the range of clear focus decreases as the pupil diameter increases. These findings could inform the design of better AR systems with an extended DOF, especially for users with smaller pupil diameters.
Reference
Kim, S.K., Kwon, Y. & Yoon, KH. Extended depth of field in augmented reality. Sci Rep 13, 8786 (2023). https://doi.org/10.1038/s41598-023-35819-9
