With the development of satellite internet backbone network communications, the intersatellite coherent laser communication technology is gradually developing in the direction of multi-node and multi-system compatibility. Therefore, it is necessary to develop the dense wavelength division multiplexing (DWDM) technology to meet the growing demand for high-throughput data transmission, while ensuring flexible interconnection and efficient intercommunication of intersatellite laser communication terminals. The core component of the DWDM technology is a tunable narrow-linewidth laser, whose wavelength must be aligned with the International Telecommunication Union (ITU) grid. Therefore, the laser must have a narrow linewidth, a wide range of wavelengths, and precise tuning and locking capabilities to flexibly match the transmit-receive wavelengths of different satellites.

The widely-tunable distributed Bragg reflector (DBR) laser is combined with a high-Q silicon nitride (Si₃N₄) micro-ring resonator (MRR) to form a self-injection locked laser with wide tunability. The MRR acts as a wavelength locker and a narrowband feedback filter at the same time, and wavelength locking and linewidth narrowing are realized synchronously based on the all-optical feedback method. The performance test of the laser spectrum, laser wavelength, frequency noise, and linewidth of the wavelength-locked self-injection locked (WL-SIL) laser is done.

The WL-SIL laser achieves wavelength tuning from 1528.38 nm to 1570.84 nm, with a wavelength tuning range of more than 42 nm, covering the entire C-band, supporting 107 ITU channels, and the frequency deviation from the ITU channels is less than ±1.5 GHz. In addition, within the wide tuning range of 42 nm, the side mode suppression ratio (SMSR) is always better than 40 dB, and the intrinsic linewidth is narrowed to 1.88 kHz, meeting the needs of high-coherence application scenarios. The innovation of this solution is to use Si₃N₄ MRR to simultaneously achieve the functions of wavelength locking and linewidth narrowing. Through the independent temperature control technology, the resonance peak of the MRR can be accurately aligned with the ITU-grid, and the narrowband optical feedback from the MRR locks the output frequency of the DBR laser to the resonance frequency, which can achieve high-precision wavelength locking.

In this paper, we propose and realize a self-injection locked DBR semiconductor laser based on a high-Q Si₃N₄ MRR, successfully addressing limitations in the conventional wavelength locking schemes such as restricted tuning range, excessive system complexity, and linewidth compression challenges. By self-injection-locking the DBR laser into a Si₃N₄ MRR with an ultrahigh Q-factor of 1.16×10⁶, we simultaneously achieve broadband wavelength locking and linewidth narrowing via a fully optical feedback mechanism. Experimental results show that the tuning range of the laser wavelength covers the entire C-band, supporting 107 ITU channels with frequency deviations all below ±1.5 GHz. Furthermore, the SMSR remains superior to 40 dB across a tuning range exceeding 42 nm, while the intrinsic laser linewidth is compressed to the kHz level. These advancements effectively meet the requirements for high-coherence application scenarios.