On-Chip Multi-Wavelength Lasers for All-Optical THz Signal Processing

The behavior of semiconductor lasers has been extensively explored for all-optical information processing, ranging from all-optical flip-flop memories [1] to neuro-inspired computing [2]. When it comes to processing of THz signals, so-called P1 dynamics have been exploited for microwave generation, frequency conversion, and amplification [3]. This approach, however, decreases in efficiency beyond 100 GHz due to the weakened interaction between the injected signal and the laser process. Here, we propose a novel approach for THz processing based on feedback-controlled multi-wavelength lasers (MWL), whose mode spacings and thus beatnote frequencies can be tailored and are, in principle, only limited by the gain bandwidth of the active medium; for instance, reaching up to 10 THz in InP. As a first proof-of-concept demonstration, using a dual-mode laser, we show selective filtering and amplification of two CW optical signals separated by 1.3 THz. We obtain power gain values above 15 dB and suppression ratios of more than 18 dB. By adjusting the MWL operation conditions or design, additional offset frequencies can be obtained, thus enabling the processing of broadband THz signals.