Scientists use 'negative light' to send secret messages hidden inside heat

Researchers have developed a technology to invisibly transmit information disguised as background thermal radiation. Using a phenomenon called "negative light," they transferred 100 kilobits of data per second in a way that was completely undetectable to outside observers.

Most methods for concealing data during transfer involve hiding it among other data or encrypting it in a way that makes it impossible to read without a cipher or other means of decryption. The new technique, by contrast, makes the data almost impossible to intercept because there's no indication it's being sent at all. It can also be encrypted through traditional means to further harden security, the team wrote in a paper published March 5 in the journal Light: Science & Applications.

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

The negative luminescence the team used could make that glow dimmer, rather than brighter. In a statement, Michael Nielsen, a professor of engineering at the University of New South Wales Sydney and lead author of the study, compared it to a flashlight that could "project darkness" as compared to background light, rather than simply turning off.

Using devices called thermoradiative diodes, the team created patterns of brighter- or darker-than-usual states that blended into typical infrared background "noise" but that can be read as data by specialized receivers.

The thermoradiative diodes were born as part of another project, in which the team proved that it was possible to generate solar power even after the sun had set. This "night-time solar" tech captured infrared radiation that Earth had absorbed during the day and was releasing at night as it cooled. The team then used thermoradiative diodes to generate a small amount of power.

While the initial transfer rate of 100 kbps is quite modest, Nielsen said higher speeds are achievable. The main hurdle was the availability of some of the sophisticated electronics the team required. In principle, there's nothing stopping this method from transferring tens of megabits per second with existing devices, with better devices and detector design pushing the speed to gigabits per second, the team said.

In fact, a commercial product delivering megabit-per-second data rates may be possible in just a few years, Ned Ekins-Daukes, a professor of photovoltaic and renewable energy engineering at UNSW and co-leader of the research, said in the statement.

By using graphene ‪—‬ a single-atom-thick sheet of carbon atoms arranged in a honeycomb pattern ‪—‬ instead of the current semiconductor material in the diodes, "we can potentially achieve data transfer rates in the gigabits-per-second range, if not hundreds of gigabits," Ekins-Daukes said.

Improved data security would have major applications in a variety of industries, including health care, 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 technique is that the very signal or act of communication is hidden if an outside observer doesn't have the same technology required to intercept the communication," Nielsen told Live Science in an email.