Low-Noise Tunable Quantum-Dot Lasers for Coherent FMCW Ranging and High-Speed Optical Communications

Overview

Photonic integrated circuits (PICs) are key enablers for next-generation coherent optical communications and emerging sensing applications such as frequency-modulated continuous-wave (FMCW) LiDAR. In these systems, laser linewidth and frequency noise critically determine detection sensitivity, phase stability, and ranging precision. However, achieving narrow-linewidth and low-noise on-chip lasers often relies on complex grating structures, epitaxial regrowth, or low-loss external cavities, which increases fabrication complexity and cost.

In this seminar, I will present our recent progress in developing low-noise and highly linear frequency-chirped tunable lasers based on quantum-dot (QD) gain media. Owing to their discrete density of states, QD lasers exhibit a near-zero linewidth enhancement factor, which intrinsically suppresses phase noise by decoupling carrier fluctuations from refractive index variations. We introduce a novel tunable laser architecture enabled by dynamic population gratings (DPGs), offering simplified processing while achieving state-of-the-art coherence on a monolithic QD platform. The demonstrated devices provide over 50 nm tuning range, SMSR above 52 dB, and a record intrinsic linewidth of 12.6 kHz with strong optical feedback tolerance. We further explore chirp dynamics and apply pre-distortion algorithms to achieve high sweep linearity (~10⁻⁵), MHz-level sweep rates, and 29.5 GHz/V modulation efficiency. Finally, using self-injection locking, we achieve ultra-narrow linewidth below 20 Hz, paving the way for scalable ultra-coherent integrated light sources.