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Xiao Bian's mobile phone lens is not very prominent, but it can no longer be placed flat on the table. Get up and go to the toilet. Your new phone is on the table without a phone case. The lens protruding from the body makes it unstable on the table. All of a sudden, the phone calls, and your phone vibrates and squirms toward the table. The moment you come out of the toilet, it falls to the ground under your gaze. With the mobile phone screen together with the fragmentation, is the gentleman love money heart.

I don't know when it became commonplace for people to have lens modules protruding from the back of their phones, and no one complained why the lens protruded so much from the body. Without a phone case, some phones can slide off the table because the lens module protrudes too much, and the vibration of the message alert can even make the phone slide off the table. From mobile phones to smartphones today, mobile phones have become so thin over the years, can't we make the lens thinner?

It really didn't work. The miniaturization of electronic components has led us to the information age, where we can build complex structures on chips smaller than fingernails, with countless currents moving exactly according to the rules set by engineers on nanosecond time scales. But the lenses we use today are not fundamentally different in principle from those used by Louis Daguerre in 1839 when he first photographed people, except for improvements in the quality of the images, such as light, phase difference, and chromatic aberration. For imaging optical systems, there has been no essential progress in technology, as if the basic technology had been locked by "Zhizi."

The first photograph of a man was taken in 1839. Photo credit: Louis Daguerre / public domain Traditional lenses are equivalent to a convex lens when imaging. But a lens cannot consist of only one convex lens because it has aberrations and chromatic aberrations. Therefore, the lens needs to be composed of multiple lenses, each with its own responsibility, some responsible for deflecting light, some responsible for eliminating chromatic aberration, some responsible for eliminating distortion. Each lens needs to go through a complex grinding process, and assembly also requires a high degree of precision. After all, optics is the most sophisticated subject that humans have mastered. The lithography machine that makes chips and the laser interferometer that detects gravitational waves are all optical instruments. Behind the precision is the high cost.

As cameras become more widely used, our demand for high-quality images increases. Whether it is autonomous driving or unmanned aircraft obstacle avoidance, a large amount of imaging data is required. Even if the lens size of mobile phones is small now, it can also rely on mass production to reduce costs. However, due to the limitation of the traditional optical lens principle, it must be realized by multiple lenses, and the thickness and cost cannot always be reduced to a satisfactory level.

What we need is not the lens itself, but the image that the lens ultimately presents on the sensor. If there is any light and simple structure that can replace the traditional lens, it is naturally the best. Metalens are such optical instruments.

When you see "meta," the most people think of is the meta-universe. But in fact, the field of materials science has used this term for a long time. The term "metalens" is also derived from the concepts of metamaterial and metasurface. The word Metamaterial comes from the Greek meta, meaning "beyond." Metamaterials go beyond ordinary materials and have properties that ordinary substances do not have. Metamaterial is not so much a substance as a special man-made structure composed of conventional substances such as metals, silicon and plastics. If the structure as a whole is regarded as a substance, it may have special properties, such as a negative refractive index.

An example of a possible superlens pattern captured by an electron microscope. (Image credit: Science) The dimensions of a metamaterial's microstructure determine what wavelengths of light it can interact with. If the microstructure is tens of nanometers, it is a metamaterial of visible light. At the same time, in order to improve the light transmittance, all the microstructures can be made on a two-dimensional surface, and the metamaterial becomes a supersurface, where each microstructure looks like a tiny pillar and acts like a waveguide. The supersurface can change the direction of light propagation, and use it as a lens, that is, a superlens.

An example of a possible superlens pattern captured by an electron microscope. (Image source: SCIENCE · 18 Jul 2014· Vol 345, Issue 6194· pp. 298-302 In general, what an optical system needs in order to form an image is the ability to concentrate light. Light is a kind of electromagnetic wave, wave has phase property, the plane composed of electromagnetic waves of the same phase is called wavefront. The microstructure on the superlens can adjust the phase of incident electromagnetic waves according to their shape and arrangement, thus controlling the shape of the wavefront. As long as the microstructure of the superlens adjusts the shape of the wavefront to the converging shape, it acts like a convex lens and can form an image.

Convex lenses can focus light by changing the wavefront, and so can the wavefront. Image credit: Oleg Alexandrov / wikimedia Traditional lenses are lenses that require fine grinding, while hyperlenses are ultra-thin flat structures. The lens with thickness will produce chromatic aberration due to the different refractive index of the material for different colors of light, while the super-surface is ultra-thin, and all wavelengths of light pass through the lens almost at the same time, and will not produce chromatic aberration. And, even better, supersurfaces aren't that hard to produce. The ability to fabricate microscopic repeating structures has been the main driver of electronic technology progress in the past few decades. In fact, supersurfaces can be mass-produced by existing semiconductor foundries.

So, if the technology for superlenses is mature, we just need to stack sensors that sense light, glass that provides thickness, and superlenses that bend light to get a near-perfect lens. It can form images, it has no chromatic aberration, it has no complicated lens structure, it is much thinner-and it costs less.

Meta's curse, however, the word meta seems to have a curse in general, everything with it looks so good prospects, but from the actual life landing, seems to have a distance. Superlens technology has always given people a sense that gimmicks are bigger than reality, and few people can really give the actual commercial time of superlens technology. However, this phenomenon is rapidly changing.

Last week, Li Tao's team at Nanjing University used superlens technology to create an ultra-thin, high-quality single-layer metalens array integrated wide-angle camera (MIWC). The results were published in Optica magazine. The MIWC camera size is 1×1×0.3 cm and the viewing angle is 120°. Compared with previous single super-lens cameras, the super-lens array in MIWC cameras can compensate for the degradation of image quality at the edges of different super-lenses and achieve higher image quality. At the same time, because the camera is composed of only two components, CMOS light sensor and super lens array, it is expected to reduce costs in mass production. In the future, the research team plans to increase the diameter of individual superlenses in the array from 0.3 mm to 1 to 5 mm, thus further improving the imaging quality.

Comparison of image quality between conventional single superlens camera and MIWC camera. Photo source: Tao Li, Nanjing University When taking portrait photos, people often need the shallow depth of field brought by "large aperture" to blur the background of the photo so as to highlight the subject. But for data acquisition, the camera's depth of field is as large as possible, and it is ideal to be able to see distant and nearby objects at the same time. Inspired by the trilobite compound eye, Xu Ting's team at Nanjing University has developed a super-large depth-of-field miniature camera with a bifocal lens that can clearly image objects within 3 cm and 1.7 km away simultaneously in a single photo. The study was published in Nature Communications.

Schematic diagram of the imaging principle of bifocal lenses (Image credit: Kelley / NIST) Rome was not built in a day, and the development of superlenses also takes time. Now, the development of hypersurfaces is getting faster and faster, and perhaps we can expect that with the help of hypersurface technology, we can return to the era when mobile phone lenses are not prominent.

Reference link:

https://www.eurekalert.org/news-releases/949421

https://www.radiantvisionsystems.com/zh-hans/blog/going-meta-how-metalenses-are-reshaping-future-optics

https://opg.optica.org/optica/home.cfm

https://www.nature.com/articles/s41467-022-29568-y#auth-Ting-Xu

https://iopscience.iop.org/article/10.1088/0034-4885/79/7/076401/meta

This article comes from Weixin Official Accounts: Global Science (ID: huanqiukexue), written by Wang Yu, revised by: Erqi

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