Researchers made a new discovery about how light behaves in complex media, which distorts light significantly. They demonstrated that ‘distortion’ is a matter of perspective by laying out a simple rule that applies to all light and a wide range of media, including underwater, optical fiber, transmission in the atmosphere, and even transmission through living biological samples. Their novel quantum approach to the problem resolves a long-standing debate about whether some forms of light are robust or not, correcting some community misconceptions.
A team led by researchers at the University of the Witwatersrand in Johannesburg, South Africa, with collaborators from the University of Pretoria (South Africa), Mexico, and Scotland, has made a new discovery on how light behaves in complex media, which distorts light significantly. They demonstrated that “distortion” is a matter of perspective by laying out a simple rule that applies to all light and a wide range of media, including underwater, optical fiber, transmission in the atmosphere, and even through living biological samples.
Their novel quantum approach to the problem resolves a long-standing debate about whether some forms of light are robust or not, correcting some community misconceptions. Importantly, the work outlines that all light has an unchanging property, which holds the key to unraveling the rest of the perceived distortion. To validate the discovery, the team demonstrated robust transport through otherwise highly distorted systems, with the result used for error-free communication over noisy channels.
We discovered that the vectorness of light is the single attribute of light that does not change when it passes through any complex medium.
Professor Andrew Forbes
The Wits team’s research, led by Professor Andrew Forbes of Wits University’s School of Physics, was published online today in Nature Photonics. The team explains the simple rules that govern complex light propagation in complex media in their paper titled Revealing the invariance of vectorial structured light in complex media. For starters, they discover that all such media can be treated the same way, and that the analysis is independent of the type of light used. Previously, each medium and light beam configuration was treated as a separate case; this is no longer the case; the new general theory encompasses everything.
Secondly, they show that despite the distortion, there is a property of the light — its “vectorness” — that remains unchanged, invariant to the media. This is always true and had not been noticed before. It holds the key exploiting light even under non-ideal conditions.
Light is distorted when it passes through an imperfect medium, such as the atmosphere. For example, the shimmering mirage effect near hot roads or the twinkling of stars are both examples of light that becomes distorted due to atmospheric turbulence. Light can also be deliberately distorted, such as the mirrors at a fun fair that make you appear taller, thinner, or rounder. In this case, we all understand that the distortion is simply a matter of perspective – a quick glance in the mirror reveals the truth – but is this also true in other distorting systems? Is there a way to look at the light so that the distortion disappears?
Is there a way to look at the light to remove the distortion? The Wits-led team demonstrates that, while some properties are never distorted, others can be unraveled with a shift in perspective.
The question is how to comprehend what happens to light, how it is distorted, and how to discover a new perspective. To answer these questions, the team used vectorial light, the most general type of light. Light has an electric field, and its direction can change across the field, pointing upwards, downwards, left, right, and so on. The’vectorness’ of a light refers to how mixed up the direction of its electric field is.
In other words, it is a measure of how similar the directions of a light’s electric fields are at different locations: if they are the same everywhere (homogenous), the value is 0, and if they are different everywhere (inhomogeneous), the value is 1. Even if the pattern of the electric field changes, this vectorial homogeneity remains constant. The explanation is hidden in quantum entangled states, which appear to have little in common with optical distortions. The new discovery was made possible by applying quantum-world tools to optical distortions.
“We discovered that the vectorness of light is the single attribute of light that does not change when it passes through any complex medium,” says Professor Andrew Forbes of the Wits School of Physics. “This means we have something unique that can be used when communicating or sensing with light.”
“This is a specific aspect of the light pattern — how the polarisation pattern looks,” Forbes explains. “‘Polarisation’ is simply a fancy term for the direction of the electric field that makes up light.” The pattern is distorted as well, but its intrinsic nature (whether homogeneous or inhomogeneous) is not.
The team’s approach allows researchers to identify how to correct any distortions through the media in a way that doesn’t cost any light. In other words, there is no loss.
“We demonstrate that, despite the fact that the light is highly distorted, the distortion is simply a matter of perspective. Light can be viewed in such a way that its original ‘undistorted’ properties are restored. It’s amazing how complex light in complex media can be universally understood by following very simple rules.”
For example, by simply changing how a measurement is made, any communication over a highly distorted medium can be rendered “distortion free.” This was demonstrated experimentally by the team using a variety of systems, including turbulence, liquid, and optical fiber.
