In the carefully processed waveguide, the light wave produces a band pattern (middle), but due to the different width of the waveguide, a light wave of a specific wavelength can propagate infinitely fast, thereby illuminating the entire waveguide.

A research team composed of physicists and engineers recently announced that in a nanoscale device, the speed of visible light can reach infinitely fast. Of course, this small invention will not bring instant communication, and the famous speed limit proposed in Einstein's theory of relativity is still valid, but this little thing will have various uses, including acting as a Elements.

In a vacuum, light travels at a speed of about 300 million meters / second. In materials such as glass, the propagation speed will be slower. However, scientists can use strange methods to manipulate the interaction of light and matter to adjust the refractive index of light, for example, to make it negative, which can cause light to bend.

"Science" magazine reported online that now, the Netherlands Institute of Atomic and Molecular Physics physicist Albert Polman, the University of Pennsylvania electrical engineer Nader Engheta and colleagues have achieved a very strange "feat."

They invented a tiny device, where the refractive index of visible light is zero, so the light wave propagates rapidly at a particular wavelength, and the speed even reaches infinitely fast.

The device consists of a rectangular rod of insulating silicon dioxide that is 85 nanometers thick and 2000 nanometers long and is surrounded by silver. Light usually cannot penetrate this rectangular rod. The result is an optical transmission space called a waveguide.

The researchers also made different devices with silica widths ranging from 120 nanometers to 400 nanometers, and published the research results in the "Physical Review Letters."

Here, light behaves differently, because the electromagnetic field must obey certain "boundary conditions". Generally speaking, when the peaks and troughs of oppositely propagating light waves overlap, bright and dark bands are produced. Once the cutoff wavelength is correct, interesting things happen. At that time, the entire waveguide was illuminated instead of producing a stripe pattern. Therefore, the light oscillates synchronously along the length of the waveguide.

Previously, the research team led by Engheta had also produced zero refractive index for longer wavelength radiation. However, repeating this work on visible light is more difficult because the device is too small to accommodate the light source.

Therefore, the researchers generated all wavelengths of light in the waveguide by hitting an electron beam, and measured the amount of light leaked. The researchers found that the amount of light radiated at a particular wavelength depends on whether the electron beam enters a certain point, where there may be a bright or dark spot for this wavelength. So by scanning the electron beam along the waveguide and detecting the output, the researchers tracked the light image at each wavelength.

Why does this phenomenon not violate the theory of relativity? Because light has two speeds, Engheta explained. "Phase velocity" refers to how fast a given wavelength propagates, while "group velocity" refers to how fast light can carry energy or information. Only the group velocity must be slower than the speed of light traveling in a vacuum.

The device will have multiple uses, Engheta said, and it can help make the desired nanoscale optical circuit catheter.

A batch of such waveguides can even produce a loose material with zero refractive index. However, making this arrangement can be very challenging. Wenshan Cai, an electrical engineer at the Georgia Institute of Technology in the United States, said: "It is simple in theory, but difficult to operate.

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