New way to filter light

(new version) - New way to filter light: For the first time, it can provide a selective way of direct light waves.

Light waves can be filtered based on three basic properties, namely color (or wavelength length), polarization and direction of light. While it has long been possible to selectively filter light based on its color and polarization, however, choosing based on light direction is still a difficulty.

But now, MIT technology scientists have invented a system for the first time, allowing all the light of every color to pass through only when it comes from a particular angle. This technique reflects all the light coming from other directions. This new approach could lead to new advances in solar photovoltaic technology, telescopes and microscopes, and separate filters for display screens.

This study was described in an article published this week in the Science magazine, by MIT graduate student Yichen Shen, professor of physics Marin Soljačić and four other scientists.'We are very excited about this discovery, as it is a basic building block in our ability to control light '.

The new structure consists of a stack of ultrathin layers of alternating materials where the thickness of each layer is precisely controlled.'When you have 2 materials, then at the intersection of the two materials you will have the reflection ' Soljačić explained. But at these common surfaces, 'there is a magic angle named Brewster 's angle , and when the light enters that corner and the polarization is correct, it will not be reflected'.

While the total amount of reflected light at each of these common surfaces is very small, by combining multiple layers of material with the same properties, most of the light can be reflected - except in the case of light. correct that angle and the polarity correctly.

By using a layer of about 80 layers of accurate thickness material, Shen said, 'We can reflect light at most corners, over a very wide range of colors: the entire luster frequency. The light is visible to the naked eye '.

Previous research has demonstrated how to reflect light selectively except for a precise angle, but those approaches are limited by a narrow range of colors of light. The expansion of the new system could open up many potential applications, the team said.

Shen said: 'This research can have excellent applications in the field of energy, and especially in thermophotovoltaic ' , harnessing solar energy by using sunlight to do Heat a material, then emit light with specific colors. That light emission can be exploited using an adjustable photovoltaic cell to maximize the use of that color of light. But for this approach, to operate it is necessary to limit heat and light from reflections, and re-emit, so the ability to control selectively those reflexes can lift High efficiency.

These findings can be very useful in optical systems, such as microscopes and telescopes, to help see faint objects near brighter objects - for example, when a planet Bright dimming beside a bright star. By using a single light receiving system from a certain angle , these devices can improve the ability to detect unclear targets. Filtering can also be applied to the display of the phone or computer, so that only the viewers from the front of the screen can view it directly.

In principle, selection of angles can be made more elaborate simply by adding more layers of stack, the researchers say. For the experiments performed so far, the selection angle is about 10 degrees, 90% of incident light in this corner has passed through the system.

While these experiments were conducted using layers of glass and titanium oxide, Shen said, in principle, any two materials with different refractive indices could be used.

John Pendry, a professor at Imperial College London, who was not involved in the study, called the study a 'clever application'.

'On a macro scale, this is equivalent to observing the world through a set of louvers . that only allows light to enter from one direction,' Pendry said. 'However, this new device is much more sophisticated, operating on the length of the wavelength of light'.

The team also includes scientists at MIT Research Institute Ivan Celanovic; Steven Johnson, John Joannopoulos, Francis Davis Wright professor of physics and Dexin Ye of Zhejiang University in China. The research was partially supported by the Army Research Office, through the MIT S3TEC Energy Research Frontier Center.