Glasses-Free 3-D From Almost Any Angle

Grid of gratings could create 3-D displays for smartphones and other small devices

4 min read
A transparent prototype display from HP Labs produces glasses-free 3-D images over a 90-degree field of view.
Photo: Kar Han Tan

03NW3DPhonesf1Levitating Logo: A transparent prototype display from HP Labs produces glasses-free 3-D images over a 90-degree field of view.Photo: Kar Han Tan

A relatively simple way of controlling the direction of light could lead to effective, inexpensive glasses-free 3-D screens for cellphones or tablets that function over a wide field of view, say researchers who developed the technique.

“We designed this technology to be particularly well-suited for mobile applications,” says David Fattal, a researcher in the Information and Quantum Systems Lab at Hewlett-Packard Laboratories, in Palo Alto, Calif. Fattal was speaking during a telephone press briefing on the project, which was described in a paper published in Nature yesterday.

Three-dimensional displays work by delivering images with a slight spatial offset to each of the viewer’s eyes. In the days of movies like Creature From the Black Lagoon, that meant showing overlapping red and blue images, each of which was blocked from one eye by glasses with a red filter and a blue filter. Modern autostereoscopic—or glasses-free—displays use a variety of techniques to deliver dual images, but they often require the viewer to be in just the right spot, and they’re too bulky for something as small as a cellphone screen. Holography can also produce a 3-D image, but currently that technology works too slowly for video.

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Video: Fattal et al, Nature

The HP team started with a standard LED backlight, in which light from LEDs arrayed along the side of a device are delivered through light guides to a plane behind a liquid crystal display. On top of the light guide, the team added a grid of diffraction gratings, each with one of 192 different combinations of pitches and orientations, to act as individual pixels. A portion of the light traveling through the waveguide exits through each of the gratings and is sent in a slightly different direction. By modulating the light going to each grating, the researchers produced a series of images each angled to produce a 3-D picture from a different point of view.

Other displays, such as that of the Nintendo 3DS, produce 3-D images from just two points of view. But this new technique can produce images from 64 points of view. The images are spaced close enough together to allow the viewer to experience a smooth transition from one to another and to see them through a 90-degree field of view. “It’s like having 64 displays running in parallel,” Fattal says. “You actually see the object really extruded up to a centimeter either in front [of] or below the screen of the display.” Someone viewing an image of the globe could see all of the continents simply by moving her head, he says.

03NW3DPhonesf2Grid of Gratings: Gratings of different pitches and orientations cast light to form up to 64 images, producing the illusion of 3-D viewable from a variety of angles.Image: Albert Jeans

“We do want to re-create the feeling that you have a virtual object coming out of the screen in front of you, so we don’t want it to disappear as soon as you tilt your head,” Fattal adds.

The actual prototype the researchers built, which they used to display a 3-D HP logo as well as a video of a turtle swimming, produced still images with 64 points of view and video images for 14. Fattal says it shouldn’t be technically difficult to increase the number of images.

The display was also dim, because the light from each LED is divided among the gratings, so each individual image receives only a fraction of it. Fattal says they used inexpensive LEDs in their prototype, but better LEDs, in which the light is distributed over a narrower range of angles, will help increase brightness. The design allows red, green, or blue light to be delivered to each pixel, removing the need for a typical LCD’s color filters, which would further dim the output. The lack of filters also means the display can be transparent. The team is exploring applying their technique to other systems besides LCDs, although Fattal wouldn’t say what those are.

Raymond Beausoleil, another researcher on the project, says he can’t speculate on when or if such a display would be commercially available. Some sort of static, decorative display might be possible in the short term, he says. “Something that would work at, let’s say, the tablet level would require a fairly significant investment and a lot of engineering,” he points out.

“This is a really exciting technology,” says Gordon Wetzstein, a postdoctoral researcher in MIT’s Media Lab who also devises 3-D displays. He says the HP technology may work best when combined with a sophisticated computer algorithm for creating moving images. “I believe it to be the first step toward practical, glasses-free 3-D displays in small form factors.”

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Video: Fattal et al, Nature

About the Author

Neil Savage, based in Lowell, Mass., writes about strange semiconductors, unusual optoelectronics, and other things. In the April 2013 issue he reports on a breakthrough that could lead to a way to combined CT scanners and MRI machines.

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The Inner Beauty of Basic Electronics

Open Circuits showcases the surprising complexity of passive components

5 min read
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A photo of a high-stability film resistor with the letters "MIS" in yellow.
All photos by Eric Schlaepfer & Windell H. Oskay
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Eric Schlaepfer was trying to fix a broken piece of test equipment when he came across the cause of the problem—a troubled tantalum capacitor. The component had somehow shorted out, and he wanted to know why. So he polished it down for a look inside. He never found the source of the short, but he and his collaborator, Windell H. Oskay, discovered something even better: a breathtaking hidden world inside electronics. What followed were hours and hours of polishing, cleaning, and photography that resulted in Open Circuits: The Inner Beauty of Electronic Components (No Starch Press, 2022), an excerpt of which follows. As the authors write, everything about these components is deliberately designed to meet specific technical needs, but that design leads to “accidental beauty: the emergent aesthetics of things you were never expected to see.”

From a book that spans the wide world of electronics, what we at IEEE Spectrum found surprisingly compelling were the insides of things we don’t spend much time thinking about, passive components. Transistors, LEDs, and other semiconductors may be where the action is, but the simple physics of resistors, capacitors, and inductors have their own sort of splendor.

High-Stability Film Resistor

A photo of a high-stability film resistor with the letters "MIS" in yellow.

All photos by Eric Schlaepfer & Windell H. Oskay

This high-stability film resistor, about 4 millimeters in diameter, is made in much the same way as its inexpensive carbon-film cousin, but with exacting precision. A ceramic rod is coated with a fine layer of resistive film (thin metal, metal oxide, or carbon) and then a perfectly uniform helical groove is machined into the film.

Instead of coating the resistor with an epoxy, it’s hermetically sealed in a lustrous little glass envelope. This makes the resistor more robust, ideal for specialized cases such as precision reference instrumentation, where long-term stability of the resistor is critical. The glass envelope provides better isolation against moisture and other environmental changes than standard coatings like epoxy.

15-Turn Trimmer Potentiometer

A photo of a blue chip
A photo of a blue chip on a circuit board.

It takes 15 rotations of an adjustment screw to move a 15-turn trimmer potentiometer from one end of its resistive range to the other. Circuits that need to be adjusted with fine resolution control use this type of trimmer pot instead of the single-turn variety.

The resistive element in this trimmer is a strip of cermet—a composite of ceramic and metal—silk-screened on a white ceramic substrate. Screen-printed metal links each end of the strip to the connecting wires. It’s a flattened, linear version of the horseshoe-shaped resistive element in single-turn trimmers.

Turning the adjustment screw moves a plastic slider along a track. The wiper is a spring finger, a spring-loaded metal contact, attached to the slider. It makes contact between a metal strip and the selected point on the strip of resistive film.

Ceramic Disc Capacitor

A cutaway of a Ceramic Disc Capacitor
A photo of a Ceramic Disc Capacitor

Capacitors are fundamental electronic components that store energy in the form of static electricity. They’re used in countless ways, including for bulk energy storage, to smooth out electronic signals, and as computer memory cells. The simplest capacitor consists of two parallel metal plates with a gap between them, but capacitors can take many forms so long as there are two conductive surfaces, called electrodes, separated by an insulator.

A ceramic disc capacitor is a low-cost capacitor that is frequently found in appliances and toys. Its insulator is a ceramic disc, and its two parallel plates are extremely thin metal coatings that are evaporated or sputtered onto the disc’s outer surfaces. Connecting wires are attached using solder, and the whole assembly is dipped into a porous coating material that dries hard and protects the capacitor from damage.

Film Capacitor

An image of a cut away of a capacitor
A photo of a green capacitor.

Film capacitors are frequently found in high-quality audio equipment, such as headphone amplifiers, record players, graphic equalizers, and radio tuners. Their key feature is that the dielectric material is a plastic film, such as polyester or polypropylene.

The metal electrodes of this film capacitor are vacuum-deposited on the surfaces of long strips of plastic film. After the leads are attached, the films are rolled up and dipped into an epoxy that binds the assembly together. Then the completed assembly is dipped in a tough outer coating and marked with its value.

Other types of film capacitors are made by stacking flat layers of metallized plastic film, rather than rolling up layers of film.

Dipped Tantalum Capacitor

A photo of a cutaway of a Dipped Tantalum Capacitor

At the core of this capacitor is a porous pellet of tantalum metal. The pellet is made from tantalum powder and sintered, or compressed at a high temperature, into a dense, spongelike solid.

Just like a kitchen sponge, the resulting pellet has a high surface area per unit volume. The pellet is then anodized, creating an insulating oxide layer with an equally high surface area. This process packs a lot of capacitance into a compact device, using spongelike geometry rather than the stacked or rolled layers that most other capacitors use.

The device’s positive terminal, or anode, is connected directly to the tantalum metal. The negative terminal, or cathode, is formed by a thin layer of conductive manganese dioxide coating the pellet.

Axial Inductor

An image of a cutaway of a Axial Inductor
A photo of a collection of cut wires

Inductors are fundamental electronic components that store energy in the form of a magnetic field. They’re used, for example, in some types of power supplies to convert between voltages by alternately storing and releasing energy. This energy-efficient design helps maximize the battery life of cellphones and other portable electronics.

Inductors typically consist of a coil of insulated wire wrapped around a core of magnetic material like iron or ferrite, a ceramic filled with iron oxide. Current flowing around the core produces a magnetic field that acts as a sort of flywheel for current, smoothing out changes in the current as it flows through the inductor.

This axial inductor has a number of turns of varnished copper wire wrapped around a ferrite form and soldered to copper leads on its two ends. It has several layers of protection: a clear varnish over the windings, a light-green coating around the solder joints, and a striking green outer coating to protect the whole component and provide a surface for the colorful stripes that indicate its inductance value.

Power Supply Transformer

A photo of a collection of cut wires
A photo of a yellow element on a circuit board.

This transformer has multiple sets of windings and is used in a power supply to create multiple output AC voltages from a single AC input such as a wall outlet.

The small wires nearer the center are “high impedance” turns of magnet wire. These windings carry a higher voltage but a lower current. They’re protected by several layers of tape, a copper-foil electrostatic shield, and more tape.

The outer “low impedance” windings are made with thicker insulated wire and fewer turns. They handle a lower voltage but a higher current.

All of the windings are wrapped around a black plastic bobbin. Two pieces of ferrite ceramic are bonded together to form the magnetic core at the heart of the transformer.

This article appears in the February 2023 print issue.

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