Optical Diffusers Improve Definition, Viewing Angle for 3D Holograms

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.

The 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).