A narrowband terahertz signal generated by a unitravelling carrier photodiode (UTC-PD) interfaced
with a dual-mode Fabry–Pérot laser diode is demonstrated. A beat tone corresponding to the free
spectral range is generated on the UTC-PD, and radiated by a transverse-electromagnetic-horn
antenna. A terahertz signal at a frequency of 372 GHz, featuring a linewidth of 17 MHz is recorded
by a subharmonic mixer coupled to an electrical spectrum analyzer. All components involved in this
experiment operate at room temperature. The linewidth and the frequency of the emitted terahertz
wave are analyzed, along with their dependency on dc-bias conditions applied to laser diode.