Monolithically integrated tunable DFB laser array for the generation of wide-range continuously tunable THz signals

We present a monolithically integrated photonic chip that generates continuously tunable optical beat-note signals for terahertz applications. The device integrates four distributed feedback lasers, each independently current-controlled, enabling thermal wavelength tuning without the need of external control loops. By carefully designing the initial emission frequencies and tuning characteristics, pairwise combinations of the lasers provide continuous wavelength spacing coverage from 0.46 nm to 40 nm, corresponding to beat frequencies ranging from 60 GHz to 4.96 THz, which is approximately twice the range achieved in conventional four-DFB systems reported so far. DFB lasers operate in a stable single mode over a moderate tuning range, with measured linewidths of around 5 MHz and side-mode suppression ratios exceeding 50 dB. An on-chip semiconductor optical amplifier equalizes optical power between channels, ensuring consistent beat-note intensity even at large wavelength separations. Optical beat signals are characterized in both spectral and temporal domains, confirming high coherence and stability across the whole tuning range. This enables a fully electrically controlled platform that requires no external tuning components, offering a compact and scalable solution for broadband heterodyne sources in THz sensing, spectroscopy, and communication systems.