Monolithic InP Laser System for Wide-Range Tunable THz Beat-Note Generation with Machine-Learning-Based Automatic Tuning

We present a monolithically integrated indium phosphide photonic chip that provides a broadband, tunable two-tone optical source for terahertz beat-note generation. The device combines a widely tunable sampled-grating (SG) laser with a stable distributed-feedback laser, enabling compact and robust optical operation. To address the multi-parameter bias-control challenge in SG lasers, we develop a fully automated tuning framework that integrates database-assisted initialization, machine-learning-based prediction, and particle swarm optimization (PSO). This approach achieves efficient convergence toward optimal bias conditions, yielding single-mode tuning over 41 nm (1520–1561 nm) with side-mode suppression ratios above 20 dB across the full range and exceeding 30 dB in the 1523–1561 nm region, while maintaining linewidths below 90 kHz. Optical measurements confirm two-tone operation with tunable frequency spacing from 1.02 to 5.93 THz. These results establish a compact, scalable platform for integrated broadband THz sources with strong potential for wireless communications, spectroscopy, and sensing.