A new printer produces digital 3D holograms with an unprecedented level of detail and realistic color

Researchers developed a new system that prints holograms such as the one shown with an unprecedented level of detail and realistic color. Credit: C Yves GENTET

Technology offers high-speed, high-quality printing that could be useful for architecture models, fine art, exhibits and other applications

Researchers have developed a new printer that produces digital 3D holograms with an unprecedented level of detail and realistic color. The new printer could be used to make high-resolution color recreations of objects or scenes for museum displays, architectural models, fine art or advertisements that do not require glasses or special viewing aids.

“Our 15-year research project aimed to build a hologram printer with all the advantages of previous technologies while eliminating known drawbacks such as expensive lasers, slow printing speed, limited field of view and unsaturated colors,” said research team leader Yves Gentet from Ultimate Holography in France. “We accomplished this by creating the CHIMERA printer, which uses low-cost commercial lasers and high-speed printing to produce holograms with high-quality color that spans a large dynamic range.”

In The Optical Society (OSA) journal Applied Optics, the researchers describe the new printer, which creates holograms with wide fields of view and full parallax on a special photographic material they designed. Full parallax holograms reconstruct an object so that it is viewable in all directions, in this case with a field of view spanning 120 degrees.

The printer can create holograms from 3D computer generated models or from scans acquired with a dedicated scanner developed by the researchers. The high-quality holograms can even be used as masters to produce holographic copies.

Building a better printer

When developing the new hologram printer, the researchers carefully studied two previously developed holographic printer technologies to understand their advantages and drawbacks.

“The companies involved in developing the first two generations of printers eventually faced technical limitations and closed,” said Gentet. “Our small, self-funded group found that it was key to develop a highly sensitive photomaterial with a very fine grain rather than use a commercially available rigid material like previous systems.”

The CHIMERA printer uses red, green and blue low-power commercially available continuous wave lasers with shutters that adjust the exposure for each laser in a matter of milliseconds. The researchers also created a special anti-vibrating mechanical system to keep the holographic plate from moving during the recording.

Holograms are created by recording small holographic elements known as hogels, one after another using three spatial light modulators and a custom designed full-color optical printing head that enables the 120-degree parallax. After printing, the holograms are developed in chemical baths and sealed for protection.

The hogel size can be toggled between 250 and 500 microns and the printing rate adjusted from 1 to 50 hertz (Hz). For example, if a hogel size of 250 microns is used, the maximum printing speed is 50 Hz. At this speed it would take 11 hours to print a hologram measuring 30 by 40 centimeters, about half of the time it would take using previous systems based on pulsed lasers.

High brightness and clarity

The researchers used the new technology to print holograms that measured up to 60 by 80 centimeters showing various color objects including toys, a butterfly and a museum object.

“The new system offers a much wider field of view, higher resolution and noticeably better color rendition and dynamic range than previous systems,” said Gentet. “The full-color holographic material we developed provides improved brightness and clarity while the low-power, continuous wave lasers make the system easy to use.”

The researchers say that as technology improves, especially 3D software, it may be possible to expand their hologram printing approach to medical or other advanced applications.

Learn more: New Printer Creates Extremely Realistic Colorful Holograms

 

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An ultrathin display that can project dynamic, multi-coloured, 3D holographic images on existing LCD displays

Figure 1. The actual 3D holographic display, and an electron microscope image of the non-periodic pinholes.

Researchers have designed an ultrathin display that can project dynamic, multi-coloured, 3D holographic images, according to a study published in Nature Communications.

The system’s critical component is a thin film of titanium filled with tiny holes that precisely correspond with each pixel in a liquid crystal display (LCD) panel. This film acts as a ‘photon sieve’ – each pinhole diffracts light emerging from them widely, resulting in a high-definition 3D image observable from a wide angle.

The entire system is very small: they used a 1.8-inch off-the-shelf LCD panel with a resolution of 1024 x 768. The titanium film, attached to the back of the panel, is a mere 300 nanometres thick.

“Our approach suggests that holographic displays could be projected from thin devices, like a cell phone,” says Professor YongKeun Park, a physicist at KAIST who led the research. The team demonstrated their approach by producing a hologram of a moving, tri-coloured cube.

Figure 2. Three-dimensional dynamic color hologram operating at 60 Hz

Specifically, the images are made by pointing differently coloured laser beams made of parallel light rays at the small LCD panel. The photon sieve has a hole for each pixel in the LCD panel. The holes are precisely positioned to correspond to the pixel’s active area. The pinholes diffract the light emerging from them, producing 3D images.

Previous studies from Professor Park’s group have used optical diffusors for the same purpose, but the size of the device was bulky and difficult to be operated, and it took a long period of time to calibrate. In the present work, on the other hand, the group tailored their photon sieve to demonstrate a simple, compact and scalable method for 3D holographic display. This technique can be readily applied to existing LCD displays.

Applications for holograms have been limited by cumbersome techniques, high computation requirements, and poor image quality. Improving current techniques could lead to a wide variety of applications, including 3D cinema viewing without the need for glasses, watching holographic videos on television and smart phone screens.

Learn more: A Hole in One for Holographic Display

 

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Extremely compact multicolor 3D holographic display technology

Researchers developed a new way to create multicolored computer generated holograms. The experimental images they created matched well with the ones predicted by theory. The waveguide structures created using the new approach could offer easy integration and a form factor small enough for augmented reality and other displays.
Credit: Zhiqin Huang, Duke University

Lens-free holography method could bring color 3D displays to augmented reality glasses and smartphones

Researchers have developed a new approach to multicolor holography that could be used to make 3D color displays for augmented reality glasses, smartphones or heads-up displays without any bulky optical components.

In Optica, The Optical Society’s journal for high impact research, researchers from Duke University, USA describe how they encoded a multicolor image onto a 300-by-300 micron hologram in a 2D waveguide structure, a very thin structure that guides light. The computer-generated hologram produces complex multicolor holographic images when the grating coupler is illuminated by red, green and blue light.

“The hologram could be embossed directly onto the lenses of augmented reality glasses to project an image directly into the pupil of the eye without requiring any bulky lenses, beam splitters or prisms,” said Daniel L. Marks, a member of the research team. “It could also be used to project a 3D image from a smartphone onto a wall or nearby surface.”

The new fabrication method encodes holograms in a material that is compatible with integrated photonics technology. This means that the holographic devices are easy to mass manufacture with the same fabrication methods used to make computer chips. The hologram producing elements could be incorporated into tiny chip-based devices that also house the light sources required to create the 3D images.

To create multicolor holographic images, the researchers fabricated a grating coupler, or a series of fringes, and a binary hologram in a very thin waveguide structure. The resulting structure combines the colors and then precisely separates them to generate a full color image.
Credit: Zhiqin Huang, Duke University

From one color to three

The new multicolor holography technique is based on computer-generated holograms. Unlike traditional holography, which requires a physical object and laser beams to create the interference pattern necessary to form a holographic image, computer-generated holography generates interference patterns digitally.

Computer generated holograms provide high-resolution 3D images, but it has proven difficult to create them in more than one color. The Duke team overcame this challenge by fabricating a grating — a series of fringes —and a binary hologram in a waveguide made of a light-sensitive material known as photoresist. They developed a way to integrate the interference patterns for red, green and blue into a single binary hologram pattern.

“One of the difficult parts of making a multicolor display is combining the colors and then precisely separating them to generate a full color image,” said Zhiqin Huang, first author of the paper. “With our approach this is all done all in one step on a single surface without any beam splitters or prisms. This makes it extremely amenable to integration into portable devices.”

Another important achievement was creating the holographic device in a waveguide structure. “Others who have tried to create multicolor computer-generated holograms didn’t use a waveguide, which makes it a challenge to integrate the structure into a device,” said David R. Smith, leader of the research team. “Our design offers easier and more flexible integration with a form factor small enough for augmented reality and other displays.”

Single-step color images

The researchers used their new holography method to encode interference patterns for static multicolor holograms of an apple, a flower and a bird. The resulting holographic images all matched well with theoretical predictions. Although they fabricated very small holograms for the demonstration, the researchers say that the technique could be easily scaled up to create larger displays. They also believe their approach could be incorporated with existing technologies — such as those used to make liquid crystal displays — to create dynamic images.

The researchers are now working to optimize the technology by reducing the light lost by the structures that encode the holograms. They also point out that incorporating the structures into a single integrated device with lasers would be necessary to make the technique practical.

Learn more: Multicolor Holography Technology Could Enable Extremely Compact 3D Displays

 

 

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Holography and Light-Field Technology Combine For Practical 3-D Displays

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Figure 1a) A fabricated DDHOE lens array; 1b) The 3-D display system consisting of a 2-D projector and DDHOE; 1c) A computer-modeled 3-D scene of depth 6 cm; 1d) A 3-D reconstruction of a modeled scene captured by camera looking into the DDHOE. Credit: Boaz Jessie Jackin.

New approach would eliminate visual disturbances without additional bulky optics

While most interaction with digital content is still constrained to keyboards and 2-D touch panels, augmented and virtually reality (AR/VR) technologies promise ever more freedom from these limitations.

AR/VR devices can have their own drawbacks, such as a tendency to induce visual motion sickness or other visual disturbances with prolonged usage due to their stereoscopy or auto-stereoscopy based designs. One promising solution is to adapt holography or light field technology into the devices instead. This, however, requires additional optics that would increase the size, weight, and cost of these devices — challenges that have so far prevented these devices from achieving commercial success.

Now, a group of researchers in Japan and Belgium has begun to explore a combination of holography and light field technologies as a way to reduce the size and cost of more people-friendly AR/VR devices. They will present their work during The Optical Society’s (OSA) Frontiers in Optics meeting, 16–20 September, in Washington, D.C. One of the themes of the meeting is virtual reality and augmented vision, with both a visionary speaker and a series of invited talks on those subjects.

“Objects we see around us scatter light in different directions at different intensities in a way defined by the object’s characteristic features—including size, thickness, distance, color, texture,” said researcher Boaz Jessie Jackin of the National Institute of Information and Communication Technology in Japan. “The modulated [scattered] light is then received by the human eye and its characteristic features are reconstructed within the human brain.”

Devices capable of generating the same modulated light—without the physical object present—are known as true 3-D displays, which includes holography and light-field displays. “Faithfully reproducing all of the object’s features, the so-called ‘modulation,’ is very expensive,” said Jackin. “The required modulation is first numerically computed and then converted into light signals by a liquid crystal device (LCD). These light signals are then picked up by other optical components like lenses, mirrors, beam combiners and so on.”

The additional optical components, which are usually made of glass, play an important role because they determine the final performance and size of the display device.

This is where holographic optical elements can make a big difference. “A holographic optical element is a thin sheet of photosensitive material—think photographic film—that can replicate the functions of one or more additional optical components,” said Jackin. “They aren’t bulky or heavy, and can be adapted into smaller form factors. Fabricating them emerged as a new challenge for us here, but we’ve developed a solution.”

Recording, or fabricating, a hologram that can replicate the function of a glass-made optical component requires that particular optical component to be physically present during the recording process. This recording is an analogue process that relies on lasers and recording film; no digital signals or information are used.

“Recording multiple optical components requires that all of them be present in the recording process, which makes it complex and, in most cases, impossible to do,” said Jackin.

The group decided to print/record the hologram digitally, calling the solution a “digitally designed holographic optical element” (DDHOE). They use a holographic recording process that requires none of the optical components to be physically present during the recording, yet all the optical components’ functions can be recorded.

“The idea is to digitally compute the hologram of all the optical functions [to be recorded and] reconstruct them together optically using a LCD and laser,” said Jackin. “This reconstructed optical signal resembles the light that is otherwise modulated by all of those optical components together. The reconstructed light is then used to record the final holographic optical element. Since the reconstructed light had all optical functions, the recorded hologram on the photosensitive film will be able to modulate a light with all of those functions. So all of the additional optics needed can be replaced by a single holographic film.”

In terms of applications, the researchers have already put DDHOE to the test on a head-up light field 3-D display. The system is see-through, so it’s suitable for augmented reality applications.

“Our system uses a commercially available 2-D projector to display a set of multi-view images onto a micro-lens array sheet—which is usually glass or plastic,” said Jackin. “The sheet receives the light from the projector and modulates it to reconstruct the 3-D images in space, so a viewer looking through the micro-lens array perceives the image in 3-D.”

One big difficulty their approach overcomes is that light from a 2-D projector diverges and must be made collimated into a parallel beam before it hits the micro-lens array in order to accurately reconstruct the 3-D images in space.

“As displays get larger, the collimating lens should also increase in size. This leads to a bulky and heavy lens, the system consuming long optical path length and also the fabrication of the collimating lens gets costly,” said Jackin. “It’s the main bottleneck preventing such a system from achieving any commercial success.”

Jackin and colleagues’ approach completely avoids the requirement of collimation optics by incorporating its function on the lens array itself. The micro-lens array is a fabricated DDHOE, which includes the collimating functions.

The researchers went on to create a head-up, see-through 3-D display, which could soon offer an alternative to the current models that use the bulky collimation optics.

Learn more: Holography, Light-Field Technology Combo Could Deliver Practical 3-D Displays

 

 

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Activating brain cells with holography could potentially allow the blind to see or the paralyzed to feel touch

A sample hologram with 50 randomly distributed neuron targets spanning a region 500 microns square and 250 microns deep.

What if we could edit the sensations we feel; paste in our brain pictures that we never saw, cut out unwanted pain or insert non-existent scents into memory?

UC Berkeley neuroscientists are building the equipment to do just that, using holographic projection into the brain to activate or suppress dozens and ultimately thousands of neurons at once, hundreds of times each second, copying real patterns of brain activity to fool the brain into thinking it has felt, seen or sensed something.

Video showing neuron activity in three layers of a small chunk of the somatosensory cortex of a mouse’s brain. Activated neurons fluoresce green. Those neurons that are activated by holographic laser light are indicated by a purple arrow. Projected via a microscope through a window into the brain, the holographic system can activate neurons to simulate real brain activity and insert false sensations. (UC Berkeley video by Stephen McNally and Roxanne Makasdjian using Alan Mardinly footage)

The goal is to read neural activity constantly and decide, based on the activity, which sets of neurons to activate to simulate the pattern and rhythm of an actual brain response, so as to replace lost sensations after peripheral nerve damage, for example, or control a prosthetic limb.

“This has great potential for neural prostheses, since it has the precision needed for the brain to interpret the pattern of activation. If you can read and write the language of the brain, you can speak to it in its own language and it can interpret the message much better,” said Alan Mardinly, a postdoctoral fellow in the UC Berkeley lab of Hillel Adesnik, an assistant professor of molecular and cell biology. “This is one of the first steps in a long road to develop a technology that could be a virtual brain implant with additional senses or enhanced senses.”

Mardinly is one of three first authors of a paper appearing online April 30 in advance of publication in the journal Nature Neuroscience that describes the holographic brain modulator, which can activate up to 50 neurons at once in a three-dimensional chunk of brain containing several thousand neurons, and repeat that up to 300 times a second with different sets of 50 neurons.

“The ability to talk to the brain has the incredible potential to help compensate for neurological damage caused by degenerative diseases or injury,” said Ehud Isacoff, a UC Berkeley professor of molecular and cell biology and director of the Helen Wills Neuroscience Institute, who was not involved in the research project. “By encoding perceptions into the human cortex, you could allow the blind to see or the paralyzed to feel touch.”

Holographic projection

Each of the 2,000 to 3,000 neurons in the chunk of brain was outfitted with a protein that, when hit by a flash of light, turns the cell on to create a brief spike of activity. One of the key breakthroughs was finding a way to target each cell individually without hitting all at once.

To focus the light onto just the cell body — a target smaller than the width of a human hair — of nearly all cells in a chunk of brain, they turned to computer generated holography, a method of bending and focusing light to form a three-dimensional spatial pattern. The effect is as if a 3D image were floating in space.

In this case, the holographic image was projected into a thin layer of brain tissue at the surface of the cortex, about a tenth of a millimeter thick, though a clear window into the brain.

“The major advance is the ability to control neurons precisely in space and time,” said postdoc Nicolas Pégard, another first author who works both in Adesnik’s lab and the lab of co-author Laura Waller, an associate professor of electrical engineering and computer sciences. “In other words, to shoot the very specific sets of neurons you want to activate and do it at the characteristic scale and the speed at which they normally work.”

The researchers have already tested the prototype in the touch, vision and motor areas of the brains of mice as they walk on a treadmill with their heads immobilized. While they have not noted any behavior changes in the mice when their brain is stimulated, Mardinly said that their brain activity — which is measured in real-time with two-photon imaging of calcium levels in the neurons — shows patterns similar to a response to a sensory stimulus. They’re now training mice so they can detect behavior changes after stimulation.

Prosthetics and brain implants

The area of the brain covered — now a slice one-half millimeter square and one-tenth of a millimeter thick — can be scaled up to read from and write to more neurons in the brain’s outer layer, or cortex, Pégard said. And the laser holography setup could eventually be miniaturized to fit in a backpack a person could haul around.

Mardinly, Pégard and the other first author, postdoc Ian Oldenburg, constructed the holographic brain modulator by making technological advances in a number of areas. Mardinly and Oldenburg, together with Savitha Sridharan, a research associate in the lab, developed better optogenetic switches to insert into cells to turn them on and off. The switches — light-activated ion channels on the cell surface that open briefly when triggered — turn on strongly and then quickly shut off, all in about 3 milliseconds, so they’re ready to be re-stimulated up to 50 or more times per second, consistent with normal firing rates in the cortex.

Pégard developed the holographic projection system using a liquid crystal screen that acts like a holographic negative to sculpt the light from 40W lasers into the desired 3D pattern. The lasers are pulsed in 300 femtosecond-long bursts every microsecond. He, Mardinly, Oldenburg and their colleagues published a paper last year describing the device, which they call 3D-SHOT, for three-dimensional scanless holographic optogenetics with temporal focusing.

“This is the culmination of technologies that researchers have been working on for a while, but have been impossible to put together,” Mardinly said. “We solved numerous technical problems at the same time to bring it all together and finally realize the potential of this technology.”

As they improve their technology, they plan to start capturing real patterns of activity in the cortex in order to learn how to reproduce sensations and perceptions to play back through their holographic system.

Learn more: Editing brain activity with holography

 

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