This Holographic Camera Can See Around Corners, Under Human Skin

Researchers have invented a new high-resolution camera that may be able "see the unseen."

The camera could utilize scattered light to see around corners, and potentially even see through skin to allow doctors to observe organs inside the human body.

The camera represents an advance in research in a new field of science called non-line-of-sight imaging, which concerns picturing objects that are obscured or surrounded by material that prevents them from being viewed.

"Our technology will usher in a new wave of imaging capabilities," Northwestern University researcher Florian Willomitzer said. "Our current sensor prototypes use visible or infrared light, but the principle is universal and could be extended to other wavelengths."

The method used by the team also has the potential to image fast-moving objects, such as a beating heart through the chest or speeding cars around a street corner.

Willomitzer is the author of a paper detailing the development of the camera published in the journal Nature Communications.

How Does It work?

The camera works by indirectly scattering light that falls on a hidden object, and this light is then scattered back to the camera. This means using the surfaces that obscure the object, such as a wall in the case of seeing around a corner, as a mirror to bounce the light to the hidden object, and then back to the camera.

Once there, an algorithm reconstructs the light signal and creates a holographic representation of hidden or obscured targets. The method is known as Synthetic Wavelength Holography (SWH).

This means that if the light can be intercepted then it's possible to determine how long it has taken for the light to reach the object. From there it's possible to build an image that reveals the hidden object. Something that is harder than it may initially sound.

"It means that the camera developed by the team can only see an object if there is some kind of barrier between it and the camera. This technique turns walls into mirrors," Willomitzer said. "Nothing is faster than the speed of light, so if you want to measure light's time of travel with high precision, then you need extremely fast detectors."

As detectors like this don't come cheap, the Northwestern University team did away with the need for this technology by merging light waves from two lasers generating a synthetic light wave. This can be specifically tailored to holographic imaging in different scattering scenarios.

"If you can capture the entire light field of an object in a hologram, then you can reconstruct the object's three-dimensional shape in its entirety," Willomitzer explained. "We do this holographic imaging around a corner or through scatterers—with synthetic waves instead of normal light waves."

"It gets better as the technique also can work at night and in foggy weather conditions."

This means that the system could be ideal for travelers driving in dangerous conditions such as across mountain roads.

Seeing Inside The Human Body

Though the problem of seeing around a corner may seem very different from peering at an organ in the human body, Willomitzer points out that both things concern light scattering in a way that causes an object to be hidden.

"If you have ever tried to shine a flashlight through your hand, then you have experienced this phenomenon," Willomitzer said. "You see a bright spot on the other side of your hand, but, theoretically, there should be a shadow cast by your bones, revealing the bones' structure."

Instead, Willomitzer continued, the light that passes the bones gets scattered within the tissue in all directions, completely blurring out the shadow image. This means that the camera developed by the team could use that scattering just as it uses scattering from obscuring surfaces.

"The physical phenomenon that makes it impossible to image hidden objects with conventional cameras or your eye is the phenomenon of light scattering," Willomitzer said. "A wall is a 'surface scatterer' meaning that light that hits the wall is diffusely reflected in all directions. For a volume scatterer, like skin or milky plastic, the light enters the material and bounces around several times before it exits again at a different position and under different angles."

The researcher explained that in both cases the scattered light completely loses its spatial structure, which makes imaging hidden objects with conventional cameras impossible.

As a result, one day it could replace intrusive imagining methods like endoscopes that have to be inserted into a patient's body.

The team believes that the technology could be useful in a wide range of applications even beyond this, both on Earth and off its surface.

"The same method could be applied to radio waves for space exploration or underwater acoustic imaging. It can be applied to many areas, and we have only scratched the surface," Willomitzer said.

The researcher added: "There is still a long way to go before we see these kinds of imagers built in cars or approved for medical applications. Maybe 10 years or even more. We have shown a first prototype that demonstrates the first proof of principle. We are currently working on making the method faster, cheaper, and applicable to a wider range of scattering scenarios."

Update 11/26/21, 4:12 a.m. ET: This article was updated to include comments from Florian Willomitzer.