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Optical Diffusers Improve Definition, Viewing Angle for 3D Holograms

Photonics.com
Feb 2017
DAEJEON, South Korea, Feb. 17, 2017 — A wavefront-shaping technique has been used to create a dynamic 3D holographic image with a viewing angle of 35 degrees in a volume of 2 cm in length, width and height. Use of the technique was shown to yield a 3D holographic display that performed with more than 2600 times the strength of existing displays.

Current 3D hologram technology relies on wavefront modulators to control the direction of light propagation. One limitation to using modulators as 3D displays is pixel number. The large number of pixels that are packed into high-resolution displays are suitable for a 2D image. However, the amount of information contained in those pixels cannot produce a 3D image. For this reason, a 3D image created using existing wavefront modulator technology is only 1 cm in size, with a narrow viewing angle of 3 degrees.

To enhance the performance of 3D holograms, researchers from the Korea Advanced Institute of Science and Technology (KAIST) used a deformable mirror (DM) to which they added two successive holographic diffusers to scatter light. The DM scattered light in many directions, allowing for a wider viewing angle and larger image.

KAIST has novel approach to improving 3D holographic displays.
T
he optical setup consists of a deformable mirror and the scattering medium with two successive holographic diffusers. A high-numerical-aperture imaging unit mounted on a three-axis motorized translational system is utilized for wavefront optimization and imaging. Courtesy of KAIST.

The multiple scattered light resulted in random volume speckle fields, which cannot be used to display 3D images. To control the volume speckle fields and optimize the image, researchers used a novel wavefront-shaping technique. They succeeded in producing an enhanced 3D holographic image, which demonstrated a dynamic display of micrometer-sized optical foci in a volume of 8 mm × 8 mm × 20 mm, markedly stronger than an image that was generated when a DM without a diffuser was used.

“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," said professor YongKeun Park.

Various fields including biomedical imaging, scientific visualization, engineering design and displays could benefit from this technology.

“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," said researcher Hyeonseung Yu. “This approach can also be applied to AR and VR technology to enhance the image resolution and viewing angles."

The research was published in Nature Photonics (doi: 10.1038/nphoton.2016.272).  

GLOSSARY
adaptive optics
Optical components or assemblies whose performance is monitored and controlled so as to compensate for aberrations, static or dynamic perturbations such as thermal, mechanical and acoustical disturbances, or to adapt to changing conditions, needs or missions. The most familiar example is the "rubber mirror,'' whose surface shape, and thus reflective qualities, can be controlled by electromechanical means. See also active optics; phase conjugation.
hologram
An interference pattern that is recorded on a high-resolution plate, the two interfering beams formed by a coherent beam from a laser and light scattered by an object. If after processing, the plate is viewed correctly by monochromatic light, a three-dimensional image of the object is seen.  
mirrorsResearch & TechnologyeducationAsia PacificDisplaysopticsadaptive opticshologram3D imagingwavefront technologyholographic display

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