Scientists use ‘negative light’ to send secret messages hidden in heat

Researchers have developed a technique that invisibly transmits information disguised as background thermal radiation. They used a phenomenon called “negative light” to transmit 100 kilobits of data per second in a way that was completely imperceptible to outside observers.

Most methods of hiding data in transit involve hiding the data within other data or encrypting it in a way that it cannot be read without encryption or other means of decryption. In contrast, new technology makes it almost impossible to intercept data as there is no indication that it is being transmitted. It can also be encrypted using traditional means for further security, the team said in a paper published March 5 in the journal Light: Science & Applications.

This hidden transfer is made possible by a phenomenon called “negative light.” It relies on infrared light, the band just above the red end of the visible light spectrum. Infrared light is invisible to the naked eye, but can be detected with a thermal camera. We experience it as heat from warm objects, and all objects emit a faint glow in the infrared.

Article continues below

you may like

The negative luminescence the team used could darken that glow instead of brightening it. In a statement, Michael Nielsen, a professor of engineering at the University of New South Wales Sydney and lead author of the study, likened it to a flashlight that can “project darkness” by comparing it to background light, rather than just turning it off.

The researchers used a device called a thermally emitting diode to create patterns of brighter or darker states than normal. This pattern is mixed in with the typical infrared background “noise” but can be read as data by special receivers.

Thermal-emitting diodes were born as part of a separate project, where the team proved that it was possible to generate solar power even after the sun had set. This “night solar” technology captured the infrared radiation the Earth was absorbing during the day and emitting as it cooled at night. The team then used thermally emitting diodes to generate small amounts of power.

Although the initial transfer rate of 100 kbps is very modest, Nielsen says higher transfer rates are achievable. The main hurdle was the availability of the advanced electronic equipment the team needed. In principle, there is nothing to prevent this method from transferring tens of megabits per second with existing devices, the researchers say, and with better device and detector designs, speeds could increase to gigabits per second.

Indeed, commercial products delivering megabit per second data rates may be possible within a few years, Ned Ekins-Dawkes, professor of solar and renewable energy engineering at UNSW University and co-leader of the study, said in a statement.

By using graphene (a single-atom-thick sheet of carbon atoms arranged in a honeycomb pattern) instead of semiconductor materials in current diodes, Ekins-Dawkes said, “we have the potential to achieve data transfer rates in the gigabits per second range, if not hundreds of gigabits.”

Improving data security will have major applications in a variety of industries, including healthcare, defense, finance, and manufacturing. Nielsen believes that virtually any communication that could benefit from security beyond standard encryption could take advantage of his team’s breakthrough.

“The real advantage of this technology is that if an outside observer does not have the necessary technology to intercept the communication, the signals and actions of the communication itself are hidden,” Nielsen told LiveScience in an email.