3D holograms, which often appear in science fiction films, are a familiar technology to the public, but holograms in movies are created with computer graphic effects. Methods for creating true 3D holograms are still being studied in the laboratory. For example, due to the difficulty of generating real 3D images, recent virtual reality (VR) and augmented reality (AR) devices project two different two-dimensional (2D) images onto a viewer to induce optical illusions.
To create a 3D hologram that can be viewed without special equipment such as 3D glasses, the wavefront of light must be controlled using wavefront modulators such as spatial light modulators (SLMs) and deformable mirrors (DMs). A wavefront modulator is an optical manipulation device that can control the direction of light propagation.
However, the biggest limitation to using these modulators as 3D displays is the number of pixels. The large number of pixels that are packed into high-resolution displays developed in recent years are suitable for a 2D image, and the amount of information contained in those pixels cannot produce a 3D image. For this reason, a 3D image that can be made with existing wavefront modulator technology is 1 cm in size with a narrow viewing angle of 3 degrees, which is far from practicable.
As an alternative, KAIST researchers used a DM and added two successive holographic diffusers to scatter light. By scattering light in many directions, this allows for a wider viewing angle and larger image, but results in volume speckle fields, which are caused by the interference of multiple scattered light. Random volume speckle fields cannot be used to display 3D images.
To fix the problem, the researchers employed a wavefront-shaping technique to control the fields. As a result, they succeeded in producing an enhanced 3D holographic image with a viewing angle of 35 degrees in a volume of 2 cm in length, width, and height. This yielded a performance that was about 2,600 times stronger than the original image definition generated when they used a DM without a diffuser.
The new display technology was developed that allows people to see 3D holographic images and videos through a wide viewing angle without wearing 3D glasses.
A team of researchers led by Park Yong-keun, a professor at the KAIST announced on January 24 that they developed a 3D holographic display that has more than doubled the size of a 3D holographic image and expanded a viewing angle more than ten-fold by controlling the scattering of light.
3D holograms, which often appear in science fiction films, are created using computer graphics effects, and there are limitations in realizing them with current technology in good truth. For this reason, research on virtual reality (VR) and augmented reality (AR) using an optical illusion that projects two different two-dimensional images at the eyes instead of a three-dimensional image is actively conducted.
To create a three-dimensional hologram that can be viewed without 3D glasses, directions of light must be changed using an optical control device (spatial light wave front controller) that precisely controls the direction of light propagation. However, since the number of pixels of the spatial light wave front controller is too small, it cannot be used as a three-dimensional display. Even if a spatial light wave front controller is used, a 3D image size is 1 cm and viewing angle is within 3 degrees, defying commercialization.
In addition to a spatial light wave front controller, the researchers used scattered light to control the scattered light by using ground glass (glass which is translucent as it was ground) to enlarge the image size and viewing angle.
The team succeeded in producing a three-dimensional hologram with a width of about 2 cm, a height of about 2 cm, and a viewable angle of about 35 degrees.
Nature Photonics - Ultrahigh-definition dynamic 3D holographic display by active control of volume speckle fields
Professor Park said, "Scattering light has previously been believed to interfere with the recognition of objects, but we have demonstrated that current 3D displays can be improved significantly with an increased viewing angle and image size by properly controlling the scattered light."
Hyeonseung Yu, who is the lead author of this research article and a doctoral candidate in the Department of Physics, KAIST, noted that this technology signals a good start to develop a practical model for dynamic 3D hologram displays that can be enjoyed without the need for special eyeglasses. "This approach can also be applied to AR and VR technology to enhance the image resolution and viewing angles," added Yu.
Holographic displays generate realistic 3D images that can be viewed without the need for any visual aids. They operate by generating carefully tailored light fields that replicate how humans see an actual environment. However, the realization of high-performance, dynamic 3D holographic displays has been hindered by the capabilities of present wavefront modulator technology. In particular, spatial light modulators have a small diffraction angle range and limited pixel number limiting the viewing angle and image size of a holographic 3D display. Here, we present an alternative method to generate dynamic 3D images by controlling volume speckle fields significantly enhancing image definition. We use this approach to demonstrate a dynamic display of micrometre-sized optical foci in a volume of 8 mm × 8 mm × 20 mm.
SOURCES- KAIST, Nature Photonics, Business Korea