Mode control and dynamic population gratings in quantum-dot lasers

Single-mode operation is essential for integrated semiconductor lasers, yet most solutions rely on regrowth, etched gratings, or other complex fabrication steps that limit scalability. We show that quantum-dot (QD) lasers can achieve stable single-mode lasing through a simple cavity design using dynamic population gratings (DPGs). Owing to the low lateral carrier diffusion of QDs, a strong standing-wave-induced carrier grating forms in a reverse-biased saturable absorber and provides self-aligned, mode-selective feedback not attainable in quantum-well devices. A single-ring laser achieves a 46 dB side-mode suppression ratio (SMSR), while a dual-ring Vernier laser delivers a tuning range exceeding 46 nm, an SMSR of up to 52.6 dB, and an intrinsic Lorentzian linewidth of 50 kHz, with continuous-wave operation up to 80°C. The laser remains single-mode under −10.6dB external optical feedback and supports isolator-free data transmission at 32 Gbps. These results establish DPG-enabled QD lasers as a simple and scalable route to tunable, feedback-resilient on-chip light sources for communication, sensing, and reconfigurable photonic systems.