Researchers Discover the Behavior of Light in Complex Media

Researchers have made a new discovery on how light behaves in complex media, media that tends to significantly distort light has been designed by a group led by researchers at the University of the Witwatersrand in Johannesburg, South Africa, with collaborators from the University of Pretoria (South Africa), as well as Mexico and Scotland.

By laying down a straightforward rule that is applicable to all light and a wide range of media, encompassing underwater, optical fiber, transmission in the atmosphere, and even through living biological samples, they showed that “distortion” is a question of perspective.

Their cutting-edge quantum approach to the issue settles a long-running argument about whether or not particular types of light are resilient, clearing up some common misconceptions.

The experiment also highlights the fact that all light has a character that never changes, which is a vital realization for understanding the remainder of the apparent distortion. The researchers used the result for error-free communication via noisy channels to demonstrate resilient transport through otherwise severely distorted systems.

The study conducted by the Wits team, led by Professor Andrew Forbes from the School of Physics at Wits University, was published online on 24^th June 2022 in Nature Photonics. The team explains the straightforward laws that control complicated light propagation in complex media in their study titled “Revealing the invariance of vectorial structured light in complex media.”

At first, they discovered that all such media can be handled uniformly and that the analysis is independent of the light source. Before, each type of medium and light beam was considered a special case, but now everything is covered by the new general theory.

Furthermore, they established that a property of light called “vectorness” remains constant and independent of the media despite distortion. This has never been acknowledged, yet is always true. It bears the secret of utilizing light even in less than perfect circumstances.

Light becomes warped as it travels through an unreliable medium, like the atmosphere. Examples of light that is warped by the turbulence of the atmosphere include the twinkling of stars or the shimmering mirage effect near scorching highways.

Light can also occasionally be purposefully bent, like the fun-fair mirrors that make one appear taller, leaner, or rounder. It can be agreed that this distortion is only a question of perspective as all it takes is a short glance in the mirror to expose the truth.

However, is this also true for other distorting systems? Is there a method to gaze at the light that will eliminate the distortion?

The Wits-led research demonstrates that while certain qualities can be unraveled by shifting perspectives, others are never actually altered.

How can one comprehend what transpires to the light, how it gets distorted, and how can one arrive at a fresh viewpoint? The researchers employed vectorial light, the most generic type of light, to provide answers to these queries. Light has an electric field that occasionally points up, down, left, right, and in other directions throughout the field.

The “vectorness” of light refers to how erratic its electric field’s direction is. In other terms, it is a measurement of how comparable the electric field directions of light are at various locations: if they are uniform throughout (homogenous), the value is 0, and if they are inconsistent throughout (inhomogeneous), the value is 1.

Even if the shape of the electric field itself varies, this vectorial homogeneity remains constant. The cause is embedded in quantum entangled states — a topic that seemingly has less in common with optical distortions. By using tools from the quantum realm to study optical aberrations, the new finding was made feasible.

What we have found is that the vectorness is the single attribute of light that does not alter when passing through any complex media. This means we have something special that can be exploited when using light for communications or sensing.

Andrew Forbes, Professor, School of Physics, University of the Witwatersrand in Johannesburg

Forbes added, “This is a particular aspect of the pattern of the light—how the polarization pattern look. The ‘polarization’ is just a fancy way to describe the direction of the electric field that makes up light. The pattern is also distorted, but its intrinsic nature (of homogeneous or inhomogeneous) is not.”

The team’s method enables researchers to determine how to neutralize any media-related distortions in a cost-free manner. To put it another way, there is no harm.

“We show that even though the light is very distorted, the distortion is only a matter of perspective. One can view the light in such a way that it regains its original ‘undistorted’ properties. It is remarkable that complex light in complex media can be universally understood from very simple rules”, further stated Forbes.

For instance, any communications over a highly distorted media might be made “distortion free” by altering how a measurement is done. This was demonstrated experimentally by the researchers using a variety of systems, including liquid, optical fiber, and turbulence.

Journal Reference:

Nape, I., et al. (2022) Revealing the invariance of vectorial structured light in complex media. Nature Photonics. doi:10.1038/s41566-022-01023-w.

Source: https://www.wits.ac.za/