Metamaterials are materials that change the direction of light, greatly improving people's ability to control light. Recently, scientists from the National Institute of Standards and Technology (NIST) used silver, glass, and chromium to create a nanostructured new metamaterial. As a "one-way street" of visible light, it can almost completely stop light transmission in one direction, while the other direction makes light unobstructed. Researchers believe that this "one-way light path" is expected to play an important role in optical information processing and new biosensor devices.
At present, many nanostructured metamaterials can also allow microwaves or infrared light to propagate in one direction in a medium. However, unidirectional transmission of visible light has not been realized so far because existing devices are too large with respect to visible light to control visible wavelengths. . The so-called "one-way mirror" does not allow light to propagate in one direction, but is a half-mirror, which causes a visual difference by transmitting and reflecting light intensity differences on both sides.
NIST researchers Xu Ting and Han Lei Lizek combined two types of light-controlled nanostructures: a layer of silver-stacked “thousand-layer cake†made of glass and a fence made of chrome metal. According to the physicist's organization network on July 2 (Beijing time), the silver-glass structure is a typical "hypersurface" dielectric material that can handle light in different ways according to the direction of light. Since the material layer is extremely thin, only a few tens of nanometers, and the visible light wavelength is between 400 nanometers and 700 nanometers, the material is opaque to the visible light from the outside. Within the material, the light can propagate through a narrow angular range.
They used a thin-film deposition technique to create a metamaterial consisting of 20 layers of ultra-thin silica glass and silver alternately, and then added a set of “chrome grids†on both sides of the material, while the gap between the grids was smaller than the wavelength of the incident light. The incident light can be redirected only in the interior of the material; the other side of the “chrome grid†can reflect the light to be emitted back into the material. Although the second group of "chrome grids" did not completely prevent the light from "escaping," the detected light propagated in the forward direction was about 30 times larger than the light returned in the reverse direction, which surpassed any other similar materials in the existing.
The use of existing methods to make this bonding material is the key to achieving unidirectional transmission of visible light. Lizek said that if there is no silver-glass block, the "chromium gate" should be arranged more finely, which is beyond the level that can be achieved by the prior art.
These materials are promising in the field of optical communications, such as integrating them into photonic chips to separate or combine signals carried by light waves. In addition, it can also be used in the field of biosensing to detect tiny particles. Nanoparticles act like "chromium gratings," and can also redirect light through the material and out the other end, thereby acting as a detector. Lizick said: "This is a very cool device. Even if it has tiny particles on the surface, the light propagation will greatly change." (Reporter Chang Lijun)
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