Twisted light unveils a Star Wars-style nanoprinted hologram
Researchers from the Nano-Institute Munich at Ludwig-Maximilians-Universität Munich have designed a twisted light metasurface hologram that can lenslessly reconstruct a holographic video with 200 independent orbital angular momentum image channels. The research is published in the journal Nature Nanotechnology.
The development of a holographic video display, just like in the science fiction of “Star Wars: Episode IV – A New Hope”, has long been pursued by optical physicists and engineers. Traditional optical holograms designs based on a Nobel Prize invention by Dennis Gabor rely on a thick photographic plate to record the interference pattern between an object beam and a coherent reference beam.
Even though static optical holograms are prevalent nowadays on our money, credit cards, passports, and holographic stickers, creating a Star Wars style hologram that consists of a sequence of holographic images to be assembled into a holographic video has remained a great challenge.
Previous attempts to display holographic videos have included bulky technologies such as spatial light modulators, acousto-optic modulators, and sequential scanning of holograms. But these methods fail to meet a satisfactory balance among hologram resolution, image size, viewing angle, and achievable frame rate, and sometimes involve complex and costly mechanical scanners.
Metasurfaces are versatile nanotechnology-enabled platforms that use ultrathin flat optics to manipulate the amplitude, phase, and polarization of light, opening the possibility of digitalizing an optical hologram with nanoscale resolution. This could offer an unprecedented opportunity to realize ultrathin metasurface holograms with high spatial resolution, large image size, and extended viewing angle. However, the bandwidth of a metasurface hologram has remained too low to realize a holographic video display.
“To increase the bandwidth of a metasurface hologram, different degrees of freedom of light including polarization, wavelength, and incident angle have thus far been explored. However, the bandwidth of a metasurface hologram has remained too low for any practical use“, says Haoran Ren, a Humboldt Postdoctoral Research Fellow at the Nano-Institute Munich who leads this work.
“During the recent decade, storing information in twisted light carrying orbital angular momentum has become an intriguing trend, as this degree of freedom of light has an unbounded set of orthogonal helical modes that can function as independent information channels”, explains Stefan Maier, senior author of the paper, who holds the Chair in Hybrid Nanosystems at the Faculty of Physics of Ludwig-Maximilians-Universität Munich and the Lee-Lucas Chair in Experimental Physics at Imperial College London.
The researchers developed a complex-amplitude metasurface hologram for high-bandwidth orbital angular momentum-multiplexing holography. “Our complex-amplitude metasurface hologram with complete and independent amplitude and phase control allows the use of twisted light with continuous orbital angular momentum modes ranging from -50 to 50 to address 200 orbital angular momentum image frames”, says Haoran Ren.
The physicists used 3D direct laser printing technology to manufacture a large-scale (2.5 mm × 2.5 mm) complex-amplitude metasurface. “This 3D metasurface could unlock the full potential of meta-optics by extending its design degrees of freedom from a 2D transverse plane to 3D space”, says Haoran Ren.
“Our 3D laser printing of metasurfaces may inspire novel metasurface designs for a wide range of photonic applications in which current flat optics has made significant impacts”, Stefan Maier adds. “We envision that our work has impact across industry and scientific research, including smart head-up displays, wearable devices for augmented reality, and deep-learning microscopy”.
The paper was co-authored by Xinyuan Fang (co-lead first author), University of Shanghai for Science and Technology, China, Jaehyuck Jang (co-lead first author) and Junsuk Rho, Pohang University of Science and Technology, Korea, and Johannes Bürger, Ludwig-Maximilians-Universität Munich.