Ultra-narrow-linewidth DFB laser array based on dual-cavity feedback.

Herein, we propose a structure to simultaneously compress the distributed feedback (DFB) laser array's linewidth. The proposed structure is meticulously designed to ensure single longitudinal mode operation via the interference phenomenon between the laser's primary cavity and the dual-cavity feedback. Given the weak feedback effect for each wavelength in the laser array, the proposed structure could realize the intense compression of the laser linewidths. The study results show that the side-mode suppression ratios of each DFB laser are over 40 dB, and the linewidths have been compressed from 3 MHz to ∼800 Hz. Thus, we believe the idea of an overall compression linewidth scheme in the present study can be adopted for integrated laser arrays.