At the 2020 world artificial intelligence conference held on July 9 this year, Ma Yun and musk were "on the same stage" again.Affected by the epidemic situation that day, waic adopted the cloud form for the first time in its history. As the final speaker of the opening ceremony of the conference, Ma Yun was in Yunnan. A technology connected him with us - holographic projection.In fact, this technology has a history of more than 70 years.
As early as 1947, the British Hungarian physicist g bor D NES invented holographic projection. Based on this achievement, he won the young's prize of the British Physical Society in 1967 and the Nobel Prize in physics in 1971.Recently, Samsung, known as the "display overlord", has made a new breakthrough in this field - proposed an ultra-thin interactive holographic display, which can provide high-resolution and highly realistic 3D video from multiple angles. In the future, it can be integrated into mobile devices to support office or home.What is holography?
The scientific research team to achieve this breakthrough comes from Samsung Institute of advanced technology (sait), the optical research group of sait Russia and Seoul University.On November 10, 2020, his paper was published in nature communication, a subsidiary of nature, entitled slim panel holography video display.Before understanding this paper, what is holography is the first problem to understand.
Holographic projection is essentially a 3D technology. Its English name is holographic projection, in which holo comes from Greek, meaning "complete information".To deliver a "complete message", you need two steps:Shooting: using the interference principle (that is, when two or more columns of waves overlap in space, they will be superimposed to form a new waveform), the object beam formed by the subject under laser irradiation and the laser reference beam emitted on the holographic negative will be superimposed to generate interference and recorded. After certain processing, the hologram is obtained.
Imaging: Based on the diffraction principle (i.e. the wave will deviate from the original linear propagation when encountering obstacles), the hologram is illuminated by coherent laser. The diffracted light wave of a linearly recorded sinusoidal hologram can give two images, which enhances the three-dimensional sense of the image and has a real visual effect.In short, the principle of holographic projection technology can be understood as: skillfully take an object into a photo by using two physical phenomena, and then create a three-dimensional feeling.For this reason, holographic projection is also called virtual imaging.
It is worth mentioning that when real objects and holograms are in the same space, they can be perceived without difference.For example, in the following photo, a real hand holds a holographic display screen, on which is the image of an elf. Both the hologram and the hand are 0.3 meters away from the camera that took the picture.Holographic display provides natural depth perception, and the audience pays more attention to the spirit itself than the screen.
In contrast, if it is a traditional three-dimensional 3D image using binocular parallax and convergence (i.e. convergence of eyes when looking at near objects), the audience may not be able to clearly see the elf image and hand at the same time, and there will be visual fatigue caused by reconciliation convergence conflict.Therefore, holographic display can be said to be an important part of the future video system.In fact, since its discovery in 1947, holographic technology has become a classic element in science fiction films, and people's cognition of it has always been that it can reproduce the most real 3D images without visual discomfort.
The viewing angle is expanded by 30 times, and 4K high-resolution holograms are generated in real timeIn 1990, the MIT Media Lab developed the first holographic video system. Since then, the commercialization of holographic video has become a major research direction in this field.In May 2018, American camera giant red launched the world's first commercial holographic projection smartphone hydrogenone.
At that time, although this mobile phone attracted great attention from the outside world, when the product was launched, people in the industry and the media said that this mobile phone failed to give a satisfactory user experience in holographic projection. In fact, until today, there is still a bottleneck in the realization of "commercial holographic video display".Samsung Seoul University team said in the paper: commercial holographic video displays have not been introduced in batches, mainly due to narrow viewing angle, bulky optical equipment and high requirements for computing power.Specifically, to build a mobile holographic video display suitable for commercialization, three obstacles need to be overcome:
1. The limitation of space bandwidth product (SBP), which determines the size and viewing angle of holographic image.2. In order to produce large coherent background light, complex optical elements and considerable space are needed to process light. Therefore, it is not easy to realize a holographic video display as thin as a tablet.3. Real time holograms usually require a lot of calculation, and the amount of calculation will increase with the increase of spatial bandwidth product.
Based on the above problems, the ultra-thin interactive holographic display proposed by Samsung & Seoul University team has two special designs:One is the steering backlight unit composed of coherent Blu (c-blu) and beam deflector (BD). On the one hand, it expands the effective spatial bandwidth product (i.e. viewing angle) by 30 times, thus realizing the dynamic hologram with the largest viewing angle in history; On the other hand, its diffractive waveguide architecture ensures the final ultra-thin design of the display screen, with a total thickness of no more than 10 cm.The two blue arrows in the following figure are the expanded visual range.
The second is a holographic video processor including data propagation unit (DPU), filter and scaling unit (FSU) and 32 fast inverse Fourier transform processors. A single chip can generate 4K high-resolution holograms in real time.Finally, the prototype of holographic video display screen is shown in the figure below. The marks in the figure below are: spatial light modulator, geometric phase lens, coherent backlight unit, beam deflector and holographic video processor from top to bottom.Moreover, the system bus used by Samsung Seoul University team is ambaaxi4, which is widely used in smartphone application processor. Therefore, embedding holographic video processor into smartphone application processor can also be realized in the future.
Finally, let's feel a 4K turtle swimming map projected by this holographic display screen that supports multi angle viewing. The direction the turtle swims can be controlled by pressing the key directly.It seems ordinary, but in fact, due to the different depth of all objects in the picture, the definition of holographic objects will change with the focus of the camera.The following figure is a video screenshot. In the illustration at the upper right corner of figure a, coral is clearer than tortoise; In the illustration of figure B, turtles are clearer than corals.
This is the same as whether our camera focuses or not. Naturally, it also reflects the uniqueness of holograms - they can provide debugging, and the final image is no different from the real object.So far, holographic projection, a magical technology with a history of more than 70 years, has made an important breakthrough. We are not far from holographic projection on mobile phones. Editor ajx