Two holograms in one surface

December 11, 2017

A team at Caltech has figured out a way to encode more than one holographic image in a single surface without any loss of resolution. The engineering feat overturns a long-held assumption that a single surface could only project a single image regardless of the angle of illumination.

The technology hinges on the ability of a carefully engineered surface to reflect light differently depending on the angle at which incoming light strikes that surface.

Holograms are three-dimensional images encoded in two-dimensional surfaces. When the surface is illuminated with a laser, the image seems to pop off the surface and becomes visible. Traditionally, the angle at which laser light strikes the surface has been irrelevant--the same image will be visible regardless. That means that no matter how you illuminate the surface, you will only create one hologram.

Led by Andrei Faraon, assistant professor of applied physics and materials science in the Division of Engineering and Applied Science, the team developed silicon oxide and aluminum surfaces studded with tens of millions of tiny silicon posts, each just hundreds of nanometers tall. (For scale, a strand of human hair is 100,000 nanometers wide.) Each nanopost reflects light differently due to variations in its shape and size, and based on the angle of incoming light.

That last property allows each post to act as a pixel in more than one image: for example, acting as a black pixel if incoming light strikes the surface at 0 degrees and a white pixel if incoming light strikes the surface at 30 degrees.

"Each post can do double duty. This is how we're able to have more than one image encoded in the same surface with no loss of resolution," says Faraon (BS '04), senior author of a paper on the new material published by Physical Review X on December 7.

"Previous attempts to encode two images on a single surface meant arranging pixels for one image side by side with pixels for another image. This is the first time that we're aware of that all of the pixels on a surface have been available for each image," he says.

As a proof of concept, Faraon and Caltech graduate student Seyedeh Mahsa Kamali (MS '17) designed and built a surface that when illuminated with a laser straight on (thus, at 0 degrees) projects a hologram of the Caltech logo but when illuminated from an angle of 30 degrees projects a hologram of the logo of the Department of Energy-funded Light-Material Interactions in Energy Conversion Energy Frontier Research Center, of which Faraon is a principal investigator.

The process was labor intensive. "We created a library of nanoposts with information about how each shape reflects light at different angles. Based on that, we assembled the two images simultaneously, pixel by pixel," says Kamali, the first author of the Physical Review X paper.

Theoretically, it would even be possible to encode three or more images on a single surface--though there will be fundamental and practical limits at a certain point. For example, Kamali says that a single degree of difference in the angle of incident light probably cannot be enough to create a new high-quality image. "We are still exploring just how far this technology can go," she says.

Practical applications for the technology include improvements to virtual-reality and augmented-reality headsets. "We're still a long way from seeing this on the market, but it is an important demonstration of what is possible," Faraon says.
-end-
The research was published in a paper titled "Angle-Multiplexed Metasurfaces: Encoding Independent Wavefronts in a Single Metasurface under Different Illumination Angles." Faraon and Kamali's coauthors include Caltech graduate students Ehsan Arbabi (MS '17), Yu Horie, and Mohammad Sadegh Faraji-Dana; and Amir Arbabi of the University of Massachusetts Amherst. This work was supported by the Department of Energy, the Defense Advanced Research Projects Agency, and Samsung Electronics.

California Institute of Technology

Related Laser Articles from Brightsurf:

Laser technology: New trick for infrared laser pulses
For a long time, scientists have been looking for simple methods to produce infrared laser pulses.

Sensors get a laser shape up
Laser writing breathes life into high-performance sensing platforms.

Laser-powered nanomotors chart their own course
The University of Tokyo introduced a system of gold nanorods that acts like a tiny light-driven motor, with its direction of motion is determined by the orientation of the motors.

What laser color do you like?
Researchers at the National Institute of Standards and Technology (NIST) and the University of Maryland have developed a microchip technology that can convert invisible near-infrared laser light into any one of a panoply of visible laser colors, including red, orange, yellow and green.

Laser technology: The Turbulence and the Comb
While the light of an ordinary laser only has one single, well-defined wavelength, a so-called ''frequency comb'' consists of different light frequencies, which are precisely arranged at regular distances, much like the teeth of a comb.

A laser for penetrating waves
The 'Landau-level laser' is an exciting concept for an unusual radiation source.

Laser light detects tumors
A team of researchers from Jena presents a groundbreaking new method for the rapid, gentle and reliable detection of tumors with laser light.

The first laser radio transmitter
For the first time, researchers at Harvard School of Engineering have used a laser as a radio transmitter and receiver, paving the way for towards ultra-high-speed Wi-Fi and new types of hybrid electronic-photonic devices.

The random anti-laser
Scientists at TU Wien have found a way to build the 'opposite' of a laser -- a device that absorbs a specific light wave perfectly.

Laser 'drill' sets a new world record in laser-driven electron acceleration
Combining a first laser pulse to heat up and 'drill' through a plasma, and another to accelerate electrons to incredibly high energies in just tens of centimeters, scientists have nearly doubled the previous record for laser-driven particle acceleration at Berkeley Lab's BELLA Center.

Read More: Laser News and Laser Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.