QCL-Based Cryogen-Free THz Optical Wireless Communication Link

The increased demand for high-speed (terabit-per-second) wireless data transmission has driven the shift of the frequency carrier from ubiquitous radio frequency systems toward the 1–5 THz range, triggering a new interest for THz quantum cascade laser (QCL)-based free-space optical (FSO) links. As compared to standard telecom-band FSO links, platforms based on THz frequency sources are inherently robust against Rayleigh scattering. Atmospheric absorption, mainly due to water vapor, limits the achievable link distance range, but at the same time, it shifts channel security on the physical layer. THz QCL-based FSO links are reported with setups requiring cryogenic cooling, seriously limiting their development for mass applications. Here, a cryogen-free, transportable THz FSO communication system is presented relying on a directly modulated 2.83 THz QCL transmitter, hosted in a closed-cycle Stirling cryocooler, and exploiting a room-temperature graphene-based receiver, implementing a binary on-off keying modulation scheme with Manchester encoding. Power-versus-distance measurements and communication tests are performed, and propose a propagation model to extrapolate the performances of the THz link in an optimized configuration. This approach reduces complexity and costs, as compared to the state-of-the-art THz FSO links, and paves the way for the deployment of optical wireless communication systems exploiting the 1–5 THz frequency range.