12 Apr 2023
USTC approach exploits scattering to improve realism.USTC) has developed a new approach to the creation of dynamic 3D holographic projections, one that could be employed in virtual reality and other applications.
Published in Optica, the research aimed to tackle low axial resolution and high levels of crosstalk, two long-standing issues holding back digital holographic techniques.
"For virtual reality, our method could be used with headset-based holographic displays to greatly improve the viewing angles, which would enhance the 3D viewing experience," said Lei Gong from USTC. "It could also provide better 3D visuals without requiring a headset."
The project believes that its three-dimensional scattering-assisted dynamic holography (3D-SDH) approach can achieve a substantial improvement in depth resolution when compared with state-of-the-art methods for multiplane holographic projection.
Conventional holography of 3D objects involves using a spatial light modulator (SLM) to project a sequence of layers and build up a complete image of an object from individual planes, but this inherently impacts the quality of that image. The USTC platform incorporates a scattering medium, whose inherent randomness can suppress cross-talk between the light fields at different depths in the image.
"Since multiple scattering intermixes spatial and polarization properties, all the information of a 3D scene, including polarization, can be converted into a 2D optical wavefront for hologram rendering," noted the project in its paper.
Current methods to minimize cross-talk in holograms include random vector-based computer-generated holography (RV-CGH), which also introduces a random factor but does so manually, embedding random phase masks onto the wavefront modulator. USTC's scattering-medium approach produces superior depth-control, by greatly reducing the depth-of-fields of the image planes and suppressing the inter-plane crosstalk simultaneously.
Improvements for VR, encryption and sensing
In trials, the project's numerical simulations suggested that 3D-SDH could project a 3D rocket model with 125 successive image planes at a depth interval of 0.96 mm in a single 1000×1000-pixel hologram, compared to 32 image planes with a depth interval of 3.75 mm using RV-CGH methods.
For practical testing, a prototype 3D-SDH projector created dynamic 3D projections and compared them to conventional 3D Fresnel computer-generated holograms, showing that 3D-SDH achieved an improvement in axial resolution of more than three orders of magnitude.
Although the platform currently creates only point-cloud objects rather than a solid body, the project anticipates its platform ultimately bringing a significant improvement in depth control for realistic-looking 3D displays, with potential applications in VR, encryption, imaging and sensing.
"Our new method overcomes bottlenecks in current digital holographic techniques that limit the quality of the 3D display,” said Gong. "This approach could also improve holography-based optical encryption by allowing more data to be encrypted in the hologram."