The new holographic camera sees the invisible with high precision

One setup of a camera prototype in the lab. Credits: Florian Willomitzer / Northwestern University

Researchers at Northwestern University have invented a new high-resolution camera that allows you to see invisible things around the corners and through scattering media such as skin, fog, and in some cases human skulls.

This new method, called synthetic wavelength holography, works by indirectly scattering. Coherent light It moves to the hidden object, which scatters again and returns to the camera.From there, the algorithm rebuilds Scattered light A signal to reveal a hidden object. Due to its high time resolution, this method can also image fast-moving objects such as heartbeats from the chest and speeding up cars on street corners.

The study will be published in the journal on November 17th. Nature Communications.

A relatively new field of study that images objects behind occlusions or scatter media is called non-line-of-sight (NLoS) imaging. Compared to related NLoS imaging techniques, the northwestern method can quickly capture large area full-field images with submillimeter wave accuracy. At this level of resolution, computational cameras can potentially create images through the skin and even see the smallest capillaries at work.

While this method has obvious potential for non-invasive medical imaging, early warning navigation systems for automobiles, and industrial testing in tight spaces, researchers believe the potential uses are endless. I am.

“Our technology will usher in a new wave of imaging capabilities,” said Florian Willomizer of Northwestern University, the first author of this study. “Our current sensor prototype is visible or InfraredHowever, the principle is universal and can be extended to other wavelengths. For example, the same method can be applied to radio waves for space exploration and underwater acoustic imaging. It can be applied in many areas and we just scratched the surface. “

Willomitzer is an assistant professor of electrical and computer engineering at Northwestern University’s McCormick Engineering Department. Northwest co-authors include Oliver Cossert, an associate professor of computer science, electrical and computer engineering, and a former PhD. Student Fengqiang Li. Researchers in the northwest have worked closely with all researchers at Southern Methodist University, Plazan Narangarajan, Muraridar Baraj, and Mark Christensen.

Blocking scattered light

Looking around the corners and imaging the organs of the human body may seem like a very different task, but Willomizer said they are in fact closely related. Both deal with scattering media. Light Hit object It then scatters in such a way that the direct image of the object is invisible.

“If you’ve ever tried to illuminate a flashlight through your hands, you’ve experienced this phenomenon,” Willomizer said. “You can see bright spots on the other side of the hand, but in theory the bone should cast a shadow and reveal the structure of the bone. Instead, the light passing through the bone is scattered in all directions within the tissue. The shadow image is completely blurred. “

Therefore, the goal is to block scattered light, reconstruct unique information about its travel time, and reveal hidden objects. But it presents its own challenge.

“Nothing is as fast as the speed of light, so if you want to measure light travel time with high accuracy, you need a very fast detector,” says Willomizer. “Such detectors can be terribly expensive.”

Tailored wave

To eliminate the need for fast detectors, Willomitzer and his colleagues merged the light waves from the two lasers to produce synthetic light waves that could be specially tuned for holographic imaging in different scattering scenarios. bottom.

“If we can capture the entire light field of an object with a hologram, we can reconstruct the entire 3D shape of the object,” explains Willomitzer. “This holographic imaging uses synthetic waves instead of regular light waves, at corners and through scatterers.”

Over the years, there have been many NLoS imaging attempts to recover. image Of hidden objects. However, these methods usually have one or more problems. They have low resolutions, very small viewing angles, require time-consuming raster scans, or require a large probe area to measure scattered light signals.

However, the new technology overcomes these problems and is the first method of imaging around corners and through scatter media, combining high spatial resolution, high temporal resolution, a small probing area, and a large viewing angle. This means that the camera can image small features in tight spaces or hidden objects in large areas in high resolution, even when the objects are moving.

“Turn the wall into a mirror”

Light only follows a straight path, so opaque barriers (walls, shrubs, cars, etc.) must be present for new devices to appear around the corner. Light is emitted from a sensor unit (which can be mounted on top of a car), bounces off a barrier and hits an object around a corner. The light then bounces off the barrier and eventually returns to the sensor unit’s detector.

“It’s like having a virtual computing camera in every remote location and seeing the world from a surface perspective,” Willomizer said.

For those driving on roads around mountain passes or meandering in rural forests, this method can prevent accidents by revealing other cars and deer that are invisible around the corner. “This technology turns the wall into a mirror,” Willomizer said. “This technique works better at night and in foggy weather conditions.”

In this way, high resolution technology can also replace (or supplement) endoscopes for medical and industrial image processing. Instead of requiring a flexible camera that can turn corners and twist tight spaces, such as colonoscopy, synthetic wavelength holography uses light to look around many folds in the intestine. I can.

Similarly, synthetic wavelength holography can image the interior of industrial equipment during operation. This is not possible with current endoscopes.

“If the turbine is running and you want to inspect internal defects, you usually use an endoscope,” Willomizer said. “But some flaws only show up when the device is moving. You can’t use an endoscope to see the inside of the turbine from the front while it’s running. Our sensors are running. You can inspect the inside of your turbine and detect structures less than 1 millimeter.

This technology is currently a prototype, but Willomizer believes it will eventually be used to help drivers avoid accidents. “There’s still a long way to go before we see these types of imagers built into cars or approved for medical use,” he said. “Maybe 10 years or more, but it will come.”

Non-line-of-sight imaging with picosecond time resolution

For more information:
High-speed, non-line-of-sight imaging with high resolution and wide field of view using synthetic wavelength holography, Nature Communications (2021). DOI: 10.1038 / s41467-021-26776-w

Quote: The new holographic camera is a high precision (November 2021) obtained from https: // on November 17, 2021. 17th) Recognize what you cannot see

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The new holographic camera sees the invisible with high precision

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