Scientists have invented a “Mirror” that reverses electromagnetic waves in time
Through the Looking Glass: Scientists at the City University of New York (CUNY) have created a “mirror” capable of reflecting an electromagnetic wave back in time. This is not the first time this has been done, but for signals in this frequency range this is a breakthrough. The team hopes the research will pave the way for ultra-fast communication and computing applications using light.
Mirror that the CUNY team built doesn’t look like your bathroom mirror, but works similarly. Therefore, it is useful to return to the reflection of light in order to better understand the mechanics.
Light in the visible spectrum allows us to see objects and their colors. The color we see is the wavelength reflected from the object, while the rest of the frequencies are absorbed. The entire spectrum is reflected from white-colored objects, but only to some extent – in most cases, about 80-90 percent.
A home mirror creates a non-uniformity that reflects 100 percent white light, so the image looks like what’s in front of it, but spatially inverted. In other words, left-right, or what we call a mirror image. Wavelengths are reflected without diffusion, so they hit your eye at the same frequency as a mirror.
“Light bounces off a mirror because the impedance of the mirror material is very different from air resistance, so waves hitting the mirror have to bounce back, they can’t penetrate the mirror,” study co-author Andrea Alu told Motherboard. .
What is CUNY created it is a mirror that reverses the waves in time. Thus, if the signal reaches the mirror at 1234, it is reflected as 4321. To apply what this means to our bathroom mirror, imagine that it reflects the image that a camera filming you from behind would produce. You would see the back of your head, and your right would be the right of your mirror image.
However, this is not the only difference, because now the mirror will reflect the light waves back, so that all colors will be spoiled. Orange will look blue, yellow will look purple, and red will look green. But this is just a thought experiment by analogy with mechanics.
The mirror created by scientists does not reflect visible light. It operates at much lower frequencies. In fact, it’s just a board with a built-in strip of metal with numerous switches woven into it, turning it into a “metamaterial”. Switches can switch very quickly. When the frequency of the mirror is higher than the frequency of the incoming wave, it creates an impedance or discontinuity that reflects the stretched and inverted wave—signs of time reversal. They “see” this change by sending a known frequency at different amplitudes and measuring the reflection.
This time the reflection is not new. it is a form of modulation that scientists have been studying for about 60 years.
“It’s actually a very common operation. The reflection of time is actually the key to many technologies,” Alu said.
It was used for signal processing in radio communications to eliminate distortion and noise in signals. This processing is done digitally and assumes single frequency operation. What CUNY has done is to unwrap a wave of multiple frequencies without digitizing.
This research is a tiny step towards computers that use laser light to store and process data. However, this is far in the future. Switches in the metamaterial should be much, much, much faster.
“Our experiment shows that you can do this at almost any frequency,” Alu said. “[However,] usually the switching technology starts to break down when you go to terahertz frequencies.”
The current experiment is in the low gigahertz range. The team’s next task will be to experiment in the hundreds of GHz range. Even if they succeed in this higher range, they will still be far from the visible light frequencies of 400 THz. So don’t expect such a breakthrough. This is unlikely to happen in our lifetime, if at all.