Pinhole-based 'photon sieve' widens viewing angle of dynamic holographic displays
Spatial-light-modulator-based holographic displays' narrow viewing angles are widened by diffraction from pinholes.
|The actual 3D holographic display (left), and a scanning electron microscope image of the nonperiodic pinholes (right). (Image: KAIST)|
Dynamic 3D holographic images can be (and are often) created and projected using a liquid-crystal-based spatial light modulator (SLM); however, due to the nature of SLMs, the viewing angle of such a setup is typically limited to only a few degrees, with the viewing angle becoming narrower as the resolution is made greater.
Now, researchers at the Korea Advanced Institute of Science and Technology (KAIST) have developed an ultrathin SLM-based holographic display that can projects dynamic multicolored, 3D images over a wider angle.1
The system’s critical component is a thin film of titanium filled with very small nonperiodic pinholes that are precisely paired with each pixel of the SLM. The film acts as a "photon sieve" – each pinhole diffracts light emerging from itself widely, resulting in a high-definition 3D image observable from a wide angle. Note: this is not the same as the photon sieves used to form lightweight telecope imaging systems.)
The entire system is very small: they used a 1.8-inch off-the-shelf SLM panel with a resolution of 1024 x 768 pixels. The titanium film, whose substrate is attached to the back of the panel, is 300 nm thick.
"Our approach suggests that holographic displays could be projected from thin devices, like a cell phone," says YongKeun Park, a physicist at KAIST who led the research. The team demonstrated their approach by producing a hologram of a moving, tricolored cube (using lasers of three different colors as a light source).
Previous studies from Professor Park's group used optical diffusers for the same purpose, but the size of the device was bulky and difficult to be operated, and it took a long period of time to calibrate. In the present work, the group tailored the photon sieve to demonstrate a simple, compact and scalable method for a 3D holographic display.
Applications could include 3D cinema viewing without the need for glasses, watching holographic videos on television, and smartphone screens.
1. Jongchan Park et al., Nature Communications (2019); https://doi.org/10.1038/s41467-019-09126-9