3D digital holograms could be coming to your phone
Researchers at the Korea Institute of Science and Technology (KIST) have realised 3D digital holograms, by developing a polarisation image sensor with no additional polarisation filter. This could, with the further miniaturisation of the entire holographic camera sensor module, lead to the appearance of Star Wars-like holograms generated by smartphones.
Until now, 3D holograms based on phase-shifting holography could be captured only using a large specialised camera with a polarising filter.
However, the new technology developed by scientists at KIST and Yonsei University allows holograms to be captured on portable devices, such as smartphones. This involved using 2D semiconductor materials to develop a photodiode that detects the polarisation of light in the near-infrared (NIR) region without additional polarisation filters.
Photodiodes, which convert light into electrical signals, are essential components within the pixels of image sensors in all digital cameras. Introducing the ability to sense the polarisation of light on the image sensor of an ordinary camera provides a variety of new information, enabling the storage of 3D holograms.
Previous polarisation-sensing cameras have an additional polarisation filter of several hundred μm in size, attached to an ultra-small optical diode image sensor less than 1μm in size. Therefore, they cannot be integrated and miniaturised for implementation into portable electronic devices.
The research group developed a photodiode by stacking an n-type semiconductor (rhenium diselenide) which exhibits a difference in light absorption dependent on the linear polarisation angle of light in the NIR (980nm) region, and a p-type semiconductor (tungsten diselenide) which exhibits no difference in photo-response dependent on polarisation, but does enable much-improved performance.
The device is excellent in the photodetection of wavelengths ranging from ultraviolet to NIR, even capable of selectively detecting the polarisation characteristics of light in the NIR region. The research group utilised the device to create a digital holographic image sensor that records polarisation characteristics to successfully capture holograms.
Dr Do Kyung Hwang of KIST, co-lead of the study, said: “Research on the downsizing and integration of individual elements is required to ultimately miniaturise holographic systems. The results of our research will lay the foundation for the future development of miniaturised holographic camera sensor modules."
Fellow co-lead, Dr Min-Chul Park, added: “The new sensor can further detect NIR light, as well as previously undetectable visible light, opening up new opportunities in various fields such as 3D night vision, self-driving, biotechnology, and NIR data acquisition for analysing and restoring cultural assets.”
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