Hybrid integrated self-injection locked narrow linewidth laser based on feedback tunable silicon nitride micro-ring resonator

We propose and demonstrate a feedback tunable self-injection locked (SIL) narrow linewidth laser, the feedback light intensity is dynamically adjusted to find the best locking state. The self-injection locked laser is composed of distributed feedback (DFB) semiconductor laser and high quality (Q) factor silicon nitride (SiN) external cavity, tunable sagnac loop reflector is used to achieve arbitrary ratio of feedback light and output light on the basis of add-drop type high Q microring resonator (MRR). The results show that the SIL state is closely related to the ratio of feedback light. When the optical feedback ratio is higher than -14 dB, a robust SIL state can be achieved, and the locking state is independent of the phase of the feedback light, the intrinsic linewidth is narrowed from 130 kHz to 1 kHz. By optimizing the ratio of feedback light to -9.3 dB, a narrow linewidth output of 345 Hz can be achieved. This work has important application value in the field of coherent laser communication and coherent detection.