This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Researchers from Graz University of Technology (TU Graz), Harvard and the University of Texas at Austin (UT Austin) have developed an innovative method for coupling light non-linearly. This opens up new possibilities for telecommunications and quantum technology.
Using a newly developed combination of a semiconductor layer and a metasurface, the research team has achieved a breakthrough in converting light into new frequencies. Their method transforms light around 72,000 times more efficiently than previous materials. The researchers published their findings in the journal Nature Nanotechnology.
Light is well-known as a medium for transmitting information; its linear propagation, for example, enables communication in modern fiber-optic networks. However, linear propagation is insufficient for complex computational operations, quantum technology and cryptography, or frequency combs for high-precision measurement technology. Here, non-linear polarization is required, enabling photons to interact with one another and exchange information.
"Traditionally, extended crystalline structures such as lithium niobate are used to couple light waves non-linearly," says Marcus Ossiander from the Institute of Experimental Physics at TU Graz. "However, this requires quite large volumes and a great deal of light energy, which has so far stood in the way of miniaturization and many applications. Our method makes it possible to generate non-linear polarization with light in smaller structures and with significantly less energy consumption." The starting point for developing the "light converter" was an idea from the research group led by Seth Bank at the University of Texas at Austin.
Using molecular beam epitaxy, they grew nanometer-scale semiconductor layers of gallium arsenide and aluminum gallium arsenide containing asymmetrically coupled quantum wells. These wells restrict the movement of electrons spatially to such an extent that quantized, atom-like states arise. Because the quantum wells are deliberately designed to be asymmetrical, the electrons move predominantly in one direction when exposed to light.
In this artificially created one-way street, asymmetric or non-linear electron oscillations build up, enabling light waves to interact with one another extremely efficiently. However, this development from Texas still had one limitation: To harness the full effect of the semiconductor layers, light had to propagate parallel to them, a configuration that is cumbersome in most applications. In technical implementations, the electrons would therefore not have moved along the artificial one-way street, and much of the non-linear effect would have been lost.
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