Fig. 2: Principle of operation.
From: Free-space optical communications at 4 Gbit/s data rate with a terahertz laser
Experimental arrangements of the THz FSO communication system. The data is generated offline and loaded onto the AWG. The transmitter (blue box) includes an AWG for generating the NRZ-OOK and PAM-4 signals, a 27 dB gain RF amplifier, a QCL driven by a bias-tee to combine the DC and RF components, and a 90∘ off-axis parabolic mirror to collimate the beam. The modulated THz signal travels through free-space to the receiver section (red box) and is focused onto a Schottky barrier diode 4th harmonic mixer used as an envelope detector to detect the signal. The received signal passes through another bias-tee, followed by a 15 dB gain low-noise amplifier before being captured on an oscilloscope (OSC). The OSC converts the signal into digital samples, which are then processed offline to evaluate the signal performance.
