The NTU team developed a new flat wide-angle camera: ultra-thin and light, wide-angle imaging without distortion

Text | “China Science News” intern Ma Jing reporter Li Chenyang

Edit | He Tao

Why take a group photo and don’t stand on the side? Because the camera lens has distortion, the more serious it is to the edge, and the whole person may be deformed.

In addition to the expensive traditional SLR camera, what is the biggest pain point? The lens is too heavy.

Today, The team of Professor Li Tao of Nanjing University has designed a new type of planar wide-angle camera, the metalens array integrated wide-angle camera (MIWC), which solves the above problems in one fell swoop. The biggest breakthrough is in the newly developed lens, which is very thin and light, only 1 micron. However, higher quality wide-angle imaging is possible and there is no distortion.

Recently, the research results were published in Optica, a top journal in the field of optics.

When you look closely at the ordinary camera lens, you will find that its interior is composed of many curved lenses superimposed on top of each other.

Why not use a single lens?

This is due to the fact that traditional lenses have different refractive indexes for different wavelengths of light, and single-layer lenses cannot focus various rays of light at the same point, which is prone to chromatic aberration and aberration. The presence of aberrations limits the field of view of the lens, making it impossible for a single lens to obtain a clear image of a wide angle. Therefore, lens manufacturers have superimposed multiple lenses of different thicknesses and materials to solve the problem of chromatic aberration and aberration in imaging.

Even so, lens modules that eliminate chromatic aberration often have problems like distortion in wide-angle imaging, as mentioned at the beginning of this article, the dilemma that everyone encounters when taking a group photo.

Moreover, this lens superposition also brings new problems: the more lenses superimposed, the better the image quality will indeed be, but the weight of the lens will also increase – such a “long gun and short cannon” often brings a lot of carrying burden to the photographer.

So, is there a thin and light flat lens that can effectively reduce the weight of the lens? Is it possible to achieve portability for professional imaging systems that require higher requirements, such as astronomical telescopes and high-power microscopes?

Driven by these problems, Li Tao’s research team launched an in-depth study of micro-nano optics and found a breakthrough in a new type of lens called “superstructure lens”.

Metastructured lenses are derived from metastructured materials and hyperstructured surfaces, and are a new type of lens with a nanostructured flat surface (superstructured surface). Compared with traditional lenses, superstructured lenses have the characteristics of thin and compact, flat structure, etc., which can greatly improve the ability of lenses to focus light while reducing distortion.

With the advantages of ultra-light and ultra-thin superstructured lenses, Li Tao’s team designed a planar wide-angle camera based on superstructured lens arrays, which realizes high-quality wide-angle imaging functions with a viewing angle of more than 120°.

Ultra-thin flat superstructured lens wide-angle camera physical photo

“Considering that a single lens could not obtain a relatively large viewing angle, we chose a different approach.” Li Tao introduced to China Science Daily, “No longer vertical superimposed, but a series of superstructured lenses are horizontally tiled to form a single-layer superstructure lens array, giving full play to the advantages of ultra-thin lenses, so that each lens can capture a part of the wide-angle scene.” The sharpest parts of each image are then spliced together by calculations, resulting in a final high-quality wide-angle image. ”

In the demonstration experiment, the researchers used a single superstructure lens and an array of superstructure lens wide-angle cameras to image the words “NANJING UNIVERSITY” projected on a curved screen.

The results show that the planar camera composed of the superstructured lens can greatly expand the field of view without reducing the resolution, and can obtain distortion-free and clear imaging in the range of 120 degrees.

Left: Schematic diagram of the imaging apparatus; Top right: Imaging results of a single superstructure lens; Bottom right: Imaging results of a hyperstructured lens wide-angle camera

Traditional wide-angle imaging typically uses fisheye composite lenses or other types of multilayer lenses, and the application of the scene is often limited due to its large size.

The superstructure lens is thin and light, which can not only be applied to scenarios such as automatic driving and drone monitoring to improve the performance and safety of wide-angle imaging, but also can be applied to microscopic scenes such as microscopes, under the premise of ensuring image quality, expand the observation field of view of the microscope, so that the details and the overall picture are “perfect”.

Even, in the near future, superstructured lenses can reach small spaces, such as the interior of precision experimental instruments, bringing great convenience to the inspection and maintenance of experimental instruments.

“The hyperstructured lens imaging technology we are doing is not completely aimed at alternative applications, but is expected to develop new application areas, making the previous impossible possible and making the imagination a reality.” Li Tao said.

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