Integrated optical frequency combs for continuous-wave terahertz generation

The generation of continuous-wave terahertz radiation remains challenging, as it is difficult to access using traditional electronic or photonic methods. However, accessing this part of the electromagnetic spectrum is important for the study of many astronomical phenomena. This paper presents results on the generation of continuous-wave terahertz radiation at 0.383 THz through the photomixing of comb lines from a low-noise, phase-coherent Kerr soliton frequency comb. A dual-mode pumping scheme was used during comb generation to overcome the thermal issues faced when moving from a modulation instability comb to the soliton state. A waveguide-integrated photodiode antenna was used to emit the signal into free space, while a WR 2.2 waveguide-based mixer was used to down-convert the signal to an intermediate frequency for characterisation. The RF linewidth of the beat note was 5.88 kHz, while the stability of the signal over 5 minutes was 123 kHz, showing that a good level of phase coherence exists between the comb lines. This method of continuous-wave terahertz generation is easily scalable to higher frequencies.