# Free-space optical communications at 4 Gbit/s data rate with a terahertz laser

## TL;DR

This paper demonstrates a 4 Gbit/s free-space optical communication system using a terahertz laser, paving the way for ultra-fast wireless data transmission.

## Contribution

The first experimental demonstration of multi-gigabit-per-second free-space optical communication using a terahertz quantum cascade laser.

## Key findings

- A 2.4 THz quantum cascade laser achieved 4 Gbit/s data rate using NRZ-OOK modulation.
- Bit error rate was analyzed under varying received power and modulation conditions.
- The system shows potential for high-speed wireless communication with relaxed pointing requirements.

## Abstract

Terahertz-frequency (THz) carrier waves in free-space optical (FSO) communications offer the potential for  > 1 Tbit/s data rates and stable latency. They offer wider bandwidths than available in the microwave region, together with reduced scattering and relaxed pointing requirements compared with visible and near-infrared regions. However, 1–10 THz FSO communications systems have thus far been limited to data rates several orders of magnitude lower than those of infrared systems. This work describes an experimental demonstration of multi-gigabit-per-second FSO communication using a THz quantum cascade laser (QCL), opening a new frontier for next-generation wireless communications. The FSO communication system consists of a 2.4 THz QCL source as the transmitter and a room-temperature Schottky barrier diode detector as the receiver. By directly modulating the terahertz QCL, we achieved non-return-to-zero on-off keying (NRZ-OOK) with a transmission rate of up to 4 Gbit/s. We evaluated the performance of the communication link by analyzing the bit error rate (BER) of the demodulated signal at the receiver while examining its relation to received optical power, QCL modulation power, and various bias points. Our work establishes the foundation for high-speed optical wireless communication based on terahertz QCL technology systems.

Terahertz-frequency communications promise ultra-high data rates and stable latency, yet current systems lag behind infrared technologies. Here, the authors demonstrate a pioneering multi-gigabit-per-second free-space optical communication using a terahertz quantum cascade laser, setting the stage for advanced wireless networks with significant implications for high-speed data transmission.