Encrypted Holograms Are Coming

Here’s a suggestion for the next Mission: Impossible film—Ethan Hunt receives his top secret assignment through a chiral meta-hologram.

I’m not talking about the fake kind of “hologram” used to briefly resuscitate iconic rappers. This type of hologram looks like a flat surface that displays different images, and it could be embedded in something as unsuspecting as a newspaper or a restaurant menu. It can also only be unlocked by someone with the corresponding secret holographic key—a message encrypted with light.

A paper published Friday in the journal Science Advances authored by Reza Khorasaninejad, a postdoc at Harvard, and his colleagues, describes how such a hologram would work.

Meta-holograms, which can be contained on a surface 100 times thinner than the width of a human hair, get their name from the “metasurfaces” used to create them. These surfaces are able to control light in ways not found in nature by creating structures smaller than the wavelengths of light they interact with. To make a metasurface, one must literally arrange structures on the molecular scale.

The meta-hologram Khorasinejad and his colleagues created transmits different images depending on the polarity of the light shone on it. Ambient light, which interacts with normal holograms, is composed of photons that vibrate in pretty much all directions, while polarized light is composed of photons that vibrate in a specific manner. Polarized light can also be linear (like a laser) or circular, and circular light can also be either “right handed” or “left handed” (chiral) depending on the direction the photons spin.

The hologram Khorasinejad describes can distinguish the spin direction of the photons hitting it. You can think of the hologram’s surface as something that can subtract away or add to the light shone on it, depending on its chirality.

One would need to know where the hologram was hidden, what flavor of polarized light to shine on it, and what wavelength

There have been earlier efforts to make holograms using metasurfaces, Khorasinejad told Motherboard. But he and his colleagues are the first to construct a binary hologram (one where each pixel can essentially be ‘on’ or ‘off’) that works across the entire spectrum of visible light that can also produce different images based on the chirality of that light.

That means that it could theoretically be engineered to react not only the the polarity and chirality of the light, but also to a specific wavelength of light unknown to anyone but the intended viewer, he said.

For Hunt to receive his message, he would need to know where the hologram was hidden (not an easy task for something that can be 100 times thinner than a human hair), what flavor of polarized light to shine on it, and what wavelength to shine on it. Only then would the message be revealed.

Perhaps more practically, Khorasaninejad expects this new technology—which he says has the ability to be mass produced—to find its way onto our most secure documents and identifications as an anti-counterfeiting tool. But for any producers attached to the next Mission: Impossible reading this, it would be a pretty dope way to conceal a message, and it might even render that whole self-destruction sequence irrelevant.