Tunable Self-Injected Fabry–Perot Laser Diode Coupled to an External High-Q Si₃N₄/SiO₂Microring Resonator

The fast-growing fields of coherent optical communications, light detection and ranging (LIDAR), etc., have huge demand for narrow linewidth lasers. While laboratory-scale lasers have high stability with narrow linewidth down to few Hz, they are usually in large size and unable to be integrated with chip-scale optical systems. In this paper, we develop a new on-chip semiconductor laser by introducing the Vernier effect and the self-injection locking effect simultaneously between a Fabry-Perot diode laser and an external microresonator on silicon chip. The proposed laser is demonstrated with a narrow linewidth of 8 kHz and wide switchable range of 17 nm. This paper explores a new scheme to realize narrow linewidth with wide tunability for on-chip semiconductor lasers.