“This Isn’t Just Light-Bending — It’s Mind-Bending.”

The single piece of glass creates razor-sharp panoramic images.

To capture panoramic views in a single shot, photographers typically use fisheye lenses – ultra-wide-angle lenses made from multiple pieces of curved glass that distort the incident light and create wide, bubble-like images. Their spherical, multi-part design makes fish-eye lenses inherently bulky and often expensive to manufacture.

Now engineers at WITH and the University of Massachusetts at Lowell developed a wide-angle lens that is completely flat. It is the first flat fish-eye lens that produces razor-sharp 180-degree panoramic images. The design is a kind of “metal”, a gossamer material that is structured with microscopic features that work together to manipulate the light in a certain way.

In this case, the new fisheye lens consists of a single flat, millimeter-thin piece of glass covered on one side with tiny structures that precisely diffuse the incident light to create panoramic images, just like a conventional curved fisheye lens assembly with multiple elements Case. The lens works in the infrared portion of the spectrum, but the researchers say it could be modified to take pictures with visible light as well.

The new design could potentially be adapted for a range of uses, with thin wide-angle lenses built right into smartphones and laptops rather than physically attached as bulky add-ons. The low profile lenses can also be incorporated into medical imaging devices such as endoscopes, as well as into virtual reality glasses, wearable electronics, and other computer vision devices.

“This design is a bit surprising because some thought it was impossible to make metals with an ultra-wide field view,” said Juejun Hu, associate professor in the MIT Department of Materials Science and Engineering. “The fact that this can actually produce fisheye images is completely beyond expectations.

It’s not only easy, it’s mind-blowing too. ”

Hu and his colleagues published their findings in the journal on September 18, 2020 Nano letters. Hu’s MIT co-authors are Mikhail Shalaginov, Fan Yang, Peter Su, Dominika Lyzwa, Anuradha Agarwal and Tian Gu, and Sensong An and Hualiang Zhang from UMass Lowell.

Design on the back

Metalenses are still at an experimental stage, but they can change the field of optics significantly. Scientists previously developed metal lenses that produce high-resolution and relatively wide-angle images of up to 60 degrees. Traditionally, to further expand the field of view, additional optical components would be required to correct for aberrations or blurring – a workaround that would add bulk to a metal design.

Instead, Hu and his colleagues developed a simple design that requires no additional components and has a minimal number of elements. Your new metals are a single transparent piece of calcium fluoride with a thin film of lead telluride on one side. The team then used lithographic techniques to carve a pattern of optical structures into the film.

Any structure or “metaatom“As the team calls it, is shaped into one of several nanoscale geometries, such as a rectangular or a bone-shaped configuration, that refracts light in a certain way. For example, it can take longer for light to move from one shape to another scattered or spread from it – a phenomenon known as phase lag.

With conventional fish-eye lenses, of course, the curvature of the glass creates a distribution of phase delays that ultimately creates a panoramic image. The team determined the corresponding pattern of the meta-atoms and carved that pattern into the back of the flat glass.

“We designed the back structures so that each part can create a perfect focus,” says Hu.

On the front, the team placed an optical screen or opening for light.

“When light enters through this opening, it is refracted on the first surface of the glass and then distributed in an angular manner,” explains Shalaginov. “The light then hits different parts of the back from different, yet continuous angles. As long as you design the backside correctly, you can be sure that you will get high quality imaging across the entire panoramic view. ”

About the panorama

In a demonstration, the new lens will be adjusted to work in the mid-infrared range of the spectrum. The team used the imaging setup equipped with the metallers to take pictures of a striped target. They then compared the quality of the images taken at different angles across the scene and found that the new lens produced images of the stripes that were sharp and clear even at the edges of the camera view, stretching nearly 180 degrees.

“It shows that with our methods we can achieve perfect imaging performance over almost the entire 180-degree view,” says Gu.

In another study, the team designed the metals to operate at a near infrared wavelength using amorphous silicon nanoposts as meta-atoms. They put the metals in a simulation that was used to test imaging instruments. Next, they fed the simulation with a scene from Paris, which consisted of black and white images that were stitched together to form a panoramic view. They then ran the simulation to see what kind of image the new lens would produce.

“The key question was whether the lens covers the entire field of view. And we see that everything covers the panorama, ”says Gu. “You can see buildings and people, and the resolution is very good whether you are looking in the center or at the edges.”

The team says the new lens can be adapted to other wavelengths of light. For example, to make a similar flat fisheye lens for visible light, the optical features may need to be made smaller than they are now in order to better break that particular wavelength range. The lens material would also have to change. However, the general architecture that the team designed would remain the same.

The researchers are investigating applications for their new lens, not only as compact fisheye cameras, but also as panorama projectors and depth sensors that are built directly into smartphones, laptops and portable devices.

“Right now, all 3D sensors have a limited field of view. If you put your face away from your smartphone, you won’t be recognized,” says Gu. “What we have here is a new 3D sensor that enables panoramic depth profiling that could be useful for consumer electronics devices.”

Reference: “Single-Element Diffraction-Limited Fisheye Metalens” by Mikhail Y. Shalaginov, Sensong An, Fan Yang, Peter Su, Dominika Lyzwa, Anuradha M. Agarwal, Hualiang Zhang, Juejun Hu and Tian Gu, September 18, 2020, Nano letters.
DOI: 10.1021 / acs.nanolett.0c02783

This research was funded in part by DARPA under the EXTREME program.