Echoless Light Observed For The First Time

EWS light modes inside an optic fiber / CUDOS

For the first time, scientists have observed an echoless state of light, something that could improve the quality of signals in technologies such as Wi-Fi routers, mobile phones, and lasers. On top of that, it could be used in several medical applications.

The phenomenon, known as Eisenbud-Wigner-Smith (EWS) states, was first theorized in 1948. A wave in this state will reach its destination unchanged, independently of the scattering it might have experienced during transmission.

The researchers, from the ARC Centre for Ultrahigh bandwidth Devices for Optical Systems (CUDOS), have drawn similarities between light used in the experiment to shouting a message through a tunnel. The sound waves would bounce off the tunnel walls, creating echoes and interfering with themselves. The final result would be a message significantly less clear.

The same happens to light in optical fibers. Optical fibers are used in telecommunication because they permit transmission over a longer distance and at higher data rates than wire cables, which can lead to losses in signal strength due to heat dispersion. Optical fibers are used because light bounces around inside them and only a tiny fraction is lost. This internal reflection does, however, create echo-like distortions that reduce the quality of the signal received. A light pulse in this special EWS-state always arrives intact to the receiver no matter what might have happened in its journey through the optical fiber.

"There's a lot of applications where you want to send light through something complicated and have all the light arrive at the same time at the other end." Dr. Joel Carpenter, one of the researchers that developed this experiment, told IFLScience. "For example, in a high-power laser, you want to split the light up inside the laser itself so it doesn't blow up, but at the output/target you want the opposite; all the light to arrive at the same place at the same time."

The EWS states were produced experimentally by using a spatial light modulator that is able to control the amplitude, phase and polarization of light pulses. 

This phenomenon could also have important medical applications, such as in endoscopy, which uses microfibers to look at areas difficult to see in the body without major surgery. Light traveling through such fibers gets significant distortions, making it difficult for images to be interpreted. The EWS-states were demonstrated in super-thin microfibers, about 100 microns thick (around the width of a strand of hair), which are used in biomedical imaging. Using these special light pulses, doctors would be able to see better quality images of a patient's internal organs.    

The team also included Professor Benjamin Eggleton from the University of Sydney and Dr. Jochen Schröder from RMIT University. The paper can be read in the journal Nature Photonics.

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