In sci-fi movies, we often see such scenes: on a large screen, 3D objects (or people) that move like ghosts “float” in front of our eyes, lifelike and vivid, we can from all angles See them.
In real life, we can also achieve similar photographic effects, which involves a photographic technique called holography.
In 1947, Dennis Gabor, a British Hungarian physicist, invented the holographic technology, and he won the 1971 Nobel Prize in Physics for this. Since its birth, holography has a history of nearly 70 years.
In 2018, the American camera company RED launched the world’s first holographic projection smartphone; in 2019, South Korea’s Samsung company issued a holographic projection patent. The information is presented in the air through holographic projection, with a full sense of science and technology.
However, because traditional holographic video displays have problems such as narrow viewing angles of optical devices, huge optical systems required and powerful computing capabilities, holographic dynamic video has not yet been widely used in commercial fields.
Recently, a study published in the journal Nature Communications proposed an ultra-thin interactive holographic display that allows viewers to watch high-resolution 3D videos from multiple angles. Let the holographic video display better integrate into mobile devices.
The researchers used a special background light and light swing mechanism to increase the viewing angle of 3D video by 30 times and realized an ultra-thin interactive holographic display design with a total thickness of less than 10 cm, and successfully projected a full screen that can be viewed from multiple angles 4K interactive 3D sea turtle swimming video.
Holography refers to a method of creating unique photographic images without using a lens. The photographic record of this image is called a hologram. The word Hologram is derived from the Greek word, where “holos” means “whole view” ( whole view), gram means “written” (written).
Ordinary photos record the changes in the intensity of the reflected light from the object, resulting in dark areas where there is less reflected light and bright areas where there is more reflected light. However, holography not only records the intensity of light but also records its phase or the degree of coherence between the wavefronts that make up the reflected light.
The hologram displays the “whole” image of the object in a 3D stereoscopic manner. By recording and reconstructing the light field reflected from the observed object, the depth information of the object is preserved and the light field reflected in multiple directions is preserved.
The holographic image is the same as the distance between the human hand and the camera, which provides natural depth perception, prompting the observer to focus on the object itself instead of the screen.
Holograms are widely used in the fields of art, science, and technology. For example, there are holographic images on our credit cards and ID cards to prevent counterfeiting; in medical imaging, 3D holograms of human organs such as the liver can provide doctors with a more comprehensive perspective; in industrial production, The hologram can be used to check the cracks on the product and perform product quality control; in the field of art, the hologram can also be a 3D pure optical artistic creation space.
Previous studies have shown that the holographic video system is achievable. By using a spatial light phase modulator (SLM) that directly modulates the light wavefront, the hologram can be updated at a video rate. However, using a larger optical system can only produce holograms with vertical parallax.
The wide coverage of 4G and 5G networks allows people to watch videos on smartphones anytime and anywhere. However, to make holographic technology “inhabit” in portable monitors devices and construct a mobile holographic video display (mobile holographic video display), technically, the following obstacles must first be overcome:
- The limitation of the space-bandwidth product (SBP) determines the size and viewing angle of the holographic image. The SBP of the currently available spatial light phase modulator is usually several hundred times smaller than the SBP of the static holographic medium, and only small size Or a dynamic hologram with a narrow viewing angle.
- To produce a large coherent backlight, complex optical components and considerable space are required to manipulate the light. However, it is difficult for the current commercial flat panel displays to meet the requirements of realizing holographic displays in thinness.
- Calculating holograms in real-time usually requires a huge computational cost, and with the increase of SBP, the amount of calculation will also increase. After algorithm optimization, cluster processors or high-performance parallel processing systems are still needed to calculate high-quality holograms at the video frame rate.
Dynamic hologram with the largest viewing angle ever
This research demonstrates for the first time a real-time interactive ultra-thin holographic video display. By introducing a steering backlight unit (S-BLU) composed of a coherent BLU (C-BLU) and a beam deflector (BD), the effective SBP is increased than the original value. By 30 times, a dynamic hologram with the largest viewing angle in history is realized.
Optical architecture and key components: a. The optical architecture consists of a beam deflector, a coherent-backlight unit, a geometric phase lens, and a spatial light modulator; b. The principle of the beam deflector, it optically guides the transmitted light like a prism: the angular resolution of the vertical and horizontal phase array guided light is 0.02, when the wavelength is 520nm, the angular resolution of the guided light can reach ~ 15; c. Use waveguide to configure coherent-backlight unit: the first waveguide of red and green light and the second waveguide of blue light are superimposed together to improve the overall efficiency; d. The holographic video processor is implemented on a single FPGA.
S-BLU is a key component to expand the viewing angle of holographic displays. In the traditional beam steering, the maximum steering angle will decrease with the increase of the light source area due to the limitation of light concentration. In the holographic video system designed by this research institute, the researchers successfully solved the problem of light concentration by using the C-BLU waveguide structure.
One disadvantage of the small viewing angle is the long viewing distance. The researchers reduced the viewing distance by 25 times by using a lens with a focal length of 1 m.
For the display of real-time interactive holographic video, it is often necessary to accurately calculate the position of the viewer’s glasses to update the 3D image. The layer method is used to use a large number of two-dimensional inverse fast Fourier transform (2D IFFT) operations to be true. The scene generates high-quality holograms.
In this study, the researchers used a highly parallel architecture and reduced the use of hardware to build a holographic video processor based on IFFT. The processor can calculate two holographic images of the left and right eyes at the same time, and finally combine them into a hologram.
The holographic video processor is constructed with a single-chip FPGA and can generate 3840*2160 pixel binocular holographic color images at a speed of 30 frames per second (fps). Researchers successfully projected a full-screen 4K interactive 3D turtle swimming video that can be viewed from multiple angles.
Gently move the finger to control the keyboard, the turtle in the video can be rotated in any direction, which also proves that the dynamic holographic image can be updated in real-time using the holographic video processor.
The research uses a 10.1-inch ultra-high-definition commercial liquid crystal display to achieve the world’s first ultra-thin full-color holographic video display, and the holographic video processor can be easily embedded in the smartphone application processor.
People often experience visual fatigue after watching movies with 3D glasses. The holographic display screen can create 3D images in space, allowing the audience to watch real objects in multiple dimensions without fatigue. The system calculates the two holographic images of the left and right eyes at the same time in the design, further reducing the viewer’s discomfort in the video.
The researchers said that this research result will strongly promote the development of a mobile holographic video. Perhaps in the near future, scenes from science fiction films may appear in our lives. Take out our smartphones and a 3D holographic video can be easily staged
The news source:https://kiperline.com/