One-Way Light Could Be Produced Soon

Photons – the basic particles that make up light – have a tendency to move about unimpeded, and in whichever direction they choose. But new materials currently being developed could allow experts to create one-way streets for light, in which photons travel in a single direction.

These nonlinear materials can be based on either glass or plastic compounds, and they have the ability to select in favor of a single direction from the many directions in which photons travel. The stuff can basically block light coming in from a particular direction, say two physicists from Italy.

Directional discrimination is not something that physicists learn in school. In fact, textbooks are adamant that this cannot happen. However, new studies are demonstrating that the theoretical limits can indeed be breached.

While the behavior of light in normal, linear materials does respect this limitation, the same thing does not apply for their nonlinear counterparts. This happens because the way photons travel is significantly changed in the latter category of materials.

In normal light transmission mediums, the reciprocity theorem applies all the time. This theory shows that a beam of light coming from the right produces the same type of reflection on a surface as a beam coming from the left, Science News reports.

“Without nonlinearity this asymmetry would not be possible,” Giulio Casati says of the newly-found behavior of light. The expert holds an appointment as a physicist at the University of Insubria, in Como, Italy.

In a paper published in the April 22 issue of the esteemed scientific journal Physical Review Letters, the experts explain how the new materials can allow for directional discrimination within their inner structure. They say that the way photons influence the materials is very important.

In nonlinear materials, as light particles pass through, they tend to influence the way the material itself is organized within. This in turn changes the way light is influenced as it passes through the material.

The final form that light will take as it exits the materials is therefore a result of both its influence on the material and the shifting influence of the material on its photons. In some cases, experts have discovered, it is possible that the changes can be tailored to specific needs.

In certain setups, the frequency light needs to pass through can only be achieved or maintained if the beam of photons comes from a particular direction. Photons coming in from any other side would get lost in the nonlinear materials.

“Other people have used nonlinearity, but they use it in a different way,” explains mathematical physicist Panayotis Kevrekidis. The expert, who is based at the University of Massachusetts Amherst, was not involved in the new research.

“This simple model may also apply to more general situations, like acoustics or different kinds of waves,” adds study coauthor and Italian National Research Council Institute for Complex Systems physicist Stefano Lepri.