# Balancing positive and negative luminescence for thermoradiative signatureless communications

## TL;DR

This paper introduces a new method for secure communication using thermal infrared radiation modulated at high speeds to avoid detection.

## Contribution

The novel contribution is using rapid electrical modulation of photon emission to achieve covert communication with no optical signature.

## Key findings

- Data rates up to 100 kbps are achieved using thermoradiative diodes.
- Modulation rates exceed 1 MHz, allowing signals to be hidden from slow detectors.

## Abstract

Ambient-temperature thermal infrared radiation is an underutilised resource for secure communications. Demonstrations of free-space data transfer using thermal radiation have been few, and have relied on intrinsically slow modulation of either the emissivity and/or physical temperature of a broadband blackbody emitter, severely limiting data transfer rates ( < 1 kHz). Here, we demonstrate a covert communications method in which photon emission is rapidly electrically modulated both above and below the level of a passive blackbody at the emitter temperature. The time-averaged emission can be designed to be identical to the thermal background, realizing communications with zero optical signature for detectors with bandwidth lower than the modulation frequency. We demonstrate this scheme using both electro- and negative luminescence in thermoradiative diodes, enabling data rates up to at least 100 kbps and modulation rates above 1 MHz. Future prospects for ultra-high-bandwidth (up to THz) emitters and detectors utilising meta-optics and 2D materials are discussed.

We demonstrate covert transmission of data by rapidly modulating mid-infrared photodiodes, balancing forward and reverse bias luminescence. Only fast detectors resolve the signal; slow observers observe no evidence of communication.