Featured Research

from universities, journals, and other organizations

New way to filter light: May provide first directional selectivity for light waves

Date:
March 27, 2014
Source:
Massachusetts Institute of Technology
Summary:
Light waves can be defined by three fundamental characteristics: their color (or wavelength), polarization, and direction. While it has long been possible to selectively filter light according to its color or polarization, selectivity based on the direction of propagation has remained elusive. But now, for the first time, researchers have produced a system that allows light of any color to pass through only if it is coming from one specific angle; the technique reflects all light coming from other directions.

In this photo of the angular-selective sample (the rectangular region), a beam of white light passes through as if the sample was transparent glass. The red beam, coming in at a different angle, is reflected away, as if the sample was a mirror. The other lines are reflections of the beams. (This setup is immersed in liquid filled with light-scattering ­particles to make the rays visible).
Credit: Weishun Xu and Yuhao Zhang

Light waves can be defined by three fundamental characteristics: their color (or wavelength), polarization, and direction. While it has long been possible to selectively filter light according to its color or polarization, selectivity based on the direction of propagation has remained elusive.

But now, for the first time, MIT researchers have produced a system that allows light of any color to pass through only if it is coming from one specific angle; the technique reflects all light coming from other directions. This new approach could ultimately lead to advances in solar photovoltaics, detectors for telescopes and microscopes, and privacy filters for display screens.

The work is described in a paper appearing this week in the journal Science, written by MIT graduate student Yichen Shen, professor of physics Marin Soljačić, and four others. "We are excited about this," Soljačić says, "because it is a very fundamental building block in our ability to control light."

The new structure consists of a stack of ultrathin layers of two alternating materials where the thickness of each layer is precisely controlled. "When you have two materials, then generally at the interface between them you will have some reflections," Soljačić explains. But at these interfaces, "there is this magical angle called the Brewster angle, and when you come in at exactly that angle and the appropriate polarization, there is no reflection at all."

While the amount of light reflected at each of these interfaces is small, by combining many layers with the same properties, most of the light can be reflected away -- except for that coming in at precisely the right angle and polarization.

Using a stack of about 80 alternating layers of precise thickness, Shen says, "We are able to reflect light at most of the angles, over a very broad band [of colors]: the entire visible range of frequencies."

Previous work had demonstrated ways of selectively reflecting light except for one precise angle, but those approaches were limited to a narrow range of colors of light. The new system's breadth could open up many potential applications, the team says.

Shen says, "This could have great applications in energy, and especially in solar thermophotovoltaics" -- harnessing solar energy by using it to heat a material, which in turn radiates light of a particular color. That light emission can then be harnessed using a photovoltaic cell tuned to make maximum use of that color of light. But for this approach to work, it is essential to limit the heat and light lost to reflections, and re-emission, so the ability to selectively control those reflections could improve efficiency.

The findings could also prove useful in optical systems, such as microscopes and telescopes, for viewing faint objects that are close to brighter objects -- for example, a faint planet next to a bright star. By using a system that receives light only from a certain angle, such devices could have an improved ability to detect faint targets. The filtering could also be applied to display screens on phones or computers, so only those viewing from directly in front could see them.

In principle, the angular selectivity can be made narrower simply by adding more layers to the stack, the researchers say. For the experiments performed so far, the angle of selectivity was about 10 degrees; roughly 90 percent of the light coming in within that angle was allowed to pass through.

While these experiments were done using layers of glass and tantalum oxide, Shen says that in principle any two materials with different refractive indices could be used.

John Pendry, a professor at Imperial College London who was not connected to this research, calls this an "ingenious application."

"On a macroscopic scale this is equivalent to observing the world through a set of louvers … that allow light to enter from one direction only," Pendry says. "However, the new device is infinitely more refined, operating as it does on the length scale of a wavelength."

The team also included MIT research scientist Ivan Celanovic; associate professor of mathematics Steven Johnson; John Joannopoulos, the Francis Wright Davis Professor of Physics; and Dexin Ye of Zhejiang University in China. The work was supported in part by the Army Research Office, through MIT's Institute for Soldier Nanotechnologies, and the U.S. Department of Energy, through the MIT S3TEC Energy Research Frontier Center.


Story Source:

The above story is based on materials provided by Massachusetts Institute of Technology. The original article was written by David Chandler. Note: Materials may be edited for content and length.


Journal Reference:

  1. Y. Shen, D. Ye, I. Celanovic, S. G. Johnson, J. D. Joannopoulos, M. Solja i . Optical Broadband Angular Selectivity. Science, 2014; 343 (6178): 1499 DOI: 10.1126/science.1249799

Cite This Page:

Massachusetts Institute of Technology. "New way to filter light: May provide first directional selectivity for light waves." ScienceDaily. ScienceDaily, 27 March 2014. <www.sciencedaily.com/releases/2014/03/140327142447.htm>.
Massachusetts Institute of Technology. (2014, March 27). New way to filter light: May provide first directional selectivity for light waves. ScienceDaily. Retrieved July 24, 2014 from www.sciencedaily.com/releases/2014/03/140327142447.htm
Massachusetts Institute of Technology. "New way to filter light: May provide first directional selectivity for light waves." ScienceDaily. www.sciencedaily.com/releases/2014/03/140327142447.htm (accessed July 24, 2014).

Share This




More Matter & Energy News

Thursday, July 24, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Robot Parking Valet Creates Stress-Free Travel

Robot Parking Valet Creates Stress-Free Travel

AP (July 23, 2014) — 'Ray' the robotic parking valet at Dusseldorf Airport in Germany lets travelers to avoid the hassle of finding a parking spot before heading to the check-in desk. (July 23) Video provided by AP
Powered by NewsLook.com
Boeing Ups Outlook on 52% Profit Jump

Boeing Ups Outlook on 52% Profit Jump

Reuters - Business Video Online (July 23, 2014) — Commercial aircraft deliveries rose seven percent at Boeing, prompting the aerospace company to boost full-year profit guidance- though quarterly revenues missed analyst estimates. Bobbi Rebell reports. Video provided by Reuters
Powered by NewsLook.com
Europe's Car Market on the Rebound?

Europe's Car Market on the Rebound?

Reuters - Business Video Online (July 23, 2014) — Daimler kicks off a round of second-quarter earnings results from Europe's top carmakers with a healthy set of numbers - prompting hopes that stronger sales in Europe will counter weakness in emerging markets. Hayley Platt reports. Video provided by Reuters
Powered by NewsLook.com
9/11 Commission Members Warn of Terror "fatigue" Among American Public

9/11 Commission Members Warn of Terror "fatigue" Among American Public

Reuters - US Online Video (July 22, 2014) — Ten years after releasing its initial report, members of the 9/11 Commission warn of the "waning sense of urgency" in combating terrorists attacks. Mana Rabiee reports. Video provided by Reuters
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins