What may be the world’s thinnest hologram could also be the harbinger of what’s to come in consumer electronics: the introduction of 3D holography compact enough to be integrated into everyday electronics such as smartphones, laptops and TVs.
Developing holograms that are thin enough to work with electronics has been a challenge. Holography currently has extensive applications in optical microscopy and imaging, 3D displays and metrology; but to integrate holography with modern low-dimensional electronic devices, holograms need to be thinned to a nanometric scale.
Conventional holograms modulate the phase of light to give the illusion of three-dimensional depth. To generate enough phase shifts, these holograms need to be at the thickness of optical wavelengths, making them unsuitable for integration with ultrathin devices.
An RMIT research team, working with the Beijing Institute of Technology (BIT), has broken this thickness limit, developing a 60 nm binary hologram, 3 x 3 mm in size, using a topological insulator — a novel quantum material that holds the low refractive index in the surface layer but the ultrahigh refractive index in the bulk.
The team observed that nanometric topological insulator thin films act as an intrinsic optical resonant cavity due to the unequal refractive indices in their metallic surfaces and bulk. The resonant cavity leads to enhancement of phase shifts that enable holographic imaging.
The team calculated a binary phase-only hologram on a computer; then recorded it into the topological insulator thin film. A home-built direct laser writing (DLW) system was used to fabricate the hologram. The binary holograms were converted into a series of phase diagrams, then uploaded onto the spatial light modulator; then printed into the thin film.
The DLW method does not require a complicated substrate treatment and a mask preparation process, making it more suitable for large-scale practical applications, compared with fabrication methods used for metasurface holograms.
By illuminating a laser beam on the surface of the topological insulator hologram, the holographic images were diffracted from it with a small projection angle of 10°. The team used a full color CCD to capture the reconstructed images. The team’s nanohologram, which was relatively simple to make, can be seen without 3D goggles and is 1,000 times thinner than a human hair.
“Integrating holography into everyday electronics would make screen size irrelevant — a pop-up 3D hologram can display a wealth of data that doesn't neatly fit on a phone or watch,” said professor Min Gu. “From medical diagnostics to education, data storage, defense and cyber security, 3D holography has the potential to transform a range of industries and this research brings that revolution one critical step closer.”
Researcher Zengyi Yue said, “The next stage for this research will be developing a rigid thin film that could be laid onto an LCD screen to enable 3D holographic display. This involves shrinking our nano-hologram's pixel size, making it at least 10 times smaller.
“But beyond that, we are looking to create flexible and elastic thin films that could be used on a whole range of surfaces, opening up the horizons of holographic applications,” said Yue.
The research was published in Nature Communications (doi: 10.1038/ncomms15354).
An Australian-Chinese research team has created a nano-hologram, paving the way toward the integration of 3D holography into everyday electronics like smart phones, computers and TVs. Courtesy of RMIT University.